Transformer is a static power equipment that can convert a certain AC voltage into another voltage with the same frequency and a different value. It is used to transmit and distribute electric energy. It is the most important regulating equipment for power supply reliability and power quality. , if the transformer fails, it will seriously affect the safety and stability of the power supply system. Therefore, in our daily maintenance work, we must strengthen the operation and maintenance of the transformer, be familiar with the composition and technical parameters of the transformer, promptly summarize the causes of abnormalities and faults in its operation, accurately determine the abnormality and fault points of the transformer, and take preventive and treatment measures .
1. Daily maintenance
The Huatai Cableway uses SC(B)10-1600/10 dry-type transformer. Daily operation and maintenance should pay attention to the temperature of the three-phase winding of the transformer, ambient temperature, abnormal noise, fan status, etc.
The main reasons for abnormal operation of transformers include: line inrush interference, closing overvoltage, voltage peak, line fault, flashover and other power transmission and distribution problems. If the transformer is in an overload state for a long time and the temperature rises abnormally, it will cause the insulation of the transformer to age; if the transformer is damp and the internal bolt connections are loose, routine maintenance is not in place.
Therefore, daily maintenance must be carried out carefully. The equipment must be dusted regularly, and dehumidification and moisture-proofing must be carried out regularly to keep the environment dry. The operation of the temperature control equipment must be checked regularly and inspected regularly to ensure that the connection points are tight and reliable.
Transformer overload can be divided into two situations: normal overload and accident overload. Normal overload is caused by the increase in user power consumption under normal power supply conditions. It will increase the temperature of the dry-type transformer, causing the insulation of the dry-type transformer to accelerate aging and reduce its service life. Under normal circumstances, overload operation is not allowed. Dry-type transformers can be overloaded in a short period of time under special circumstances, but they must not exceed 30% of the rated load in winter and 15% of the rated load in summer. In addition, the overload capacity of the dry-type transformer should be determined based on the temperature rise of the dry-type transformer and the manufacturer's regulations. When an accident occurs in the power system or user substation, in order to ensure continuous power supply to important equipment, the dry-type transformer is allowed to operate overloaded for a short period of time, that is, accidental overloading. An accidental overloading will cause the coil temperature to exceed the allowable value, thus affecting the insulation It ages faster than normal conditions. However, there are few chances of accidental overload. Under normal circumstances, dry-type transformers will not operate at full load, so short-term overload can easily damage the insulation of dry-type transformers.
Pay attention to the sound of the transformer operating. When the transformer is operating normally, there is generally a uniform "buzzing" electromagnetic sound. The sound should not be too loud and there should be no abnormal sound. Observe that the voltage running on the high-voltage side of the transformer is 10±5%KV, the current does not exceed the rated current value, and the three-phase current imbalance does not exceed 5%. Observe that there should be no local overheating in each component part of the transformer, and the temperature displayed on the thermostat does not exceed 80 degrees, when the three-phase load of the transformer is balanced, the three-phase temperature should be about the same.
2. Regular maintenance
Maintenance steps: Disconnect the low-voltage side circuit breaker of the transformer for maintenance and hang the "No closing" sign. Disconnect the circuit breaker on the high-voltage side of the transformer for maintenance, close the grounding switch, fully discharge the transformer, lock the high-voltage cabinet, and hang a "no closing" sign on the switch handle.
To maintain a dry-type transformer, first clean the iron core, then check the casing. Most importantly, check whether the coil is broken, cracked, discharge traces or the rubber pad is aging, and whether the cables and busbars are deformed. If there is any rupture, replace it. Check whether the busbar contact surface is kept clean. The oxide layer should be removed from the contact surface and coated with electrical compound grease. Check whether the grounding of the transformer is good and whether the ground wire is corroded. If the ground wire is severely corroded, replace it. Tighten the lead terminals, pins, grounding screws, and busbar screws. If any are loose, remove the screws, or lightly file the contact surface with a fine flat file, or replace the spring washers and screws until the contact is good. Clean the dust around the transformer and accessories, and check whether the fire protection facilities and ventilation system are in good condition.
Disconnect the grounding switch on the high-voltage side and measure the insulation resistance with a 2500V megger. And compared with the value measured before the transformer leaves the factory, the insulation resistance should not be lower than 70% of the original data when it leaves the factory. If it is unqualified, it should be dealt with in time. Close the grounding switch on the high voltage side again and allow the transformer to discharge. Check whether there are any tools left behind in the transformer room and transformer. Connect the low-voltage side circuit breaker control power supply operation fuse, and re-hang the "No closing" sign to prevent reverse power transmission to the transformer. Disconnect the high-voltage side grounding switch and check the control lines on the transformer site and low-voltage side again. If correct, close the high-voltage side circuit breaker of the transformer and allow the transformer to be put into trial operation. Remove the high-voltage side sign. Carry out maintenance and trial operation in detail, and note the maintenance time.
3. Common faults
(1) Abnormal rise in transformer temperature
Check whether the thermostat and thermometer are malfunctioning; check whether the blower device and indoor ventilation are normal; check the load condition of the transformer and the insertion of the thermostat probe, and troubleshoot the thermostat and blower device. If the temperature continues to rise under normal load conditions, If it rises, it should be confirmed that there is an internal fault in the transformer, and the operation should be stopped for maintenance. Common causes of failure: local short circuit between layers or turns of the transformer winding, loose internal contacts, increased contact resistance, short circuit on the secondary line, etc.; partial short circuit in the transformer core, core grommets used to clamp the core Screw insulation damage; long-term overload operation or accidental overload; deterioration of heat dissipation conditions, etc.
The main board of this cableway temperature controller was damaged once, and the three-phase temperature displays of A, B, and C all reported fault codes. Find the corresponding instructions and the main board needs to be replaced. After replacing the main board, the test was normal. During the inspection, it was found that the single-strand insulation of the power cord of the temperature controller was aging, possibly due to the high temperature in the transformer, so the wiring was changed and replaced. The circuit board inside the original temperature controller was yellow and had a lot of dust. The reason is summarized. The first reason is that the internal temperature of the transformer is relatively high, which is prone to insulation aging. Second, there is a blind spot in annual maintenance, and the inside of the temperature controller must also be dusted and cleaned.
(2) Abnormal sound of transformer
When abnormal sound occurs in the transformer, first analyze and determine whether the sound is inside or outside the transformer: if it is inside, it may be that the iron core is not tightly clamped and loose, and a "ding-dong" and "whirring" sound will be emitted; the iron core is not grounded. There will be a slight discharge sound of "squeaking" and "squeaking"; poor contact of the switch will produce "squeaking" and "crackling" sounds, which will become louder as the load increases; when the surface of the casing is seriously oily, it will make a "hissing" sound. "Voice. If it is external, overload operation will emit a heavy "buzzing"; if the voltage is too high, the transformer will sound louder and sharper; when running out of phase, the transformer will sound sharper than usual; when magnetic resonance occurs in the power grid system, the transformer will emit uneven sound. noise; when there is a short circuit or grounding on the low-voltage side, the transformer will make a huge "booming" sound; when the external connection is loose, there will be arc light or sparks. It needs to be shut down for corresponding inspection.
(3) The transformer does not alarm after opening the door
The travel switch is a device that protects the operator when the transformer is running with power. If the transformer is live, when any housing door is opened, the contacts of the travel switch should be closed immediately to connect the alarm circuit and alarm. The reason why there is no alarm after opening the door may be: poor connection or fixation of the limit switch or fault of the limit switch. It is necessary to check the wiring and terminals to make sure they are in good contact. Check and tighten retaining bolts. If there is a problem with the travel switch, replace the travel switch.
4. Summary
Transformers are key equipment in the power distribution system, and their maintenance is also a top priority for maintenance personnel. They must continue to learn the operation and maintenance knowledge of transformers at work, improve their shortcomings, and ensure the safety of the power supply system. At the same time, every abnormal point needs to be treated more carefully during daily inspections, and the sound and temperature of the transformer should always be paid attention to. Any abnormal noise requires further inspection to ensure the safety of the equipment.