Single phase and three phase capacitive-load switching in transmission & distribution systems

Interruption of capacitive currents

The interruption of capacitive currents is a usual switching case, unlike the making and breaking of fault currents. The usual cases, in which a capacitive current is switched, are switching of unloaded overhead transmission lines, local substation components, cables, capacitor banks and others.

First, let’s explain the basic nature of these cases in which a capacitive current is switched and then in details 1-phase and 3-phase cases.

Contents:

1. Capacitive-load switching cases
   1. Switching of unloaded overhead transmission lines
   2. Switching of local substation components
   3. Switching of cables
   4. Switching of capacitor banks
2. Single-phase capacitive-load switching
3. Three-phase capacitive-load switching

1. Capacitive-load switching cases

1.1 Switching of unloaded overhead transmission lines

In this case, the load is already switched off by a breaker at the remote end of the line, but due to the stray capacitance of the overhead-line, a small capacitive current is still flowing in the system, to be interrupted by the substation breaker.

The current to be interrupted depends on the voltage level and the length of the line, and possibly on some station components.