ABSTRACT
Under normal conditions, it is generally believed that clouds contain positive and negative charges that, being unlike, combine and neutralize each other resulting in substantially zero charge and hence zero voltage difference within the cloud. Polarity refers to the clouds and the earth's relationship in that the earth's charge is positive and the cloud's charge is negative in 90% of the recorded measurements. Several other sources of overvoltages discussed are as follows: In three-phase circuits, single-phase switching, fuse blowing, or a broken conductor can result in overvoltages when ferroresonance occurs between the magnetizing impedance of the transformer and the system capacitance of the isolated phase or phases. A silicon carbide surge arrester has silicon carbide valve elements that are protected from continuous power-frequency voltage by a series gap which acts as the insulator during normal voltage conditions and interrupts the power-frequency current that follows any transient current discharged by the arrester.
