Fault diagnosis method of the hottest electrical e

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Electrical equipment fault diagnosis method "six diagnosis, nine methods, three priorities"

electrical equipment is a general term for generators, transformers, power lines, circuit breakers and other equipment in the power system

one, "six diagnosis"

six diagnostic methods: oral, eye, ear, nose, hand model and table test. In short, they are to find out the abnormal conditions of electrical equipment through "ask, see, listen, smell, touch and test", so as to find out the cause and location of the fault. The first "five diagnosis" refers to the targeted diagnosis of electrical equipment faults by using people's senses, which is called sensory diagnosis, also known as visual inspection method. Similarly, due to differences in personal technical experience, the diagnostic results are also different. The "multi person consultation method" can be used to get the correct conclusion. "Meter measurement" refers to the application of electrical instruments to measure the size of some electrical parameters, and determine the cause and location of the fault through comparison with normal values

1. Oral question

when the electrical system of a device fails, the maintenance personnel should first understand the detailed "condition" like the doctor. That is to know the equipment usage, equipment medical records and the whole process of failure from the equipment operators or users. If the fault occurs during or after the relevant operation, you should also ask about the operation content, methods and steps at that time. In general, understanding the situation should be as detailed and true as possible, which is often the key to quickly find out the cause and location of the fault

2. Look at

① look at the scene and carefully check the external condition or operating condition of the equipment according to the situation asked. For example, whether the appearance and color of the equipment are abnormal, whether the fuse is fused: whether the electrical circuit is burned, scorched, open circuit, short circuit, whether the mechanical part is damaged, whether the position of the switch, knife switch, button plug-in wire is correct, whether the modified wiring is wrong, whether the replaced components are consistent, etc.: also observe the signal display and instrument instructions. 1. The basic state of Anyang's industrial development ②. When reading drawings and data, you must carefully consult the electrical schematic diagram and installation wiring diagram related to the failure. You should first understand the schematic diagram, and then read the wiring diagram, so as to guide "practice" with "theory". After understanding and getting familiar with the electrical schematic diagram of the faulty equipment, analyze the fault that has occurred and which part of the control circuit is not conducive to the industrialization of poly amino acids, and those electrical components are related to what problems can be described. Then, after analyzing and deciding to check those places, we can find out the fault step by step

3. Listen carefully to the sound of electrical equipment during operation. Electrical equipment will have some noise during operation, but the noise is generally uniform and regular, and the noise intensity is also low. The noise of electrical equipment operating with faults usually changes, and listening carefully can often distinguish it from the noise of normal equipment operation. Judging faults by hearing is a complicated job. However, as long as we follow the scientific attitude of "seeking truth from facts", proceed from reality, be good at exploring the law, and make scientific analysis, we can diagnose the causes and parts of electrical equipment faults. Sound is produced by the vibration of objects. If you find out the regularity of sound, you can know the cause of invisible faults through it. For example, the factors that affect the sound of the motor are: ① temperature. Some noises of the motor appear or increase with the increase of temperature, while others weaken or disappear with the increase of temperature. ② Load. The load has a great influence on the sound, and the sound increases with the increase of the load, which is the general law of sound. ③ Lubrication. No matter what noise, when the lubrication condition is poor, it is generally serious. ④ Stethoscope. A screwdriver, metal stick, thin metal tube, etc. can be used to touch the test point with a stethoscope, and the sound will become louder for diagnosis. Auscultation with auscultation instruments directly touching the noisy part is called "real listening", auscultation with ears separated by a certain distance, be called "Virtual listening", the two methods should be used together. Rich experience should be accumulated in daily production in order to play a role in practical application.

4. Nose smell

use people's smell to judge the fault according to the smell of electrical equipment. For example, overheating, short circuit, breakdown fault, it is possible to smell the smell of burning, smoke, plastic, rubber, paint, lubricating oil and other heat volatilization odor. For oil injection equipment, internal short circuit, overheating The smell of the oil sample will also change after the water is wet, such as sour taste. Odor, etc

5. Hand mold

touch the relevant parts of the mold equipment by hand, and judge the fault according to the temperature and vibration. If the equipment is overloaded, its overall temperature will rise: such as local short circuit or mechanical friction, Local overheating may occur. "If the machine is blocked or the balance is not good, its amplitude will increase. In addition, in actual operation, you should also pay attention to observe the relevant safety regulations, master the characteristics of the equipment, and master the touch (touch) Methods and skills, touch what you should, touch what you can't, and don't touch randomly. The force of the hand mold should be appropriate to avoid endangering personal safety and damaging the equipment

6. Meter measurement

check the electrical equipment with instruments. According to the size of some electrical parameters measured by the instrument, the cause and location of the fault can be determined after comparing with the normal data

two and nine methods

the faults of electrical equipment can be divided into two categories. One is dominant fault, that is, the fault part has obvious appearance characteristics and is easy to find. For example, the coil of relay and contactor is overheated, smoking and burnt, the contact is burnt, the joint is loose, and the sound is abnormal. Only more than 5000 molds are used for production, which has large vibration, inflexible movement, inflexible rotation, etc. The other is hidden fault, which has no appearance characteristics and is not easy to find. If the fuse is blown. The insulation conductor is broken internally, the setting value of thermal relay is adjusted improperly, and the contact is not synchronized. Therefore, in order to solve the problem, we should be familiar with the circuit principle of the fault equipment on the basis of preliminary sensory diagnosis, combined with our own technical level and experience, and need to think carefully to determine a scientific and effective method to test the cause and location of the fault. There are nine common methods for fault diagnosis of electrical equipment

1. Analysis method

according to the working principle, control principle and control circuit of electrical equipment, combined with preliminary sensory diagnosis of fault phenomena and characteristics. Clarify the system to which the fault belongs, analyze the cause of the fault, and determine the scope of the fault. When analyzing, first start with the main circuit, then analyze each control circuit in turn, and then analyze the signal circuit and other auxiliary circuits. When analyzing, we should make good use of the logical reasoning method

2. Short circuit method

① short circuit somewhere in the electrical channel or jumper a certain intermediate link with wires. When using the short-circuit method, attention should be paid not to affect the working condition of the circuit. For example, capacitors are usually used for short-circuit AC signals rather than wires. In addition, in the commissioning of electrical and instrument equipment, it is often necessary to use short-circuit connecting wires. Short circuit method is a very simple maintenance method. For example, in automatic circuits controlled by travel switches, limit switches, photoelectric switches, etc., when multiple switches are installed and it is not easy to check and distinguish, such methods can be used for actual operation. For example, the car control system can quickly eliminate faults by using the short-circuit method. ② Note that the "test button" must be used when using the short-circuit method to find faults, and wires cannot be used instead. It is unsafe to hold the short-circuit wire by hand for live operation, and the wiring terminal touched by the short-circuit wire is easy to be scarred by sparks. In addition, remember that when using the short-circuit method to find faults, only the wires and contacts with a small voltage drop in the control circuit can be short circuited, and it is not allowed to short circuit the resistance and coil with a large voltage drop in the control circuit, otherwise a short circuit or electric shock accident will occur

3. Open circuit method

open circuit method, also known as open circuit method. That is, throw away the subsequent load (mechanical or electrical load) connected to the fault suspect, which is unloaded or temporarily connected to the false load. For multi-level connected circuits, you can step by step or selectively step away from the next stage. Check the current level after shaking off the load. If the circuit works normally, the fault may be at the later level; if the circuit is still abnormal, the fault is before the open circuit point. This method is mainly used to check overload and low voltage faults, and it is also applicable to working point drift and frequency characteristic change in electronic circuits. For example, when judging the failure of large equipment, this method is often used to distinguish between electrical reasons and mechanical reasons. For example, the induced draft fan of the boiler can be disconnected from the coupling, turned separately, and the cause of the fault can be checked at the same time

4. Cutting method

cut and partition the electrically connected parts to gradually reduce the suspicious range. For example, to find the specific grounding point of a line, or to find the specific fault point of faulty equipment, the cutting method can also be used. To find the grounding point of the feeder, it is usually to make further division at the branch point equipped with branch switch or convenient for division, or focus on the weak links according to the operation experience: to find the fault point inside the electrical equipment, it is usually the cutting point at the convenient division point according to the structural characteristics of the electrical equipment

5. Substitution method

substitution method, that is, the suspected electrical components or parts are replaced with normal and intact electrical components or parts to determine the cause and location of the fault. For electrical components such as plug-ins and embedded relays, the substitution method is simple and easy. Electronic components such as transistors and thyristors are difficult to judge by general inspection methods, and the substitution method is also applicable. When adopting the substitution method, it must be noted that the electrical appliances used for substitution should be consistent with the specifications and models of the original electrical appliances, and the wires should be connected correctly and firmly to avoid new faults

6. Menu method

according to the fault phenomenon and characteristics, list the possible causes of this fault in sequence, and then search and verify them one by one until the real fault cause and fault location are found. ※ Take the heating and smoking of three-phase induction motor as an example, list the following reasons and phenomena: ①, bearing part heating ②, stator and rotor friction ③, overload or low voltage or large three-phase voltage difference ④, power supply disconnection ⑤, winding disconnection ⑥, partial short circuit of stator in-phase coil ⑦, stator phase to phase short circuit ⑧, rotor disconnection ⑨, stator winding grounding ⑩, no fault, which will not affect the operation

7 Comparison method

compare the relevant parameters or operating conditions of the faulty equipment with the normal equipment. The relevant parameters of some equipment can not be found from the technical data, and the performance parameters of some electrical components in the equipment are difficult to judge on site. If there are multiple electrical equipment, they can be adjusted or replaced by comparing with each other and referring to the normal ones. This method is mostly used in the "surface test" of the "six diagnoses". For example, measuring the insulation resistance of power transformer can preliminarily judge the insulation state of transformer. The insulation resistance of newly installed and overhauled transformers by comparison method shall not be less than 70% of the manufacturer's test value

8. Disturbance method

artificially disturb the electrical equipment in operation, observe the changes of equipment operating conditions, and capture the phenomenon of faults. Some faults of electrical equipment are not permanent, but random faults that occasionally occur in a short-term area, which is difficult to diagnose. In order to observe the instantaneous phenomenon of failure, human factors are usually used to control the operation

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