Impulse Protective Levels of an Arrester   IEC

1. Fast front protective level: The highest of either the steep current residual voltage or the front-of-wave impulse spark over voltage.


2. Standard lightning impulse protective level: The highest of the residual voltage at nominal current or 1,2/50 lighting impulse spark over voltage.


3. Switching impulse protective level: The highest of either the maximum residual voltage for the specified switching current or the specified switching impulse spark over voltage.