Earthing Switch

 Earthing Switch is necessary to earth the conducting parts before maintenance and also to provide deliberate short-current while testing. There can be three  types of  Earthing witches in metal-clad Switches manually operated automatic high speed Earthing Switch, protective Earthing Switch for Earthing the installation.

There are several versions of Earthing Switches for following applications

1 - Maintenance Earthing Switches. These are single pole or three pole units; manually operating mechanism with a provision of filling motor mechanism.

   2 - High Speed Earthing Switches. These are operated by spring energy. Spring is charged by motor-mechanism

Fig (1)

 

Fig (2) the one pole Earthing Switch

Earthing Switch:
1- Moving contact
2- Operating lever
3- Position indicator

 

Closed position                                                     Open position

The earth Switch is mounted direct on the enclosure Fig. (1) Earthing Switch has to satisfy various requirements. For Earthing isolated sections of Switchgear for protection of personal during maintenance and over-hauls or erection, the maintenance Earthing Switches are employed. For Earthing higher capacitances (cables, overhead line etc.) high speed Earthing Switch are employed. Depending on the substation scheme, the Bus-Bars may be earthed either by maintenance                                            

or high-speed Earthing Switches.

 

Special high speed Earthing Switches with interrupting capability are also available. These are suitable for interrupting capacitive and inductive currents

from parallel overhead lines. In certain cases, Earthing Switches are fitted to

the enclosure with interposed insulation.

 

This enables various tests to be performed on the Switchgear or item of equipment, such as testing the current Transformer of measuring the operating time of breakers, without having to open the enclosure. During normal operation the insulation is bypassed by a short-circuit-proof link.

 

To check whether a point to be earthed really is dead, the Earthing Switch can be equipped with a capacitive tap for connecting a voltage test unit. This additional safety device reduces the risk of closing onto a live conductor.