Abnormal Operation of Transformer and Its Processing Method

2019-01-08

The main abnormal conditions of transformer operation are: overtemperature of upper oil, abnormal oil level, alarm of gas relay, failure of cooling system and Abnormal Chromatographic analysis. Operators should timely analyze the causes, nature and impact of abnormal operation of transformers, and take appropriate measures to prevent the expansion of faults and protect the safe operation of transformers.
I. Increase of Upper Oil Temperature
1. Check whether the load of the transformer and the temperature of the cooling medium have changed greatly, and compare the oil temperature of the load and the temperature of the cooling medium according to the relevant technical records.
2. Check whether the cooling device of the transformer fails, such as the fan, the oil pump, the cooling water pressure, the power supply of the cooling device is put in or switched on normally.
3. Check whether the meter and its circuit are normal. Comparing the counting value of field meter with remote measurement, the result of comparison should be based on the higher temperature as the basis of transformer temperature control.
4. If it is found that the oil temperature is 5-10 C higher than usual under the same load and cooling conditions, and the cooler is running normally, it is considered that the transformer has malfunction, and the transformer should be shut down immediately by contact with the dispatch.
5. Any phase oil temperature anomaly of single-phase transformer should also be regarded as anomaly, and must be analyzed and dealt with quickly.
2. Abnormal oil level.
Normally, the oil level of transformer varies with temperature. The oil temperature depends on the load of the transformer, the ambient temperature and the operation of the cooling system. If the relevant part of the transformer leaks, the oil level will be reduced accordingly. There are two main cases of abnormal transformer oil level:
1. Excessive oil level. The reason is that the transformer is affected by high temperature for a long time, and the oil level rises due to thermal expansion; the oil level is higher when refueling; and the water intake of the transformer. When the oil level is too high, it will cause oil spill. Therefore, when the oil level is found to be high, the oil should be discharged through the maintenance personnel in time, but the oil level should be controlled to correspond with the oil temperature at that time.
2. Low oil level. The main reasons are transformer oil leakage; when transformer load suddenly decreases or ambient temperature significantly decreases; forced oil circulation directional cooling transformer cooling oil leakage, resulting in transformer oil infiltration into water for a long time. Generally speaking, transformer oil level will not leak in a very short time. Operators should monitor the change of transformer oil level at any time. Alarm will be given when oil level is lower than gas relay. When the oil level is too low, it may make the core winding directly contact with the air, and the consequences are quite serious. When the oil level of main transformer is abnormally lowered, it should be checked comprehensively, whether there is oil leakage, whether the accident discharge valve has been opened by mistake or oil leakage, and stop it in time. If the oil spill can not be stopped for a while, the power outage should be contacted immediately. Heavy gas protection shall not be changed to "signal" position. If the oil temperature is low, the cooler and cooling water can be adjusted, the oil temperature can be raised, and the maintenance personnel can be contacted to refuel. When refueling, the heavy gas protection should be put in the "signal" position. After more than 24 hours of operation, the gas relay can not be put into the "tripping" position until no gas is discharged.
3. Fault of cooling system.
When the cooling system fails, the transformer may be forced to reduce its output, and in serious cases, the transformer may be forced to shut down or even burn out.
1. Causes of cooling system failure. There are power failure of cooling system; switch failure tripping of single cooler; fault of oil pump and fan; leakage of connecting pipeline; low or no water pressure of cooling water.
2. Treatment of cooling system failure. For oil-immersed air-cooled transformer, when fan power supply failure occurs, the load should be adjusted immediately so that it does not exceed 70% of the rated capacity. When a single fan failure occurs, the load of transformer can not be reduced.
3. Transformers with forced oil circulation cooling should be restored within 10 minutes if the power supply of the cooling device is interrupted. At the same time, we should pay close attention to the upper oil temperature of the transformer and reduce the load operation properly. If 10 minutes can not be restored, the transformer will be immediately shut down. If some coolers are damaged, the transformer load should be adjusted according to the relationship between the number of coolers and the corresponding load. At the same time, standby cooler or auxiliary cooler can be properly put in, without adjusting transformer load.
4. Faults and Treatment of Transformer Cooling System (Examples)
1. Power failure. If the power supply is interrupted, the power supply should be restored quickly. In case of failure of working power supply and bad switching of standby power supply, manual help should be provided immediately. Cooler shutdown protects the outlet pressure plate from short-term withdrawal and reduces the active load.
2. Standby cooler input. The standby cooler should be checked for good input first. Then check the fault reason of the fault cooler and deal with it.
3. Interruption of cooling water. Check the water pressure indication or valve position, and switch the water source in time. If the signal is sent by mistake, the maintenance personnel shall be notified to handle it.
4. disconnect. Usually it is fused and replaceable by power supply insurance. If re-fuse, the circuit and submersible pump may have short circuit, power cut to take measures to notify the maintenance treatment.
5. Analysis of Serious Abnormal Phenomena in Transformer Operation
1. There is strong and uneven noise and discharge sound in the tank of transformer. The noise is due to the loose core caused by the insensitive clamp of the core screw, which causes the vibration between the silicon steel sheets. Discharge squeaks are caused by flashover discharge of windings or lead wires to the outer shell, or breakage of ground wire of iron core, resulting in high voltage discharge of iron core induced to the outer shell (ground).
2. Transformer oil pillow or explosion-proof tube injection. This indicates that the transformer has a serious fault. Due to the decrease of oil level, the gas relay may operate, which causes the switch on both sides of the transformer to trip.
3. variable pressure