Page 134 - Practical Power System and Protective Relays Commissioning

Chapter 12

Disconnecting Switches and

Earthing Switches Theory
Testing and Commissioning

12.1 INTRODUCTION
A disconnect switch (DS, also known as a disconnector or isolator switch) is
a mechanical device used to isolate the equipment undergoing maintenance,
such as a circuit breaker, in a safe manner. It can also be used to transfer the
circuit bay from one busbar to another busbar, for example, in a bus coupler
circuit in a substation.
These devices can be provided with a safety earthing switch (ES) for the
safety of the personnel who will work in the electric circuit within a substa-
tion or power station yards.
Whilst a DS can carry load current, it can only disconnect or close the
circuit in a no-load condition; there is an interlocking circuit in substations
to prevent them from operation under load conditions.
Mechanisms are normally installed to permit the operation of the DS by
an operator standing at ground level. The operating mechanisms provide a
swing arm or gearing to permit operation with reasonable effort by utility
personnel. Motor operating mechanisms are also available and are applied
when remote switching is necessary.
The DS operation can be designed for vertical or horizontal operating of
the switch blades.
Several configurations are frequently used for switch applications, as
seen in Figs. 12.1 12.7. These configurations include the following:
Horizontally-upright mounted DS
Vertically-mounted DS
Double break switches
V switches
Hook-stick switches
Pantograph switches
Earthing switches

Practical Power System and Protective Relays Commissioning.
DOI: https://doi.org/10.1016/B978-0-12-816858-5.00012-5 133
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