SERGI - Research Program

SERGI Research

The MTH Model [1], [2]

In 1995, an extensive research programme on the energetic transfer phenomenon that occurs within a transformer during a short-circuit was implemented by SERGI. The mechanism of oil decomposition under thermal effects was analysed and resulted in the development of a Magneto-Thermo-Hydrodynamic model (MTH) [1]. Accurate calculations were performed on transformers whose operational characteristics were previously measured experimentally. SERGI therefore successfully validated the MTH model calculation in collaboration with SCHNEIDER ELECTRIC, France Transfo [2].

Electrical arc simulation Meshing


Power Plant Transformers [3]

	Due to the generator inertia, power plant transformers suffer harsher fault conditions than transmission and distribution transformers. Therefore, SERGI decided to investigate the explosion of a power plant step-up transformer to design a system capable of preventing any kind of incident on any kind of transformer.

		During this investigation, SERGI discovered that electrical arcs inside transformer oil could produce pressure gradients from 300 up to 930 bar/second (4 300 to 13 500 psi/s). The besides picture shows the MTH technique used by SERGI to simulate electrical arcs.

Pressure Relief Valve [4]

For more than 30 years, Pressure Relief Valves have been used to protect transformer tanks. However, all transformers that explode are equipped with this device. The incapability of Pressure Relief Valves to release the pressure in these cases led SERGI to conduct their dynamic mechanical study. In fact, such calculation could not be conducted until the pressure gradients during short-circuit conditions were discovered by SERGI [1], [3].

Pressure Relief Valves are limited by:
•The spring inertia that delays their response time and opening;
•The U-shaped exhaust evacuation that creates energy losses and reduces the pressure evacuation speed;
•Their geometry as when it is half opened, the evacuation surface does not exceed 15% of the maximum evacuation surface.




		2-D Pressure Relief Valve fluid flow image, 60% opened

TRANSFORMER PROTECTOR and Pressure Relief Valve Comparison [4]

The TRANSFORMER PROTECTOR and Pressure Relief Valve behaviours have been simulated under the same short-circuit conditions in order to compare their performances. For each simulated case:

•the TRANSFORMER PROTECTOR surpassed the Pressure Relief Valve and prevented the transformer tank explosion;
•the Pressure Relief Valve never avoided transformer tank explosion.




		Evolution of pressure with different protection systems for a small 60 bar/second (870 psi/second) pressure gradient