Offload Disconnector

EHV Disconnector

 

General

Disconnector is equipment used in the transmission and grid substations for the purpose of disconnecting the power source either for maintenance purpose or for bus transfer.

Function

Disconnector functions as continuous current carrying device to the other connected equipments such as Circuit Breaker, CT’s, PT’s etc from the main busbar in each of the bay in a sub-station.

These are used primarily for the isolating of equipment and sectionalising electric circuit or even portion of main feeders for special purposes, such as testing and maintenance. Generally these devices are not rated to make or break load.

Type and application

The following types of Disconnectors are used in substations depending on the site-specific requirement,

  • Horizontal Centre Break
  • Horizontal Double Break
  • Pantograph
  • Vertical Break

Horizontal Centre Break / Horizontal Double Break

These types of the disconnectors are used in the normal height of the bus to transfer the current to the other equipments in the bay and will function as a no load switch. This will be installed in incoming and outgoing sides of the distribution equipment according to the substation bay requirement. This will be operated in conjunction with the Circuit breaker for any switching on / off and maintenance purpose.

Earthing switches shall be provided in the disconnectors based on the requirement and for earthing purposes. The earthing switches will be closed when the disconnector is in off condition and vice versa for earthing the induced current and voltages on the busbar when the circuit is open condition / maintenance purpose. This also will take care of the short circuit current when the main disconnector is in open condition.

The disconnectors are normally horizontal upright mounted. In case to bring the bus from the gantry and to meet busbar configuration, either under hung type or vertical type shall be used.

Pantograph type

The Pantograph type disconnectors are used for current transfer / coupling of buses at two different heights. Through the pantograph, current will be transferred from the top-level buses from the transmission side to the normal level bus in the substation.