TOV, as it is related to renewable generation, generally occurs on the grid as a result of a grid fault. This article will explore some of the causes of TOV and remedies to help protect inverter-based generators. Today’s grid standards require a certain level of TOV ride-through capability of inverter-based generators.
TOV can be caused by several anomalies on an AC grid. A lightning strike to an electrical conductor, or in the vicinity of a conductor, will likely result in a voltage spike on that grid segment. If a generating plant suddenly opens its main breaker at the substation, the voltage will spike instantaneously until the inverter controls trip the inverter.
Lightning strikes are remedied by the design of the electrical system and components called lightning arrestors. The AC grid system is purposefully designed to mitigate lightning strikes. This includes; but, is not limited to, conductor separation distances, strategically placed lightning rods and grounded electrical structures. Lightning arrestors are devices connected directly to live electrical conductors. They are designed to be passive at normal voltages. When a TOV occurs, the arrestor creates an electrical path to ground effectively grounding the conductor to which it is connected for a period of time.
For inverters, TOV is mitigated by the design of the AC components such that they can withstand voltages up to two times nominal for a short period of time. When the TOV exceeds that time period, the inverter trips to protect the internal components. Inverter manufacturers follow the electrical standards of the bulk power system and distribution systems when designing inverters. Inverter designs accommodate TOV to ride through grid events as required by the applicable standard.
For further reading
NERC Reliability Guideline
Gary Custer, PE