Ten basic principles of electrical Equipment Maintenance
1. Talk before you do
For faulty electrical equipment, do not start in an emergency, should first ask the fault before and after and fault phenomenon.
For unfamiliar equipment, should be familiar with the circuit principle and structure characteristics, 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. In the case of no assembly diagram, we should disassemble while drawing a sketch and mark it
2. First the outside and then the inside
The equipment should be checked for obvious cracks and defects, to understand its maintenance history and service life, and then to check the machine. Before disassembly, the peripheral fault factors should be queued and dismantled only after the fault is determined to be inside the machine. Otherwise, blind disassembly may make the equipment worse and worse.
3. Mechanical before electrical
Electrical inspection should be carried out only after the mechanical parts are confirmed to be faultless. When checking the circuit fault, the detection instrument should be used to find the fault part. After confirming that there is no bad contact fault, the operation relationship between the line and the machine should be targeted to avoid misjudgment.
4. First static and then dynamic
When the equipment is not energized, judge the quality of the electrical equipment button, contactor, thermal relay and fuse, so as to determine the fault. Power test, listen to its sound, test parameters, determine the fault, and finally repair. If the motor phase is missing, if the three-phase voltage value can not be measured to distinguish, you should listen to the sound, separately measure each relative voltage, in order to determine which phase defect.
5. Clean before repair
For heavily polluted electrical equipment, first clean its buttons, wiring points and contact points, and check whether the external control key is out of order. Many faults are caused by dirt and conductive dust, once the cleaning fault is often removed.
6. Power the device first
The failure rate of the power supply part accounts for a high proportion of the whole faulty equipment, so the first overhaul of the power supply can often get twice the result with half the effort.
7. First common, then special
The faults caused by the quality of assembly parts or other equipment faults generally account for about 50 of the common faults. The special fault of electrical equipment is soft fault more, want experience and instrument to measure and maintain.
8. First the outside and then the inside
Do not replace the damaged electrical components in a hurry. Replace the damaged electrical components after confirming that the peripheral circuits are normal.
9. Dc first, then AC
During maintenance, the static working point of dc loop must be checked first, and then the dynamic working point of AC loop must be checked.
10. Fault first, debug later
For the electrical equipment where the debugging and fault coexist, the fault should be removed before the debugging, and the debugging must be carried out under the premise of the electrical line speed.
two Check methods and practices
1. Intuitive method
Intuitive method is based on the external performance of electrical fault, by looking, smelling, listening and other means, check and determine the fault method.
(1) Check steps:
Investigation situation: ask the operator and the fault on-site personnel about the situation, including the external performance of the fault, the general location, the environment when the fault occurs. If there is no abnormal gas, open fire, heat source is close to the electrical appliances, there is no corrosive gas intrusion, there is no water leakage, whether anyone has been repaired, the contents of the repair and so on. Preliminary inspection: according to the investigation, see whether the outside of the electrical appliance is damaged, whether the connection is broken, loose, insulation is burned, whether the screw fuse fuse indicator jump out, electrical appliances without water, oil scale, switch position is correct, etc.
Test run: through the preliminary inspection, confirm to have can make the fault further expand and after cause accident of person, equipment, can further test run check, test run should notice to have no serious jump fire, abnormal smell, abnormal sound and so on phenomenon, once discover should stop immediately, cut off power supply. Whether the temperature rise that pays attention to check electrical appliance and the action program of electrical appliance accord with the requirement of electrical equipment principle diagram, discover fault position thereby.
(2) Inspection method:
Observation of sparks: electrical contacts in the closed, broken circuit or wire loose sparks will be generated, so according to the presence of sparks, size and other phenomena to check electrical fault. For example, when a spark is found between a normally tight wire and a screw, it indicates loose or poor contact. Electrical contacts in the closed, broken circuit fire indicates that the circuit, not fire indicates that the circuit is not blocked.
When the main contact of the contactor of the control motor has sparks in two phases and no sparks in one phase, it indicates that the contact of one phase without sparks is bad or the circuit of this phase is broken; The spark of two phases in the three phases is larger than normal, and the other one is smaller than normal, which can be preliminarily determined as short circuit or grounding between phases of the motor; The sparks of all three phases are larger than normal, possibly because the motor is overloaded or the mechanical part is stuck. In the auxiliary circuit, the armature does not pull after the contactor coil circuit is powered on, so it is necessary to distinguish whether the circuit is broken or the mechanical part of the contactor is stuck. Press the start button, such as the button normally open contact closed position when a slight spark, indicating that the circuit path, fault in the mechanical part of the contactor; If there is no spark between the contacts, the circuit is open.
Operation procedure: the operation procedure of the electrical appliance should comply with the requirements of the electrical instruction and drawings. If the electrical appliances on a circuit act too early, too late or do not act, it indicates that the circuit or electrical appliances are faulty. In addition, according to the electrical sound, temperature, pressure, smell and other analysis to determine the fault. By using the intuitionistic method, not only the simple faults can be determined, but also the more complex faults can be reduced to a smaller range.
2. Measuring voltage method
Measuring voltage method is based on the electrical power supply mode, measuring the voltage value and current value of each point and compared with the normal value. Specifically, it can be divided into fractional measurement method, subsection measurement method and point measurement method.
3. Method of measuring the resistance
It can be divided into step measurement method and subsection measurement method. These two methods are suitable for switches and electrical equipment with large distribution distance.
4. Contrast, displacement element, stepwise open circuit (or access) method
(1) Comparison method:
The test data is compared with the drawings and normal parameters recorded at ordinary times to determine the fault. No data and no usual records of electrical appliances, can be compared with the same model of intact electrical appliances. Electrical components in the circuit belong to the same control nature or multiple components jointly control the same equipment, can use other similar or the same power supply components action to determine the fault.
(2) The conversion element method:
Some circuit failure causes are not easy to determine or check the time is too long, but in order to ensure the utilization of electrical equipment, can convert the same phase of good performance of the components of the experiment, to confirm whether the fault caused by electrical appliances. The attention should be noticed when using transform element method to check, after demolish original electric appliance when, should check seriously whether had been damaged, be to cause damage as a result of factor of this electric appliance itself surely only, ability changes new electric appliance, lest new change element to be damaged again.
(3) Step-by-step open circuit (or access) method:
Multiple branches in parallel and complex control circuit short circuit or grounding, generally have obvious external manifestations, such as smoke, spark, etc. Motor internal or with a cover circuit short circuit, grounding, in addition to the fuse fuse, it is not easy to find other external phenomena. This can be checked by the stepwise open circuit (or access) method.
Step by step open circuit method: it is difficult to check the short circuit or ground fault, can replace the melt, the multi-branch cross-linked circuit, one way one way step by step or key from the circuit interrupt open, and then the power test, if the fuse again and again, the fault is just disconnected on the circuit. The branch is then divided into several sections, which are then connected to the circuit. When the fuse is connected to a certain section of the circuit, the fault is on this section of the circuit and an electrical component. This kind of method is simple, but burn the electrical element with damage not serious easily thoroughly.
Step by step access method: circuit short circuit or ground fault, replace the new fuse step by step or key to each branch of a power supply, re-test. When the fuse is connected to a certain section, the fault is in the circuit that has just been connected and the electrical components it contains.
5. Forced closure
In line electrical failure, after visual inspection found no fault point and staff have not appropriate measuring instrument, can use an insulating rod will be related to relay, contactor, electromagnet or use outside force press, make its normally open contact closure, then observe the electrical or mechanical parts of various phenomena, such as motor never turn to turn, The corresponding part of the equipment from never moving to normal operation.
6. Short connection
The fault of equipment circuit or electrical appliances can be classified into six categories: short circuit, overload, circuit break, grounding, wiring error, electromagnetic and mechanical faults of electrical appliances. Most of the faults are open circuit faults. It includes wire break, virtual connection, loose, contact contact bad, virtual welding, false welding, fuse fuse, etc.
In addition to using resistance method, voltage method to check this kind of fault, there is a more simple and feasible method, is the short-circuit method. The method is to use a good insulation wire, the suspected short circuit part of the connection, such as short to a place, the circuit work is restored to normal, the part of the broken. The specific operation can be divided into local short connection method and short connection method.
The above inspection methods should be used flexibly and comply with safety operation regulations. For the components that are continuously burned out, the reasons should be found out before replacement; The voltage drop of the conductor should be taken into account in the voltage measurement; Do not violate the principle of equipment electrical control, the hand should not leave the power switch during the test, and the insurance should use the same amount or slightly less than the rated current; Pay attention to the selection of measuring instrument gear.