Understanding and Preventing Transformer Explosions

Transformer explosions can be catastrophic.  They can cause loss of lives and severe damage to the substation and surrounding area and long interruption to the power supply.

Transformer explosion occur due to low impedance faults within the transformer.  Such low impedance faults result in extremely high currents.  The arcs created during the faults result in very high temperatures which vaporizes the oil.  This heated and vaporised oil results in a sharp spike in pressure within the transformer.

Improper contact between the terminals of the online tape changer has also resulted in Transformer explosions. Hence, it is necessary that all Power Transformers be equipped with a reliable Explosion Protection System.

This pressure waves bounce off the transformer walls and this results in multiple waves due to reflection.  The superimposition of these reflected waves can result in extremely high pressures which result in the explosion.

Conventional methods of pressure relief such as the safety valve and devices such as the Buccholz relay take too long to respond and may not be sufficient to relieve the pressure or to activate a shutdown.  Relay Protection such as Differential Relays will not be adequate to protect the transfer as they take more than 60ms to operate including the time taken for the breaker to trip. 

Transformer Explosion prevention systems work by quickly depressurizing the transformer by activating a valve.   A sensor detects the initial pressure wave and opens a valve leading to a separate chamber to facilitate depressurization.  Thus the pressure is relieved quickly before it can build up.

The explosive gases which are produced by the arc need to be expelled into a separate chamber by pumping inert gas into the system.  This is usually taken care of by the Transformer Explosion Protection System. Failure to do this can result in a severe explosion when the transformer  is opened by technicians resulting in death or injury.

Below is a video on a transformer explosion captured on video