10 principles for equipment maintenance

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10 Principles: Speak before acting. 01 For faulty electrical equipment, do not rush to take action; first inquire about the circumstances surrounding the fault and its symptoms. For unfamiliar equipment, it is also necessary to first become familiar with the circuit principles and structural features, and to follow the relevant rules. Before disassembly, it is necessary to fully understand the function, location, connection method of each electrical component, as well as its relationship with other components around it. In the absence of assembly diagrams, sketches should be drawn while disassembling, along with appropriate markings. Start with the outside before moving on to the inside. First, check whether there are any obvious cracks or defects in the equipment, and find out its maintenance history and service life, before proceeding with an inspection of the interior. Before disassembly, the faulty factors in the surrounding area should be identified; disassembly can only be carried out after it is confirmed that the fault lies within the device. Otherwise, blind disassembly may end up worsening the condition of the equipment. Mechanical first, then electrical: 03. Electrical checks should only be carried out after confirming that the mechanical parts are free of faults. When checking for circuit faults, testing instruments should be used to locate the faulty area. Only after confirming that there are no issues with poor connections should one examine the relationship between the circuits and the mechanical components, in order to avoid misdiagnosis. First static, then dynamic: 04. When the device is not powered on, it checks the condition of the electrical equipment’s buttons, contactors, thermal relays, and fuses in order to determine where the fault lies. Conduct a power-on test, listen to the sounds, measure parameters, determine the fault, and finally carry out repairs. In the case of a motor with an absent phase, when it is not possible to determine the situation by measuring the three-phase voltages, one should listen to the sound produced; by measuring the voltage of each phase relative to ground separately, it is possible to determine which phase is missing. Clean first, then repair. For electric devices that are heavily polluted, clean their buttons, wiring points, and contacts first, and check whether the external control buttons are not functioning properly. Many failures are caused by dirt and conductive dust particles, and the faults can often be resolved once cleaning is done. Power supply first, then the equipment. 06 The failure rate of the power supply component is quite high among all faulty devices; therefore, addressing the power supply issue first can often yield twice the result with half the effort. From common to exceptional 07: Failures caused by the quality of mounting components or other equipment issues account for about 50% of common failures. Most exceptional failures of electrical equipment are soft failures, which require measurement and repair based on experience and instruments. Start with the peripheral components before dealing with the internal ones. Do not rush to replace the damaged electrical components; wait until it is confirmed that the circuits of the peripheral devices are functioning properly before considering replacing those damaged components. DC first, then AC: During maintenance at 09, it is necessary to first check the static operating point of the DC circuit, and then the dynamic operating point of the AC circuit. 10. Fix the fault first, then carry out debugging. For electrical equipment that has both faults and issues that need to be addressed, the faults should be resolved first before debugging can take place; debugging must be carried out under the condition that the electrical circuits are functioning properly. Inspection Methods and Practical Procedures 1: Visual Inspection Method. The visual inspection method is a technique for detecting and diagnosing faults by observing the external signs of electrical failures, using methods such as looking, smelling, and listening. (1) Inspection steps: Investigate the situation: Ask the operators and those present at the time of the fault about the details, including the external manifestations of the fault, its approximate location, and the environmental conditions at the time it occurred. Whether there are any abnormal gases, open flames, or heat sources near electrical appliances; whether corrosive gases have penetrated; whether there is any water leakage; whether anyone has repaired the equipment and what was repaired, etc. Preliminary inspection: Based on the findings of the investigation, check whether there is any external damage to the electrical appliance, whether the wiring is broken or loose, whether the insulation is scorched, whether the fuse indicator on the fuse is activated, whether water or oil contamination is present in the appliance, and whether the switch is in the correct position. Testing: After a preliminary inspection to confirm that there are no factors that could lead to further escalation of the fault or cause accidents to personnel or equipment, further testing can be carried out. During testing, attention should be paid to any signs of severe arcing, unusual odors, or abnormal noises; if such things are detected, the machine must be stopped immediately and the power supply cut off. Pay attention to checking the temperature rise of electrical appliances and whether their operating procedures meet the requirements specified in the electrical equipment schematic diagrams, so as to identify the location of faults. Image (2) Inspection method: Observe sparks: Sparks are generated when the contacts of electrical devices close or open a circuit, or when the wire connections are loose; therefore, electrical faults can be detected by observing the presence or absence of sparks, as well as their size. For example, if sparks are observed between a properly tightened wire and screw, it indicates that the wire end is loose or there is poor contact. If the contacts of an electrical appliance spark when closing or breaking the circuit, it indicates that the circuit is connected; if no sparks occur, it means the circuit is not connected. When there is sparking in two phases and no sparking in one phase of the main contacts of the contactor that controls the motor, it indicates that the contact in the phase without sparking is poor, or that the circuit for that phase is broken ； The sparks in two of the three phases are larger than normal, while those in the third phase are smaller than normal; this suggests a possible inter-phase short circuit or ground fault in the motor ； The sparks in all three phases are larger than normal; this could be due to an overload of the motor or a jam in the mechanical parts. In the auxiliary circuit, when the contactor coil circuit is powered, the armature does not engage; it is necessary to determine whether this is due to an open circuit or a jam in the mechanical parts of the contactor. You can press the start button; if there is a slight spark when the normally open contact of the button is opened, it indicates that the circuit is intact and the fault lies in the mechanical part of the contactor ； If there is no spark between the contacts, it indicates that the circuit is open. Operation procedure: The operation procedure of electrical appliances shall meet the requirements specified in the electrical instructions and drawings. If an appliance in a circuit operates too early, too late, or not at all, it indicates that there is a fault with that circuit or appliance. Additionally, faults can also be analyzed and identified based on the sounds, temperature, pressure, odor, etc., emitted by the electrical appliance. By using the intuitive method, not only can simple faults be identified, but also more complex faults can be narrowed down to a smaller scope. 2 Voltage measurement method: The voltage measurement method involves measuring the voltage and current values at various points based on the power supply method of the electrical appliance, and comparing these values with the normal values. Specifically, it can be divided into stepped measurement method, segmented measurement method, and point measurement method. 3 The resistance measurement method can be divided into step-by-step measurement and segmented measurement methods. These two methods are suitable for electrical equipment with switches and appliances that are spaced far apart from each other. 4 Comparison, replacement element, and gradual open/closed circuit method: (1) Comparison method: Faults are determined by comparing the test data with the data from drawings and the normal parameters recorded over time. For electrical appliances with no data or regular records, they can be compared with intact appliances of the same model. When the electrical components in a circuit are of the same control type or when multiple components work together to control the same device, it is possible to determine faults by observing the operation of other similar components or those powered from the same source. (2) Replacement component method: When the cause of a fault in certain circuits is difficult to determine or when the inspection time is too long, but in order to ensure the efficiency utilization of electrical equipment, components with good performance from the same phase can be replaced for testing, in order to confirm whether the fault is caused by that particular component. When using the conversion element method for inspection, it is important to carefully check whether the original electrical component is damaged after it has been removed. Only when it is confirmed that the damage is caused by issues with the component itself should a new one be installed, in order to prevent the new component from being damaged as well. (3) Gradual open-circuit (or connection) method: In circuits with multiple parallel branches and complex control systems that are short-circuited or grounded, there are usually obvious external signs, such as smoking or sparks. When there is a short circuit or ground fault inside the motor or in a circuit with a cover, apart from the fuse blowing, no other external signs are easily detectable. This situation can be checked using the step-by-step open-circuit (or connection) method. (4) Gradual open-circuit method: When encountering difficult-to-diagnose short-circuit or ground fault problems, the fuse can be replaced again. For a multi-circuit cross-linked circuit, one circuit at a time is gradually or selectively disconnected from the circuit, after which power is applied for testing. If the fuse blows repeatedly, the fault lies in the circuit that was just disconnected. Then, this branch is divided into several sections, which are connected to the circuit one by one. When connecting to a certain circuit the fuse blows again, indicating that the fault lies in that circuit or in some electrical component. This method is simple, but it easily burns out electrical components with minor damage completely. Step-by-step connection method: When there is a short circuit or ground fault in the circuit, replace the fuse with a new one and gradually, or selectively, connect each branch to the power supply one by one before conducting another test. When a fuse blows after a certain section is connected, the fault lies in the circuit that has just been connected and the electrical components it contains. 5 Forced closing method: When an electrical appliance is malfunctioning and no fault point can be identified through visual inspection, and no appropriate instruments are available for measurement, an insulating rod can be used to force relevant relays, contactors, electromagnets, etc. to be pressed down, thereby closing their normally open contacts. After that, various phenomena that occur in the electrical or mechanical parts can be observed, such as the motor going from not rotating to rotating, or the corresponding parts of the equipment going from not functioning to operating properly. 6 Short-circuit method: Faults in equipment circuits or electrical appliances can be roughly classified into six categories: short circuit, overload, open circuit, ground fault, wiring errors, and faults in the electromagnetic and mechanical components of the electrical appliances. Among various types of faults, open circuit faults are the most common. It includes wire open circuits, loose connections, looseness, poor contact at contacts, weak soldering, failed soldering, and blown fuses. Apart from using the resistance method and voltage method to check for such faults, there is another simpler and more feasible method: the short-circuit method. The method is to use a well-insulated wire to short-circuit the suspected broken circuit; if the circuit resumes normal operation after short-circuiting at a certain point, it indicates that there is a break at that location. The specific operations can be divided into the local short-circuit method and the long-short circuit method. These various inspection methods should be used flexibly, while adhering to safety operating procedures. For components that have been damaged continuously, the cause should be identified before replacing them ； The voltage drop of the wires should be taken into account when measuring voltage ； Without violating the principles of equipment and electrical control, the power switch must not be released during testing, and fuses should be used with a current rating equal to or slightly less than the rated current ； Pay attention to the selection of the gear for the measuring instrument.