Lightning Impulse Protection for Grid-connected Solid-state Transformers

A lightning protection scheme is designed and experimentally verified for protecting a 7.2 kV soft-switching solid-state transformer from lightning-induced overvoltage surges. The general design procedures of the lightning protection scheme as well as device selection guidelines are discussed in detail. A prototype has been constructed based on economical, off-the-shelf surge protective devices with unique choices of gapped metal-oxide varistors and air-core inductors. Lightning impulse tests have been performed to evaluate the lightning impulse protective level of the protection scheme, which also experimentally confirm a satisfactory protective ratio between the lightning protection scheme and the solid-state transformer according to the criteria of IEEE Std. C62.22. Working as an independent surge attenuator, the lightning protection scheme is able to protect various kinds of grid-connected converters and facilitate their field deployment in distribution systems.