Regenerative PWM source for power transformer loading tests

Most of power transformers, before being commercialized, must undertake a series of tests with the objective of analyzing their operational behavior under real operating conditions. Such tests sometimes demand a high amount of power increasing significantly their costs. The paper presents a proposed system which allows testing in closed loop, reducing the energy consumption to the natural losses of the equipment, thus constituting a regenerative system. A VSI-based test environment for power transformers where controlled active and reactive power can be supplied is designed, simulated and realized as a 50KVA- prototype. Special care is taken concerning the ac-filters in order to keep the harmonics within the limits set by standards valid for testing of power transformers. The simulation and experimental results show that the prototype fulfills the given requirements.