Question

What is the “three-position” scheme for MV switchgear? Describe the interlocking of the three positions.

Short answer

The three position schemes and their interlocking position is explained.

Step-by-step solution

Define the MV switch gear

The MV switch gears are capable of handling the high voltage of up to 36 kV. The MV switchgears have the high value of the charges that is trapped in it even if it is disconnected from the source. The trapped charges must be energized by grounding to the earth.

Determine explanation for the answer.

Consider the three schemes of the MV switch gear is shown in Figure below.

Consider the MV breaker have a upstream vacuum disconnecting load to break the switch of the circuit breaker also there is a downstream vacuum disconnecting switch that provide isolation between the cables and the busbars.

The three operations shown gives the high speed for the discharging the trapped charge. The vacuum interrupter provides the fast and compact operation for the device in terms of the switching and the disconnection. The downstream cable earthing is done in controlled and fast manner for breaking and making capacity.

In order to prevent the operator from any hazard the interlock is provided between the disconnecting point of switch and the circuit breaker and the earthing switch. This is done to as earth switch cannot be closed before the opening or the disconnecting the breaker.

Therefore, the three position schemes and their interlocking position is explained.