A near lightning strike can cause a very high voltage surge which can damage equipment by breaking down the insulating medium between elements in a circuit or between those elements and a ground. The amount of damage will be determined by the current from the charge and/or current from the power source. In order to protect a circuit from damage, a surge arrestor must conduct sufficient charge from the surge to lower the surge voltage to a safe level quickly enough to prevent circuit insulation from breaking down.
During a high voltage surge, a surge arrestor will begin to conduct the charge, bleeding it out of the circuit. As the charge is removed from the circuit, the surge voltage will fall. As the charge approaches zero the surge voltage will approach zero. If this happens quickly enough the apparatus will be protected.
A PV system typically is mounted such that it is vulnerable to lightning. A flash of lightning is an electrical arc from the earth to a cloud that is the result of an electrical potential between the earth and the cloud. The resistance between the earth and the cloud is the ohmic resistance of air, hence the ohmic resistance will be less for a device that is physically above the earths surface (less distance to the cloud). By connecting a PV array to earth via a grounding conductor a path is provided for the discharge current. |
