Investigation of load compensation features of smart transformer in medium voltage grid

Harmonics and load unbalance create several adverse issues in power distribution system, which are generally mitigated by bulky shunt active power filter (SAPF). This paper explores load compensation features of smart transformer (ST) in a two-feeder city center, where conventional power transformer (CPT) in one feeder is replaced by the ST whereas other feeder is continued to be supplied through the CPT. The ST is controlled not only to supply its own loads connected at the low voltage side, but also to compensate reactive, unbalance and nonlinear loads of the other feeder. This makes total MV grid currents of the combined city center balanced, sinusoidal, and in unity power factor at the point of common coupling (PCC) voltage. Therefore, in addition to providing continuous and reliable support to the ST based loads, the ST eliminates need of bulky SAPF and isolation transformer from the city center which are used for achieving reactive and harmonic current compensation. A switching model of the system is developed in power system computer aided design (PSCAD) software and implemented on a developed experimental prototype to show the capability of the ST.


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