Temporary Overvoltages (TOV)
Temporary overvoltages (TOV) can be caused by a number of system events, such as
switching surges, line-to-ground faults, load rejection and ferroresonance. The system
configuration and operating practices should be evaluated to identify the most probable
forms and causes of temporary overvoltages. If detailed transient system studies or
calculations are not available, it is acceptable, as a minimum, to consider the overvoltages
due to single line-to-ground faults. The configuration and details of the system grounding will
determine the overvoltages associated with single line-to-ground faults. The arrester
application standard, ANSI 62.22, can give the reader guidance in determining the magnitude
of overvoltages associated with single line-to-ground faults. The primary effect of TOV on
metal-oxide arresters is the increased current and power dissipation, and a rising arrester
temperature. These conditions affect the protection and survivability characteristics of the