Crompton Greaves Lightning Arresters

High Voltage Power System experiences overvoltages that arise due to natural lightning or the inevitable switching operations. Under these overvoltage conditions, the insulation of the power system equipment are subjected to electrical stress which may lead to catastrophic failure.

Broadly, three types of overvoltages occur in power systems: (i) temporary over-voltages,(ii) switching overvoltages and(iii) lightning overvoltages. 

The duration of these overvoltages vary in the ranges of microseconds to sec depending upon the type and nature of overvoltages. Hence, the power system calls for overvoltage protective devices to ensure the reliability.

 

Conventionally, the overvoltage protection is obtained by the use of lightning / surge arresters . Under normal operating voltages, the impedance of lightning arrester, placed in parallel to the equipment to be protected, is very high and allow the equipment to perform its respective function. Whenever the overvoltage appears across the terminals, the impedance of the arrester collapses in such a way that the power system equipment would not experience the overvoltage. As soon as the overvoltage disappears, the arrester recovers its impedance back. Thus the arrester protects the equipment from overvoltages.

 

The technology of lightning arresters has undergone major transitions during this century. In the early part of the century, spark gaps were used to suppress these overvoltages. The silicon carbide gapped arresters replaced the spark gaps in 1930 and reigned supreme till 1970. During the mid 1970s, zinc oxide (ZnO) gappless arresters, possessing superior protection characteristics, replaced the silicon carbide gapped arresters. Usage of ZnO arresters have increased the reliability of power systems many fold.