How to handle abnormal operation of transformers?

As soon as the transformer is powered on, there is a buzzing sound, mainly due to the effect of high-voltage magnetic flux. During normal operation, the sound of the transformer is uniform. When there are other noises, the cause should be carefully investigated and dealt with.

November 14, 2023

PART 1. The sound of the transformer is abnormal

As soon as the transformer is powered on, there is a buzzing sound, mainly due to the effect of high-voltage magnetic flux. During normal operation, the sound of the transformer is uniform. When there are other noises, the cause should be carefully investigated and dealt with.


01 The sound of the 01 transformer increases compared to usual, and the sound is uniform, which may be due to the following reasons:

(1) Overvoltage occurs in the power grid. When single-phase grounding or resonant overvoltage occurs in the power grid, the sound of the transformer will increase. When this situation occurs, comprehensive judgment can be made based on the indication of the voltmeter.

(2) When the transformer is overloaded, it will make a heavy "buzzing" sound. If the load of the transformer exceeds the allowable normal overload value, the transformer load should be reduced according to the on-site regulations.

Solution: Analyze the cause, keep records, strengthen monitoring, and restore normal operation of the transformer as soon as possible. If it is caused by overload, the principle of overload treatment shall be followed.

02 Transformer has noise

It is possible that the vibration is caused by some loose components on the transformer. If the sound of the transformer increases significantly and there is no obvious abnormality in the current and voltage, it may be due to the loosening of internal clamps or screws that compress the iron core, causing an increase in vibration of the silicon steel sheet.

Handling method: If it does not affect the operation of the transformer, it can be temporarily left untreated. Keep records, strengthen monitoring, report to the dispatch and relevant leaders for power outage inspection and handling.

03 Transformer has discharge sound

The transformer has a "popping" discharge sound. If there is a blue corona or spark near the transformer bushing at night or in rainy weather, it indicates that the porcelain parts are seriously polluted or the equipment line card has poor contact. If the internal discharge of the transformer is caused by electrostatic discharge of ungrounded components or coil turn to turn discharge, or discharge due to poor contact of the tap changer.

Solution: At this point, the dispatch and relevant leaders should be reported to apply for power outage inspection and handling of the transformer.


04 Transformer has a popping sound

 If the insulation inside or on the surface of the transformer is broken, the transformer should be immediately stopped for inspection.


05 Transformer has water boiling sound

If there is a sound of water boiling in the transformer, and the temperature changes rapidly and the oil level rises, it should be judged as a serious overheating caused by a short circuit in the transformer winding or poor contact of the tap changer. The transformer should be immediately stopped for inspection.



PART. 2 Upper oil temperature high

Usually, the upper oil temperature of the transformer needs to be detected during operation, and the temperature of the winding is controlled by monitoring the upper oil temperature to prevent its insulation level from decreasing and aging. Under normal load and cooling conditions, if the oil temperature of the transformer is higher than usual by more than 10 ℃ or the transformer load remains unchanged, and the oil temperature continues to rise. If the inspection results prove that the cooling device is in good condition and the thermometer is not faulty, it is considered that the transformer has experienced internal faults (such as iron core fire and winding inter turn short circuit). At this point, the transformer should be immediately stopped to prevent the expansion of transformer accidents.



PART. 3 Abnormal oil color

Normally, the transformer oil should be bright yellow and transparent. When the color of the oil in the oil level gauge changes during operation, it should be contacted to take an oil sample for laboratory analysis. If the oil color of the transformer suddenly deteriorates during operation, and there is carbon in the oil and other abnormal phenomena, the power should be immediately cut off for inspection and handling.



PART4 Abnormal oil level

The oil conservator of the transformer is equipped with an oil level gauge, which generally indicates three oil level lines at temperatures of -30 ℃,+20 ℃, and+40 ℃. Based on these three markings, it can be determined whether refueling or draining is necessary.


01 High oil level:

When the oil level of a transformer in operation is too high or oil overflows from the conservator, it is necessary to first check whether the load and temperature of the transformer are normal. If the load and temperature are both normal, it can be determined that the false oil level is caused by the blockage of the respirator or oil gauge pipe. At this point, with the consent of the on duty dispatcher, the gas (heavy gas) protection should be switched to signal, and then the respirator should be unblocked for processing. If there is oil overflow from the conservator due to high ambient temperature, oil should be drained.


02 Low oil level:

If the oil level of the transformer is too low, it will cause the gas (light gas) protection to act; When there is a serious shortage of oil, the iron core and winding are exposed to the air, which is prone to moisture and may cause insulation breakdown. Therefore, vacuum oil injection method should be used to refuel the transformer in operation. If the oil level rapidly decreases due to a large amount of oil leakage, drops below the gas relay or continues to decrease, the transformer should be immediately stopped.


PART. 5 Overload

When the transformer in operation is overloaded, the ammeter indication may exceed the stable value, and signals and alarm bells may act. Operators should follow the following principles for handling:


01 should check whether the current on each side exceeds the specified value and report to the duty officer on duty.

02 Check if the oil level and temperature of the transformer are normal, and put all the coolers into operation.

03 Adjust the operation mode in a timely manner, and if there is a backup transformer, it should be put into operation.

04 Contact the dispatcher to adjust the load distribution in a timely manner.

05 If it is a normal overload, the allowable operating time can be determined based on the multiple of the overload, and the monitoring of oil level and temperature should be strengthened to not exceed the allowable value. If the time exceeds, the load should be immediately reduced.

06 If it is an accident overload, the allowable multiple and time of overload should be implemented according to the manufacturer's regulations. If the overload multiple and time exceed the allowable value, the compliance of the transformer should also be reduced according to regulations.

07 Conduct a comprehensive inspection of the transformer and its related systems. If any abnormalities are found, they should be reported and dealt with.



Part. 6 Cooling system malfunction

When the transformer cooling system (referring to the submersible oil pump and cooling water system) malfunctions and the transformer sends signals for the standby operation of the cooler and the complete shutdown of the cooler, the following measures should be taken:


01 should immediately check if the backup cooler has been put into operation.

02 Immediately check the cause of the power outage and restore the normal operation of the cooling device as soon as possible.

03 Strengthen the monitoring of the upper oil temperature and oil level of the transformer, especially during the full shutdown time of the cooling device.

04 If the cooling system cannot be restored for a while, an application should be made to reduce the load or to withdraw the transformer from operation, in order to prevent the transformer from operating beyond the specified no cooling time and causing overheating and damage.




Part. 7 Gas protection action

The reason for the gas protection action may be:


01 There is a slight fault inside the 01 transformer, producing weak gas.


02 Air has invaded the transformer.


03 The oil level has decreased.


04 Secondary circuit fault (such as two point grounding of the DC system), causing misoperation.


After the gas protection signal appears, the operating personnel should immediately conduct an external inspection of the transformer. Firstly, the oil level and color in the conservator should be checked, as well as the presence, quantity, and color of gas in the gas relay. Then, the transformer body and forced oil circulation system should be checked for any oil leakage. At the same time, check the changes in load, temperature, and sound of the transformer. After external inspection, if no abnormal phenomena are found, the gas from the transformer should be extracted to determine the nature of the gas. If necessary, an oil sample should be taken for testing to jointly determine the nature of the fault.




Part. 8 Areas and causes of heat generation during operation


01 Poor contact of tap changer

Poor contact leads to increased contact resistance, increased consumption, and severe heating. This situation is particularly likely to occur after switching the tap and during transformer overload operation.


02 Winding interturn short circuit

 Interturn short circuit refers to insulation damage between adjacent wire turns. This will create a closed short-circuit loop and reduce the number of turns of the winding in that phase. There is a short-circuit current induced by alternating magnetic flux in the short-circuit loop, which will generate high heat and may cause the transformer to burn out.


03 There is a short circuit circuit between the 03 iron core silicon steel sheets

 Due to external force damage or insulation aging, the paint insulation between silicon steel sheets is damaged, which can increase eddy currents and cause local overheating. In severe cases, it can also cause melting damage, which is called iron core fire.


04 Local overheating caused by poor contact with other parts

Handling suggestions: closely monitor the temperature changes of the overheated parts to ensure operational safety, analyze the causes of overheating, contact the dispatch, and handle power outages.

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