During transformer operation, internal faults can sometimes be difficult to identify and address in a timely manner, potentially leading to accidents. Using a gas relay for protection can mitigate such incidents to some extent. This article briefly describes how a gas relay collects gas to identify the fault and explains the reasons for the activation of light and heavy gas protection. The scope of transformer gas protection includes: multi-phase short circuits within the transformer; inter-turn short circuits; short circuits between turns and the core or outer sheath; core faults (overheating and burning); oil level drops or leaks; poor contact in the tap changer or poor welding of wires. The advantages of gas protection are that it can detect not only various faults inside the transformer tank but also minor inter-turn short circuits and core faults that differential protection cannot detect. Furthermore, it also detects air entering the transformer. Therefore, it is a highly sensitive, simple, and fast-acting protection system. Its disadvantages are that it cannot detect external transformer faults (bushings and leads), therefore, gas protection cannot be the sole protection against various transformer faults. Gas protection has poor resistance to external interference; for example, severe vibration can easily cause false activation. If the oil prevention issue is not properly addressed during the installation of the gas relay, or if the gas relay is not adequately waterproof, oil leakage may corrode the cable insulation or water may enter the relay, causing malfunction. The operating principle of a gas relay is as follows: When an internal fault occurs in the transformer, the generated gas will accumulate in the upper part of the gas relay, causing the oil level to drop. When the oil level drops to a certain level, the upper float sinks, closing the mercury contacts and sending a signal. In the case of a serious fault, the oil flow will impact the baffle, causing it to deflect and drive the connecting rod behind the baffle to rotate upwards. This triggers the connecting ring connected to the mercury contact retaining ring, causing the mercury contacts to rotate to both sides perpendicular to the oil flow. Both mercury contacts close simultaneously, causing the switch to trip or send a signal. There are two commonly used types of gas relays: float type and baffle type. The baffle type gas relay replaces the lower float of the float type with a baffle structure. The difference between the two is that the baffle structure of the baffle type does not activate as the oil level drops, but only when the oil flow rate reaches 0.6-1.0 m/s. Therefore, the baffle-type gas relay will not cause a false trip due to heavy gas when the oil level drops or there is a severe oil shortage. Gas relay gas collection for fault diagnosis: After the gas relay trips, if it cannot be clearly determined whether the fault is caused by an internal transformer fault, the gas accumulated inside the gas relay should be collected immediately. Further diagnosis can be made by identifying the nature of the gas. Generally, a special glass bottle is inverted, with the opening close to the gas relay's vent valve to collect the gas. If the collected gas is colorless, odorless, and cannot be ignited, it indicates that the gas relay tripped due to air being released from the oil. If the collected gas is yellow and difficult to ignite, it indicates a fault in the wooden parts of the transformer; if the collected gas is pale yellow with a strong odor and can be burned, it indicates a fault in the paper parts; if the gas is gray or black and flammable, it indicates a fault in the insulating oil. When determining whether a gas is flammable, for outdoor transformers, the vent valve of the gas relay can be opened directly, and the gas discharged from the vent valve can be ignited. If it is a flammable gas, a bright flame will be seen along the airflow direction. During the test, it is important to ensure safety; the vent valve must be closed promptly before oil begins to overflow. Gas collected from indoor transformers should be placed in a safe location for ignition testing. When the gas is colored, the action must be swift; otherwise, the color will quickly disappear, resulting in an incorrect result. Reasons for the activation of light and heavy gas protection: (1) Reasons for light gas protection activation. The light gas protection activation of a transformer generally acts as a signal to indicate abnormal transformer operation. The main reasons are: air entering the oil tank during oil filling, oil filtering, oil changing, or silica gel replacement; oil level dropping due to temperature decrease or oil leakage; minor faults in the oil tank producing a small amount of gas; and grounding or insulation damage in the light gas circuit. The principle for handling these faults is to stop the audible signal. Check the transformer's temperature, audible signal, oil level, and voltage and current indications. If no abnormalities are found through the first check, the gas at the top of the relay should be collected for fault diagnosis. If the collected gas is air, the on-duty personnel can purge the gas from the relay, and the transformer can continue operating. If it is flammable gas and the relay trips frequently, the supervisor should be notified first, and the situation handled according to orders. If there is no gas and the transformer shows no abnormalities, the secondary circuit may be faulty. The on-duty personnel should change the heavy gas protection from tripping to signaling and report the situation to the relevant person in charge, awaiting further instructions. Reasons for heavy gas protection tripping: The reason for the heavy gas protection tripping of the transformer is a serious internal fault, a circuit fault, or a near-zone through-short circuit fault. The principle of handling this is to check the transformer's upper oil temperature, external characteristics, explosion-proof oil spray, the tripping status of switches on each side, and the power outage range. If a backup transformer is available, it should be put into operation immediately, and the relevant supervisor should be notified. Gathering gas to determine the fault: If it is an internal fault, power should not be attempted. Switches on each side should be opened according to regulations, and safety measures should be taken while waiting for repairs. If the gas is non-flammable and the meter does not fluctuate, power can be attempted. If there is no gas inside the gas relay and no external abnormalities, the problem may lie in the secondary circuit of the gas relay. However, power should not be supplied until the transformer is confirmed to be functioning properly. Sometimes, gas relays may malfunction, so certain preventative measures should be taken: Replace the lower float type of the gas relay with a baffle type, and change the contacts to a vertical type. This will improve the reliability of heavy gas tripping. The gas relay leads should use oil-resistant insulated wire. The gas relay leads and the secondary cable leading indoors should pass through a junction box. Inside the box, the leads should be connected to the bottom of the terminal blocks, and the cable to the top, to prevent oil corrosion of the cable insulation; the lead arrangement should separate the heavy gas trip terminal from the positive terminal. When handling false oil levels, take precautions to prevent the gas relay from malfunctioning. The gas relay end cover and cable terminal box should be rainproof. A sealing test should be performed on the float of newly installed gas relays, and periodic tests should be conducted during operation. If plastic cables are used, check for damage from rodents, termites, etc.