1. First start the mouth and then start the operation for the electrical equipment, should not be anxious to start, should first inquire about the fault before and after the failure and the phenomenon of failure. For unfamiliar equipment, we should first familiarize ourselves with circuit principles and structural features, and comply with the corresponding rules. Before disassembly, we should be fully familiar with the function, position, connection mode of each electrical component and the relationship with other devices around it. In the case of no assembly drawing, it should be dismantled at the same time, drawing a sketch and marking it.

2. Inspect the equipment from the outside to the inside first to find out whether there are obvious cracks and defects, to know the maintenance history and service life of the equipment, and then to inspect the equipment inside. Before disassembly, the failure factors around the machine should be queued up and determined as in-machine failure before disassembly. Otherwise, blindly disassembly may worsen the equipment.

3. after the first mechanical, electrical only after determining the mechanical parts without fault, then conduct electrical examination. When checking the fault of the circuit, the detection instrument should be used to find the fault location, and the operation relationship between the line and the machine should be checked again, so as to avoid the misjudgement.

4. static and dynamic after the equipment is not electrified, determine the electrical equipment button, contactor, thermal relay and fuse, so as to determine the location of the fault. Electricity test, listen to its voice, test parameters, determine the fault, and finally repair. If the motor is short of phase, if the measurement of the three phase voltage can not be judged, it should listen to its sound and measure the relative voltage separately, which can determine which phase defect.

5. First clean and then repair the heavily polluted electrical equipment, first clean its buttons, wiring points, contact points, check whether the external control key failure. A lot of faults are caused by dirty and conductive dust blocks. Once a cleaning fault occurs, it will often be eliminated.

6. The failure rate of power supply after equipment power supply is very high in the whole fault equipment, so the maintenance of power supply can often be twice the result with half the effort.

7. General first and then special for the quality of assembly accessories or other equipment failure caused by the fault, generally accounting for about 50 common failures. The unusual breakdown of electrical equipment is soft fault, it is necessary to measure and maintain by experience and meter.

8. Do not rush to replace the damaged electrical components inside the peripheral first, and then consider replacing the damaged electrical components when confirming the normal circuit of the peripheral equipment.

9. when DC is first fed and overhauled, the static working point of the DC loop must be checked first, then the dynamic working point of the AC circuit will be exchanged.

10. to debug and debug the electrical equipment that coexists with the debugging and fault. The fault should be eliminated first, then debug, and the debugging must be carried out on the premise of the electric line speed.

Two. Inspection method and operation practice

1. The intuitive method is a method of checking and judging the faults by means of watching, smelling and listening according to the external manifestations of the electrical faults.

(1) inspection steps: Investigation: inquire about the operator and the fault present, including the external performance of the fault, the general position, and the circumstances of the failure. If there is no abnormal gas, open fire, heat source near electrical equipment, corrosive gas intrusion, water leakage, whether anyone repaired, repair content and so on. Preliminary examination: according to the investigation, see whether the electrical appliances are damaged, the wires are broken, loose, the insulation is burnt or not, whether the fuse indicator of the spiral fuse jumps out, the electric appliance has water or oil scale, the switch position is correct, and so on. Test: through the preliminary examination, it is confirmed that there will be further expansion of the fault and cause the accident of the person and equipment, and the test can be further tested. In the test, we should pay attention to the phenomenon of serious jumping fire, abnormal smell, abnormal sound and so on. Once found, it should stop immediately and cut off the power supply. Attention should be paid to checking the temperature rise of the electrical apparatus and whether the operating procedure of the electrical apparatus meets the requirements of the schematic diagram of the electrical equipment, so as to find the fault location.

(2) inspection method: observe the spark: the contact of the electrical appliance will produce sparks when it is closed, broken circuit or the wire head is loose, so the electrical fault can be checked according to the phenomenon of whether the spark has the presence or not, the size and so on. For example, when a spark is found between the wires and screws that are normally tightened, it indicates that the thread is loose or poorly contacted. When the contacts of the electrical appliances are closed or broken, the fire jump indicates that the circuit is connected. When the main contact of the contactor of the control motor has sparks and a phase free spark, it shows that the spark free contact contact is bad or the phase circuit breaker. The two phase spark in the three-phase is larger than normal, and the other is smaller than normal. It can be preliminarily judged as the short circuit or grounding of the motor, and the three phase sparks are all larger than normal and may be The motor is overloaded or the mechanical part is stuck. In the auxiliary circuit, when the coil circuit of the contactor is energized, the armature does not close, so it is necessary to distinguish whether the circuit is broken or the mechanical part of the contactor is stuck. You can press the start button, such as the button often open the contact closed position when there is a little spark, indicating the circuit path, failure in the mechanical part of the contactor; for example, no spark between the contacts, indicating that the circuit is a circuit breaker. Action procedure: the action procedure of electrical appliances should conform to the requirements of electrical manuals and drawings. If an electrical appliance on a circuit acts too early or late or does not act, it indicates that the circuit or electrical appliance is faulty. In addition, faults can be judged according to the sound, temperature, pressure and smell emitted by electric appliances. By using the intuitive method, we can not only identify simple faults, but also reduce the more complex faults to a smaller range.

2. Voltage measurement is based on the supply mode of electrical appliances, measuring the voltage and current value of each point and compared with the normal value. It can be divided into three steps: step measurement, sectional measurement and point measurement

3. measuring resistance method can be divided into step measurement and sectional measurement. 

These two methods are suitable for electrical equipment with larger distribution distance between switches and electrical appliances.

4. comparison, replacement elements, gradual open circuit (or access) method

(1) contrast method: the fault is judged by comparing the test data with the normal data of the drawings and normal records. Electrical appliances without data and no usual records can be compared with the same type of intact electrical appliances. When the electrical components in a circuit are of the same control nature or multiple components control the same device, the fault can be judged by the action of other similar or identical power components.

(2) switch element method: the fault causes of some circuits are not easy to determine or check time for too long, but in order to ensure the utilization of electrical equipment, the same phase performance test can be converted to verify whether the fault is caused by the electrical apparatus. When using the conversion element method, we should pay attention to the inspection. When the electric appliance is dismantled, it should be carefully checked whether it has been damaged. Only when the electrical apparatus itself is damaged, can the new electric appliance be replaced in order to avoid the new damage to the new component.

(3) step by step (or access) method: when multiple circuits are parallel and control more complex circuits short circuited or grounded, there is generally obvious external performance, such as smoke and sparks. When the circuit inside or inside the motor is short circuited and grounded, it is not easy to detect other external phenomena except fuse fuses. This situation can be checked by gradual open circuit (or access) method. Step by step approach: when it comes to a short circuit or grounding fault that is difficult to check, the melt can be replaced and the multi - Branch Cross - linking circuit is reconnected. The circuit is interrupted gradually or emphatically from the circuit, and then the power test is carried out. If the fuse is repeatedly fused, the fault is on the newly broken circuit. Then the branch is divided into several sections, and the circuit is pieced into segments. When a segment of the circuit is connected, the fuse will fuse again, and the fault will be on this circuit and an electrical component. This method is simple, but it can burn the damaged electrical components thoroughly. Step-by-step access method: when a short circuit or grounding fault occurs in a circuit, a new fuse is replaced to gradually or emphatically connect each branch one by one into the power supply and re-test. When a fuse is fused, the fault is just in the circuit and the electrical components it has just accessed.

5. when the forced closure is in the line of electrical fault, after a visual inspection, no fault points are found and there are no proper instruments to measure. An insulating rod is used to press the related relay, contactor, electromagnet and so on by external force, so that it is often closed, and then the electrical or mechanical parts are observed. Various phenomena, such as motors never turn to rotation, and the corresponding parts of the equipment never move to normal operation.

6. short connection equipment circuit or electrical fault roughly induction into short circuit, overload, circuit breakage, grounding, wiring error, electrical electrical and mechanical parts of the six types of failure. There are many breakdowns in all kinds of faults. It includes wire breakage, virtual connection, loosening, poor contact contact, virtual welding, false welding, fuse fuses, etc. There is a simpler and more reliable way to detect such faults besides resistance and voltage. The method is to use a well insulated wire to short circuit the suspected circuit breakers, such as short connection to a certain place, the circuit work is restored to normal, indicating that the site is broken. Specific operations can be divided into local short connection and long short connection. The above inspection methods should be learned and applied in accordance with safety regulations. For the continuous burning of the components should be identified after the replacement; voltage measurement should take into account the voltage drop of the wire; not violating the principle of equipment electrical control, the hand should not leave the power switch, and the insurance should use equal or slightly less than the rated current; pay attention to the selection of measuring instrument.