Relay protection action generally indicates that there is a fault inside the transformer. Gas protection is the main protection of transformers, which can monitor partial faults that occur inside the transformer. Often, the signal is sent out by a light gas action, and then the switch is removed by a heavy gas action.

1. The reasons for the light gas action are as follows:

(1) Due to inadequate oil filtration, refueling, and cooling systems, air enters the transformer;

(2) The temperature drop and oil leakage cause the oil level to slowly decrease;

(3) Internal fault of transformer, producing a small amount of gas;

(4) Internal short circuit of transformer;

(5) Secondary circuit fault of protective device.

2. When no abnormal phenomena are found in the transformer during external inspection, the properties of the gas in the gas relay should be identified

(1) If the gas accumulated in the gas relay is non flammable and odorless, and the mixed gas is mainly inert gas with an oxygen content greater than 16%, and the flash point of the oil does not decrease, it indicates that air has entered the gas relay. At this time, the transformer can continue to operate.

(2) If the gas is flammable, it indicates that there is a fault inside the transformer. The nature of the fault inside the transformer should be identified based on the properties of the gas accumulated in the gas relay, such as the color of the gas being:

a、 Yellow is non flammable and contains more than 1-2% carbon monoxide, indicating damage to wooden insulation;

b、 Gray and black are flammable, with a hydrogen content of less than 30%, have a tar smell, and a reduced flash point, indicating that the oil has decomposed due to overheating or that a flashover fault has occurred in the oil;

c、 Light gray with strong odor and flammable, indicating insulation damage to paper or cardboard.

(3) If the above analysis cannot make a correct judgment on the latent faults inside the transformer, gas chromatography can be used to make an appropriate judgment.

When conducting gas chromatography analysis, internal faults in transformers can be determined by changes in the content of hydrogen, hydrocarbons, carbon monoxide, carbon dioxide, and acetylene. Generally:

a、 When the content of hydrogen and hydrocarbons increases sharply, while the content of carbon monoxide and carbon dioxide does not change significantly, it is a bare metal (such as tap changer) overheating fault;

b、 When the content of carbon monoxide and carbon dioxide increases sharply, it is a thermal failure of solid insulation materials (wood, paper, cardboard);

c、 When hydrogen and hydrocarbon gases increase, the acetylene content is very high, which is a discharge fault such as inter turn short circuit or multi-point grounding of the iron core.