The electrician can judge the operation status of the transformer at any time by changing the sound, vibration, smell, discoloration, temperature and other phenomena, and analyze the cause, location and extent of the accident. Therefore, based on the grasped situation, a comprehensive analysis is made, and the final judgment of the operating state of the transformer is made in combination with various detection results.
(1) Intuitive judgment
1, sound
In normal operation, due to the alternating current passing through the transformer winding, a periodic alternating magnetic flux is generated in the iron core, causing magnetostriction of the electric steel sheet, magnetic force between the joint of the iron core and the lamination, and the wire of the winding. The electromagnetic force between them causes vibration and gives an average "click" sound. If an uneven sound or other sound is produced, it is abnormal.
(1) If the sound is more uniform and uniform than usual, one may be an overvoltage in the power grid, and the other may be an overload of the transformer. In large power equipment (such as a large motor), the load changes greatly. Subharmonic action, a "wow" sound instantly in the transformer. At this point, the voltage and the indication of the circuit meter can be used to judge the nature of the fault. Then, depending on the specific situation, change the operation mode of the power grid and reduce the load of the transformer, or stop the operation of the transformer.
(2) When the sound is loud and noisy, it may be a problem with the transformer core. For example, when the clamp or the screw that presses the iron core is loose, the indication of the instrument is generally normal, and the color, temperature and oil level of the insulating oil are not greatly changed. At this time, the operation of the transformer should be stopped for inspection.
(3) When there is a “beep†sound in the sound, it may be a partial discharge of the surface of the transformer or the bushing. If it is a casing problem, in the harsh weather or at night, you can also see corona glow or blue, purple small sparks. In this case, remove the dirt on the surface of the casing, and then apply paint such as silicone oil or silicone grease. . If it is a problem with the body, put the ear close to the fuel tank of the transformer, you will hear the sound of "å±å±" or "噼啪" in the transformer due to local or electrical contact failure, and the sound is close to the fault location. Variety. If you stand in front of the transformer, you can hear the “beep†sound, and there is a possibility that the grounded metal or ungrounded metal part will be electrostatically discharged. At this point, to stop the transformer operation, check whether the grounding of the core and the distance from each live part to the ground meet the requirements.
(4) If there is a boiling sound of water in the sound, the winding may have a serious fault, causing severe heat generation in the nearby parts. This sound is necessary when the tap changer is in poor contact and the local point is severely overheated. At this point, the operation of the transformer should be stopped immediately and repaired.
(5) When there is a popping sound in the sound, which is large and uneven, it may be that the transformer body is insulated and has a breakdown phenomenon. At this time, the operation of the transformer should be stopped immediately and repaired.
(6) When there is continuous, regular impact or friction in the sound, it may be that some parts of the transformer are mechanically contacted by the vibration of the iron core. If it occurs on the oil pipe or wire on the outer wall of the fuel tank, it can be solved by increasing the spacing or reinforcing the fixing. In addition, the cooling fan, the bearing wear of the oil pump and the ball bearing have cracks, and the mechanical friction sounds.
2, smell, color
Internal faults in the transformer and overheating of various components will cause a series of changes in odor and color.
(1) The fastening part of the porcelain bushing terminal is loose, and the surface is in contact with the superheated oxidation, which may cause discoloration and abnormal odor.
(2) The magnetic disconnection capability of the transformer leakage magnetism is not good and the magnetic field distribution is not uniform. The eddy current is induced, which will cause the paint to discolor due to local overheating of various parts of the fuel tank.
(3) Corrosion of the porcelain casing will produce a corona, which will give off a strange smell. The cooling fan will burn out and burn out.
(4) The hygrometer's discoloration is caused by excessive moisture absorption, damage to the gasket, and too much water entering the oil chamber.
3, temperature
(1) Many faults of the transformer are accompanied by a sharp temperature rise. For the transformer in operation, it should be checked frequently whether the connection between each terminal of the bushing and the busbar or cable is tight and there is no sign of heat generation.
(2) Overload, ambient temperature exceeds the specified value, the cooling fan and the oil pump are faulty, the radiator valve is forgotten to open, the oil leakage is insufficient, the thermometer is damaged, and the internal fault of the transformer will cause the reading on the thermometer to exceed the operating standard. The specified allowable temperature.
The above judgment based on sound, vibration, odor, discoloration, temperature phenomenon on the transformer accident can only be used as a preliminary judgment on the scene. Because the internal fault of the transformer is not only a direct reflection of a single aspect, it involves many factors, and sometimes even illusions. Therefore, measurement must be carried out and comprehensive analysis is carried out in order to accurately and reliably identify the cause of the failure, identify the nature of the accident, and propose a more complete and reasonable treatment method.
(2) Analysis and judgment
1, the core is damaged
Insulation damage between the transformer core silicon steel sheets increases the eddy current loss in the core. The increase in eddy current loss is proportional to the square of the thickness of the silicon steel. If the insulation between the silicon steel sheets is damaged, the thickness of the silicon steel sheet is doubled, the eddy current loss will be increased by four times, and the adjacent core insulation will be more damaged after the heat is generated. At the same time, the oil temperature rises and the oil quality deteriorates. In severe cases, the gas relay operates.
2, iron core ground crack
When the transformer is in operation, its internal metal parts will generate a floating potential due to induction. If the grounding is poor or the grounding lug is broken, an intermittent discharge will occur. When the voltage rises, a slight click may occur inside. In severe cases, the gas relay will act and the oil chromatographic analysis will be unqualified. The reason may be that the grounding piece is not inserted, for which the core can be inspected for the grounding piece and the damaged grounding piece is replaced.
3, winding turn-to-turn short circuit
In the case of a short circuit between turns, the gas of the general gas relay is grayish white or blue, and the trip circuit operates. When the fault is serious, the differential protection action. The overcurrent protection action is installed on the power supply side, and the high voltage fuse is blown. If the short circuit between the turns is not found in time, the molten copper (lead) particles will be scattered back to the adjacent windings. The reason for the short circuit between the windings is that the poor heat dissipation or long-term overload causes the insulation between the turns to be damaged; the short circuit of the transformer or other fault causes the winding to be vibrated and deformed by the impact of the short-circuit current, thereby damaging the inter-turn insulation, and the oil level is lowered to make the winding The oil surface line is exposed to the insulation breakdown of the oil line; the atmospheric overvoltage intrusion damages the inter-turn insulation during lightning strike; no defects are found during the winding winding or the winding arrangement and the transposition, the winding is not properly pressed, etc., so that the inter-turn insulation is damaged.
4. Short circuit of grounding part during winding
After the transformer oil is damp, the insulation strength is reduced, the oil level is lowered or the insulation is aging; the lightning atmospheric voltage and the operating overvoltage, the winding is deformed by the impact of the short-circuit current, the main insulation is aging, broken, broken, etc.; In the event of such an accident, the gas relay is generally operated and the explosion-proof pipe is sprayed. If the center point of the transformer is grounded, the differential and DC protection will also operate. In general, measuring the insulation resistance of the winding to ground can find out whether there is winding grounding.
5, winding and lead disconnection
The wire is broken due to poor connection or short-circuit stress; the internal welding of the wire is poor, and the short circuit between the turns causes the wire to blow. The arcing at the wire breakage will cause the grounding of the winding and the phase-to-phase short circuit. The oil decomposition causes the gas relay to operate. The core can be inspected during processing, and the DC resistance of the winding is measured by the bridge to judge the fault phase and rewind the winding.
6, winding phase-to-phase short circuit
When the winding has a turn-to-turn short circuit or a ground fault, the arc and the molten copper (lead) particles may cause the accident to spread and may develop into a phase-to-phase short circuit. When a phase-to-phase short circuit occurs, a strong short-circuit current will produce a violent arc. At this time, the gas relay, differential protection and overcurrent protection will operate. The explosion-proof pipe is seriously injecting oil and the oil temperature is increasing sharply. By measuring the insulation resistance and measuring the DC resistance and transformation ratio of the winding, the damage of the winding can be judged.
7, the casing is broken or the outlet connection is loose
The surface of the transformer bushing is dirty and foggy, rainy, cloudy, causing corona discharge and causing a "beep" sound. The casing fouling produces corona, flashover will cause strange odor; the casing outlet connection is loose, the surface When the contact surface is overheated, oxidation will cause discoloration and abnormal odor; the external protection device will act when the ground is broken or the casing is discharged.
8, gas relay
When the gas relay operates and gas accumulates therein, it cannot be proved that there is a fault inside the transformer, for example, the degassing of the insulating oil is not complete, and the vacuum is not injected. If the cooling system is not tight, the air will enter the gas relay and act to send a signal. After the air is discharged, the transformer can continue to operate, but when the internal fault occurs in the transformer, the situation is different. The gas inside the gas relay accumulates gas, but it is not ordinary air. Therefore, these gases should be collected, and the quantity, flammability color and chemical composition should be analyzed to judge the nature of the fault. In areas where chromatographic analysis is not possible at one time, you can sign as follows:
(1) Colorless, non-flammable is air.
(2) Yellow, flammable is the gas generated by wood failure.
(3) Light yellow, flammable and odorous are gases caused by paper failure.
(4) Gray-black, flammable is the gas generated by the decomposition of insulating oil caused by iron failure.
In summary, when a transformer fails, it can accurately determine the cause of the fault according to the state of the fault, and provide an accurate basis for the fault to ensure the recovery in the shortest time. . At the same time, in the daily operation to strengthen the inspection of the state of the transformer, it can also prevent the occurrence of faults and improve the reliability of power supply.
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