Testing of Isolators

Testing of Isolator

Introduction to Isolators :

• When carrying out inspection or repairs in a sub – station or charged line repairs it is essential to disconnect the section of line on which the work is to be carried out.
• This disconnecting device is a isolator. As the name suggests it solates the of the section from the live lines.
• It assures the safety to the team of electricians and lineman’s who are expected to work on such sections. The isolator makes a visible break without any arcing/sparking.

• So isolator is defined as a device used to open or to close a circuit either when negligible current is interrupted or when no significant change in the voltage across the terminals of each pole of isolator occurs.
• The above circuit shows the location of the isolators in the system Interlocking arrangement is provided between circuit breaker and isolutors. Sequence of operation is as given below.

For Opening : First C. B. tripped (opened), Then isolator is opened Isolator cannot be opened unless C.B. is Then earth switch is closed opened due to interlocking.

For Closing : First earth switch is opened, Circuit breaker cannot be closed unless Then isolators are closed, Lastly C.B. is closed isolator is closed, due to interlocking.

• Thus, operation of isolator is when “no current” in the section. So they are not expected to be designed for current breaking capacity. Isolators on 3-phase lines, are provided with a mechanism that all the three will operate at a time. Their operating mechanism may be manual plus one of the following :

1. Electrical motor mechanism
2. Pneumatic mechanism

The different tests to be performed on isolators are tabulated in Table.