Hybrid Bypass Protection of Hybrid Smart Transformers for Advanced Grid Support

Due to the rapid transformation of traditional grid into a complex meshed network along with an exponential integration of volatile distributed energy resources (DERs); wind and photovoltaic (PV) farms, and converter-based loads; electric vehicles (EVs) etc., traditional grid operation strategies are stressed, and mitigation measures are required. Accordingly, a myriad of dynamic mitigation devices have been proposed in the last few decades where these devices are installed at strategic points in the grid. Transformer-less power electronics-based modules, integrated between the neutral and substation ground of traditional transformers, have been proposed introducing a variety of advanced grid mitigation and support features; DC elimination, voltage regulation, voltage and impedance balancing, harmonics isolation and power flow control. However, the protection of these series-connected modules against high voltage development during ground faults or inrush currents is critical as it could damage these converter-based mitigation devices or exceed the transformer BIL rating, thus, severely threatening the energy security. This paper presents an effective transformer and the module protection scheme utilizing a hybrid AC/DC solid-state switch. The proposed scheme is evaluated on an emulated 25-kVA, 7.2kV/240V single-phase hybrid smart transformer (HST), utilizing Typhoon HIL that verifies its promising performance.