Transformer faults can be divided into internal faults and external faults. Internal fault refers to the internal insulation or winding fault of the transformer body, and external fault refers to the auxiliary equipment fault of the transformer. The degree of failure varies from light to heavy. When the fault is light, the transformer can continue to run, but measures must be taken to monitor the development and change of the fault. When the fault is serious, the operation of the transformer must be stopped immediately to prevent the fault from expanding.
When the transformer fails, it is necessary to accurately judge and properly handle it to prevent the fault from expanding, and do not stop the transformer operation rashly. This requires operators to improve fault identification ability and accumulate operation experience, so as to correctly judge transformer faults and deal with them in time.
Judgment and treatment methods of several common anomalies or faults.
1. Transformer overheating
Overheating does great harm to transformers. Transformer insulation damage is mostly caused by overheating, and the increase of temperature reduces the pressure resistance and mechanical strength of insulation materials. C354 "Guide to Transformer Operating Load" points out that when the hottest temperature of transformer reaches 140℃, bubbles will be generated in oil, which will reduce insulation or cause flashover, resulting in transformer damage.
Overheating of transformer also has a great influence on the service life of transformer. According to the International Electrotechnical Commission (IEC), in the temperature range of 80- 140℃, the effective service life of transformer insulation will be doubled for every 6℃ increase in temperature, which is the 6℃ rule for transformer operation. The national standard GB 1094 stipulates that the average temperature rise limit of oil-immersed transformer windings is 65℃, the top oil temperature is 55℃, and the iron core and oil tank are 80℃. IEC also stipulates that the coil hot spot temperature shall not exceed 140℃ at any time, and 130℃ is generally taken as the design value. The reasons for the abnormal rise of transformer oil temperature may be as follows: ① transformer overload; (2) The cooling device fails (or the cooling device is completely put into operation); (3) Internal fault of transformer; (4) The temperature indicating device indicates an error.
If it is found that the transformer oil temperature rises abnormally, check the above possible reasons one by one, make an accurate judgment, and check and deal with them in time:
(1) If the operating instrument indicates that the transformer is overloaded, the indications of the three-phase thermometer of the single-phase transformer group are basically the same (there may be several degrees of deviation), and there are no signs of failure of the transformer and the cooling device, then the oil temperature rise is caused by overload, and it shall be treated as overload.
(2) When the cooling device is not fully put into operation or has a fault, it should be handled immediately to eliminate the fault; If the fault cannot be eliminated immediately, the operating load of the transformer must be reduced and operated according to the cooling performance of the corresponding cooling device and the corresponding value of the load.
(3) If the remote temperature measuring device sends out a temperature alarm signal, indicating that the temperature value is high, but the on-site thermometer indicates that it is not high, and there are no other faults in the transformer, it may be a false alarm of the remote temperature measuring circuit fault, and such faults can be eliminated at an appropriate time.
(4) If the oil temperature of a phase in a three-phase transformer group is higher than that of the same phase under the same load and cooling conditions in the past, and the cooling device and thermometer are normal, the overheating may be caused by some fault inside the transformer, and professionals should be notified to take oil samples immediately for chromatographic analysis to further identify the fault. If chromatographic analysis shows that there is an internal fault in the transformer, or the oil temperature of the transformer continues to rise under constant load and cooling conditions, the transformer should be taken out of operation according to field regulations.
(5) The main reasons for abnormal temperature rise of main transformer are:
A) The internal joint is heated.
B) coil has turn-to-turn short circuit.
C) iron core has short circuit or abnormal eddy current.
2. Cooling device failure
The cooling device helps the winding and iron core to dissipate heat through transformer oil. Whether the cooling device is normal or not is an important condition for the normal operation of transformer. When the cooling equipment fails or the cooling efficiency fails to meet the design requirements, the transformer is not suitable for full load operation, let alone overload operation. It should be noted that in the process of oil temperature rising, the temperature of winding and iron core rises rapidly, while the oil temperature rises slowly. On the surface, the oil temperature may not rise much, but the temperature of iron core and winding is already very high. Therefore, when the cooling device fails, we should not only observe the oil temperature, but also pay attention to other changes in the operation of the transformer to comprehensively judge the operation of the transformer.
Common faults of cooling device and their treatment methods are as follows.
(1) Power failure of cooling device. Common faults of cooling devices are power supply faults, such as blown fuse, poor contact of wires or broken wires. When it is found that the cooling device is shut down as a whole or individual fans are shut down, and the submersible pump is shut down, check the power supply, find the fault point and deal with it quickly. If the power supply has returned to normal and the fan or submersible pump still cannot work, you can try by pressing the thermal relay reset button. If the power failure cannot be recovered for a while, and the transformer load is heavy, temporary power supply can be used to make the cooling device run first, and then check and deal with the power failure.
(2) Mechanical failure. Mechanical failures of cooling device include motor bearing damage, motor winding damage, fan blade deformation and submersible pump bearing damage. It needs to be replaced or repaired as soon as possible.
(3) Control loop failure. When the components in the control small loop are damaged, the lead wire is in poor contact or broken, and the contact is poor, the reason should be found out and dealt with quickly.
3. Abnormal transformer oil level
The oil level of transformer corresponds to the oil temperature, and the manufacturer shall provide the oil level and temperature curve. When the oil level and oil temperature do not conform to the oil level-temperature curve, the oil level is abnormal. 500kV transformer generally adopts diaphragm or capsule oil storage tank, and the oil level is reflected by pointer oil level meter. Abnormal oil level will occur under the following conditions:
(1) There are some faults in the pointer oil level meter, such as stuck needle;
(2) gas is stored under the diaphragm or capsule, so that the diaphragm or capsule is higher than the actual oil level;
(3) The respirator is blocked, so that air cannot enter when the oil level drops, and the oil level indicator will be on the high side;
(4) The rupture of the diaphragm or diaphragm causes oil to enter the space above the diaphragm or diaphragm, and the oil level indicator may be low;
(5) The thermometer indication is inaccurate;
(6) Transformer oil leakage reduces the oil quantity.
If the transformer oil level is abnormal, find out the reason quickly and deal with it according to the specific situation. Especially when the oil level indicator exceeds the full scale or will reach the zero scale, the cause of the fault should be confirmed immediately and handled in time. At the same time, the running state of the transformer should be monitored, and measures should be taken immediately if there is any abnormality. The oil level of the main transformer can be judged by the relationship curve between oil level and oil temperature, and the microswitch of the oil level meter sends out the signal of oil level.
(7) If the oil level indicator is abnormal, check whether the oil tank breather is blocked and whether there is oil leakage; Find out the reason and report to the dispatcher and relevant leaders.
(8) If the abnormal decrease of oil level is caused by oil leakage of main transformer, measures to prevent oil leakage should be taken quickly, and the relevant departments should be notified immediately to arrange treatment. If a large amount of oil leakage significantly reduces the oil level, it is strictly forbidden to change the heavy gas into a signal.
(9) If the oil level rises gradually due to the temperature rise, if the oil level at the highest oil temperature may be higher than the oil level indication, it is not a false oil level after analysis, and the oil should be discharged to an appropriate height to avoid overflow. Should be handled by the maintenance unit.
4. The pressure relief valve sends out a continuous alarm signal, which can only be released manually by restoring the indicator rod. After the pressure relief valve is started, the following treatment shall be carried out:
(1) Check whether the pressure relief valve injects oil;
(2) Check the protection action, gas signal action and gas state of the gas relay;
(3) Whether the oil temperature and winding temperature of the main transformer are normal;
(4) Whether the pressure relief valve malfunctions;
(5) Before finding out the reason at the end, the main transformer shall not try to send it.
5. Light gas action of main transformer
(1) Check whether it is caused by oil leakage of main transformer;
(2) Check the oil level and winding temperature of the main transformer, and the sound is normal;
(3) Check whether there is gas in the gas relay, and if there is gas, take the gas for analysis;
(4) Check whether the secondary circuit is faulty;
(5) If the gas in the gas relay is colorless, odorless and nonflammable, and the chromatographic analysis shows that it is air, the main transformer can continue to run; If the signal action is because the residual air in the oil escapes or the strong oil circulation system sucks air, and the signal action time interval is shortened one after another, which will cause tripping, the heavy gas should be switched to the signal; If the gas is combustible, its content exceeds the normal value through chromatographic analysis, and a comprehensive judgment is given through routine tests. If there is a fault inside the main transformer, the main transformer must be shut down, so as to analyze the cause of action and carry out inspection and test.
6. The main transformer has heavy gas action, and it is combustible gas after inspection. The main transformer is not allowed to be put into operation without inspection and test.
Under the following circumstances, heavy gas needs to change the trip signal.
(1) When filtering oil, refueling and replacing silica gel in the operation of main transformer, switch the heavy gas to the signal first, and other protections will trip. After the work is finished and the air in the main transformer is exhausted, the heavy gas can be tripped again.
(2) When the oil level gauge of the main transformer indicates that the oil level is abnormally high or the oil circuit system is abnormal, in order to find out the reason, all deflation or oil drain valves must be opened, the dehumidifier must be checked or other work can be carried out, and the heavy gas cannot start working until the signal is changed.
(3) When the main transformer is overhauled, the ontology protection should be stopped.
7. Transformer tripping
When the transformer automatically trips, it should be thoroughly checked immediately, and the cause of tripping should be found out before handling. Specific inspection contents include:
(1) According to the action display or print record of monitoring devices such as protection or signal and event recorder, judge whether it is a transformer fault trip;
(2) Before tripping, check the transformer load, oil level, oil temperature and oil color, check the transformer for oil injection and smoke, and check the porcelain sleeve for flashover or damage. Whether the pressure reducing valve operates or there are other obvious signs of failure, and whether there is gas acting on the signal in the gas relay.
(3) analyzing the fault wave record waveform;
(4) Understand the system situation, such as whether there are short-circuit faults inside and outside the protected area.
If the inspection results show that the automatic tripping of the transformer is not caused by the transformer fault, the transformer can be put into operation again after the external fault is eliminated.
If one of the following conditions is found in the inspection, it should be considered that there is a fault inside the transformer, and the reason must be further found out and the fault must be eliminated. After the fault is proved by targeted tests such as electrical test and chromatographic analysis, it can be put into operation again.
A) analyzing the gas extracted from the gas relay and judging it as combustible gas;
B) The transformer has obvious internal fault characteristics, such as shell deformation, abnormal oil level and strong oil injection;
C) transformer bushing has obvious flashover trace or damage or fracture, etc.
D) There are two or more sets of differential, gas and pressure relay protection devices.
8. Main transformer differential protection action
(1) Check the protection action, make records, and check all connected electrical equipment within the range of differential protection for obvious faults such as short circuit and flashover.
(2) Check whether there is gas in the gas relay, and whether the pressure relief valve acts and injects oil.
(3) If there is no obvious fault phenomenon and no action is recorded, it may be differential protection misoperation, but trial delivery is not allowed until it is determined.
(4) The commissioning of the main transformer must be approved by the chief engineer.
9. Main transformer fire accident treatment
(1) When the main transformer is on fire, immediately disconnect the power supply of switches and cooling devices on each side, so that there is at least one obvious breakpoint on each side, then use a fire extinguisher to extinguish the fire, and immediately put the sprinkler into operation and notify the fire brigade.
(2) If the oil overflows to the top cover of the main transformer and catches fire, open the lower throttle to discharge the oil to a proper position; If the internal fault of the main transformer causes a fire, it is not allowed to drain oil to prevent the main transformer from serious explosion.
(3) When the fire brigade comes to put out the fire, it is necessary to designate a special person to supervise, and indicate the live parts and matters needing attention.
10. Emergency stop of transformer
In case of any of the following conditions, the running transformer shall be stopped immediately.
(1) The internal noise of the transformer is abnormal or obviously increased;
(2) The casing is seriously damaged and discharged;
(3) The transformer smokes, catches fire and injects oil;
(4) The transformer fails, and the protection device refuses to operate or the action is not clear;
(5) The fire and explosion near the transformer pose a serious threat to the transformer.