Visit：2546 Date：2020-10-29

1. Move your mouth first, then do it
　　 For electrical equipment with faults, do not rush to do it, and you should first ask about the process and the phenomenon of the fault. For unfamiliar equipment, you should also be familiar with the circuit principles and structural features, and follow the corresponding rules. Before disassembling, be fully familiar with the function, location, connection mode of each electrical component and the relationship with other components around. If there is no assembly drawing, draw a sketch while disassembling and mark it.
2. First outside, then inside
　　 The equipment should be inspected for obvious cracks and defects, and the maintenance history, service life, etc., should be checked first, and then the inside of the machine should be inspected. Before dismantling, you should queue up the surrounding fault factors, and dismantle only after determining that it is an internal fault. Otherwise, blind dismantling may cause the equipment to be repaired and damaged.
3. Mechanical first, then electrical
　　Only after confirming that the mechanical parts are not faulty, conduct electrical inspections. When inspecting circuit faults, you should use the detection instrument to find the fault location, confirm that there is no bad contact fault, and then check the operating relationship between the circuit and the machine in a targeted manner to avoid misjudgment.
4. First static and then dynamic
　　 When the equipment is not powered on, determine the quality of the electrical equipment buttons, contactors, thermal relays, and fuses to determine the fault. Power-on test, listen to the sound, measure the parameters, determine the fault, and finally repair it. For example, when the motor is lacking phase, if the measurement of the three-phase voltage value cannot be distinguished, you should listen to it and measure each phase to ground voltage separately to determine which phase is defective.
5. Clean first and then repair
　　 For electrical equipment with heavy pollution, clean the buttons, wiring points, and contact points first, and check whether the external control keys fail. Many faults are caused by dirt and conductive dust, and the faults are often eliminated after cleaning.
6. Power first and then equipment
　　 The failure rate of the power supply part accounts for a high proportion of the entire faulty equipment, so repairing the power supply first can often get twice the result with half the effort.
7. First universal and then extraordinary
　　 Failures caused by assembly parts quality or other equipment failures generally account for about 50 common failures. The extraordinary faults of electrical equipment are mostly soft faults, which must be measured and repaired with experience and instruments.
8. Peripheral first and then internal
　　 Don't rush to replace the damaged electrical components. When confirming that the peripheral equipment circuit is normal, consider replacing the damaged electrical components.
9. DC before AC
　　 During maintenance, the static operating point of the DC loop must be checked first, and then the dynamic operating point of the AC loop.
10. Debug after failure
　　 For electrical equipment with both debugging and faults, the faults should be eliminated before debugging. The debugging must be carried out under the premise of the speed of the electrical line.
1. Inspection method and operation practice
　　1, intuitive method
　　 The intuitive method is a method of checking and judging the fault based on the external manifestation of electrical faults by looking, smelling, and listening.
　　1) Checking steps
　　　　Investigation: Ask the operator and the personnel present at the fault about the situation, including the external appearance of the fault, general location, and environmental conditions at the time of the fault. If there is abnormal gas, open flame, whether the heat source is close to the electrical appliance, whether there is corrosive gas intrusion, whether there is water leakage, whether someone has repaired it, the content of the repair, etc. Preliminary inspection: According to the investigation, check whether the electrical equipment is damaged, whether the connection is open or loose, whether the insulation is burnt, whether the fuse indicator of the screw fuse jumps out, whether the electrical appliance has water or grease, and the switch position Is it correct?
Test run: After the preliminary inspection is confirmed that the fault will further expand and cause personal and equipment accidents, further test run inspections can be carried out. During the test run, attention should be paid to whether there are serious flashovers, abnormal smells, abnormal sounds, etc., and stop immediately when found. cut the power. Pay attention to checking whether the temperature rise of the electrical appliance and the action program of the electrical appliance meet the requirements of the electrical equipment schematic diagram, so as to find the fault location.
　　2) Inspection method
　　　　 Observe sparks: sparks will be generated when electrical contacts are closed, circuit breakers or wire ends are loose. Therefore, electrical faults can be checked according to the presence and size of sparks. For example, when a spark is found between a normally tightened wire and a screw, it indicates that the wire end is loose or has poor contact. The electrical contacts flash when the circuit is closed or break, indicating that the circuit is on, and if there is no flash, the circuit is not working.
When the main contact of the contactor of the control motor has sparks in two phases and no spark in one phase, it indicates that the non-sparking one-phase contacts are in poor contact or the circuit of this phase is open; the sparks of two of the three phases are larger than normal, and the other If it is smaller than normal, it can be preliminarily judged to be a short circuit or grounding between the motor phases; the three-phase sparks are larger than normal, which may be caused by the motor overload or the mechanical part jam. In the auxiliary circuit, after the contactor coil circuit is energized, the armature does not pull in. It is necessary to distinguish whether the circuit is open or the contactor mechanical part is stuck. You can press the start button. If there is a slight spark when the normally open contact closed position of the button is disconnected, it indicates that the circuit is connected and the fault lies in the mechanical part of the contactor; if there is no spark between the contacts, the circuit is open.
　　 Action procedure: The action procedure of the electrical appliance should meet the requirements of the electrical manual and drawings. If the electrical action on a certain circuit is too early, too late or inactive, it means that the circuit or electrical device is faulty. In addition, you can also analyze and determine the fault based on the sound, temperature, pressure, and odor of the electrical appliance. Using intuitive methods, not only can simple faults be identified, but also more complex faults can be reduced to a smaller range.
　　2, measuring voltage method
　　　　 voltage measurement method is to measure the voltage value and current value of each point according to the power supply mode of the electrical appliance and compare with the normal value. Specifically, it can be divided into step measurement method, segment measurement method and spot measurement method.
　　3. Resistance measurement method
　　　　 can be divided into step measurement method and segmented measurement method. These two methods are suitable for electrical equipment with large distances between switches and electrical appliances.
　　4, comparison, replacement of components, gradual opening (or access) method
　　1) Contrast method
　　　　 Compare the test data with the drawings and the normal parameters recorded at ordinary times to determine the fault. For electrical appliances that have no data and no usual records, it can be compared with intact electrical appliances of the same model. When the electrical components in the circuit belong to the same control property or multiple components control the same device together, the operation of other similar or the same power components can be used to determine the fault.
　　2) Method of setting conversion element
　　　　 some circuit failure causes are not easy to determine or the inspection time is too long, but in order to ensure the utilization of electrical equipment, the same phase of good performance component experiments can be converted to verify whether the failure is caused by the electrical appliances. Pay attention to the inspection using the conversion element method. After the original electrical appliance is removed, carefully check whether it has been damaged. Only when the damage is definitely caused by the electrical appliance itself can be replaced with a new electrical appliance to avoid damage to the new component.
　　3) Step-by-step opening (or access) method
　　　　 When multiple branches are connected in parallel and a complicated control circuit is short-circuited or grounded, there are usually obvious external manifestations, such as smoke and sparks. When the inside of the motor or the circuit with a shield is short-circuited or grounded, it is not easy to find other external phenomena except for the fuse. This situation can be checked by the gradual opening (or access) method.
Step-by-step open circuit method: When encountering a short circuit or ground fault that is difficult to check, you can replace the melt, and disconnect the multi-branch cross-linking circuit from the circuit step by step or focus all the way, and then energize the test. If the fuse repeatedly blows The fault lies in the circuit that was just disconnected. Then divide this branch into several sections and connect to the circuit section by section. When a certain section of the circuit is connected, the fuse blows again, and the fault lies in this section of the circuit and an electrical component. This method is simple, but it is easy to completely burn the electrical components that are not seriously damaged. Step-by-step connection method: When a short circuit or a ground fault occurs in the circuit, replace the new fuse and gradually or focus on connecting each branch to the power source one by one, and retest. When a certain section is connected, the fuse blows again, and the fault lies in the circuit and the electrical components it contains.
　　4) Forced closing method
When queuing for electrical faults, after visual inspection, the fault point is not found and the hand does not have a proper instrument to measure. An insulating rod can be used to force the relevant relay, contactor, electromagnet, etc. to press externally to make the normally open contact. Close, and then observe various phenomena that occur in the electrical or mechanical parts, such as the motor never turning to rotation, and the corresponding part of the equipment from stationary to normal operation.
　　5) Short circuit method
　　　　Equipment circuit or electrical faults can be roughly classified into six categories: short circuit, overload, open circuit, grounding, wiring error, electrical electromagnetic and mechanical part faults. Most of the faults are open circuit faults. It includes wire disconnection, virtual connection, looseness, poor contact, virtual welding, false welding, fuse blown, etc.
　　　　 In addition to the resistance method and voltage method, there is a simpler and more feasible method for this type of fault, which is the short-circuit method. The method is to use a well-insulated wire to short-circuit the suspected open circuit. If it is short-circuited to a certain place, the circuit works back to normal, indicating that the place is open. The specific operation can be divided into partial short connection method and long short connection method.
　　Summary:
　　 The above inspection methods should be used flexibly and comply with safe operation regulations. For components that are continuously burnt out, the cause should be found out before replacement; the voltage drop of the wire should be considered when measuring the voltage; the principle of equipment and electrical control should not be violated, and the hand should not leave the power switch during the test run, and the insurance should be equal or Slightly less than the rated current; pay attention to the selection of the gear of the measuring instrument.