Implications of temporary overvoltages for insulation coordination for equipment within low-voltage systems

“Temporary overvoltages (TOVs)” and their effects are addressed in the product safety standards for information and communication technology equipment both as one of the causes of VDR (voltage dependent resistor) fire and burst, and also as a factor in the determination of working voltages. Unlike sudden impulsive transient overvoltages, TOVs at power frequencies are due to the fault in low-voltage (LV) power distribution system and medium-voltage or high-voltage power distribution systems from which the LV system is derived, and are more persistent and potentially more destructive. This paper will attempt to provide an overview of the causes of TOVs and their implications for insulation coordination for equipment within LV systems.