Abstract
The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as high as ten times its rated current. This could cause many problems from mechanical stress on transformer windings to harmonics injection, and system protection malfunction. There have been numerous researches focusing on calculation and mitigation of the transformer inrush current. With the development of smart grid, distributed generation from independent power producers (IPPs) is growing rapidly. This paper investigates the inrush current due to black start of an IPP system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software. The study demonstrates that a single genset is capable of energizing a group of transformers since the overall inrush current is slightly above the inrush of the transformer directly connected to the generator. In addition, a simple method is proposed to mitigate the inrush current of the transformers using an auxiliary transformer.
Highlights
IntroductionIn an event when the circuit breaker is closed between a transformer and a power source, a transient current (which could be as high as ten times the transformer rated current) follows for a short period before reaching a steady state
This paper investigates the inrush current due to black start of an independent power producers (IPPs) system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software
In an event when the circuit breaker is closed between a transformer and a power source, a transient current follows for a short period before reaching a steady state
Summary
In an event when the circuit breaker is closed between a transformer and a power source, a transient current (which could be as high as ten times the transformer rated current) follows for a short period before reaching a steady state This transient current, known as magnetizing inrush current of a transformer, is caused by the transformer’s saturated core. A number of other techniques have been proposed to reduce the core flux prior to circuit energization [12,13,14,15] This approach appears to be simple, based on waveform measurements at the transformer connection point, but inrush currents may not be reduced when the transformer is energized without any history [14]. The results demonstrate the effectiveness of the proposed method in inrush current mitigation
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