SERGI - Explosions Studies

Why do transformers explode more and more?

A growing concern for Corporate Risk Managers and Insurance Companies

Transformers are considered by Corporate Risk Managers and Insurers as the most critical equipment inside plants because of the large quantity of oil in contact with high voltage elements [5].

Loose international transformer norms and lack of regulation

The Norm IEC 76 only includes basic electrical measurements and does not cover mechanical design or protection. This weakness, in addition to the globalisation market, has opened the door to a disturbing drop in the quality of new transformers. By comparison, pressure vessels have to comply with adequate rules and controls. Such directives do not exist for transformers, which are obviously more dangerous.

Transformer electrical and mechanical protection limits

• Pressure Relief Valve inadequacy: pressure gradients developed during low impedance faults are too fast for mechanical devices [4]. All transformers that explode are protected with Pressure Relief Valves.
• Buchholz and Rapid Pressure Relay inefficiency: transformer electrical protections are not designed to react to sharp pressure gradients. During the 62 TRANSFORMER PROTECTOR tests, the Buchholz always failed to detect any gas and oil movement or pressure variation.
• Electrical Breaker opening time: the best breaker technology trips in 50 milliseconds, far too late to prevent the explosion, which occurs 10 to 50 milliseconds after the low impedance fault [1 to 4]. Additionally, the tank pressure keeps increasing after breaker opening [1].

For how long are your going to endanger your plant and company?

Increase of transformer explosion and fire incidents
A one-year Internet search led to the discovery of 730 transformer explosions in the USA only [5]. Many experts anticipate that the number of failures will increase significantly in the near future, from 1% in 2001 to 2% in 2008 [17]. In addition, the shorter lifetime of new transformers will sharply above increase this rate after 2008 [18].

Company privatisation and market deregulation
Protecting transformers against explosion and fire has become a priority because:
• The worldwide privatisation programs of electricity production and distribution companies have resulted in a reduction of investments ;
• Today’s competitive markets demand longer life, greater production, which results in aging equipment and overloaded transformers ;