Preface Gas relays are important safety protection devices on oil-immersed transformers. They are installed on the connecting pipe between the transformer tank cover and the oil conservator. Under the action of gas or oil flow generated by internal faults in the transformer, they connect the signal or trip circuit, causing relevant devices to issue alarm signals or disconnecting the transformer from the power grid, thus protecting the transformer. If not used correctly or improperly, it may cause damage to the transformer. Keywords: relay, transformer, relay protection 1 Problems with the transformer (1) Transformer A, model SZ9-4000/35, was manufactured in July 1999 and installed and put into operation in August of the same year. On October 31, 2001, chromatographic analysis showed that there was an internal arc discharge fault and solid insulation damage, so a power outage was arranged for maintenance. On November 2, a power outage was carried out to check the core and found that there were multiple inter-turn short circuits in the high-voltage coil of phase B, with obvious discharge traces and a lot of free carbon in the transformer; the gas relay installed was not put into use (no wiring). This transformer was operating under high temperature arc, and there was a risk of fire and burning at any time. Because the fault was diagnosed in time and power outage measures were taken, the equipment was effectively prevented from continuing to be damaged, and the transformer was returned to the factory for repair on the same day. (2) Transformer B, model SZ9-6300/35, was manufactured in March 2001 and installed and put into operation in September 2002. On February 23, 2004, the transformer gas relay tripped and then tripped again after power was restored. The oil sample was sent for chromatographic analysis and it was found that there was an internal arc discharge fault. When the transformer was returned to the factory for repair, it was found that the discharge part was inside the high-voltage coil of phase B. 2 Relay protection analysis method: (1) The gas relay installed on transformer A was not put into use and there were no other effective safety protection devices, so it was impossible to realize the safety protection of the transformer in the event of a fault. (2) After the gas relay of transformer B was activated, power was restored again without finding out the cause, which caused the fault to develop and continue to damage the equipment. (3) The above two transformers were manufactured by the same manufacturer. The fact that the equipment had a short service life before a serious fault occurred indicates that there was a problem with the product quality. 3. Precautions for the use and maintenance of gas relays (1) According to regulations, gas relay protection devices should be installed on power transformers of 800 kV·A and above and workshop power transformers of 400 kV·A and above. (2) The gas relay should be qualified before use and installed and put into operation at the same time as the transformer. Regular calibration and daily inspection and maintenance of gas relays should be carried out to ensure the reliability of operation. (3) In the initial stage of operation after the transformer is installed and repaired, gas may accumulate in the gas relay. At this time, the trip protection should be turned off and only the signal protection should be turned on. The trip protection should be turned on again after the residual gas in the transformer is discharged. (4) When the transformer is in operation, a large amount of oil is drained, oil is replenished, oil is filtered under live current, oil absorbent is replaced, and valves of the relay connection pipeline are opened and closed. The relay may be prone to malfunction. The trip protection should be turned off and the signal protection should be turned on. (5) The normal oil level of the oil tank should be checked and maintained frequently, the breather should be kept unobstructed, and the gas relay should be prevented from malfunctioning due to the oil level drop and lack of oil. The sealing performance of the circulating oil pump should also be checked to prevent negative pressure air intake. (6) After the gas relay trips, check whether there is gas in the relay chamber, whether there are any problems with the secondary circuit of the protection device, whether the oil level in the oil conservator is normal, and whether there is any negative pressure gas inlet. Pay attention to preserving the gas in the relay, and try to take gas and oil samples as soon as possible for chromatographic analysis to find out the transformer fault and tripping cause. If necessary, perform electrical tests and inspections, and never blindly energize. (7) The gas relay will only react when the internal fault of the transformer has been going on for a long time or is serious. It is not sensitive to early latent faults. Chromatographic analysis of the gas in the oil is needed to detect and diagnose early latent faults. Therefore, pay attention to regular chromatographic analysis and electrical tests when equipment is abnormal. Adhere to prevention first and do a good job in the safety protection of operating transformers.