Electrical Isolator or Electrical Isolation switch — Engineering Notes Online
Isolator is a mechanical switch which isolates apart of circuit from system as required. Electrical isolators separate a part of the system from rest for safe maintenance works. Isolator is a manually operated mechanical switch which separates a part of the electrical power system at off load condition.
Isolator in a switchyard
Types of Isolators
* Double Break Isolators
* Single Break Isolators
Double Break Isolators
Double break isolator have three stacks of post insulators. The central post insulator carries a tubular or flat contact which can be rotated horizontally with rotation of central post insulator. This rod type contact is also called moving contact. The fixed contacts are fixed on the top of the other post insulators which are located at both side of central post insulator. The fixed contacts are generally in the form of spring loaded contacts. The rotational movement of moving contact causes to come itself into fixed contacts and isolators becomes closed. The rotation of moving contact in opposite direction make to it out from fixed contacts and isolators becomes open. Rotation of the central post insulator is done by a driving lever mechanism at the base of the post insulator and it is connected to operating handle. Operating handle can be operated manually or by a motor.
Single Break Isolators
In single break isolators, the contact arm is divided into two parts. one carries rod or tubular shape contact and other
carries hollow type contact. The contact arm moves due to rotation of the post insulator upon which the contact arms are fitted. Rotation of both post insulators stacks in opposite to each other causes to close the isolator by closing the
contact arm. Counter rotation of both post insulators stacks open the contact arm and isolator becomes in off condition. Operating handle can be operated manually or by a motor.
Operation of Electrical Isolator
It must be operated when there is no current flowing through the circuit. A complete live closed circuit must not be opened by isolator operation and also a live circuit must not be closed by isolator operation to avoid huge arcing in between isolator contacts. That is why isolators must be open after circuit breaker is open and these must be closed before circuit breaker is closed. Isolator can be operated by hand locally as well as by motorized mechanism from remote position.
For voltages up to 145 KV system hand operated isolators can be used whereas for higher voltage systems like 220 KV and above motorized isolators are used.
Application of isolator
* Isolators are used at the both side of circuit breaker in case of supply from both side.
* In case of supply from one side only the isolators are used at the downstream of circuit breaker, this means at the grid connection side.
Earthing Switches
Earthing switches are mounted on the base of mainly line side isolator. Earthing switches are normally vertically break switches. Earthing arms (contact arm of earthing switch) are normally aligned horizontally at off condition
During switching on operation, these earthing arms rotate and move to vertical position and make contact with earth contacts fitted at the top of the post insulator stack of isolator at its outgoing side. The earthing arms are so interlocked with main isolator moving contacts that it can be closed only when the main contacts of isolator are in open position. Similarly the main isolator contacts can be closed only when the earthing arms are in open position.
Circuit breaker, Isolator and Earth switch application
Load break switch
Load break switch is a mechanical switch which isolates a part of circuit from system as required. Load break switch separates a part of the system from rest for safe maintenance works. It is a manually operated mechanical switch
which separates a part of the electrical power system at load condition. Provision of arc extinction is made in these
switches so these are capable to disconnect and reconnect the circuit at load current.
Originally published at https://engineeringnotesonline.com on June 18, 2020.