Abnormal operation analysis of transformer

I.  Abnormal transformer sound

As soon as the transformer is powered on, there will be a buzzing noise, which is mainly due to the high voltage magnetic flux. During normal operation, the sound of the transformer is uniform. When there are other noises, carefully find out the causes and deal with them.

1. The sound of the transformer is higher than usual, and the sound is even, which may be caused by the following reasons:

(1) Overvoltage occurs in the power grid. When single-phase grounding or resonance overvoltage occurs in the power grid, the sound of the transformer will increase. In this case, the comprehensive judgment can be made in combination with the indication of the voltmeter.

(2) When the transformer is overloaded, it will make the transformer emit a heavy "buzzing" sound. If the load of the transformer is found to exceed the allowable normal overload value, the transformer load shall be reduced according to the provisions of the site regulations.

Treatment method: analyze the causes, make records, strengthen monitoring, and restore the normal operation of the transformer as soon as possible. If it is caused by overload, the overload treatment principle shall be followed.

2. The transformer has noise

It may be caused by the looseness of some parts on the transformer. If the sound of the transformer is obviously increased and the current and voltage are not obviously abnormal, it may be caused by the looseness of the internal clamp or the screw pressing the iron core, which increases the vibration of the silicon steel sheet.

Treatment method: if it does not affect the operation of the transformer, it can be left untreated temporarily. Make records, strengthen monitoring, report to the dispatcher and relevant leaders for power failure inspection and treatment.

3. The transformer has discharge sound

The transformer has a "crack" discharge sound. If there is 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 is in poor contact. In case of internal discharge of transformer, it is electrostatic discharge of ungrounded parts or coil inter-turn discharge, or discharge due to poor contact of tap changer.

Treatment method: report to the dispatcher and relevant leaders at this time and apply for power failure inspection and treatment of the transformer.

4. The transformer has a crack

It indicates that the internal or surface insulation of the transformer is broken, and the transformer should be stopped immediately for inspection.

5. The transformer has water boiling sound

If the transformer has water boiling sound, and the temperature changes sharply and the oil level rises, it should be judged that the transformer winding has short circuit or serious overheating caused by poor contact of tap changer, and the transformer should be immediately stopped for inspection.

II.  High upper oil temperature

Generally, the upper oil temperature of the transformer shall be detected during operation, and the winding temperature shall be controlled through the supervision of the upper oil temperature to prevent its insulation level from falling and aging. Under normal load and normal cooling conditions, the oil temperature of the transformer is more than 10 ℃ higher than usual or the transformer load is unchanged, and the oil temperature is rising continuously. If the inspection results prove that the cooling device is good and the thermometer is not faulty, it is considered that the transformer has internal faults (such as iron core fire and winding inter-turn short circuit, etc.). At this time, the transformer should be stopped immediately to prevent the expansion of the transformer accident.

III. Abnormal oil color

The transformer oil shall be bright yellow and transparent under normal conditions. If the color of oil in the oil level gauge changes during operation, contact to take oil samples for chemical analysis. If the oil color of the transformer deteriorates suddenly during operation, and there is carbon in the oil and other abnormal phenomena, the power shall be cut off immediately for inspection and treatment.

IV.  Abnormal oil level

The oil conservator of the transformer is equipped with an oil level gauge, which generally shows three oil level lines when the temperature is - 30 ℃,+20 ℃ and+40 ℃. According to these three marks, we can determine whether it is necessary to refuel or drain oil.

High oil level:

When the oil level of the transformer in operation is too high or oil overflows from the conservator, first check whether the load and temperature of the transformer are normal. If the load and temperature are normal, it can be judged that the false oil level is caused by the blockage of the breather or the oil level gauge. At this time, the gas (heavy gas) protection shall be switched to signal after being approved by the dispatcher on duty, and then the respirator shall be dredged for treatment. If the oil overflows from the conservator due to high ambient temperature, the oil shall be drained.

Low oil level:

If the oil level of transformer is too low, the gas (light gas) protection will act; In case of serious oil shortage, 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 oil the transformer in operation. If the oil level drops rapidly due to a large amount of oil leakage and falls below the gas relay or continues to drop, the transformer shall be stopped immediately.

V.  Overload

When the transformer in operation is overloaded, the ammeter indication may exceed the stable value, and the signal and alarm bell may act. The operating personnel shall handle according to the following principles:

① Check whether the current at each side exceeds the specified value and report to the on-duty attendant.

② Check whether the oil level and temperature of the transformer are normal, and put all coolers into operation at the same time.

③ Adjust the operation mode in time. If there is a standby transformer, it should be put into operation.

④ Contact the dispatcher to adjust the load distribution in time.

⑤ In case of normal overload, the allowable operation time can be determined according to the multiple of overload, and the monitoring of oil level and oil temperature shall be strengthened. The allowable value shall not be exceeded. If the time is exceeded, the load shall be reduced immediately.

⑥ In case of accidental overload, the allowable multiple and time of overload shall be in accordance with the provisions of the manufacturer. If the overload multiple and time exceed the allowable value, the compliance of transformer shall also be reduced according to regulations.

⑦ Conduct a comprehensive inspection of the transformer and its related systems, and report and deal with any abnormality found.

VI.  Cooling system failure

When the transformer cooling system (refers to the submersible oil pump and cooling water system) fails, and the transformer sends the signal of cooler standby input and cooler full stop, the following measures shall be taken:

1. Check whether the standby cooler has been put into operation immediately.

2. Check the cause of power failure immediately and restore the normal operation mode of the cooling device as soon as possible.

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

4. If the cooling system cannot be restored for a time, apply for reducing the load or applying for the transformer to be out of operation to prevent the transformer from running beyond the specified non-cooling time, causing overheating and damage.

VII.  Gas protection action

The reasons for the action of gas protection may be:

1. There is a slight fault in the transformer, producing weak gas;

2. Air intrudes into the transformer;

3. The oil level decreases;

4. Secondary circuit fault (such as two-point grounding of DC system) causes misoperation.

After the gas protection signal appears, the operator shall immediately conduct external inspection on the transformer. First, check the oil level and color in the conservator, whether there is gas in the gas relay, the amount and color of gas, and then check whether there is oil leakage in the transformer body and forced oil circulation system. At the same time, check the load, temperature and sound of the transformer. After external inspection, if no abnormal phenomenon is found, the gas from the transformer shall be drawn to find out the nature of the gas, and the oil sample shall be taken for testing if necessary to jointly determine the nature of the fault.

VIII.  The parts and reasons easy to heat during operation

1. Poor contact of tap switch

Poor contact makes contact resistance increase, consumption increase, and heat is severe. This is especially likely to happen after switching the tap and when the transformer is overloaded.

2. Winding interturn short circuit

Inter-turn short circuit refers to insulation damage between adjacent wire turns. This will cause a closed short circuit loop and reduce the number of winding turns of this 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.

3. There is short circuit circuit between iron core silicon steel sheets

The paint insulation between silicon steel sheets is damaged due to external force damage or insulation aging, which will increase eddy current, cause local overheating, and even melt damage in serious cases, which is the so-called iron core fire.

4. Poor contact of other parts causes local overheating.

Treatment suggestions: closely monitor the temperature change of overheated parts, ensure operation safety, analyze the cause of overheating, contact the dispatcher, and deal with power failure.

Accident treatment of transformer

General: According to 6.1.2 of DL/T572-95 Power Transformer Operation Specification:

The transformer shall be shut down immediately in case of any of the following conditions. If there is a standby transformer in use, it shall be put into operation as soon as possible:

A. The noise of the transformer is obviously increased, very abnormal, and there is a crack inside;

B. Serious oil leakage or oil injection causes the oil level to fall below the indicated limit of the oil level gauge;

C. The bushing is seriously damaged and discharged;

D. The transformer smokes and catches fire.

I.  Automatic tripping of transformer

After automatic tripping of transformer, the following checks and treatment shall be carried out:

① After the automatic tripping of the transformer, the operator shall carry out systematic treatment, that is, put the standby transformer into operation, adjust the operation mode and load distribution, and maintain the operating system and its equipment in normal condition.

② Check which protection action and whether it is correct.

③ Understand whether the system has faults and the nature of faults.

④ The power supply can be tested once without external inspection under the following conditions: personnel touch, misoperation and protection misoperation; only

Low-voltage overcurrent or time-limited overcurrent protection acts, and the next level equipment of the transformer trips at the same time, but its protection does not act, and the fault point has been isolated.

⑤ In case of differential protection, gas protection or quick-break overcurrent protection and other protection actions, and there is impact in case of fault, the transformer and its system need to be inspected in detail, power cut and insulation measurement. It is forbidden to put the transformer into operation until the cause is found out or handled properly.

II.  Gas protection action (trip)

When the gas protection action of transformer trips, the following inspection and treatment shall be carried out:

a) Collect the gas of the gas relay for chromatographic analysis. If there is no gas, check whether the terminal and lead insulation of the secondary circuit and gas relay are good.

b) Check whether the oil level, oil temperature and oil color change;

c) Check whether the explosion-proof pipe is broken and spray oil;

d) Check whether the transformer shell is deformed and whether the welding seam is oil injected.

e) If no abnormality is found after inspection, and it is confirmed that the malfunction is caused by the secondary circuit fault, the gas protection can be connected to the signal or exited when the differential protection and overcurrent protection are put into operation, and the power supply can be tested once, and the monitoring shall be strengthened.

f) If there is gas in the gas relay or there is a problem in the above items a, b, C and d, power off inspection and corresponding treatment shall be carried out, and it can be put into operation after passing the inspection and test.

III.  Overcurrent protection action of voltage transformer

When the transformer overcurrent protection acts and trips, the following inspection and treatment shall be carried out:

a) Check the bus and the equipment on the bus for short circuit and sundries;

b) Check whether several measuring devices of the transformer are short-circuited;

c) Check whether the low-voltage side protection acts and whether the protection of each line acts.

d) When confirming that the bus is dead, the line managed by the bus should be opened.

e) In case of bus failure, consider switching bus or transferring load.

f) If it is confirmed that the trip is a skip, contact the dispatcher on duty and try to power on once.

g) When the test power supply is good, find out the fault line one by one.

h) If it is caused by the circuit, the power can be transmitted after the fault factor is eliminated.

IV.  Transformer differential protection action

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After the transformer differential protection action trips, the following inspection and treatment shall be carried out:

a) Check whether the transformer is abnormal, and whether the insulators within the differential protection range have flashover and damage,

Check whether the lead is shorted.

b) If the equipment within the scope of differential protection has no obvious fault, check whether the relay protection and secondary circuit have fault

Check whether the DC circuit is grounded at two points.

c) After the above inspection, there is no fault, and the report is approved by the chief engineer, the progressive pressure test shall be carried out when the load is disconnected

Put it into operation after it is proved to be good.

d) In case of misoperation caused by electrical and secondary circuits, the differential protection can be exited with the approval of the chief engineer

Put the transformer into operation.

e) When the differential protection and gas protection act simultaneously to trip the transformer, it is not allowed to

The transformer is put into operation.

V. Pressure vessel on fire

Treatment principle of transformer fire: power failure -- oil drainage -- fire extinguishing.

① Power failure: if the transformer is on fire and the protection does not trip automatically, the circuit breaker and the isolation

Leave the switch off, and exit the cooler to disconnect its power supply. In case of endangering the operation of adjacent equipment, timely contact

Stop the operation of adjacent equipment.

② Oil drain: If the oil overflows on the top cover of the transformer and catches fire, open the oil drain valve at the bottom of the transformer to drain the oil to

Emergency oil pool, so that the oil level of transformer is lower than the fire level; If the internal fault of the transformer causes fire

Drain oil to prevent explosion; If the transformer shell is broken and there is oil overflow, the transformer oil pool shall be closed for water and electricity drainage

Open the oil drain electric valve to drain the oil to the emergency oil pool of the main transformer.

③ Start the fire pump and open the fire water valve to spray the transformer to extinguish the fire. ④ Report to the superior and start the emergency plan.

⑤ Notify the fire department and assist in handling.

Note: You can participate in fire fighting without endangering personal safety. It is better to use carbon dioxide, four

Chlorinated carbon, dry powder fire extinguisher and dry sand; Fire fighters should wear gas masks; Special personnel shall be assigned to command the fire fighting,

Prevent casualties.

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