Transformer Controlled Switching to Eliminate Inrush Current - Part II: Field Tests on a 100MVA Three-phase Transformer

Transformers are generally energized by random closing of the circuit breaker contacts, with the system voltage being applied on the transformer windings at random instants. This kind of switching normally introduces initial asymmetrical magnetic flux in the windings, driving the transformer into saturation. As a result, high transient magnetizing inrush currents are generated in the transformer, which may cause system disturbances. One of the solutions for mitigating these high inrush currents is to control the instants of the transformer energizing such that the magnetic flux produced in the windings corresponds, in magnitude and polarity, to the prospective core flux. This strategy is discussed in Part I of this work. This Part II presents the results of field test of energizing a 100 MVA, 230/138 kV, three-phase three-limbed iron core type transformer, carried out to validate the proposed strategy.