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1 Accident Handling Procedures 1.1 Principles of Accident Handling 1.1.1 Tasks of accident handling: To limit the progression of the accident as quickly as possible, eliminate threats to the safety of people and equipment, remove or isolate the cause of the accident, maintain the normal operation of the equipment as much as feasible, and restore power supply to important users promptly. 1.1.2 In the event of an accident, the on-duty personnel shall promptly and thoroughly determine the switch that tripped, the operation status of the protective devices, as well as the readings of signals and instruments, in order to identify the scope and nature of the accident. They shall also check the condition of the primary equipment to determine the cause of the accident. 1.1.3 Report the accident situation to the dispatching department promptly. When dealing with the accident, follow the dispatch instructions; if the orders from other personnel conflict with these instructions, the dispatch instructions shall be followed. If following the instructions would pose a threat to human safety or equipment integrity, such instructions must not be carried out, and the reasons for not doing so should be reported to the dispatching department and the team leaders. 1.1.4 A detailed record of the entire accident handling process should be kept, and phone calls should be recorded. 1.1.5 In the event of any one of the above situations, the duty officer may handle the accident first and then report to the relevant supervisors and dispatchers. 1.1.5.1 Shut down equipment that poses a direct threat to the safety of personnel and equipment ； 1.1.5.2 Isolate damaged and compromised devices ； 1.1.5.3 Restoring power supply and power consumption for critical users ； 1.1.5.4 Forced power restoration after passive line tripping, and accident handling in the event of bus voltage loss ； 1.1.5.5 Accident handling permitted in the site procedures in case of communication interruption. 1.2 Handling of Transformer Accidents 1.2.1 Activation of the Light Gas Alarm in Transformers 1.2.1.1 Accident symptoms: The microcomputer monitoring system triggers an alarm, and the alarm display indicates that the main transformer numbered х has activated its light gas alarm. 1.2.1.2 Possible causes 1.2.1.2.1 Air entering the transformer due to oil filtering or refilling ； 1.2.1.2.2 The oil level drops slowly due to a drop in temperature or oil leakage ； 1.2.1.2.3 Gas generated due to minor internal faults in the transformer ； 1.2.1.2.4 Light gas secondary circuit fault. Gas, properties Types of faults Colorless, odorless, non-flammable Slightly yellow, non-flammable Light gray, flammable, with a strong odor Gray-black and flammable Air Damage to wooden insulation Faults in paper and cardboard Faults in insulating oil 1.2.1.3 Treatment methods 1.2.1.3.1 Check the operation status of the main transformer, whether there is gas inside the gas relay, and ensure that the temperature and oil level are normal. 1.2.1.3.2 When gas is detected inside the gas relay (the oil level can be seen), (this step shall be carried out with the approval of the dispatch center; the same applies below), the duty personnel should temporarily redirect the heavy gas signal, check the oil level of the main transformer, determine whether there is oil in the oil conservator, and verify whether the valve connecting the oil conservator to the main transformer is open. If everything is normal, the nature of the gas should be identified by examining its color and whether it is flammable, in order to determine the nature of the fault. 1.2.1.3.3 Upon investigation, if it is air, the transformer can continue to operate after air release, but enhanced monitoring is required. 1.2.1.3.4 Depending on the properties of the gas, in the event of an internal fault, the gas switch should be set to the tripping position; the situation must be reported immediately to the dispatch center and the relevant team, and the load should be adjusted as per the dispatch instructions before shutting down the power supply. 1.2.1.3.5 If there is no gas inside the gas relay, it is considered a fault in the secondary circuit; the heavy gas signal should be switched to the alarm position, and the cause should be identified before reporting to the dispatch team and the relevant work area. 1.2.1.3.6 Upon inspection, it was found that when the oil conservator and the main connection pipe valves were not open, the heavy gas circuit was temporarily connected to a signal; the gas exhaust valve was opened for venting, and after that, the oil conservator valve was opened to fill the gas relay with oil. Once everything was functioning normally, the heavy gas trip function was reactivated. 1.2.1.3.7 Gas venting identification method: Light a match at a height of 45 degrees and 5–6 cm from the vent valve, then slowly release the gas to prevent it from blowing out the match; observe whether the gas is flammable, as well as its intensity, color, odor, etc. 1.2.1.3.8 If gas is seen inside the gas relay but it cannot be released, the vent valve should be closed promptly to prevent backflow of gas. The situation should be reported to the dispatch team, who will then instruct that the heavy gas signal be switched to another position, in order to determine whether negative pressure is caused by a clogged breather or similar issues. 1.2.2 Tripping due to heavy gas operation of transformer 1.2.2.1 Accident symptoms: Microcomputer monitoring triggers an alarm; the alarm display shows that the main transformer has entered heavy gas operation mode, the 10kV automatic switching device activates, the switches on both the high-voltage and low-voltage sides of the main transformer trip, the 1050 switch closes, the current value of the main transformer is 0, and the fault recorder activates. 1.2.2.2 Possible causes 1.2.2.2.1 Internal transformer failure ； 1.2.2.2.2 Severe oil leakage from the transformer ； 1.2.2.2.3 Severe vibration ； 1.2.2.2.4 There is a fault in the Gas relay and the secondary circuit. 1.2.2.3 Handling Methods 1.2.2.3.1 Check the operation status of automatic backup switching (handling of 10kV automatic backup switching operations 9.5). 1.2.2.3.2 When the main transformer’s heavy gas protection trips, it is necessary to first check the status of the protection signals, whether the switch has tripped, if there are any shocks in the system, and whether there are any transverse faults. The situation should be reported to the dispatch center, the time should be recorded, and the audible signals should be restored. 1.2.2.3.3 Check the load on the operating transformer; if necessary, adjust its load first to bring it back to normal levels. 1.2.2.3.4 If a gas trip causes a section of the bus to lose power, it shall be handled as a bus voltage loss. 1.2.2.3.5 Determine whether the gas relay is operating correctly by checking whether there is gas inside the relay, as well as whether there are any shocks or vibrations in the system. 1.2.2.3.6 If there is a fault inside the transformer, it is not allowed to force power supply or attempt to restart the transformer’s operation. The duty personnel should isolate the faulty transformer and inform the dispatching department as well as the maintenance team. 1.2.2.3.7 If a fault in the secondary circuit causes abnormal operation, deactivate the gas protection and restart the main transformer. 1.2.2.3.8 If malfunction occurs due to a transverse fault, restore the signal and attempt to restart the main transformer once; once there are no issues, normal operation can be resumed. 1.2.3 Tripping due to transformer differential protection activation 1.2.3.1 Incident symptoms: The microcomputer monitoring system triggers an alarm; the alarm display indicates that differential protection of Main Transformer No. X has activated, the switches on both the high-voltage and low-voltage sides trip, the current value of the main transformer becomes 0, the fault recorder activates, the 10kV automatic transfer device comes into operation, and Switch 1050 closes. 1.2.3.2 Possible causes 1.2.3.2.1 There is a fault inside the transformer ； 1.2.3.2.2 Equipment failures between the differential CTs on both sides of the main transformer ； 1.2.3.2.3 Secondary circuit fault, differential protection malfunction ； 1.2.3.2.3 Penetrating faults cause differential protection to malfunction. 1.2.3.3 Handling Methods 1.2.3.3.1 Check the operation status of the standby auto-transfer device (for handling the operation of the 10kV standby auto-transfer device, see 1.5) ； 1.2.3.3.2 Record the time, check the current and power values of the tripped main transformer, and examine the operation status of the protection system ； 1.2.3.3.3 Reporting Scheduling ； 1.2.3.3.4 Check whether the gas protection operates simultaneously, and whether there is gas in the gas relay; if gas is present, follow the procedures for handling gas-related operations ； 1.2.3.3.5 Check whether there are any obvious faults in the equipment within the range of the differential CT of the faulty main transformer; if a fault is detected, report it to the dispatching team and isolate the faulty main transformer ； 1.2.3.3.6 If no problems are found after the above checks, it may be that a fault in the secondary circuit or a transverse fault has caused the differential protection to operate erroneously; in such cases, it is possible to request the dispatch to disable the differential protection for a trial operation (the gas protection must remain active). 1.2.4 Tripping due to composite voltage lockout overcurrent protection 1.2.4.1 Accident symptoms: The microcomputer monitoring system emits an alarm; the alarm display indicates that the No. X main transformer has triggered its composite lockout overcurrent protection, the 10kV voltage circuit is disconnected, the switches on both the high-voltage and low-voltage sides trip, the current value of the main transformer is 0, and the fault recorder activates. 1.2.4.2 Possible causes 1.2.4.2.1 Faults on the corresponding busbars or lines causing hierarchical tripping, or faults in the secondary circuit. 1.2.4.2.2 Failure of differential protection due to faults within the CT ranges on both sides of the transformer. 1.2.4.3 Handling methods 1.2.4.3.1 Restart the audio system after timing has passed, check the status of the protection mechanisms and keep records. Inspect the exterior of the main transformer as well as the area covered by the differential protection to determine if there are any obvious faults; if such faults are found, report to the dispatch team and isolate the equipment. 1.2.4.3.2 If two of the protections such as gas protection, differential protection, and overcurrent protection operate simultaneously to trigger a trip, the main transformer shall not be powered on without conducting a comprehensive inspection and testing. 1.2.4.3.3 Check all devices on the de-energized bus. If there are no abnormalities with the bus devices, and the line protection trips but the switch fails to operate, it is a cross-pole trip; in such a case, open the non-functional switch to isolate the faulty line, restart the transformer, and restore power to the remaining lines. 1.2.4.3.4 Upon inspection, if there is no signal indicating that the line protection has activated, it may be due to a line fault; the failure of the protection to trigger a trip results in over-level switching. In such cases, all line switches on the busbar should be disconnected, the transformer should be brought back online, and then each line switch should be tested one by one. If closing a certain line switch causes the main transformer switch to trip, that line should be disconnected again, after which power supply to the transformer and the remaining lines can be restored. 1.2.4.3.5 If power is supplied normally to all lines, it may be due to a malfunction of the protection device; report to the dispatching team to deactivate this protection. 1.2.5 Tripping due to zero-sequence overcurrent protection of the transformer 1.2.5.1 Accident symptoms: The microcomputer monitoring system triggers an alarm; the alarm display indicates that there is a zero-sequence overcurrent fault in the main transformer, the 10kV voltage circuit has been disconnected, the switches on both the high-voltage and low-voltage sides trip, the current value of the main transformer is 0, the fault recording system activates, the 10kV automatic switching device comes into operation, and switch 1050 closes. 1.2.5.2 Possible causes 1.2.5.2.1 Ground fault on the 110kV line causing stepped tripping or secondary circuit failure. 1.2.5.2.2 Ground fault within the CT range on the 110kV side of the transformer. 1.2.5.3 Handling Methods 1.2.5.3.1 For handling accidents involving automatic backup switching, refer to 1.5. 1.2.5.3.2 Refer to the handling method for tripping due to the composite voltage-locked overcurrent protection. 1.2.6 Transformer Fire 1.2.6.1 If there is a spare transformer, it should be brought online immediately to transfer the load. 1.2.6.2 Open the switch disconnectors on all sides of the firing transformer and shut down the cooler. 1.2.6.3 Organize fire fighting immediately. 1.2.6.4 Notify the fire department, but safety measures must be taken. 1.2.6.5 If the transformer is equipped with an accident oil discharge valve located away from the main body, the oil discharge valve should be opened. 1.3 Handling of Line Switch Tripping Incidents 1.3.1 Handling of 110kV line switch tripping incidents (with Line 1 and Line 2 fully open, North Line open, or Line 3 as a separate line) under normal operating conditions 1.3.1.1 Incident symptoms: The microcomputer monitoring system emits an alarm; the alarm display indicates that Line 1 at 110kV has tripped, the switch for Line 1 flashes, and the displayed current value, active power value, and reactive power value are all zero. 1.3.1.2 Possible causes 1.3.1.2.1 Tripping of the switch caused by a fault in the fully open line circuit, or by faults in the outgoing circuit breaker, line PTs, PBs, bushings, and leads ； 1.3.1.2.2 Loss of power on the opposite side of the fully open circuit ； 1.3.1.2.3 Malfunction-induced tripping of the protection on the same side at full opening, or malfunction of the switch ； 1.3.1.3 Treatment Methods 1.3.1.3.1 Check the operation of the full-open primary protection ； 1.3.1.3.2 Check for any abnormalities in the equipment within the station, make records, and report to the dispatch center ； 1.3.1.3.3 Check the fully open circuit for any obvious fault points and isolate them; if no obvious fault points are found, report to the dispatch team, who will then give instructions to restore power supply. 1.3.2 Handling of 10kV line switch tripping 1.3.2.1 Accident symptoms: An alarm is displayed in the microcomputer system indicating that the 10kVxx switch has tripped; the switch flashes, and information regarding the protection and reclosing functions of that switch is shown. The current value is zero, as is the active power value, and a voice message indicating an accident-related trip of the xx switch is emitted. 1.3.2.2 Handling methods 1.3.2.2.1 In the event of a trip on a passive overhead line, if no reclosing device is installed or the reclosing device does not function, power can be restored once manually, after which the duty operator at the dispatch center should be informed. Following the instructions given by the dispatch operator, power can be restored once for important users. Before restoring power and attempting to restart it, the protection devices must be reactivated, and it is necessary to ensure that the switch is in good condition and that the number of trips has not exceeded the specified limit. 1.3.2.2.2 When most of the length of the line consists of cables, power supply is not forced; depending on the importance of the load and the status of the switches, a trial power supply can be attempted once with the approval of the dispatch operator. For lines where reclosing is unsuccessful, power supply is not forced either, but a trial power supply can be attempted once after obtaining the dispatcher’s approval. 1.3.2.2.3 If a trial power supply is unsuccessful, power is generally not supplied again. 1.3.2.2.4 When there are live work on the line and the low-frequency protection activates, indicating a fault, forced power restoration or trial power supply must not be carried out; the cause must be identified first. 1.3.2.2.5 After the capacitor switch trips, forced power supply or trial power supply shall not be carried out. *: The term \"forced power restoration\" as used in these procedures refers to the operation of closing the switch immediately to restore power supply, without conducting any visual inspection of the switch after it has tripped. Test power supply refers to the visual inspection of the switch after it trips, followed by attempting to close the switch and supply power. 1.3.3 Handling when the low-frequency load shedding device operates 1.3.3.1 Accident phenomenon: The microcomputer alarm display shows that the 10kVxx switch has tripped due to low-frequency operation, and an accident alarm sound is emitted. 1.3.3.2 Handling method: Check the operation of the protection devices, verify whether the switch has operated correctly, and determine the sequence of operations. If it is found that the switch supposed to trip has not done so, the duty officer must immediately manually trip the switch, make a record of it, report to the dispatch center, and wait for further instructions. The duty officer is not allowed to close the switch and restore power to it without authorization. In the event of a low-frequency malfunction caused by secondary misoperations or accidental touches, the on-duty personnel should immediately close the trip switch to restore power supply, make proper records, and report to the dispatching office and the team leaders. 1.4 Handling of 110kV automatic transfer switch failures (under normal operating conditions) 1.4.1 Once the voltage on the 110kV bus loses its strength, it is necessary to immediately determine whether the automatic transfer switch has activated, as well as the status of the bus differential protection and the operation of the switches. 1.4.2 When the bus differential protection triggers and causes the switches to trip, the automatic transfer switch is disabled and cannot operate; in such a situation, the 10kV automatic transfer switch should activate and close switch 1050 (not due to an overcurrent protection trigger on the main transformer) ； 1.4.3 If, after all the circuit breakers on Section I or Section II of the 110kV line trip or if the power supply on the opposite side is lost, the automatic backup switching system fails to operate or operates unsuccessfully, and the 110kV sectional switch does not close, then the automatic backup switching function should be disabled immediately. It is necessary to confirm that the circuit breaker of the line affected by voltage loss is indeed disconnected, and then the 1150 sectional switch should be closed. If the sectional switch refuses to close, the cause must be identified promptly so that it can be closed. 1.4.4 When forcing the disconnection switch to operate, it is necessary to ensure that all outgoing switches on the de-energized bus have been disconnected. 1.4.5 If, after the automatic transfer to the standby unit takes place, the protection associated with this automatic transfer causes another trip, power supply should not be forced to be restored. It is necessary to immediately check whether there is a fault in the equipment on the busbar where voltage is lost, report the situation to the dispatch center, and restore power supply in accordance with the instructions given by the dispatch center. 1.4.6 Regardless of whether the automatic backup switching operation is successful or not, the equipment within the station should be inspected to determine the cause of the voltage loss on the relevant line, and the situation should be reported to the dispatch center. 1.5 Accident handling for 10kV automatic transfer switching (operational with 10kV system in segmented mode) 1.5.1 When the voltage on the 10kV Phase I bus is lost, it is necessary to immediately determine whether the automatic transfer switching has activated, as well as the status of the main transformer protection and switches. To prevent further accidents, the bus should be re-energized within 3 minutes. 1.5.2 When the main transformer overcurrent protection trips and the switch opens, the automatic transfer device is locked and cannot operate; in this case, the automatic transfer switch should be disengaged immediately, and the accident should be handled in accordance with the procedures for dealing with main transformer overcurrent protection trips. 1.5.3 In the event that the overcurrent protection for non-main transformers trips the switch, and the automatic backup switching device fails to operate or operates unsuccessfully, as well as when the 10kV sectional switch does not close, the automatic backup switching function should be disabled immediately, and the 10kV sectional switch should be closed. If the sectional switch refuses to close, the cause must be identified promptly so that it can be closed. 1.5.4 When the switch of the transformer under voltage loss has not been tripped, first open that switch, and then close the 10kV sectionalizing switch. 1.5.5 If the automatic backup switching function operates successfully, after the 10kV sectional switch is closed, an overcurrent trip from the operating main transformer will occur; immediately thereafter, the automatic backup switching switch should be disengaged, and all outgoing switches on the busbar that has lost voltage should be opened. Once it is confirmed that there are no faults on that busbar, the 10kV sectional switch can be closed again, and the outgoing switches can be turned on one by one ； If there is a fault in the busbar, or if the main transformer protection or automatic switching device malfunctions, the faulty equipment should be isolated, the situation reported to the dispatch center, and power supply to the other equipment restored. 1.5.6 After the automatic transfer to a backup transformer is successful, check the load on the operating main transformer; if necessary, contact the dispatching team to reduce the load. 1.5.7 Once power supply is restored to normal, investigate the condition of the faulty transformer, report to the dispatching team to isolate the faulty transformer, take safety measures, and inform the relevant departments to handle the situation. 1.6 Total station voltage loss 1.6.1 Accident symptoms: Microcomputer monitoring triggers an alarm; the alarm display indicates a broken AC circuit, with zero voltage applied. All values for voltage, current, and power are zero. The 10kV capacitor protection activates and causes a trip, while the DC panel gives an alarm as well as the on-site UPS. 1.6.2 Possible causes 1.6.2.1 The Sankai line, Kaibei line, Mankai 1 line, and Mankai 2 line trip simultaneously due to line failures or malfunctioning protection systems ； 1.6.2.2 Short-circuit fault in bus I or bus II at 110kV; incorrect operation or failure to operate of the bus differential protection ； 1.6.2.3 System failure causes the power supply on the opposite side of Line 1 at full open, Line 2 at full open, Line 3 at full open, and Line North to be lost. 1.6.3 Handling Methods 1.6.3.1 Activate the emergency lighting, check whether the protections for the three-way line, Kaibei line, Full Open Line 1, and Full Open Line 2 are activated, whether the bus differential protection is activated, and whether the 110kV sectionalizer is disconnected ； 1.6.3.2 Check whether there are any abnormalities in the equipment within the substation; if the 110 kV line switches on either side trip, special attention should be paid to devices such as the line switches, CTs, line disconnectors, line PTs, and PBs ； If the bus differential protection trips, it is necessary to carefully check for any abnormalities in the bus equipment and report to the regional and local control centers. 1.6.3.3 If the switches on the 110 kV line trip simultaneously or the power supply on the opposite side is lost, and there are no abnormalities with the equipment at this station, power supply shall be restored in accordance with the dispatch instructions ； In the event of a communication outage, the 110 kV sectionalizers can be disconnected, leaving one circuit per bus section to wait for power to be restored ； Power supply can also be restored based on whether the line PT voltage indicates voltage presence. 1.6.3.4 If there is a fault in the equipment within the substation, and the bus differential protection operates erroneously or fails to operate, resulting in a loss of voltage throughout the substation, the faulty equipment should be isolated to restore power supply as quickly as possible. 1.6.3.5 Keep all kinds of records. 1.7 Handling of Voltage Loss Incident on the 110kV Bus Section 1.7.1 Incident symptoms: Microcomputer monitoring system triggers an alarm; the alarm display indicates that the 110kV system is in normal operation, while all voltage, current, and power values for that section are zero; the 10kV automatic backup system activates. 1.7.2 Possible causes 1.7.2.1 The Sanbei Line, Kaibei Line, Mankai Line 1, or Mankai Line 2 fail to activate the automatic backup supply due to the tripping of switches on the same side or the opposite side, as well as the loss of power on the opposite side, or because the automatic activation does not succeed ； 1.7.2.2 Bus differential protection operates in case of a fault in the 110kV I bus or II bus equipment ； 1.7.2.3 Maloperation of differential protection. 1.7.3 Handling Methods 1.7.3.1 Check the operation status of protections, switches, and signals; check the operation of the 110kV and 10kV automatic transfer devices; ensure that the load on the main transformer is normal. Check for any malfunctions in the equipment at the checkpoint and report to the dispatcher. 1.7.3.2 If the circuit breaker on this side trips or the power supply on the opposite side is lost, and the 110kV automatic switching device does not activate, then, in accordance with the dispatch instructions, the automatic switching device shall be disabled, the 110kV circuit breaker for that section shall be disconnected, the 110kV sectionalizing switch shall be closed, and power supply shall be restored ； If the automatic transfer switch operation is unsuccessful, and no abnormalities are found in the equipment within that section after inspection, power shall be supplied using the method described above. 1.7.3.3 If the bus differential protection trips, it is necessary to carefully check whether there are any abnormalities in the equipment connected to that bus section. If a fault is detected, the faulty component should be isolated promptly, and the situation reported to the dispatch center. Other equipment can then be reconnected to the power supply in accordance with the instructions given by the dispatch center ； If there are no abnormalities, it is a false trip of the bus differential protection; in accordance with the dispatch instructions, the bus differential protection is disabled and power supply is restored. 1.8 Handling of 10kV bus voltage loss accidents 1.8.1 Accident symptoms: The alarm area indicates that a certain main transformer has tripped, the protection system has activated, an audio alarm is issued; the voltage of that bus is shown as zero, and the currents on all outgoing lines are also shown as zero. 1.8.2 Possible causes 1.8.2.1 Busbar fault, causing overcurrent operation of the main transformer and tripping of the corresponding switch ； 1.8.2.2 Outlet fault: the protection or switch for that outlet fails to operate, resulting in the tripping of the main transformer switch ； 1.8.2.3 If the main transformer switch trips accidentally or the power supply is lost, the 10kV automatic backup switching system does not activate ； 1.8.2.4 The main transformer’s gas, differential, and zero-sequence protections activated, the switch tripped, and the 10kV automatic backup system did not function. 1.8.3 Handling Methods 1.8.3.1 If the main transformer differential, gas, or zero-sequence protection triggers a switch trip, or if the power supply is lost and the 10kV automatic transfer device does not activate, then disconnect the low-voltage switch of the main transformer, close the 1050 switch to force power supply to the busbar, inform the dispatch center, and keep a record of the incident. 1.8.3.2 If the backup protection of the main transformer trips, a thorough inspection should be carried out to determine whether there are any obvious fault points on that busbar, as well as to check the operation status of the protections connected to each outlet and the status of switch tripping; all findings should be recorded. 1.8.3.3 If there are no obvious fault points on the busbar and none of the outgoing line protections have triggered, then disconnect all the outgoing line switches, restore the protection settings for the main transformer, activate the 10kV sectional charging protection, close the 10kV sectional switch or the 10kV switch of the main transformer, and attempt to supply power to the busbar. Then close the outgoing line switches one by one to try to supply power to the respective lines. If supplying power to a certain line causes the busbar voltage to drop again, disconnect that switch as well as the circuit breakers on both sides, attempt to supply power to the busbar again, and resume power supply to the other lines. 1.8.3.4 If it is detected that the protection device for a certain circuit has failed and the switch will not operate, then disconnect that switch as well as the disconnect switches on both sides, and restore power supply in the sequence mentioned above. 1.8.3.5 If there is a fault point on the busbar and it can be isolated and eliminated, the fault point shall be removed and isolated, after which power shall be supplied to the busbar and the circuits one by one. 1.9 Grounding of 10kV systems (segmented operation) Single-phase grounding in 10kV systems is divided into transient grounding and permanent grounding. 1.9.1 Phenomenon: The microcomputer monitoring alarm sounds; the alarm area indicates ground fault in busbar I or II. The low-current ground selection device activates, the indication for the grounded phase on the voltage bar graph decreases or becomes zero, while the indications for the other two phases increase or show the line voltage. 1.9.2 Handling methods 1.9.2.1 Stop the audio alarm, start timing, record the status of signal operations and current readings; use a voltage bar chart to determine the phase involved in the ground fault, and report to the dispatch center ； 1.9.2.2 Check the operation of the low-current grounding line selection device; based on the phase of ground fault indicated by the device and the line selected, disconnect the corresponding switch. 1.9.2.3 If grounding does not resolve the issue, check whether there are any abnormalities on the 10kV side of the transformer as well as inside the 10kV substation (insulated boots and gloves must be worn) ； 1.9.2.4 If the low-current grounding line selection device fails to operate or fails to send signals for some reason, and there are no abnormalities in the equipment within the station, then a line disconnection check shall be carried out in accordance with the dispatch instructions. The lines shall be disconnected in the order of unloaded lines, dual-circuit lines, long lines under light load, and lines serving important users. Once the faulty line is identified, the switch associated with that line shall be turned off ； 1.9.2.5 After grounding for 2 hours, the voltage transformers of the two busbars shall operate in rotation ； 1.9.2.6 Judgment and handling of false grounding signal activation and abnormal indications on the voltage bar graph: 1.9.2.6.1 If one phase of the high-voltage fuse in the voltage transformer blows, a grounding signal is generated; the voltage bar graph on the monitoring system shows a decrease in voltage for that phase, while the voltages of the other two phases are still indicated normally. A signal indicating a “broken voltage circuit” is sent, and the bus voltage value changes, along with a decrease in the remotely measured power values. This situation can be interpreted as a blown high-voltage fuse in the voltage transformer. Handling: After removing the PT secondary fuse, take the PT out of service and replace it with a high-voltage fuse. If it blows again after attempting to restart operation, the PT should be taken out of service. Check that the high-voltage coil of the voltage transformer is intact, with no deformation, charring, or overheating; ensure that the neutral point is properly grounded and that there is good insulation from the ground. If necessary, report the issue to the maintenance team for handling. 1.9.2.6.2 If the low-voltage fuse of the voltage transformer blows or there is a break in the secondary circuit, the voltage meter will show that the voltage of one phase decreases while the voltages of the other two phases remain normal; a signal indicating a \"break in the voltage circuit\" will be generated, and the relevant power telemetry readings will decrease. This situation can be used to determine that there is a break in the secondary circuit of the voltage transformer. Treatment: The secondary fuse of the voltage transformer should be checked; if it is blown or has poor contact, it should be replaced. If it is caused by poor contact of the circuit breaker auxiliary contacts and can be resolved on its own, it should be dealt with promptly; if it cannot be resolved, it should be reported to the relevant departments without delay. If necessary, measure the insulation resistance of the secondary circuit. 1.9.2.6.3 When the unloaded busbar and the voltage transformer are connected at the same time, the imbalance in the capacitance of the busbar with respect to ground causes the neutral point to shift, resulting in a ground fault signal and abnormal readings in the phase voltage telemetry. Handling: It is advisable to avoid connecting the voltage transformer to an unloaded busbar. If necessary, it is possible to operate with one circuit connected, or connect one circuit first and then the voltage transformer. 1.9.2.6.4 Due to ferroresonance caused by the primary excitation current of the voltage transformer and the line capacitance current, the phase voltage telemetry values increase, triggering a ground fault signal. Solution: Reconnect the voltage transformer, change the operating mode or procedures – that is, disconnect certain lines or connect others, or alter the sequence in which the lines are operated. nbsp; Handling of Tripped Auxiliary Transformers 1.10.1 Accident phenomenon: The microcomputer monitoring system emits an alarm, and the alarm display indicates that the protection device of auxiliary transformer No. X has activated, causing the switch to operate. The load connected to a certain section lost power. 1.10.2 Possible causes 1.10.2.1 Faults in the transformer and high/low voltage leads ； 1.10.2.2 Fault in the low-voltage X-section bus or a fault in one of the outgoing cables causes a cascade failure. 1.10.2.3 Malfunction of the switching mechanism ； 1.10.3 Handling Method 1.10.3.1 Check the operation status of the switch protection and report to the dispatch center. 1.10.3.2 Pull out all the circuit breakers for the outgoing lines in the low-voltage X section being used. 1.10.3.3 After checking for any abnormalities in the transformer and its high- and low-voltage leads, as well as in the low-voltage busbars, if no abnormalities are found, the transformer can be powered on for testing. After charging is normal, restore each of the X outgoing circuits one by one; if tripping occurs again, disconnect the circuit breaker for that outlet before restoring power. 1.10.3.4 In the event of a fault in the service transformer or the high/low voltage leads, the faulty section can be isolated, the low voltage sectional switch can be closed, and the other service transformer can take over all the load; the fault should then be reported to the relevant departments for handling. 1.10.3.5 If the low-voltage bus being used fails and cannot be repaired temporarily, the fault location should be isolated, and the important loads in that section should be transferred to another operating section. 1.10.3.6 If a trial startup fails due to improper operation of the switching mechanism, isolate the switch, and let another step-up transformer take over the load.