Transformer Explosion Prevention System
Transformer explosion and fire result from break down of insulation caused due to over–current‚ over– voltage or short circuit. Another cause of explosion or fire is de-gradation of insulation like decay of the transformer oil due to moisture or ageing or decomposition. Once the insulation drops below a threshold value an electric arc is generated. The temperature of the oil increases and oil decomposes leading to generation of ignitable gases and pressurization of the oil tank. As a result the transformer tank or on load tap changer explodes.
Principle of Operation:
There are two modes of operation viz Transformer Explosion Prevention Mode and Transformer Fire Extinguishing Mode
a. Transformer Explosion Prevention Mode:
When an internal fault takes place large amount of flammable gases are formed in the transformer tank. As a result the gas relay closes and the electric breaker switches off. There is a pressure build-up inside the tank due to the thermal inertia. Once the pressure exceeds the set value of the pressure relief valve (PRV) the system relives the pressure by draining 10% of oil from the transformer and thereby preventing an explosion and fire. Subsequently the hot oil is cooled by injecting the Nitrogen gas.
b. Transformer Fire Extinguishing Mode:
When the transformer is on fire, the fire detectors operate along with the gas relay and which trips the electric breaker. As a result the system operates to drain the oil and inject nitrogen gas so as to sufficiently cool the transformer thereby extinguishing the fire and prevent any re-combustion.
The system is recommended as per the Indian Electricity Rules for all transformers and reactors of oil capacity above 2000 liter.