In practice, due to limitations in size and cost, rotating machines are not insulated to the same impulse levels as oil insulated apparatus of same voltage class. These machines when connected to system are subjected to surge voltage hazards. The major insulation of any machine is stressed by magnitude of the surge voltage to ground and is protected by a lightning arrester. The minor insulation of any machine is stressed by the rate of rise of Surge voltage, which can be limited by Surge Protection Capacitor.