Abnormal operation and analysis of transformer
Writer： Hengfeng you electric Time：2023-05-09 views：times
1、 Abnormal sound of transformer
When the transformer is powered on, there is a buzzing sound, which is mainly the function of high-voltage magnetic flux. During normal operation, the sound of the transformer is uniform. When there are other noises, carefully check the causes and deal with them.
1. The sound of transformer is higher than usual and the sound is uniform. There may be 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. In this case, it can be comprehensively judged in combination with the instructions of the voltmeter.
(2) Transformer overload. 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 on-site regulations.
Solution: analyze the causes, make records, strengthen monitoring, and restore the transformer to normal operation as soon as possible. If it is caused by overload, carry out treatment according to the principle of overload.
2. Transformer has noise
The vibration may be caused by the looseness of some parts on the transformer. If there is a significant increase in the sound of the transformer and there is no obvious abnormality in the current and voltage, it may be caused by the loosening 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 not be handled temporarily, make records, strengthen monitoring, and cut off power for inspection and treatment if necessary.
3. The transformer has discharge sound
The transformer has "crackling" discharge sound. If blue corona or spark is seen near the transformer bushing at night or in cloudy and 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 the electrostatic discharge of ungrounded parts or coil turn to turn discharge, or the discharge due to poor contact of the tap changer.
Treatment method: check and deal with the power failure of the transformer.
4. The transformer has a burst sound
Explain the insulation breakdown inside or on the surface of the transformer, and immediately stop the transformer for inspection.
5. The transformer has water boiling sound
If there is water boiling sound in the transformer, the temperature changes sharply and the oil level rises, it should be judged that the transformer winding is short circuited or the tap changer is seriously overheated due to poor contact, and the transformer should be stopped for inspection immediately.
2、 High upper oil temperature
Usually, 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 avoid the decline and aging of its insulation level. Under normal load and normal cooling conditions, the transformer oil temperature is more than 10 ℃ higher than usual, or the transformer load remains unchanged, and the oil temperature continues to rise. If the inspection results prove that the cooling device is good and the thermometer is free of problems, it is considered that the transformer has internal faults (such as iron core fire and winding turn to turn short circuit, etc.). At this time, the transformer shall be stopped immediately to prevent the expansion of transformer accident.
3、 Abnormal oil color
Under normal conditions, the transformer oil shall be bright yellow and transparent. When the color of the oil in the oil level gauge changes during operation, take an oil sample for laboratory analysis. If the color of transformer oil deteriorates suddenly during operation, and there are carbon and other abnormal phenomena in the oil, power off immediately for inspection and treatment.
4、 Abnormal oil level
The 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 marking lines, we can judge whether it is necessary to refuel or drain oil.
High oil level: when the oil level of the running transformer 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 respirator or oil standard pipe. At this time, change the gas (heavy gas) protection to the signal, and then dredge the respirator for processing. If there is oil overflow from the conservator due to high ambient temperature, the oil shall be drained.
Low oil level: low oil level of transformer will cause gas (light gas) protection action; 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, the vacuum oil injection method should be used to refuel the running transformer. If the oil level drops rapidly due to a large amount of oil leakage, drops below the gas relay or continues to drop, the transformer shall be stopped immediately.
5、 Overload
When the transformer in operation is overloaded, the indication of ammeter may exceed the stable value, signal, alarm bell action, etc. The operating personnel shall deal with it according to the following principles:
① Check whether the current on each side exceeds the specified value.
② Check whether the oil level and temperature of the transformer are normal, and put all coolers into operation.
③ Adjust the operation mode in time. If there is a standby transformer, it shall be put into operation.
④ Adjust the load distribution in time.
⑤ In case of normal overload, determine the allowable operation time according to the multiple of overload, and strengthen the monitoring of oil level and oil temperature, which shall not exceed the allowable value. If it exceeds the time, reduce the load immediately.
⑥ In case of accidental overload, the allowable multiple and time of overload shall be in accordance with the regulations of the manufacturer. If the overload multiple and time exceed the allowable value, the compliance of the transformer shall also be reduced according to the regulations.
⑦ Comprehensively inspect the transformer and its related systems. If any abnormality is found, it shall be handled according to the situation.
6、 Cooling system failure
When the cooling system of the transformer (referring to the submersible oil pump and cooling water system) fails and the transformer sends the signals of standby input of the cooler and full stop of the cooler, the following treatment shall be done:
1. Immediately check whether the standby cooler has been put into operation.
2. Immediately check the cause of power failure 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 while, apply for reducing the load or the transformer out of operation to prevent the transformer from running beyond the specified non cooling time, resulting in overheating and damage.
7、 Gas protection action
The reason for the action of gas protection may be:
1. There is slight fault in the transformer, producing weak gas;
2. Air intrudes into the transformer;
3. Oil level decreases;
4. Secondary circuit fault (such as two-point grounding of DC system, etc.) causes misoperation.
After the gas protection signal appears, the operator shall immediately conduct external inspection on the transformer. Firstly, check the oil level and color in the conservator, whether there is gas in the gas relay, gas quantity and color, etc., and then check whether there is oil leakage in the transformer body and forced oil circulation system. At the same time, check the changes of transformer load, temperature and sound. If no abnormality is found through external inspection, the gas of the transformer shall be absorbed to find out the nature of the gas, and its oil sample shall be taken for test if necessary, so as to jointly determine the nature of the fault.
8、 Parts and causes of heating during operation
1. Poor contact of tap changer
Poor contact increases the contact resistance, consumption and severe fever. This is especially likely to happen after switching taps and when the transformer is overloaded.
2. Winding turn to turn short circuit
Inter turn short circuit is the insulation damage between several adjacent wire turns. This will result in 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 produce high heat and may cause the transformer to burn out.
3. There is a 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. This is the so-called iron core fire.
4. Local overheating caused by poor contact of other parts.
Treatment suggestion: closely monitor the temperature change of overheating parts to ensure operation safety, analyze the causes of overheating and deal with power failure.
