Electrical Isolator Types, Function, Symbol, Diagram

An electrical isolator is a piece of equipment or an arrangement used in devices and power systems to isolate two circuits or loads from the power supply. The main function of an electrical isolator is to isolate two different circuits from each other. Or to isolate a part of the circuit from a power system. Generally, an electrical isolator mainly indicates a mechanical switch and they are also designed with electrical arrangements. The main design consideration is its contacts should be open to visible.

There are so many electrical equipments, devices such as circuit breakers, contactors, etc are available. They also can isolate the circuits. Then why do we require Electrical Isolators? The main reason is visibility. We cannot see the contacts of the circuit breaker or contactor if they are open or closed. To make sure the circuit is completely disconnected, electrical isolators are used.

Types of Electrical Isolator

There are three types of electrical isolators according to applications,

• Single Break Isolator
• Double Break Isolator
• Pantograph Type Isolator

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Single Break Isolator

An isolator is connected between two circuits or between a power circuit and a load circuit. So there are two sides of an isolator available. So the single break isolator is one that disconnects or isolates at one side only. It isolates the power supply side of the circuit from which another circuit is to be disconnected.

In the above symbolic diagram of the isolator, you can see there one side of the isolator is always connected and another side is subjected to closing or opening.

The two contacts in a single-break isolator are known as male and female contacts. These contact arms are fixed on a movable post-insulator arrangement. So when the post insulator is rotated by a motor or manually by hand, the contacts are become close or open according to the rotation. The single-break isolator provides less safety than others but has a smoother operation than others.

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Double Break Isolator

The double break isolator is designed to connect and disconnect on both two sides. In the above symbolic diagram also you can see. A double break isolator is bigger in construction than a single break isolator but it provides more safety, more features, and smooth operations.

In the double break isolator arrangement, there are three stacks of post insulators available. The center post insulator is subjected to movable or rotation. In that center post insulator, a tubular or flat male contact is available so when that post insulator rotates this male contact will connect and disconnect the two circuits. Those two circuits are connected to the rest two post insulators with female contacts. Generally, it is designed in such a way that the rotation of male contact in the opposite direction makes it disconnect or isolate from the female contacts. The rotation of the central post insulator is obtained by a lever mechanism, motor or handle.

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Pantograph Type Isolator

A pantograph-type isolator is a single-break isolator. It is constructed with a vertically placed arrangement on a post insulator and operated by a rod insulator. Pantograph type isolator requires a very small place or area and it is very compact and attractive in design. It provides much higher reliability and great operation than other conventional isolators. In modern switchgear systems in electrical substations and generating stations, pantograph-type isolators are used.

According to placement based in the power system, there are also three types of Isolators available,

• Bus Side Isolator
• Line Side Isolator
• Transformer Bus Side Isolator

Bus Side Isolators are used for coupling or connecting two Busbars in power systems and substations. All of the power systems are designed with a minimum of two buses- the main busbar and the parallel busbar. During maintenance of the power system, the Bus side isolator helps a lot to isolate the part that requires maintenance. Disconnecting of the Bus Side isolator can also affect incoming or outgoing lines also which are connected to the Bus.

The Line Side Isolator is connected between the busbar and the line feeder. It is used to isolate a particular feeder from the supply feeder. Disconnecting a Line side isolator only disconnects the power supply of the line connected to it. It does not affect other portions of the power system.

Transformer Bus Side Isolator used in both transformer incoming and outgoing ends. It is used to isolate the transformer from the power system for maintenance or any other reason. Disconnecting the Transformer Bus Isolator can affect a big portion of the power system which are getting power from that transformer.

Read Also: Importance and Operation Sequence of Isolator, Circuit Breaker, Earthing Switch

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