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one. Ten principles of electrical equipment maintenance
1. First move and then start
For faulty electrical equipment, do not respond to the emergency, should first ask before and after the failure and failure phenomenon. For unfamiliar equipment, you should also be familiar with the circuit principle and structural characteristics, and abide by the relevant rules. Before disassembling, you must fully familiarize yourself with the function, position, and connection of each electrical component and its relationship with other devices in the vicinity. In the absence of an assembly drawing, you should remove it while drawing a sketch and mark it.
2. First outside and then inside
Should first check the equipment for obvious cracks, defects, understand its history of maintenance, service life, etc., and then check the machine. Before the demolition, the fault factors in the surrounding area should be lined up, and it can be disassembled after being determined as a fault in the machine. Otherwise, blind demolition may cause the equipment to be repaired and damaged.
3. First mechanical and electrical
Only after confirming that there is no fault in the mechanical parts, conduct an electrical inspection. When inspecting circuit faults, the fault location should be found by using the testing equipment, and after confirming that there is no fault of the fault, the operational relationship between the circuit and the machine can be specifically viewed to avoid misjudgment.
4. First, after the static state of dynamic equipment in the absence of electricity, determine the electrical equipment buttons, contactors, thermal relays and fuses to determine the location of the fault. Power test, listen to its sound, test parameters, determine the fault, and finally repair. If the motor lacks phase, if the measured three-phase voltage value can not be discriminated, it should listen to the sound and measure each relative ground voltage separately to determine which phase is missing.
5. After cleaning and maintenance
For heavily polluted electrical equipment, first clean the buttons, wiring points, and contact points, and check if the external control key malfunctions. Many of the faults are caused by dirt and conductive dust, which are often ruled out by cleaning.
6. First power after the device
The failure rate of the power supply is very high in the entire faulty device, so repairing the power supply first can often do more with less.
7. First universal after special
Faults caused by the quality of assembly components or other equipment failures generally account for about 50% of common faults. The special faults of electrical equipment are mostly soft faults, which depend on experience and instrumentation to measure and repair.
8. First outside and then inside
Do not rush to replace the damaged electrical components first. When confirming that the peripheral circuit is normal, consider replacing the damaged electrical components.
9. First DC and then AC
When overhauling, it is necessary to first check the static working point of the DC circuit and then the dynamic working point of the AC circuit.
10. After the first fault debugging
For debugging and fault coexistence of electrical equipment, should be troubleshooting, and then debugging, debugging must be carried out under the premise of the electrical line speed.
two. Inspection methods and operating practices
1. Intuitive method Intuitive method is a method of checking and judging faults by means of reading, smelling, listening, etc. based on the external appearance of an electrical fault.
(1) Inspection procedures: Investigation of the situation: Inquire the operator and the person in trouble at the scene, including the external appearance of the failure, its approximate location, and the environmental conditions at the time of the failure. If there is abnormal gas, open flame, whether the heat source is close to the electrical equipment, whether there is corrosive gas intrusion, whether there is water leakage, whether there are any repairs, repairs, etc. Initial inspection: According to the investigation, to see whether the external damage to the electrical appliances, whether the connection line is broken, loose, whether the insulation is burnt, whether the fuse fuse fuse indicator jumps out, whether the electrical inlet, grease, switch position Are you correct? Commissioning: After preliminary inspections to confirm that there will be further expansion of the fault and personal and equipment accidents, it can be further test run. During the test run, attention should be paid to whether there are serious flashovers, abnormal odors, abnormal sounds, etc., and should be immediately stopped upon discovery. Cut off the power. Pay attention to checking whether the temperature rise of the electric appliance and the electric appliance's operation program comply with the requirements of the electrical equipment schematic diagram, so as to discover the fault location.
(2) Inspection method: Observe the spark: When the contacts of the electric appliance are closed, the circuit is broken, or the wire ends are loosened, sparks will be generated. Therefore, it is possible to check the electrical fault according to the presence or absence of the spark, the size, and other phenomena. For example, when a spark is found between a normally fastened wire and a screw, it indicates that the thread is loose or the contact is poor. The contact of the appliance is closed and the circuit flashes when the circuit is broken, indicating that the circuit is open, and no flashing indicates that the circuit is disconnected. When the main contact of the contactor of the control motor has sparks in two phases and there is no spark in one phase, this indicates that there is no contact between the contacts of one phase without sparks or the circuit of this phase is broken; the sparks of two phases in the three phases are larger than normal, and the other phase Less than normal, it can be preliminarily judged as a phase short circuit or grounding of the motor; three-phase sparks are larger than normal, and may be motor overload or stuck mechanical parts. In the auxiliary circuit, after the contactor coil circuit is energized, the armature does not pull in, and it is necessary to distinguish whether the circuit is broken or the mechanical part of the contactor is stuck. Click the start button, if there is a slight spark when the button normally closed contact is closed, indicating the circuit path, the fault is in the mechanical part of the contactor; if there is no spark between the contacts, the circuit is open circuit. Action procedure: The electrical action program should meet the requirements of electrical specifications and drawings. If an electrical device on a circuit moves too early, too late or does not operate, it indicates that the circuit or appliance is malfunctioning. In addition, faults can be analyzed and judged based on the sound, temperature, pressure, and odor emitted by the appliance. Using intuitive methods not only can identify simple faults, but can also narrow down more complex faults to smaller ranges.
2. Measuring voltage method The measuring voltage method is based on the power supply mode of the electric appliance. The voltage value and current value of each point are measured and compared with the normal value. Specific can be divided into sub-measurement, sub-measurement and spot measurement.
3. Resistance measurement method can be divided into sub-measurement and sub-measurement. These two methods are suitable for electrical equipment with large distances between switches and appliances.
4. Contrast, Displacement Element, Step Open (or Access) Method
(1) Comparison method: The fault is judged by comparing the test data with the drawing data and normal parameters recorded at ordinary times. For appliances that have no data and no usual record, they can be compared with intact appliances of the same model. When the electrical components in the circuit are of the same control nature or when multiple components jointly control the same device, it is possible to use other similar or same power supply components to determine the fault.
(2) Set conversion element method: When the cause of the fault of some circuits is not easy to determine or the inspection time is too long, but in order to ensure the utilization of electrical equipment, the component experiments with good phase performance can be converted to confirm whether the fault is caused by this appliance. cause. When using the conversion element method to check, it should be noted that when the original electrical equipment is removed, it is necessary to carefully check whether it has been damaged, only if it is certainly due to the electrical element itself caused damage, can be replaced with a new electrical appliance, so as not to damage the newly replaced components.
(3) Gradual open-circuit (or access) method: When there are multiple branches connected in parallel and the circuit with complicated control is short-circuited or grounded, there are generally obvious external performances such as smoking and sparks. When the internal circuit of the motor or a circuit with a shield is short-circuited and grounded, it is not easy to find other external phenomena except that the fuse is blown. This situation can be checked with a gradual open (or access) method. Step-by-step method: When it encounters a short circuit or ground fault that is difficult to check, the melt can be replaced again, the multi-branch circuit can be cross-linked, and the circuit can be disconnected from the circuit step by step or in an important way. After that, if the fuse blows again and again, The fault was on the circuit that had just been disconnected. Then divide the branch into several segments and access the circuit segment by segment. When a certain section of the circuit is connected, the fuse is blown and the fault is on this section of the circuit and an electrical component. This method is simple, but it is easy to completely burn the damaged electrical components. Step-by-step access method: When the circuit is short-circuited or grounded, replace it with a new fuse to gradually or critically connect one branch of each branch to the power supply and try again. When a certain period of time is reached, the fuse is blown again, and the fault is on the circuit just inserted and the electrical components it contains.
5. Forced closure method in the line of electrical failure, after visual inspection did not find the fault point and the man does not have the appropriate instrument for measurement, can use an insulating rod to the relevant relays, contactors, electromagnets and other external force to force to make it often The open contact is closed, and then observe various phenomena appearing in the electrical part or the mechanical part, such as the electric motor never turns to rotate, the corresponding part of the equipment never moves to normal operation and so on.
6. Short circuit method equipment circuit or electrical equipment failure is roughly classified into six categories: short circuit, overload, open circuit, grounding, wiring error, electrical and mechanical parts of the electrical fault. Many types of faults appear to be open circuit faults. It includes wire breakage, virtual connection, loosening, poor contact contact, imaginary welding, false welding, fuse blowing, etc. There is a simpler and more reliable method for this kind of fault except for the resistance method and the voltage method. It is the short circuit method. The method is to use a well-insulated wire to short circuit the suspected disconnected part. If it is short-circuited to a certain place, the circuit will work normally, indicating that the circuit is broken. Specific operations can be divided into local short-circuiting and long-short connection.
The above inspection methods should be used for livelihood and comply with the safety operation regulations. For continuous burning of components should be identified after the reasons for the replacement; voltage measurement should take into account the pressure drop of the wire; does not violate the principle of electrical equipment control, test the hand may not leave the power switch, and the insurance should use the same amount or Slightly less than the rated current; pay attention to the selection of the gear of the measuring instrument.
Abstract: Through contact and work in various fields such as supporting, engineering, design, production, R&D, etc., and constantly learning and accumulating a great deal of work experience during work, the current practice and practice of electrical equipment maintenance are common. An analysis of the elaboration.