Overall shield protects instrument cable from the effects of lightning

Abstract

Lightning can cause damage to electrical systems from direct and induced effects. A study was conducted to devise means to prevent or control the effects of lightning on instrument and control systems. The results indicate that an acceptable approach is to use instrument cables with a relatively thick overall metallic shield grounded at both ends. The overall shield functions as a magnetic shield, not because of the mere presence of metal, but because it generates a counter, or opposition, c m n t that nearly cancels out the interfering current on the signal conductors. The data show that a twisted pair by itself is not adequate to protect against lightning. The overall shield is used in conjuiction with a single point ground system to provide this protection.

A New Lightning Protection Method for Distribution Transformers

“…The shields and the armors should be connected with the ground port of the arresters at the head of the cables, and at the end of the cables the shields and the armors should be connected together only. When lightning current flows through the cores, corresponding currents will be induced in the shields and armors, and the produced electromagnetic blockade effect will make the lightning currents that flow through the cores decrease greatly [2] . Fig.…”