General Operating Procedures for 110KV Substations

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General Operating Procedures for 110kV Substations　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1. General Provisions1.1 Scope of Application: 1.1.1 These procedures apply to the 110 kV substations owned by Yancheng Power Supply Company; personnel in the monitoring centers and operation teams must strictly follow these procedures when it comes to the operation, maintenance, and handling of incidents related to the equipment. 1.1.2 The monitoring center, operation teams, technical personnel, relevant dispatchers, professionals and supervisors responsible for substation operation, as well as leaders at all levels in charge of production, shall all be familiar with these regulations. 1.1.3 New personnel assigned to monitoring and operation, as well as those who have been away from such tasks for three months or more and are returning to work, must study the on-site operating procedures; they can only take up official duty after passing the examination. 1.1.4 These regulations are general guidelines for 110 kV substations; each unit shall prepare a \"Substation On-site Operation Regulations\" (supplementary section) based on the actual wiring and equipment conditions of its respective substations. 1.1.5 This procedure and the supplementary parts of the on-site operation procedures for each substation shall be amended in a timely manner to ensure consistency with the on-site conditions at the substation. Revisions should be carried out annually by the relevant personnel and made public; in principle, revisions and reprints are conducted every four years. 1.1.6 In the event that these procedures conflict with relevant higher-level procedures and regulations, the latter shall prevail. 1.2 Referenced Documents 1.2.1 Technical Management Regulations for the Power Industry 1.2.2 Safety Work Procedures for the Electric Power Sector DL/T 408-91 1.2.3 **Safety Work Procedures for Power Grid Companies (Electrical Parts of Substations and Power Plants) 1.2.4 Procedures for Handling Electrical Accidents 1.2.5 Operating Procedures for Power Transformers DL/T 572-95 1.2.6 Guidelines for the Operation of Oil-Immersed Power Transformers GB/T 15164-94 1.2.7 Guidelines for the Operation and Maintenance of On-Load Tap Changers DL/T 574-95 1.2.8 Operating Procedures for High-Voltage Circuit Breakers 1.2.9 Technical Regulations for the Operation and Maintenance of Battery DC Power Supply Systems Used in Power Systems 1.2.10 Operating and Management Regulations for Relay Protection and Automation Devices 1.2.11 Operating Procedures for Power Cables 1.2.12 Procedures for Preventive Testing of Electrical Equipment DL/T 596-1996 1.2.13 Typical Fire Protection Regulations for Electrical Equipment DL 5027-93 1.2.14 Dispatching Regulations for Provincial and Municipal Power Grids 1.2.15 Management Systems for Substation Operations at All Levels 1.2.16 Guidelines for the Operation Management of Unmanned Substations by Provincial Companies DL Q/SD-001-1999 1.2.17 Rating Standards for Power Supply Equipment of Provincial Companies 1.2.18 Other Relevant Regulations, Systems, Countermeasures, and Technical Documents 1.3 General Requirements for Operation and Maintenance 1.3.1 During their shift, operators shall conduct thorough inspections of all equipment in the substation according to the specified inspection routes and items. The inspection cycles are as follows: 1.3.1.1 Normal inspection cycle: 1. The inspection frequency for substations without on-site staff should be twice a week. 2. Inspections of key equipment shall be carried out during peak load periods between shifts and at night, with the frequency to be determined by each unit. 3. Check the setting ranges, push-buttons, and switch positions of relay protection and automatic devices, and conduct a comprehensive verification once a month. 4. The inspection requirements for substations with single-person duty should not be reduced compared to those with manned duty. 1.3.1.2 The inspection cycle for newly installed equipment, equipment that has been modified, and equipment that has undergone major repairs should be shortened appropriately; inspections should be carried out according to the normal cycle after 72 hours. 1.3.1.3 The frequency of inspections should be increased or special inspections should be organized in the following situations: 1. When the equipment is operating under overload or when the load increases significantly. 2. When there is recent development in equipment defects. 3. During meteorological disruptions (such as high temperatures, strong winds, heavy fog, heavy snow, hail, cold snaps, etc.). 4. In the event of an accident-induced trip or when suspicious phenomena occur during equipment operation. 5. After lightning. 6. When there are clear requirements from superiors. 7. Statutory holidays. 1.3.2 Inspections are carried out by the operation team or on-site personnel. The causes, development, and consequences of the defects identified during inspections should be analyzed ； In accordance with the requirements of the equipment defect management system, make proper records and submit reports categorized accordingly. It belongs to a category of defects; in addition to immediately reporting it to the on-duty dispatcher and relevant supervisors, enhanced monitoring is required, accident scenarios should be anticipated, and appropriate measures should be taken to prevent its progression. 1.3.3 Spare equipment should always be kept in a usable state, and its operation and maintenance require the same standards as those for operational equipment. For substations that have been operating with one main transformer in service while the other remains in hot standby for an extended period, it is principle that the operation mode should be switched every month, so that the transformer that has been in standby for a long time comes online. 1.3.4 During their shift, the crew members performing operations may carry out the following tasks without a work order, but they must obtain permission from the on-duty dispatcher or supervisor, take appropriate safety measures, maintain a safe distance, and enhance supervision. 1.3.4.1 No shutdown of equipment is required for the substation lighting circuit (shift supervisor). 1.3.4.2 Cleaning of the panels of the metering panel, protection panel, and control panel (person in charge of duty). 1.3.4.3 High-voltage fuse replacement (dispatcher), low-voltage fuse replacement (shift supervisor). ； 1.3.4.4 Gas relay venting (dispatcher). 1.3.5 General requirements for switching operations 1.3.5.1 Switching operations of electrical equipment are ordered by the dispatcher; the on-duty operator receives the order, reviews the operation ticket and acts as the supervisor, while the assistant on-duty officer fills out the ticket and carries out the operation. 1.3.5.2 All operations must be carried out in strict accordance with the regulations for switching operations. If any doubts arise, the operation should be stopped and the person who gave the order informed; operations can resume only after further permission is granted by that person. The duty officer shall not change the operation tasks on their own or reverse the order of operations. 1.3.5.3 Before completing the closing procedures after equipment maintenance, the operators and the maintenance supervisor shall thoroughly inspect the condition of the equipment to restore it to its state prior to work authorization. 1.3.5.4 For equipment under dispatch control, no one other than the on-duty dispatcher shall change its operating status (except in the event of an accident). 1.3.5.5 When the equipment is taken out of service and switched from cold standby to maintenance mode, the pushbuttons that cause interlocking shutdown of other equipment at the outlet of this circuit, as well as those that cause interlocking shutdown of this circuit itself from other circuits, should be disengaged. 1.3.5.6 When operating an unattended substation, before the switch is changed to cold standby or maintenance mode, the remote/local control switch should be set to the local position (or the remote control relay should be disabled). After the switch is changed from cold standby or maintenance mode to operational or hot standby, the control switch should be set to the remote position (or the remote control relay should be activated), and this should be indicated in the operation ticket. 1.4 General requirements for equipment acceptance: 1.4.1 Equipment that is newly built, expanded, or overhauled must undergo strict quality inspection before being put into operation; it must meet the specified quality standards and have complete drawings and documentation before it can be used. 1.4.2 After the installation or maintenance of substation equipment is completed, and after the maintenance personnel have carried out thorough self-inspections and cleaned up the work site, the person in charge of the work must clearly explain to the operating staff the issues related to the maintenance, any changes made, any remaining problems, as well as the precautions to be taken once the equipment is put into operation and whether the equipment can be operated or not. All this information must be recorded in the relevant maintenance records. 1.4.3 The operators shall, together with the person in charge of the work, conduct a comprehensive inspection of the quality of the maintenance work, to gain a detailed understanding of the maintenance situation. All components of the equipment should be intact, the exterior should be clean with no debris remaining, the equipment’s transmission system should function properly, the error-prevention devices should be in good condition, and the maintenance and testing reports should be complete and meet the required standards. 1.4.4 After the maintenance is completed, the maintenance personnel shall restore the equipment to its condition when it was approved for operation, and the operators shall carry out necessary inspections. 1.4.5 When new equipment is put into operation or there are changes to existing equipment, there must be drawings and documents that correspond to the actual equipment, and the new on-site operating procedures should be revised promptly. 2. Main Transformer 2.1 Operation Mode of the Transformer 2.1.1 General Operating Conditions 2.1.1.1 The operating voltage of the transformer should generally not exceed 105% of the rated voltage at that operating tap position. For special application scenarios, operation at a voltage not exceeding 110% of the rated voltage is permitted. If there are no specific requirements regarding the relationship between current and voltage, when the load current is K times the rated current (where K≤1), the voltage U is limited using the following formula: U% = 110 – 5K2. 2.1.1.2 The capacity of each tap position of the on-load tap-changer transformer is in accordance with the manufacturer’s specifications. 2.1.1.3 During operation, the oil temperature at the upper level of the transformer should be monitored. When the maximum ambient temperature is 40°C, the monitoring value should not exceed 95℃ ； The normal monitoring value for the upper oil temperature of naturally circulating cooled transformers should not exceed 85°C. 2.1.2 Operating modes of the transformer under different load conditions 2.1.2.1 Operation under normal periodic loads 1. Under rated operating conditions, the transformer can operate at the rated current throughout the year. 2. The transformer allows periodic overloading operation as long as the average relative aging rate is less than or equal to 1. 3. Operating the transformer above its rated current is prohibited when it has serious defects (such as severe oil leakage, localized overheating, abnormal results from dissolved gas analysis in the oil, etc.) or weak insulation. 2.1.2.2 Operation under long-term emergency periodic loads 1. Operating under long-term emergency periodic loads will shorten the lifespan of the transformer to varying degrees; efforts should be made to minimize the occurrence of such operating conditions ； When it must be used, the duration of the over-current should be minimized as much as possible. 2. Operating the transformer above its rated current is prohibited when it has severe defects (such as serious oil leakage, localized overheating, abnormal results from dissolved gas analysis in the oil, etc.) or weak insulation. 2.1.2.3 Operation under short-term emergency load 1. During operation under short-term emergency load, the relative aging rate is much greater than 1, and the hotspot temperature of the windings may reach dangerous levels. When this occurs, the load should be reduced as much as possible and the time limited, generally to no more than 0.5 hours. Operating the transformer above its rated current is prohibited when it has serious defects or weak insulation. The load factor allowed for a 0.5-hour short-term emergency load is to be referred to in Table 13. When the ambient temperature is between these two values, operation should be carried out in accordance with the allowable load factor and time corresponding to the higher ambient temperature. The allowable load factors listed in the table are all limit values; operation beyond these values is prohibited. 2. In the event of a sudden surge in short-term emergency load, the personnel on duty may not be aware of the load factor K1 prior to its occurrence; in such cases, K1 can be assumed to be 1.0. K1: The ratio of the load current to the rated current before the emergency load appears. K2: When a short-term emergency load occurs, the load factor determined by K1 and the ambient temperature represents the multiple of the rated current. 2.2 Operation and Maintenance of Transformers 2.2.1 Operation Monitoring of Transformers 2.2.1.1 Items for routine inspection of transformers: 1. The thermometer of the transformer should be in good condition; the oil temperature should be normal, the remotely measured temperature should match the actual temperature on site, the oil level in the oil reservoir should correspond to the ambient temperature, and there should be no leaks of oil in any part of the transformer. 2. The oil level in the bushing should be normal; there should be no cracks or damage on the outside of the bushing, no severe oil contamination, no signs of discharge, and no other abnormal conditions. 3. The transformer’s acoustic response is normal. 4. The tactile temperatures of each cooler and the main unit should be similar, and the fans should operate properly. 5. The respirator should be in good condition, and the discoloration of the silicone gel should not exceed 3/4. 6. The transformer leads shall have no broken strands, and the connections shall show no signs of overheating, discoloration, or melting (discoloration) of the temperature sensors. 7. The pressure relief valve, safety vent, and explosion-proof membrane should be in good condition. 8. The tap positions and power supply indication of the excitation voltage regulation tap changer should be normal. 9. There should be no gas inside the vacuum relay. 10. All control boxes and secondary terminal boxes should be tightly closed. 11. The grounding of the transformer enclosure and the core must be in good condition. 12. The doors, windows, lighting, and ventilation systems in the transformer room must be in good condition; the building should not leak, and the temperature should be normal. 2.2.1.2 Special inspections of the transformer should be carried out under the following circumstances, with an increased frequency of such inspections: 1. Within 72 hours after new equipment or transformers that have been overhauled or modified are put into operation. 2. In the case of serious defects. 3. Sudden weather changes (such as strong winds, heavy fog, heavy snow, hail, cold snaps, etc.). 4. During the hot seasons and peak load periods. 5. When the transformer is operating under overload conditions. 6. After a near-zone short-circuit fault. 2.2.2 Commissioning and Decommissioning of Transformers 2.2.2.1 Before commissioning a transformer, the duty personnel should conduct a thorough inspection to ensure that the transformer and its protective devices are in good condition and ready for operation under live conditions. Also, check for any foreign objects outside, whether the temporary grounding wire has been removed, whether the tap switch is in the correct position, and whether all valves are open or closed properly. When the transformer is operated at low temperatures, it is necessary to prevent the breather from freezing and becoming blocked. 2.2.2.2 Standby transformers in use should be ready to be put into operation at any time. 2.2.2.3 To start a transformer, the circuit breaker on the power side should be closed first, followed by the circuit breaker on the load side. If two transformers are operated in parallel, the busbar-side circuit breaker should be closed first, followed by the main transformer-side circuit breaker ； If a single transformer is in operation, the switch on the power side should be closed first, followed by the switch on the load side. The sequence for disabling is the reverse. 2.2.2.4 Transformers that have been newly installed or have had their windings replaced must undergo impulse closing tests at their rated voltage. The number of impulse trials is: five times for newly installed and put into operation transformers, and three times for those with replaced windings. 2.2.2.5 In an 110 kV system with directly grounded neutral point, the normal operating mode of the switch for directly grounding the neutral point shall be carried out in accordance with dispatch instructions. When starting or stopping a transformer, the neutral point grounding switch should be closed first. 2.2.2.6 After power cutback is implemented on the power supply side, the 110 kV neutral point of the main transformer should be grounded immediately, and its normal operating mode should be restored once power supply is resumed. 2.2.3 Operation and maintenance of transformer tap changers 2.2.3.1 For on-load tap-changing transformers, when it is necessary to adjust the tap changer, the transformer must be in maintenance mode, and the task should be carried out by maintenance personnel. 2.2.3.2 Operation and maintenance of on-load tap changers 1. Monitoring personnel can perform voltage regulation operations according to the voltage curves or voltage quality requirements issued by the dispatching department. After the operation, confirm the operation of the tap changer, check the changes in voltage and current, and make proper records. In principle, the number of operations per day shall not exceed 20 (one operation for each branch adjustment). 2. When two on-load tap-changer transformers are operated in parallel, their tap-changing operations should be carried out sequentially one after another ； Tap-changing operations are allowed at 85% of the transformer’s rated current. For stepping up, the transformer with a relatively lower load current should be used first to prevent excessive circulating currents; the opposite is true for stepping down. 3. The on-load voltage regulation operation should be carried out using reverse voltage regulation. 4. When stepping up voltage using on-load tap changers, that is, without feeding reactive power back into the system, capacitors should be connected first, followed by adjusting the tap of the main transformer ； When the bus voltage exceeds the specified value, the capacitors are de-energized only after the tap changer has reached its extreme position. 5. Operating the tap changer is prohibited when the transformer is overloaded by 1.2 times or more. 6. One year after installation or after 5,000 switching operations, the new tap changer should be taken out for inspection. For a switch in operation, the cover should be opened for cleaning or oil filtering every 5,000 changes of tap position, and the core should be inspected by lifting it out every 10,000 changes of tap position. 7. In the case of the following abnormalities occurring during tap-changing operations, the following actions should be taken, and maintenance should be arranged promptly: a) If a interlocking phenomenon occurs during the operation, the power supply to the drive motor should be cut off immediately; if there is a manual operating mechanism, it should be used to adjust the tap to the appropriate position. b) When performing remote electrical control operations, if the counter and tap positions are normal but there is no corresponding change in current and voltage, the power supply for the operation should be cut off immediately to terminate the operation. c) The tap changer fails to operate or operates incorrectly ； Abnormal changes in current and voltage ； Fault in electric motor or transmission mechanism ； The tap position indication is inconsistent ； Internal switch abnormal sound ； The overpressure protection device has activated ； Operations should be prohibited or halted when the oil level cannot be seen, there is excessive oil leakage, or any other abnormal conditions that could endanger the safe operation of the tap changer and transformer. 2.2.4 Operation of the gas protection device 2.2.4.1 When the transformer is in operation and oil is filtered, replenished, or the adsorbent in the oil purifier is replaced, the heavy gas signal should be rerouted. 2.2.4.2 When the oil level in the oil gauge rises abnormally or there are abnormalities in the breathing system, requiring the opening of the venting or oil drainage valves, the heavy gas bypass signal should be activated first. 2.2.4.3 If the heavy gas protection of a transformer in operation has its signal path altered for some reason, other protection devices must not be taken out of service; the main protection must be connected to trigger a trip. 2.2.5 Parallel operation of transformers 2.2.5.1 Basic conditions for parallel operation of transformers: 1. The connection groups must be the same. 2. The turns ratio is the same. 3. The short-circuit impedances are equal. 4. The capacity ratio shall not be greater than 1:3. Transformers with different short-circuit impedances can be connected in parallel as long as no single transformer is overloaded. 2.2.5.2 For transformers with newly installed or modified internal and external connection wires, the phase must be verified before paralleling. 2.2.6 Economic operation of transformers: The number of transformers in operation should be reasonably arranged based on the load conditions, in accordance with safety and economic principles. 2.3 Abnormal Operation of Transformers and Accident Handling 2.3.1 When abnormal phenomena are detected during the operation of a transformer (such as oil leakage, abnormally high or low oil level, abnormal temperature, unusual noises, etc.), it is necessary to immediately report to the on-duty dispatcher and relevant supervisors, and take measures to resolve the fault as soon as possible. 2.3.2 The transformer should be taken out of service immediately if it is in one of the following conditions. If there is a spare transformer, it should be put into operation as much as possible: 2.3.2.1 The noise emitted by the transformer increases significantly, is very uneven, and includes cracking sounds. 2.3.2.2 Severe oil leakage or spraying, causing the oil level to drop below the indication limit of the oil gauge. 2.3.2.3 The bushing has severe damage and discharge phenomena. 2.3.2.4 The transformer smokes and catches fire. 2.3.3 When a fault occurs that endangers the safety of the transformer and the transformer protection device fails to operate, the operators should immediately shut down the transformer. 2.3.4 When equipment near the transformer catches fire, explodes, or experiences other abnormal conditions that pose a serious threat to the transformer, the operators should immediately take measures to shut down the transformer. 2.3.5 When the temperature of the transformer oil rises above the allowable limit, the monitoring personnel should inform the operation team to go to the site to determine the cause and take measures to reduce it. The inspection steps are as follows: 2.3.5.1 Check the load on the transformer and the ambient temperature, and compare them with the normal temperatures under the same load and ambient conditions. 2.3.5.2 Check the temperature measurement device. 2.3.5.3 Check the transformer cooling system. 2.3.5.4 If the oil temperature is found to be 10°C or more higher than under the same load and cooling conditions, or if the oil temperature continues to rise while the transformer’s load remains unchanged and the cooling system as well as the thermometer are functioning properly, it is considered that the transformer is faulty, and the transformer should be shut down immediately. 2.3.6 Handling of Light Gas Protection Activation 2.3.6.1 When a signal is issued indicating activation of the light gas protection, the monitoring personnel should immediately inform the operation team to inspect the transformer in order to determine the cause of the activation – whether it is due to air intrusion, reduced oil level, faults in the secondary circuit, or internal faults in the transformer. And report to relevant departments such as scheduling, work areas, and production technology. 2.3.6.2 If the on-load tap-changer is not used frequently for tap changes but the light gas protection trips often, records should be kept, reports should be submitted promptly, and tap changes should be suspended. 2.3.6.3 If there is gas inside the gas relay, it should be sampled for analysis; if the gas is colorless, odorless, and non-flammable, and analysis indicates that it is air, then the transformer can continue to operate ； If the gas is flammable, it indicates a fault inside the transformer; the transformer should be shut down, and the cause of the malfunction should be analyzed along with appropriate repairs. If there is a backup transformer, it should be brought online first. 2.3.7 Handling of Transformer Trips 2.3.7.1 If there is a spare transformer, it should be brought online immediately, after which the cause of the trip should be determined. 2.3.7.2 If it is the transformer differential or heavy gas protection that triggers the action, the inspection results show that the circuit breaker trip was not caused by an internal fault, but rather by overload, external short circuit, or a fault in the secondary circuit. After appropriate handling, and with the approval of the company’s production manager or chief engineer, the dispatch can give the order to attempt to restart the system once. Otherwise, inspection and testing must be carried out to determine the cause of the transformer tripping; once the fault is resolved, and with the approval of the company’s production manager or chief engineer, the dispatch team can give the order to attempt to restart the transformer. 2.3.7.3 If it is due to the operation of the transformer’s overcurrent protection, and no abnormalities are found upon external inspection, then with the approval of the company leader in charge of production, the dispatch center can give the order to attempt a restart. 2.3.7.4 Handling of transformer fires: When a transformer catches fire, the power supply should be disconnected first, the cooler should be shut down, and fire extinguishing equipment should be used promptly to put out the fire. If there is a spare transformer, it should be put into operation. 2.3.7.5 General settings for non-electrical protection devices of the transformer itself: Gas relay on the transformer – triggers tripping in case of severe gas accumulation, and sends a signal in case of mild gas accumulation. Gas relay on the on-load tap changer – triggers tripping. Oil level gauge of the on-load tap changer – provides alerts for high and low oil levels. Pressure relief valves (2PCs) on the transformer – send signals. Pressure relief valve of the on-load tap changer – sends a signal. Oil temperature indicators (2PCs) – provide alerts when the oil temperature is too high. Faults in the AC power supply of the cooling system; alerts are issued in case of faults in the main or backup power supply. Faults in the coolers; alerts are issued in case of faults in the oil pumps or fans. Winding temperature sensors (3PCs) – provide alerts when the temperature is too high. Online gas monitoring system – issues alerts. Complete shutdown of the coolers – sends a signal. 3. Circuit breakers 3.1 General requirements 3.1.1 Circuit breakers should operate in accordance with the specifications indicated on their nameplates; they must not be operated under overload conditions, except in emergency situations. 3.1.2 The AC and DC power supplies for operating the circuit breaker should be normal, with voltages within the specified range. 3.1.3 Before powering on the circuit breaker, it is necessary to check whether the status of the relay protection and automatic devices meets the requirements of the dispatching department. 3.1.4 The door of the circuit breaker operating mechanism box must be tightly closed during operation, and the box should be protected from water, dust, and the entry of small animals. The heating device inside the enclosure is activated when the temperature is below 0°C and deactivated when it is above 10°C. When the heater is turned on, it is necessary to check that there are no debris inside the mechanism box; when maintaining the circuit breaker, the power supply to the heater should be disconnected first. The dehumidification unit should be turned on as normal. 3.1.5 The opening and closing circuit breakers are remotely operated using control switches. 3.1.6 After the circuit breaker is operated or trips due to an accident, in addition to checking whether the mechanical indications of the circuit breaker are correct, it is also necessary to check for any signs of discharge; for vacuum circuit breakers, it is important to verify whether the vacuum level within the vacuum chamber has been compromised ； For SF6 circuit breakers, it is necessary to check whether the gas pressure is normal and whether there are any leaks. 3.1.7 In addition to reflecting the actual status of the circuit breaker, the circuit breaker’s traffic light also indirectly monitors whether its opening and closing circuits as well as the operating power supply are functioning properly. If it is found that the traffic lights are not working, the cause should be identified promptly to restore normal operation. During the inspection and handling process, care should be taken to prevent the circuit breaker from closing or tripping accidentally. 3.1.8 Manual operation is mainly used for the maintenance and adjustment of circuit breakers; under live conditions, manual operation should be avoided as much as possible at the operating mechanism box. In the event of remote control failure, manual operation can be performed at the mechanism box in emergency situations. If the breaking capacity of the circuit breaker is insufficient, manual operation is prohibited, and the electromagnetic mechanism is not allowed to close the circuit under live conditions. For circuit breakers equipped with reclosing, the reclosing function should be disabled before performing a manual disconnection. 3.2 Operation and Maintenance of Circuit Breakers 3.2.1 Operation and Maintenance of SF6 Circuit Breakers 3.2.1.1 Operating regulations for SF6 circuit breakers: 1. Before entering the SF6 switch room, ventilation must be carried out for 15 minutes first. 2. In the event of an emergency such as a large-scale leak in the SF6 switchgear room, personnel should evacuate the area immediately and activate all exhaust systems to ventilate the area. Those not wearing isolated gas masks are prohibited from entering. Personnel are only allowed to enter after adequate natural ventilation or restored ventilation has been achieved. 3. When operating an SF6 switch, maintenance personnel are prohibited from working on its enclosure. 3.2.1.2 Inspection items for SF6 circuit breakers: 1. The gas pressure should be normal. 2. The circuit breaker makes no hissing sound. 3. The ceramic insulator should be free from damage and discharge marks. 4. There is no heating or discoloration at the connection points, and no discharge sound inside. 5. The open and closed position indicators are correct. 6. The grounding is in good condition. 3.2.2 Inspection items for vacuum circuit breakers: 1. The vacuum arc chamber is free of abnormalities, and the arc extinguishing cover has not changed color. 2. The ceramic insulator should be free from damage and discharge marks. 3. The open and closed position indicators are correct. 4. There is no heating or discoloration at the connection points, and no discharge sound inside. 5. The grounding is in good condition. 3.2.3 Routine inspection items for electromagnetic operating mechanisms: 1. The mechanism box door should be flat, open smoothly, and close tightly. 2. There are no signs of burning on the closing and opening coils. 3. The wiring terminals of the DC power supply circuit are not loose, and there is no green corrosion or rust. 3.2.4 Operation and maintenance of spring mechanisms 3.2.4.1 Operating regulations for spring mechanisms: 1. For spring energy storage mechanisms, the circuit breaker should remain in its energy-stored state during operation; after closing the circuit to supply power, it is necessary to check whether the mechanism has indeed stored energy. During the operation of the circuit breaker, the switch or fuse of the energy storage power supply must not be disconnected arbitrarily. 2. Since the circuit breaker uses manual energy storage, it is necessary to first disconnect the power switch for energy storage (or remove the energy storage fuse) to prevent sudden power restoration. Once manual energy storage is complete, the handle should be removed immediately to prevent injury from its rotation, and the energy storage power switch should be closed. 3.2.4.2 Routine inspection items for spring-operated mechanisms: 1. The mechanism box door should be flat, open smoothly, and close tightly. 2. Check the storage motor; ensure that the contacts of the travel switch are not stuck or deformed, and that there are no signs of burning on the opening and closing coils. 3. The circuit breaker is in the operating state, and the power switch or fuse for the energy storage motor is in the closed position. 4. When the circuit breaker is in the open standby state, the opening linkage should be reset, the opening latch should be in place, and the closing spring should be charged with energy. 5. The driving wave heating device is in good working condition. 3.2.4.3 Before performing maintenance work on the circuit breaker, the stored energy must be released in accordance with the requirements of the work order. Releasing the stored energy should be carried out according to the following steps: 1. Pull the AC power switch for the stored energy system (or remove the fuse for the AC power supply of the stored energy system). 2. Manually close the circuit breaker and then manually open it again. After the maintenance work is completed, the relevant power supply is connected to restore spring energy storage. 3.2.5 Operation and maintenance of hydraulic mechanisms 3.2.5.1 Operating regulations for hydraulic mechanisms: 1. The hydraulic mechanism of the circuit breaker should be regularly inspected visually; the hydraulic pressure must remain within normal levels. The oil level in the hydraulic mechanism’s oil tank should also be checked periodically, and there should be no signs of oil leakage. 2. The number of starts of the oil pump in the hydraulic mechanism should be monitored; it should not start more than twice within 24 hours. 3. When a \"trip lockout\" or \"close lockout\" signal appears, it is not permitted to release the lockout or perform any corresponding operations on the mechanism. 3.2.5.2 Normal inspection items for hydraulic mechanisms: 1. The mechanism box door is flat, opens smoothly, and closes tightly. 2. Check that the fuel tank level is normal and there are no leaks. 3. The pressure of the high-pressure oil is within the allowable range. 4. There is no unusual odor inside the enclosure. 5. The driving wave heating device is in good working condition. 3.2.6 Acceptance items for new installation and maintenance of circuit breakers: 3.2.6.1 The lead connections are secure and not loose, with correct electrical and mechanical indications. 3.2.6.2 The arc extinguishing chamber of the vacuum circuit breaker is normal, and the arc extinguishing cover has not changed color. The pressure of the gas in the SF6 circuit breaker should be normal. 3.2.6.3 The ceramic insulation is intact and clean, the enclosure is firmly grounded, and there are no objects left inside the equipment unit. 3.2.6.4 The electromagnetic operating mechanism shall function correctly; the energy storage part of the spring mechanism should operate properly, and the hydraulic mechanism shall have adequate energy storage without any oil leakage. 3.2.6.5 The circuit breaker was operated electrically three times for opening and closing; the protection action and reclosing function tests were successful, and the opening/closing indications matched the mechanical indications. 3.2.6.6 The maintenance and testing documents and items are complete, the data is satisfactory; it indicates whether there have been any changes to the equipment, as well as any existing problems and precautions, along with a conclusion regarding whether the equipment can be put into operation. 3.3 Abnormal operation of circuit breakers and accident handling 3.3.1 If severe discharge sounds are heard inside a circuit breaker during operation, the circuit breaker at the higher level in the power supply chain should be turned off promptly (if there are power supplies on both sides, both circuit breakers should be turned off), and then that circuit breaker along with the disconnect switches on both sides should also be turned off ； In the event of phenomena such as melting at the pole tip, glue leakage from the bushing, cracking of the porcelain sleeve, or broken leads, the circuit breaker and the disconnect switches on both sides should be quickly disconnected. 3.3.2 If serious defects are detected during operation, such as SF6 circuit breakers leaking to the locking pressure, vacuum breakers losing their vacuum, or the pressure in the operating mechanism falling below the locking value, the circuit breaker should be set to non-automatic mode, and the dispatch center should be informed. There is a bypass circuit breaker that can be activated to provide backup power. 3.3.3 In the event that a circuit breaker fails to open or fails to close due to a self-holding circuit for closing, the control power supply for that circuit breaker should be disconnected immediately, and the situation should be reported to the dispatching staff and relevant supervisors for further handling. If there is a bypass circuit breaker, the dispatch should be requested to activate it as a backup supply, after which the faulty circuit breaker should be switched to cold standby for further handling. 3.3.4 When the circuit breaker operating mechanism is malfunctioning and there is a bypass circuit breaker available, it can be used as a substitute. After setting the bypass circuit breaker to manual mode, the disconnect switches on both sides of the circuit breaker that refuses to open can be used to isolate it. If there is no bypass circuit breaker, isolate the faulty circuit breaker by turning off the circuit breaker at the next higher level. 3.3.5 When the circuit breaker fails to trip due to a protection action, resulting in the protection of the upstream circuit breaker tripping at a higher level, it is necessary to report to the dispatching team to determine the cause and handle the situation in accordance with the relevant regulations for such over-level tripping. 3.3.6 The circuit breaker that refused to trip must be switched to cold standby before the cause can be investigated. The circuit breaker shall not be put into operation until the fault of refusal to trip is resolved. 3.3.7 In the event of a fault-induced trip of a line circuit breaker, regardless of whether reclosing is successful or not, it is necessary to investigate the operation of the protection and automatic devices and report to the dispatch center. 3.3.8 When there are abnormal conditions with the circuit breaker, it is necessary to report them to the dispatching department and relevant supervisors in a timely manner, and fill out a defect report form. 3.3.9 In the event of an accidental opening or closing of a circuit breaker, handle it in accordance with the following principles: 3.3.9.1 If a circuit breaker is accidentally opened, close it immediately if there are no parallel circuits connected, and then report the incident. For those in a parallel relationship, they are handled according to the scheduling instructions. 3.3.9.2 Any misoperation of the equipment or accidental contact with the protection wiring that results in incorrect operation of the circuit breaker shall be handled in accordance with 3.3.9.1. 3.3.9.3 In the event of a busbar power loss, report to the dispatching office immediately and follow their instructions. In case of communication failure, close the circuit breaker of the feed line to restore power supply to the main transformer; the circuit breakers of other lines should be handled after attempting to establish contact with the dispatching office. 3.3.10 Handling of Emergency Incidents and Safety Protections for SF6 Circuit Breakers 3.3.10.1 In the event that any of the following conditions are detected while an SF6 circuit breaker is in operation, it is necessary to request a power outage for maintenance immediately: 1. Severe leakage of SF6 gas that cannot be sealed up. 2. The SF6 gas pressure drops to the lockout pressure value. 3.3.10.2 In case of emergencies such as a large-scale gas leak or a pressure increase exceeding the allowable levels, emergency protective measures must be taken, and the situation must be reported immediately to the dispatch team and relevant supervisors. All ventilation systems indoors should be turned on immediately. Depending on the circumstances of the accident, the staff wear appropriate gas masks or oxygen respirators before entering the scene to handle the situation. 3.3.10.3 After handling the accident, all protective equipment should be cleaned thoroughly. 3.3.11 Common abnormalities of operating mechanisms and their handling 3.3.11.1 Common abnormalities of electromagnetic mechanisms and their handling: 1. The closing contactor or auxiliary switch lever is not suitable, resulting in the contacts failing to close. 2. The trip mechanism has not been restored. 3. The closing core is stuck, the trip mechanism fails, and the movable core of the coil gets stuck. 4. The breaker’s operating mechanism is loose. 3.3.11.2 Common abnormalities of spring mechanisms and their handling: 1. After the circuit breaker is closed, a \"spring not energized\" signal may appear for a short time; if this signal does not disappear automatically, the power supply for energy storage should be cut off promptly, after which the cause should be investigated. 2. If the energy storage motor is damaged and power needs to be supplied to the circuit breaker immediately, manual energy storage can be performed; however, manual energy storage should be carried out again right after power is supplied, to meet the requirements for reclosing. 3.3.11.3 Common abnormalities of hydraulic mechanisms and their handling: 1. If the machine starts frequently or the pressure restoration time is too long, it should be reported to the work area; the cause should be identified and resolved. In cases of severe oil leakage, power should be cut off. 2. When the hydraulic mechanism in operation sends a signal for pressure-locking opening or closing, the position of the piston rod in the pressure storage cylinder inside the mechanism box, the reading on the oil pressure gauge, and the motor power supply circuit should be checked immediately, and the situation should be reported to the dispatch center right away. 3. When an abnormal pressure signal is detected from the hydraulic mechanism during operation, it should be inspected immediately, the oil pump should be stopped from generating pressure, and the situation should be reported to the dispatch center and the work area. 4. When the pressure of the hydraulic mechanism drops to zero during operation, preventive measures against slow decompression must be taken immediately; manual pressurization of the mechanism is prohibited at this time. 3.4 Inspection items for routine inspections of switchgear and regulations during operation 3.4.1 GIS switchgear 3.4.1.1 Inspection items for routine inspections of GIS switchgear: 1. Whether the position indicators of switches, disconnectors, and grounding switches match the actual conditions. 2. Check the various signal indicators on the on-site control cabinet to determine whether the control switches are in the correct position and whether any signal relays are activated. 3. Check whether the readings of various pressure gauges are normal, whether there are any leaks in the SF6 gas and hydraulic systems, whether all pipes and valves are intact and free from rust, and whether their opening and closing positions are correct. 4. Check whether there is any change in the indication value of the arrester’s operation counter. 5. Check whether the external incoming terminal is overheating, and whether the porcelain sleeve is cracked or damaged. 6. Are there any abnormal noises or odors? 7. Check whether the casing, brackets, etc. are rusted or damaged, whether the grounding is in good condition, and whether all box doors are tightly closed. 8. Is the ventilation system good? 3.4.1.2 Regulations for the normal operation of GIS switchgear 1. In addition to complying with general safety regulations during operation, GIS units must also pay special attention to the properties of SF6 gas: firstly, SF6 gas and the products resulting from its arc decomposition can leak out, contaminating the environment and posing a risk to human health ； Secondly, there is the risk of electric shock resulting from internal failures in the equipment or errors during operation. 2. To prevent oxygen deficiency and asphyxiation accidents that could occur due to the accumulation of SF6 gas in low-lying areas, operators should turn on the ventilators to exhaust air for 15 minutes before inspecting the equipment, and maintenance personnel should do the same before entering the work area. 3. During each inspection, the operators should record the SF6 gas pressure and ambient temperature in each gas chamber of the GIS apparatus. If any abnormalities are detected during the inspection, such as a drop in gauge pressure, an unpleasant odor, or a feeling of discomfort due to gas leakage, appropriate actions must be taken in accordance with the safety protocols for dealing with SF6 gas leaks. 4. The pressure parameters of each gas chamber in the GIS switchgear during operation shall meet the specified requirements. 3.4.1.3 Operating regulations for GIS switchgear 1. During the normal operation of GIS switchgear, the switches and motorized disconnectors must be operated remotely; after operation, it is necessary to check whether the device position signals are correct. Operation via the local control panel may only be used during equipment maintenance or in special circumstances. 2. When operating GIS switchgear, everyone must stop working on the equipment enclosure and move away from the equipment until the operation is completed. When manually operating the grounding switch, the operator should wear insulating gloves and maintain a certain distance from the equipment. 3. All switch and isolator operation circuits in GIS composite apparatus are equipped with electrical interlock devices; if any obstacle occurs during operation, it is necessary to check whether the interlock devices are functioning properly. The specific locking logic is described in the section on error prevention devices. 4. To prevent the accidental closing of the grounding switch on 110 kV lines while they are under voltage, it is necessary to first remotely open the switch and the isolating switch, then check on-site to confirm that the line’s voltage transformer has indeed lost power and that the leakage current meter of the line’s arrester shows no reading. After verifying this with the dispatch center, it is then possible to close the line’s grounding switch. 3.4.1.4 Accidents and Abnormal Operation of GIS Switchgear 1. If, during inspections, abnormalities such as a drop in gauge pressure, unusual noises, or irritating odors are detected, it is necessary to immediately report to the dispatch center and the relevant work team, investigate the cause, and take appropriate measures. 2. When an alarm for a decrease in SF6 pressure is triggered, one should immediately go to the site to check the pressure indicated by the gauge as well as the gas chamber, in order to determine whether there is a leak. If a significant leak is detected, it is necessary to report this to the dispatch team right away and request that power be cut off for repairs. 3. When the SF6 pressure of the switch drops to the locking value, the switch enters a locked state for opening and closing; it is necessary to immediately switch the switch to manual mode and inform the dispatch team and the relevant work area so that appropriate action can be taken. 4. In the event of an accident in a GIS device that results in gas leakage, personnel are not allowed to enter the site casually. All ventilation systems must first be turned on to ensure proper ventilation. Those who enter the site must wear gloves and gas masks, as well as protective clothing. 3.4.1.5 Acceptance items after maintenance and installation tests of GIS switchgear: 1. GIS switchgear is generally only subjected to minor maintenance, rather than major disassembly repairs. Dismantling for major overhaul is considered only when the operation time is long (over 10 years), or when there are serious abnormalities and fault tripping occurrences during operation, as well as when the number of operations exceeds the specified limit. The normal routine maintenance cycle is once every two years. During minor maintenance, in addition to carrying out the tests related to the electromechanical properties and preventive testing of the corresponding equipment, the following tasks must also be performed: a) The water content in SF6 gas during the microwater test must meet the specified requirements. b) The leakage test standard is an “annual leakage rate” of <1%. 2. Acceptance criteria for GIS switchgear: a) It shall be firmly installed, have a clean and intact exterior, and its operating performance shall meet the specified requirements. b) The SF6 gas leakage rate and moisture content shall meet the specified requirements. c) The linkage mechanism between the circuit breaker and its actuating mechanism should function properly, without any jamming; the opening and closing indicators should be accurate. During testing, the auxiliary contacts and electrical interlock devices should operate correctly and reliably. d) The alarm and locking setpoints of the equipped density relay shall meet the specified requirements, and the signal operation shall be correct. e) The incoming line live display device shall be able to reliably lock out the incoming line quick grounding switch. f) The paint is intact, the color markings are correct, and the grounding is good. g) The pull and close tests (including remote operation) pass. h) The electrical test report is satisfactory, with complete records and a conclusion indicating readiness for operation. 3.5 10kV metal-clad withdrawable switchgear 3.5.1 10kV metal-clad withdrawable switchgear (center-mounted type). 3.5.2 The switchgear is divided into an outdoor cubicle area, a cable compartment, a busbar compartment, and an outdoor secondary control compartment by grounded metal partitions. The cubicles include switch cubicles, voltage transformer cubicles, fuse cubicles, arrester cubicles, service transformer cubicles, and isolation cubicles. 3.5.3 The switchgear is equipped with functions such as preventing the disconnection or connection of isolation plugs while under load, preventing power supply when the grounding switch is in the closed position, preventing the accidental closing of the grounding switch while the system is energized, and preventing unauthorized entry into energized compartments. 3.5.4 The switchgear compartment is equipped with a heater at the front of the bottom panel; it should be turned on during normal operation to prevent condensation on the switches. 3.5.5 The grounding switch is equipped with a mechanical interlock device and an electrical locking circuit. 3.5.5.1 One end of the interlock rod for the grounding switch is fixed to the arm of the main shaft of the grounding switch, while the other end is mounted on a stopper inside the carriage compartment. As the main shaft of the grounding switch rotates, the interlock rod swings back and forth, causing the stopper in the carriage to move up and down, thereby preventing the carriage from moving forward. In other words, the carriage can only be moved to the working position when the grounding switch is in the open position; the grounding switch can be closed only after the carriage has been pulled to the testing position or further. 3.5.5.2 To prevent the grounding switch from being closed accidentally while the line is under voltage, an electromagnetic lock is installed in the switch cabinet. When the high-voltage status indicator on the line side shows that there is voltage present, the electromagnetic lock locks, preventing operation of the grounding switch. When the high voltage is turned off, the electromagnetic lock is unlocked thanks to an external power source; at this point, it is possible to press the lever located in the socket of the grounding switch’s operating rod, thereby exposing the socket. Once the operating rod is inserted, the grounding switch can be opened or closed. 3.5.5.3 Operation method of the grounding switch: 1. For closing the switch, insert the operation handle into the operation shaft (the socket on the control lever is already open), then rotate the handle 180 degrees in a clockwise direction; the grounding switch will thus be closed. 2. The disconnection procedure is the same as the closing procedure: rotate the operation handle 180 degrees in the counter-clockwise direction, and the grounding switch will be disconnected. 3.5.6 After pulling the trolley out of the cabinet, check that the baffle is closed and hang a “Stop, High Voltage Danger” sign at the baffle. 4. High-voltage distribution installations 4.1 Operating regulations for high-voltage distribution installations 4.1.1 Distribution installations include busbars, circuit breakers, disconnect switches, instrument transformers, coupling devices, power capacitors, reactors, connection wires between devices, as well as overvoltage protection devices, etc. 4.1.2 Indoor and outdoor power distribution installations shall be equipped with dedicated grounding electrodes for installing grounding wires. The non-live metal enclosures and equipment frames of power distribution equipment shall be reliably grounded in accordance with regulations. 4.1.3 The distribution equipment shall be equipped with sufficient fire-fighting facilities suitable for electrical fire suppression as required, and these facilities shall be placed in fixed locations where they are regularly inspected and maintained. 4.1.4 Lighting facilities should be installed in the main passages of indoor and outdoor power distribution installations as well as near the main equipment. These lighting facilities should maintain a sufficient safety distance from the power distribution equipment and should be easy to maintain and repair. 4.1.5 Sufficient safety equipment and spare parts shall be provided in accordance with relevant requirements. The safety equipment must be properly stored and regularly tested; expired or substandard safety equipment is prohibited from use. 4.1.6 The building containing the switch room should be leak-proof; doors and windows must be in good condition and tightly closed. Ventilation openings and holes should be fitted with protective grids, and measures should be taken to prevent small animals from entering. Cable trench openings must be sealed in accordance with regulations. 4.2 Busbars and disconnectors 4.2.1 Inspection items: 4.2.1.1 The ceramic insulation should have no damage, cracks, signs of discharge, or abnormal discharge sounds. 4.2.1.2 The contacts of the switchgear should be in good condition, and there should be no overheating or discoloration at any connection points; increased inspection is required during peak load periods. 4.2.1.3 The switch support must be properly grounded, and the cast iron parts must be free from rust or cracks. 4.2.1.4 In winter, it is necessary to check that there is no water accumulation or freezing cracks on the switch operating lever and the porcelain insulators of the poles. 4.2.1.5 The sag of the flexible busbar should be normal, with no strand breaks or loosening ； The rigid busbars should be properly fixed, and the expansion joints should show no signs of overheating or discoloration. 4.2.1.6 There is no looseness or bolt loss at the busbar connections. 4.2.2 The knife switch is permitted to be used for the following operations: 4.2.2.1 Opening and closing voltage transformers when the system is not grounded or in a resonant state. 4.2.2.2 Operate the arrester when there is no lightning strike. 4.2.2.3 Pulling and closing the unloaded busbar. 4.2.2.4 Transformer used for pulling and closing under no-load conditions. 4.2.2.5 Bypass current of the closing/closing circuit breaker. 4.2.2.6 When the system is ungrounded, switch the arc-suppression coil on and off. When the aforementioned equipment is newly installed or has been out of use for a long time, charging must not be carried out directly using a knife switch. 4.2.3 Methods of operating the knife switch 4.2.3.1 Use the locking devices designed to prevent accidental operation correctly. 4.2.3.2 Before opening or closing the switch, it is necessary to check that the corresponding circuit breaker is indeed in the off position. When shutting down power, the load side should be disconnected first, followed by the power supply side; the reverse order applies when restoring power. After closing, it is necessary to check whether each phase of the switch has been properly opened or closed, and whether the auxiliary contacts are in good contact. 4.2.3.3 When performing equipotential operations using a knife switch, the corresponding circuit breaker must first be set to non-automatic mode. 4.2.3.4 When operating manually, actions should be quick and decisive, but force should not be applied excessively to prevent the porcelain bottle from breaking. If the disconnect switch is accidentally pulled and has been fully opened, it is prohibited to close it again ； If it is discovered that the circuit breaker has been mistakenly closed, it should be quickly reopened. During closing, if the switch is closed by mistake, it must not be opened again under any circumstances. 4.2.3.5 When operating the knife switch using an electric actuator, the following rules must be followed: 1. Before operation, it is necessary to confirm the number of the knife switch as well as the open/close indicators on the control buttons. If the knife switch does not operate during electric operation, the power supply for its operation should be disconnected immediately to determine the cause. If necessary, it can be operated manually. 2. For electrically operated circuit breakers, the operating power supply should be disconnected under normal conditions; it should only be connected before operation and disconnected after operation, in order to prevent accidental opening or closing due to circuit faults during operation. 3. If a motor-operated circuit breaker needs to be operated manually for some reason, it should be turned into position by hand, and it is necessary to ensure that the auxiliary contacts of the circuit breaker switch accordingly. 4.2.3.6 Before closing the grounding switch, it is necessary to confirm that there is no voltage present. 4.2.4 Basic technical specifications for busbar operations 4.2.4.1 Before putting newly installed, overhauled, or long-term standby busbars into service, the busbars should be charged using a circuit breaker equipped with protection. 4.2.4.2 When charging the 110KV bus with a transformer, the neutral point of the 110KV side of the transformer must be grounded. 4.2.4.3 When charging the busbar, care should be taken to prevent ferroresonance or overvoltage resulting from uneven three-phase-to-ground capacitance of the busbar. 4.2.4.4 For the sectionalized wiring with a single busbar, if sectionalizing switches are used to turn power on or off for a particular section of the busbar, it is necessary to ensure that all the outgoing circuit breakers and the main transformer circuit breaker on that section of the busbar are in the open position before carrying out the operation. 4.2.4.5 When transferring load using a bypass bus, circuit breakers must be used to open and close the circuits; any operation on the bypass switches should only be performed with the bypass circuit breaker in the open position. 4.3 Transformers 4.3.1 Normal inspection items for transformers: 4.3.1.1 The secondary instruments and relays connected to the transformer during operation should function properly. 4.3.1.2 The primary and secondary fuses as well as the current-limiting resistors of the voltage transformer must be in good condition; the connections should be secure and the grounding proper. Short circuits on the secondary side are strictly prohibited. 4.3.1.3 The primary and secondary wiring of current transformers must be secure, with proper grounding; an open circuit on the secondary side is strictly prohibited. 4.3.1.4 The bushings and enclosures shall be clean, free of cracks and discharge marks ； The oil color and level of the oil-immersed transformer are normal, with no leaks; the connections at the outlet of the transformer should be properly sealed, with no oil leakage or oozing of resin. 4.3.1.5 There should be no unusual odors or noises inside, and dry-type transformers should not produce loud vibration sounds. 4.3.1.6 The outdoor terminal box should be free from moisture, and the wiring terminals should have no dust accumulation or discharge phenomena. 4.3.1.7 The harmonic suppression device of the voltage transformer shall be in good working condition. 4.3.2 Operations and precautions for starting and stopping voltage transformers: 4.3.2.1 When starting, the primary side should be activated first and then the secondary side; the reverse order is applied when stopping. It is prohibited to allow the voltage transformer to be reverse-charged. 4.3.2.2 When deactivating a voltage transformer or removing its secondary fuse, the relay protection devices connected to that voltage transformer should be taken into consideration first, in order to prevent incorrect operation of the protection systems. 4.3.2.3 When the bus or line is restarted, the corresponding voltage transformer should be put into operation first; the reverse is true when it is shut down. (Except in cases where resonance may occur) 4.3.2.4 After the wiring of the primary and secondary circuits of the voltage transformer has been completed, phase alignment should be checked again. 4.3.2.5 When the primary busbars in sections I and II (or the main and auxiliary busbars) are operating in parallel, if one set of busbar voltage transformers is taken out of service while the corresponding busbar continues to operate, it is possible to first connect the secondary sides of the voltage transformers in parallel and then remove those transformers from service; the reverse procedure is followed when reactivating them. If the primary sides are not connected in parallel, the secondary sides of the voltage transformers must not be connected in parallel either. Two groups of voltage transformers should not be operated in parallel for a long time. 4.3.3 Faults of voltage transformers and their handling 4.3.3.1 When indications of voltage, power, electrical energy, etc. are abnormal, it is necessary to check the fuses in the secondary circuit of the voltage transformer, the air switches, the auxiliary contacts of the voltage transformer’s switchgear, as well as the condition of the voltage transformer itself, in order to resolve the faults promptly. 4.3.3.2 If the low-voltage fuse of the voltage transformer blows or the air switch trips, and no obvious abnormalities are found upon inspection, the fuse should be replaced in accordance with the original specifications or the air switch should be closed to restore normal operation. If it blows again, the cause should be identified promptly. 4.3.3.3 If the high-voltage fuse of the voltage transformer blows, it should be replaced while the device is in maintenance mode; if it blows again, the device must be shut down immediately to determine the cause. 4.3.3.4 If the AC voltage from the voltage transformer disappears, it may cause abnormalities in the protection or automatic control devices and lead to erroneous operations; if the issue cannot be resolved on its own, it is necessary to report to the dispatching department, the relevant work area, and other relevant parties so that they can send someone to handle it as soon as possible. At the same time, it is required to request the dispatching department to deactivate the relevant protections. 4.3.3.5 The voltage transformer shall be shut down immediately in the event of any of the following faults: 1. The primary fuse blows twice in a row. 2. There is a discharge sound or severe noise inside. 3. There is significant oil leakage from the body or sleeve, or severe resin leakage at the outlet of the lead wires. 4. An unpleasant burnt smell emanates from the inside, there is smoking, and a fire breaks out. 4.3.3.6 When an abnormal condition occurs in a voltage transformer (such as internal discharge sounds or smoking), which may develop into a fault, or when a single-phase ground fault has occurred in the PT bay of a low-current grounding system, the following handling principles apply: 1. The high-voltage disconnect switch of that voltage transformer must not be operated using remote control (except when the high-voltage fuse has indeed blown). 2. The secondary of this voltage transformer shall not be connected in parallel with the secondary of a normally operating voltage transformer. 3. When it is not possible to use a high-voltage isolating switch for isolation, a circuit breaker can be used to cut off the power supply to the busbar where the voltage transformer is located, and then the faulty voltage transformer can be isolated. 4.3.3.7 When resonance occurs in the system, resulting in a high overvoltage level or phase voltage imbalance, it is necessary to report to the dispatching team to immediately eliminate the conditions for resonance and put an end to it. 4.3.4 Precautions during the operation of current transformers: 4.3.4.1 When the current transformer is taken out of service along with the circuit breaker, and maintenance or testing work is carried out on the current transformer, its secondary sides for protection, metering, telemetry, etc., must be reliably short-circuited and grounded. 4.3.4.2 The secondary circuit of the current transformer must not be open-circuited. When it is necessary to replace instruments or carry out other operations that may affect the circuit, the secondary terminals should be short-circuited. Only after the work is completed and it has been confirmed that the secondary circuit forms a closed loop can the short-circuiting wires be removed ； When protecting devices are in use or being switched over (such as differential and reverse current protections), care should be taken when shorting or switching the secondary sides of current transformers. If it is impossible to avoid the generation of unbalanced currents during these operations, the relevant protection should be deactivated first according to the dispatcher’s instructions, before proceeding with any operations on the CT secondary circuit; the CT side should be shorted first, followed by the disconnection of the relevant circuits. 4.3.5 Detection and handling of open circuits in the secondary circuit of current transformers: 4.3.5.1 An open circuit in the secondary circuit of a current transformer may present the following symptoms: 1. A decrease in values such as current and power, or these values becoming zero, as well as an increase in errors in electricity measurement. 2. The current transformer has high noise and uneven vibration. 3. The current transformer itself heats up severely, with abnormal odors, discoloration, or even smoking. 4. There are discharge and arcing phenomena at the terminals of the current transformer’s secondary circuit as well as at the ends of its components. 5. Relay protection operates erroneously or fails to operate. Depending on the load conditions and the location of the break, the above phenomena generally do not occur simultaneously; when the load is light, they may be difficult to detect. Operators should conduct a careful analysis based on the actual situation in order to take timely action. 4.3.5.2 Handling of an open circuit in the secondary circuit of a current transformer: 1. Upon detecting an open circuit in the secondary circuit of a current transformer, it is necessary to immediately inform the dispatch center and the relevant work team; at the same time, efforts should be made to reduce or divert the primary load current. 2. If it can be handled by oneself, use safety tools with good insulation properties to make a short circuit at the nearest test terminal; if it cannot be handled by oneself, report it immediately to superiors so that someone can handle it. 3. In severe cases, it is necessary to report to the dispatch team, open the high-voltage circuit breaker, and cut off the power supply for handling. If smoke or fire is observed due to rheological effects, the circuit breaker can be turned off first, followed by reporting the incident. 4.4 Coupling Equipment 4.4.1 The grounding switch of the coupling capacitor must be opened while in operation; if it needs to be closed for operational reasons, permission from the dispatch center must be obtained before doing so. Work on the operating wave blockers, coupling capacitors, combined filters, and their secondary circuits must be approved by the dispatch team, and work permits must be obtained. 4.4.2 Inspection items for coupling equipment: 4.4.2.1 The porcelain bushing of the coupling capacitor should be intact, without any damage or abnormal discharge sounds. 4.4.2.2 The coupling capacitor shall show no oil leakage. 4.4.2.3 There is no looseness or overheating at the connections of the coupling capacitors and wave stoppers. When a short circuit occurs in the system, attention should be paid to ensure that the wave blocker shows no obvious deformation. 4.4.3 In the event that any of the following conditions are detected in the coupling equipment, it should be reported to the dispatcher as soon as possible: 4.4.3.1 The porcelain sleeve of the coupling capacitor is cracked or has visible fissures. 4.4.3.2 The coupling capacitor leaks oil or makes abnormal noises internally. 4.4.3.3 The core-penetrating fixing screw of the wave blocker is broken, or the coil heats up and deforms. 4.5 Power Capacitors 4.5.1 During operation, the voltage across the capacitor shall not exceed 1.1 times the rated voltage ； The current must not exceed 1.3 times the rated current, and the three-phase currents should be balanced, with a difference of no more than 5%. 4.5.2 Inspection items for capacitors: 4.5.2.1 The bushings and supporting insulators should be in good condition, without any cracks or signs of discharge, and the fuses should be intact. 4.5.2.2 No internal squealing discharge sound. 4.5.2.3 There should be no oil leakage, and the enclosure shall show no deformation or bulging. 4.5.2.4 The room temperature in the capacitor chamber should not exceed 40°C; if this temperature is exceeded, a fan should be activated. The maximum temperature on the outer surface of the capacitors should not exceed 55°C. For imported capacitors, the requirements specified by the manufacturer shall be followed, and these requirements shall be included in the supplementary provisions of the substation operation procedures. 4.5.2.5 The leads and all joints are properly connected, with no signs of looseness, heating, discoloration, or melting of the temperature-indicating elements. 4.5.2.6 The doors and windows of the capacitor room are airtight to prevent small animals from entering, and the ventilation openings are properly protected by screens. 4.5.2.7 The discharge voltage variation and indicator lights should be normal. 4.5.2.8 For compact capacitors, it is necessary to check whether the oil level indicator is functioning properly. 4.5.3 Precautions for capacitor operation: 4.5.3.1 Ensure that capacitors are put into operation as much as possible, provided that no reactive power is fed back into the system and voltage requirements are met. 4.5.3.2 When the busbar to which the capacitor is connected experiences a sudden power outage, the capacitor voltage loss protection should activate to cause the capacitor circuit breaker to trip. If it does not trip, separate them immediately. 4.5.3.3 When the bus is taken out of service, the capacitors should be disconnected first, and then the circuit breakers of each outgoing line should be opened. During power supply, the line circuit breaker is closed first, and then capacitors are connected based on the bus voltage and load conditions. 4.5.3.4 After the capacitor circuit breaker is opened or tripped, it is prohibited to close it immediately; a delay of 5 minutes is required before attempting to close it again. When performing maintenance work on capacitors, they must be fully discharged one by one in advance. 4.5.3.5 It is prohibited to use a knife switch to open or close capacitors. 4.5.3.6 Since the circuit breaker that disconnects the capacitor bank trips as a result of a protection action, it must not be closed again until the cause of the trip has been identified. 4.6 Reactors 4.6.1 Inspection items during normal operation: 4.6.1.1 During normal operation, the reactor shall not operate above its rated current. 4.6.1.2 The reactor itself should be clean and free of debris; in particular, there must be no magnetic contaminants around dry-type reactors. 4.6.1.3 The reactor support has good insulation and shows no signs of tilting or instability ； The connections at the swap points are in good condition, with no discharge sounds or burnt smell. 4.6.1.4 The oil-immersed reactor shows no oil leakage and the oil level is normal. 4.6.1.5 The concrete supports of dry-type reactors should be intact without cracks, the paint should not be peeling off, the coils should not be deformed, and the insulation should be in good condition. 4.7 Power cables 4.7.1 The normal operating voltage of the cable circuit shall not exceed 15% of the cable’s rated voltage. 4.7.2 Cables should in principle not be operated under overload; even in the event of overload during accident handling, their normal current level should be restored promptly. 4.7.3 Inspection items for cables: 4.7.3.1 Inspections of the cable trenches, tunnels, cable shafts, cable trays, and cable sections in substations shall be carried out at least once every three months. 4.7.3.2 For cables and terminal fittings connected to outdoor overhead lines, it is necessary to check whether the terminal fittings are intact, whether there is any heating at the joints of the lead wires, whether the cable’s lead coating is cracked or leaking oil, and whether there are any signs of damage caused by foreign objects (such as vehicles) on the section of cable near the ground. 4.7.3.3 For multiple cables run side by side, it is necessary to check the current distribution and the temperature of the cable insulation, in order to prevent overloading of the cables or damage to the connections due to poor quality joints. 4.7.3.4 For cables inside the tunnel, it is necessary to check whether their positions are normal, whether there is any deformation or oil leakage at the connections, whether the temperature is within normal ranges, whether any components are missing, and whether facilities such as communication systems, drainage systems, and lighting are intact. Pay special attention to whether the fire protection facilities are complete. 4.7.4 Cables in operation shall be shut down immediately if any of the following conditions occur: 4.7.4.1 The porcelain components at the cable ends are cracked or there is severe discharge. 4.7.4.2 The cable terminal is severely overheated, causing oil (sealant) to leak out and to smoke and decompose. 4.7.4.3 The cable lead is burned out or broken due to external force. 5. Overvoltage protection 5.1 Operation of lightning protection devices 5.1.1 The thunderstorm season runs from March 1st to October 31st each year; all arresters must be tested and found to be in good condition before March 1st, and then put into use. 5.1.2 The operation mode during the thunderstorm season shall be implemented in accordance with the requirements set by higher authorities for such a period. 5.1.3 If there is no arrester on the feed line side, it shall not be in hot standby mode during the thunderstorm season. 5.1.4 When any bus is put into operation, the corresponding bus arrester shall also be put into operation. 5.1.5 After a lightning strike, conduct a special inspection of arresters, lightning rods, and harmonic suppressors, and keep records of the lightning observations. 5.1.6 When inspecting high-voltage equipment during thunderstorms, insulating boots must be worn, and one should not approach lightning arresters or lightning rods. 5.1.7 Normal inspection items for lightning arresters. 5.1.7.1 The arrester shall be installed firmly and kept vertical. 5.1.7.2 The leads and grounding are in good condition, firmly connected, with no breaks or severe rust. 5.1.7.3 The porcelain should be clean and intact, without any damage, abnormal discharge sounds, or signs of arcing. 5.1.7.4 The flanges at the upper and lower sections of the arrester, as well as its insulating base, shall be free from cracks and fractures. 5.1.7.5 The action counter should be in good condition, and the wires from the arrester to the counter should not touch the ground. 5.1.7.6 For arresters equipped with online monitoring devices, it is also necessary to check whether their leakage current is within the specified range, and this value should be recorded daily. 5.1.8 During regular inspections of lightning rods, it should be ensured that the rod itself is not tilted, the tip of the rod is not bent, all welded parts are secure, and the foundation shows no signs of settlement. 5.1.9 Abnormalities of arresters and handling: 5.1.9.1 When the on-duty staff notices any of the following abnormalities in the arresters, they must immediately report to the dispatcher. The faulty arrester should be taken out of service according to the dispatcher’s instructions; if it is not possible to disconnect it immediately, close monitoring should be carried out, but no one should approach it to avoid being injured by an explosion of the arrester. 1. The ceramic sleeve has exploded or shows obvious cracks. 2. There are abnormal noises inside. 3. The lead or ground wire is broken. 5.1.9.2 Any abnormality detected in zinc oxide arresters equipped with online monitoring should be reported promptly. Under normal circumstances, if the reading on the milliammeter increases by 30% compared to the original value, caution is required. If it is not possible to shut down the power supply at that time, operation can continue, but closer monitoring is necessary. If the current increases by 50%, it is imperative to report this to the dispatch team so that the arrester can be taken out of service promptly. If the reading on the milliammeter decreases or even returns to zero, it may be due to a significant decrease in the insulation of the insulating base or a short circuit; it could also be caused by damage to the components inside the meter or recorder. This situation should be reported immediately to the dispatch team and relevant supervisors, and the work area should be informed so that someone can be sent to inspect and address the issue. 5.2 Automatic Harmonic Elimination Compensation Arc Suppression Coil Device 5.2.1 Principle and Function of the Arc Suppression Coil Device 5.2.1.1 It consists of a grounding transformer (determined by the operating mode of the system’s center point), an arc suppression coil, damping resistors, a capacitor bank (determined by the product model), and a microcomputer-based automatic tuning and compensation controller. During normal operation, the automatic tuning compensation device calculates the system’s capacitive current automatically based on the residual current and voltage at the system’s neutral point, and pre-tunes the arc-suppression coil to the desired current value (setting). When a single-phase ground fault occurs, the arc-suppression coil activates, using its inductive current to compensate for the capacitive current in the system; it also records the start and end times of the fault, the residual current, the actual voltage displacement at the neutral point, as well as the setting of the arc-suppression coil. 5.2.1.2 Functional roles 1. Grounding transformer: When the wiring configuration of the main transformer in the substation is delta connection (on the side where the arc-suppression coil is installed), a grounding transformer is used to create the neutral point of this system, and such a transformer should have a Z-shaped wiring configuration. The types are: dry-type and oil-immersed type. 2. Arc-suppression coil: When a single-phase ground fault occurs in the system, the arc-suppression coil generates an inductive current to compensate for the capacitive current in the system. 3. Damping resistor: Used to dampen resonant overvoltages and limit arc grounding overvoltages. 4. Capacitor resistance: It is installed when using a variable-capacitance arc-suppression coil compensation device. Its function is to change the capacitance of the capacitor bank in order to adjust the actual inductance of the arc-suppression coil, thereby regulating the compensation current of the arc-suppression coil. 5. Microcomputer-based automatic tuning compensation controller: It measures the residual voltage and residual current at the system’s neutral point, calculates the capacitive current of the system, and adjusts the compensation current of the arc-suppression coil. 5.2.2 General requirements for the normal operation of arc suppression coil devices 5.2.2.1 The AC and DC control and operating power supplies for this device must not be interrupted under any circumstances. 5.2.2.2 When the grounding transformer is equipped with an unbalanced wiring scheme (with unequal tap settings for the three-phase windings), the voltage in the open delta winding of its system busbar voltage transformer must not exceed the operating value of the grounding signal. 5.2.2.3 A system with the neutral point grounded through an arc-suppression coil should operate in an over-compensated state. 5.2.2.4 When the system’s capacitance current to ground exceeds 10 A, an arc suppression coil device must be installed. 5.2.2.5 When a single-phase ground fault occurs in the system, the operators should promptly check the operation signals and information of the device, examine the phase involved in the ground fault, the ground voltage, the compensation current, and the operation time, and also conduct inspections on the microcomputer-controlled automatic tuning arc-suppression coil device. 5.2.2.6 The reports or printed outputs generated after the microcomputer-based automatic tuning arc-suppression coil device operates should be stored in a centralized location. 5.2.2.7 When the device has automatic and manual operation modes, it shall operate in the corresponding mode according to the selected operation mode during normal operation. 5.2.2.8 During normal operation of the arc-suppression coil, its neutral point displacement voltage should be monitored; operation for an extended period is permitted when the displacement voltage is less than 15% of the rated phase voltage. 5.2.2.9 The load connected to the secondary winding of the arc-suppression coil grounding transformer shall be within the specified range. 5.2.2.10 Arc suppression coil units that have been out of service for half a year or more must undergo testing and inspection in accordance with relevant regulations and pass these tests before they can be put back into operation. 5.2.3 Inspection items for arc suppression coils 5.2.3.1 The equipment should have an intact appearance, with no abnormal vibrations, unusual noises, or strange odors; the outer insulation surface should be clean, free of cracks, and without any discharge phenomena. 5.2.3.2 The primary and secondary leads must have good contact; the connections must not be overheated, and there should be no heating or discoloration of any of the connection leads. The casing and the neutral point must be properly grounded. 5.2.3.3 The oil color and level of the equipment should be normal; the oil tanks, oil storage containers, insulators, bushings, valves, flanges, etc. should all be in good condition, without any cracks or signs of oil leakage ； Whether the silica gel in the humidifier is damp and has changed color. 5.2.3.4 The metal parts are free of rust, and the base and supports are firm, with no tilting or deformation. 5.2.3.5 The surface of the dry arc suppression coil should be smooth, free from cracks and moisture. 5.2.3.6 All fuses and secondary air switches in the damping resistor box are in good condition, and there is no looseness, overheating, or arcing at the lead terminals inside the damping resistor box. 5.2.3.7 All control cabinets and secondary terminal boxes shall be tightly closed and free from moisture. 5.2.3.8 For the tap-changing arc-suppression coil, manually adjust a tap to check whether the load switch is functioning properly. 5.2.4 Operation of the arc-suppression coil device 5.2.4.1 The activation and deactivation of the arc-suppression coil shall be carried out in accordance with the operating mode and dispatch instructions. When switching from the neutral point of one transformer to another while the arc-suppression coil device is in operation, it is necessary to disconnect the arc-suppression coil first before making the switch. The neutral points of two transformers must not be connected to the same arc-suppression coil. 5.2.4.2 When both the main transformer and the arc suppression coil unit are to be powered off, the isolating switch of the arc suppression coil should be opened first, followed by turning off the main transformer; the reverse sequence is applied when restoring power. 5.2.5 Operating requirements for arc-suppression coil devices during accident handling 5.2.5.1 When a single-phase ground fault occurs in the system, it is prohibited to operate or manually adjust the grounding transformer and arc-suppression coil on that busbar section. The signaling device of the arc-suppression coil shall activate to send a signal; the operators shall monitor the operation of the arc-suppression coil and record data such as the time of activation and deactivation, the phase involved in grounding, capacitive current, residual current, detuning degree, as well as neutral point voltage and current, and report this information to the dispatcher. 5.2.5.2 It is prohibited to open or close the single-phase isolating switch between the arc-suppression coil and the neutral point when the neutral point displacement voltage is greater than 15% of the phase voltage, or when there is a single-phase ground fault in the system and a humming sound from the arc-suppression coil can be heard. 5.2.5.3 When the neutral point displacement voltage is between 15% and 30% of the rated phase voltage, the allowable operating time shall not exceed 1 hour. 5.2.5.4 The neutral point displacement voltage, being within the range of 30% to 100% of the phase voltage rating, allows operation during the duration of an accident. 5.2.5.5 A single-phase ground fault must be resolved promptly; the time allowed for such a ground fault generally should not exceed 2 hours. 5.2.6 Abnormality handling of arc suppression coil devices 5.2.6.1 The operation should be stopped immediately if any of the following conditions occur in the arc suppression coil, grounding transformer, or damping resistor. 1. Under normal operation, the noise level increases significantly, with cracking sounds coming from inside. 2. Severe oil leakage or spraying, causing the oil level to drop below the indication limit of the oil gauge. 3. The sleeve has severe damage and discharge phenomena. 4. Smoking and catching fire. 5. When nearby equipment catches fire, explodes, or some other incident occurs, posing a serious threat to the complete installation. 6. When a fault occurs that endangers the safety of the complete installation, and the relevant protective devices fail to operate. 5.2.6.2 In the event of an abnormal fault in the arc suppression coil during operation with permanent system grounding that requires emergency shutdown, it is necessary to report to the dispatch immediately for further handling. When communication is lost, the grounded fault circuit should be disconnected in accordance with the regulations: if the grounded fault circuit has been identified, it must be disconnected immediately, after which the arc suppression coil should also be shut down ； When the ground point is unclear, the circuit with the ground fault and the power supply upstream of the arc-suppression coil should be immediately cut off in order to isolate the faulty arc-suppression coil. 5.3 Operation of grounding devices 5.3.1 Grounding devices include grounding conductors and grounding grids. 5.3.2 Inspection items for grounding devices: 5.3.2.1 Whether the grounding screws are loose. 5.3.2.2 Check whether there is any rust or breakage in the grounding down conductor. 5.3.2.3 Whether the enclosures of all electrical equipment are reliably grounded. 5.3.2.4 After a thunderstorm, a special inspection of the grounding system should be conducted. 5.3.2.5 Before the thunderstorm season each year, the grounding system should be inspected once. 5.3.2.6 Whether the green-yellow stripes on the surface of the exposed ground wire are clear. 5.4 Operating regulations regarding overvoltage protection 5.4.1 In systems with a directly grounded neutral point at 110 KV and above, the neutral point grounding switch must be in the closed position when the transformer is started or stopped. 5.4.2 When charging the 110KV bus with a transformer, the neutral point of the transformer’s 110KV side must be grounded. 5.4.3 For an operating transformer, if the circuit breaker on the 110 KV side is opened, the neutral grounding switch on that side should be closed. 5.4.4 When a 110KV transformer is in operation and it is shut down as part of a power restriction measure (the transformer can be energized once the circuit breaker on the power supply side is closed), the on-duty operator shall close the grounding switch for the 110KV side of the transformer. 5.4.5 In the event of a ground fault in lines of 35 KV and below, the duty officer should promptly make a judgment ； Is it a normal single-phase ground fault, or resonance overvoltage? In the former case, the voltage of the faulty phase decreases or becomes zero, while the voltage of the healthy phases increases or reaches the line voltage ； The latter is a phase voltage that rises to 2-3 times the normal phase voltage (resonant overvoltage is considered to occur as long as one of the phase voltages exceeds 2 times the normal value). At this time, the dispatcher should instruct the duty officer to quickly locate the faulty line and eliminate the fault. 5.4.6 To eliminate resonant overvoltages caused by magnetic saturation in voltage transformers of 35 KV and below, which can lead to the blowing of the high-voltage fuses in these transformers or the damage of voltage transformers, harmonic suppression devices should be installed. 5.4.7 For the handling of series resonance, refer to 12. Accident Handling. 6. Power supply system for communication 6.1 The substation should be equipped with two separate power supply units. The automatic switching device for the backup power supply of these units must be activated, and the operation staff should perform regular testing of this switching function on a monthly basis. 6.2 Two transformers connected to the same power source should not be operated in parallel, and two transformers connected to different power sources are prohibited from being operated in parallel. 6.3 All low-voltage side circuit breakers (or AC fuses) shall be accompanied by specification documents (listed in the supplementary section of the substation operation procedures); the fuse housings and the locations where the fuses are installed shall both have specification markings. 6.4 The emergency lighting should be tested for switching once a month. 6.5 Inspection items for the electrical systems in use: 6.5.1 The inspection items for the transformers in use are in accordance with those for main transformers. 6.5.2 The voice changer in use is functioning normally, with no abnormal sounds. 6.5.3 The respirator in use is in good condition, with the silicone showing discoloration not exceeding 2/3. 6.5.4 The bushings used are free of damage, cracks, and signs of discharge. 6.5.5 The used transformer enclosures, oil conservators, radiators, terminal boxes, and pressure relief valves shall be leak-free. 6.5.6 There is no heating, discoloration, or melting at any of the connections such as the variable lead connectors and cables used. 6.5.7 The doors, windows, and lighting in the transformer room used shall be in good condition; the building shall have no leaks, good ventilation, and normal temperatures. 6.5.8 The doors of the transformer cabinets used shall be properly closed, and the lighting shall be in good condition. 6.5.9 The voltage on the low-voltage side of the power supply shall not exceed 420 volts, nor be lower than 360 volts; the imbalance between the three phases shall not be greater than 5 volts. 6.5.10 The current under variable load conditions shall not exceed the rated value, and the imbalance in three-phase currents shall not be more than 25% of the rated value. 6.5.11 All indicator lights on the electrical control panel in use should be functioning properly, and there should be no unusual odors or noises inside the panel. 6.5.12 The fuses and current-limiting resistors on the high-voltage side in use are in good contact; there are no cracks in the porcelain components, and the fuses have not blown. 6.5.13 The external surface of the dry-type transformer shall be free from dirt accumulation and discharge flashover. 6.5.14 The low-voltage cables used shall have good insulation, and their outer surfaces shall be properly grounded. 6.6 After any work is performed on the electrical systems involved that may alter their phase, it is necessary to recheck that the phases are correct before bringing them back into operation. 6.7 Precautions for operating the transformers used 6.7.1 Under normal conditions, both transformers should be in operation. 6.7.2 The varying input voltage generally does not exceed 5% of the corresponding tap voltage. 6.7.3 The three-phase currents during the operation of the transformer in question should be kept as balanced as possible. If the unbalanced current approaches 25% of the current in the low-voltage windings, then the current in any one phase shall not exceed the rated value; meanwhile, the load should be adjusted to ensure symmetrical loading across the three phases. 6.7.4 When the transformer has serious defects (such as severe oil leakage, localized overheating, abnormal results from the analysis of gases dissolved in the oil, etc.) or weak insulation, it should not be operated at a current exceeding its rated value. 6.7.5 After rewiring a newly commissioned station transformer or low-voltage circuit, phase verification must be carried out before it can be put into operation; it can be operated only if the phase sequence is correct. 6.7.6 The switch or dropout fuse on the high-voltage side of the transformer can be opened and closed without any issues on an unloaded transformer. When there is a single-phase ground fault in the system or a fault occurs in the transformer itself, it is prohibited to operate the high-voltage side circuit breaker or dropout fuse to isolate the fault point. 6.7.7 It is strictly prohibited to parallel the electrical systems in use on the load side. 6.7.8 When replacing the AC power fuse on the low-voltage side, the power supply should be disconnected first, and a fuse of the same model and specifications should be used to replace the damaged one. 6.8 Switching operations of the service transformer: 6.8.1 When the service transformer is equipment under the control of the dispatching department, the operations on the high-voltage side of the service transformer shall be carried out in accordance with dispatching instructions. The low-voltage side switches and fuses are operated by the duty personnel as required by the work, with records kept after each operation. 6.8.2 The procedures for switching the high-voltage power supply of the transformers used during operation are listed in the supplementary section of the on-site operation regulations. 6.8.3 When enabling the transformer, do so first on the high-voltage side and then on the low-voltage side; when disabling it, do the opposite, to strictly prevent reverse charging from the low-voltage side to the high-voltage side. 6.9 The power supply must remain in normal operation, and any failures should be resolved as soon as possible. 6.10 The power used is dedicated to the substation; it is strictly prohibited to connect power sources outside the substation area. 6.11 Handling of Abnormalities and Accidents in the Power Systems in Use 6.11.1 When the duty personnel notice any abnormalities during the operation of the transformers in use, they should take steps to resolve them as soon as possible and report to the dispatching office and the relevant work team. Meanwhile, they must also ensure that the ventilation of the main transformers and the power supply for the DC high-frequency switches are functioning properly. 6.11.2 In the event of an abnormality in the transformer, it is strictly prohibited to disconnect the transformer by opening the high-voltage side isolating switch or the dropout fuse. 6.11.3 The transformer in use should be shut down in any of the following situations; if there is a spare transformer available, it should be put into operation as soon as possible: 6.11.3.1 When the noise produced by the transformer increases significantly, which is abnormal, and there are sounds of cracking inside it. 6.11.3.2 Severe oil leakage or spraying. 6.11.3.3 The bushing has severe damage and discharge phenomena. 6.11.3.4 The transformer used suffered from smoking and catching fire. 6.11.4 In the event of a fault that endangers the safety of the transformer and the high-voltage fuse of the transformer has not blown, the duty personnel shall immediately shut down the transformer. 6.11.5 When a fire, explosion, or other incident occurs near the transformer and poses a serious threat to it, the duty personnel shall immediately shut down the transformer. 6.11.6 In the event of a fire at any of the components, the power supply must be disconnected immediately, and fire-fighting measures must be taken promptly to prevent the fire from spreading. 6.11.7 If power supply to all equipment is lost due to some reason, the cause should be identified as soon as possible, the fault location should be isolated, and the power supply to the equipment should be restored at the earliest opportunity. During the handling of the incident, full consideration should be given to the impact of the loss of power supply on critical loads. 6.11.8 The transformer is prohibited from operating in two-phase mode on the high-voltage side. When one phase of the transformer’s high-voltage side fuse blows, the transformer must be taken out of service immediately; the cause must be identified and resolved. Only after the insulation has been verified to be satisfactory and approval is obtained from the responsible supervisor can the transformer be put back into operation. Until a clear fault location is identified for the two or three phases whose high-voltage side fuses have blown in that substation, it is prohibited to put that substation back into operation. 6.11.8.1 Phenomenon of one-phase blowout of the high-voltage fuse: The voltages of the two phases on the low-voltage side decrease by 1/2, while the voltage of the other phase remains normal. 6.11.8.2 Phenomenon of two-phase fusing of the high-voltage fuse: the voltage on the low-voltage side disappears completely. 6.11.8.3 Handling method: Report to the dispatching staff and supervising management to shut down the used transformer before replacing it. If it trips again after being connected, it should be disabled and reported to the supervisor for further handling. 6.11.9 If the air switch on the electrical distribution panel in use trips, that circuit should be inspected, and it is permissible to attempt to reset the air switch once; if this does not work, maintenance personnel should be notified to determine the cause of the fault. 6.11.10 When the used transformer is operating under overload conditions, the cause should be identified ； Cut off unimportant loads if necessary. 7. DC System 7.1 Operation Management 7.1.1 The operation and maintenance of DC power system equipment are carried out in accordance with the authority assigned for equipment management. 7.1.2 The operating authority shall conduct inspections and evaluations of the DC power supply systems under its jurisdiction on an annual basis, address any defects in the equipment of these DC power supply systems, conduct a comprehensive analysis of the problems existing in them, make accurate assessments of the equipment’s condition, and propose suggestions for technical upgrades and maintenance. 7.1.3 The on-site operation procedures shall include information regarding the operation, maintenance, and accident handling of the DC power supply system, and shall be in line with the actual conditions of the institute’s DC power supply system. 7.1.4 The operating unit shall have a maintenance management system for the DC system. 7.1.5 Regular maintenance work on the DC system should be included in the annual and monthly work plans. 7.1.6 Operators shall promptly address or report any defects found in the DC system in accordance with their maintenance responsibilities and authorities. 7.1.7 A DC system equipped with two sets of batteries shall operate in a busbar sectionalized mode; each busbar section shall be powered by an independent battery bank, and a tie switch or disconnect switch shall be installed between the two DC busbars. Under normal operating conditions, this tie switch or disconnect switch shall be in the open position. 7.1.8 DC fuses and air circuit breakers shall be of qualified quality; their fusing values or settings shall be arranged and calibrated in accordance with relevant regulations, and verified regularly to prevent accidents from escalating due to incorrect operation. 7.1.9 In the same circuit of a DC power supply system, fuses and air circuit breakers should not be used together; in particular, fuses should not be used upstream of air circuit breakers. Prevent loss of operational selectivity in the event of a circuit failure. It is strictly prohibited to use AC air circuit breakers in DC circuits.