An isolator is a mechanical switch that isolates a circuit from the system as required. Electrical isolators separate a part of the system from the rest for safe maintenance work. An isolator is a manually operated mechanical switch that separates a part of the electrical power system in an off-load condition..
Isolator in a switchyard
Types of Isolators
• Double Break Isolators
• Single Break Isolators
Double Break Isolators
Double-break isolators have three stacks of post-insulators. The central post insulator carries a tubular or flat contact that can be rotated horizontally with the rotation of the central post insulator. This rod-type contact is also called a moving contact. The fixed contacts are fixed on the top of the other post insulators, which are located on both sides of the central post insulator. The fixed contacts are generally in the form of spring-loaded contacts.
The rotational movement of a moving contact causes it to come into fixed contact, and isolators become closed. The rotation of moving contacts in the opposite direction makes them out of fixed contacts and isolators. The rotation of the central post insulator is done by a driving lever mechanism at the base of the post insulator, which is connected to the operating handle. The 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 contact, and the other carries hollow-type contact. The contact arm moves due to the rotation of the post-insulator upon which the contact arms are fitted. The rotation of both post-insulator stacks in opposite directions causes the isolator to close by closing the contact arm. The counter-rotation of both post-insulator stacks opens the contact arm, and the isolator becomes in an off condition. The 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 the circuit breaker is open and these must be closed before the circuit breaker is closed. The isolator can be operated by hand locally as well as by a motorized mechanism from a 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 both sides of the circuit breaker in case of supply from both sides.
• In case of supply from one side only the isolators are used the downstream of circuit breaker, this means at the grid connection side.
Earthing switches are mounted on the base of the main line side isolator. Earthing switches are normally vertically break switches. Earthing arms (contact arm of the earthing switch) are normally aligned horizontally at the off condition
During the switching-on operation, these earthing arms rotate and move to a vertical position and make contact with earth contacts fitted at the top of the post-insulator stack of the isolator at its outgoing side. The earthing arms are so interlocked with the main isolator’s moving contacts that they can be closed only when the main contacts of the isolator are in an open position. Similarly, the main isolator contacts can be closed only when the earthing arms are in the open position.
Circuit breaker, Isolator, and Earth switch application
Load break switch
A load break switch is a mechanical switch that isolates a part of a circuit from the system as required. A load break switch separates a part of the system from the rest for safe maintenance work. It is a manually operated mechanical switch. which separates a part of the electrical power system at load conditions. Provision for arc extinction is made in these switches, so these are capable of disconnecting and reconnecting the circuit at load current.