What is an isolator and how is it different from a circuit breaker

What is isolator and why isolator is used

The isolator is a type of switching device, it can be operated manually or automatically which separates a part of the electrical power. Isolators can be used to open a circuit under no load. The major purpose of an isolator is to isolate one portion of the circuit from the other and it won’t open while the current flows in the line. Mostly isolators are used in both ends of the breaker. There are isolation switches to isolate the circuits. These switches are used in industrial applications and distribution of electrical power etc. high voltage type isolation switches are used in the electrical substation to do the isolation of equipment like a transformer and circuit breaker. The disconnector switch is not used for circuit control instead of that they are used for isolation. The isolator is also called disconnector switch or disconnector it is a no-load switch that is designed to operate under no-load conditions. These devices are normally installed along with a circuit breaker, especially on the supply side of the circuit breaker.

How is an isolator different from a circuit breaker and functions of isolator and circuit breaker

In an instrument, we can do isolation to the parts in the instrument, so we can separate various parts in equipment by doing isolation and this could be physical or electrical. An isolator is an offload device and it doesn’t have any solenoid like a circuit breaker. Isolators must not be operated while it is having a load in order to operate it the load on it must be made zero after that it can be operated. The circuit breaker is an on load automatic device it is used to breaking circuits in case of the short circuit, overload, etc. isolator opens only after the circuit breaker and closes before the circuit breaker. The isolator is like a mechanical switch whereas the circuit breaker is an electronic apparatus made with BJT or MOSFET. Isolators have small withstood capacity when compared to circuit breakers. Circuit breakers have high withstood capacity at the condition of on-load. Circuit breaker trips during the fault condition but we won’t be able to know if the faulty area is completely isolated because the circuit breaker is installed remotely. So to make sure the system is completely isolated a physical and mechanical on-site isolation is used. The current withstanding capacity of an isolator is less than that of a circuit breaker.

How does an isolator work

Isolators are mechanically operated switch and there is manually and automatically operated isolator, isolator can isolate the phase lines. Mostly isolators are used in substations. Isolators are hand-operated up to 145KV, but higher voltages like 240 – 420 kV it is motorized. There is a mechanism box which will control the opening and closing of an isolator, the motor, and control circuit will be inside the mechanism box.

What are the types of electrical isolator

Isolators are classified according to the system requirements they are

  • Double break isolator
  • Single break isolator
  • Pantograph type isolator

Isolators can be categorized depending upon the position in the power system

  • Bus side isolator – isolator is directly connected to the main bus
  • Line side isolator – isolator would be placed in the line side of any feeder
  • Transfer bus side isolator – isolator will be directly connected with the transfer bus

Single break isolator

The contact arm is divided into two parts one carries male contact and the other carries female contact. The contact arm will move due to the rotation of the post insulator upon which the contact arms are fitted. Rotation of both post insulators stacks in opposite to each other closes to close the isolator by closing the contact arm. Counter rotation of the post insulator stacks opens the contact arm and the isolator will be in off condition.

Double break isolator

This type has a post insulator of three stacks and on the top of post insulator, female type contacts are fixed. The female contacts are generally in the form of spring-loaded contacts. The isolator will be closed when the male contacts come in contact with a female contact and it takes place because of the rotational movement of the male contact. The isolator becomes open if the rotation of the male contact in the opposite direction from the female.

Pantograph isolator

In this type of isolator both the contacts at each side, connect and disconnect because of the forces of stress or tension. Mostly there is no locking mechanism and these are widely used in electric trains to obtain electricity from overhead transmission lines.

What are the constructional features of an isolator

Isolators are installed outdoor and they are offload type, earth switches are used in isolators. Contacts in isolators would be self-cleaning type, contacts and spring shall be designed so that readjustments in contact pressure shall not be needed throughout the life of an isolator. Contact spring must not carry electrical current. The next part is base, every single pole of the isolator must be provided with a complete galvanized steel base provided with holes and they are designed to be mounted on a supporting structure. All metal parts used must be of non-rusting types of non-corroding material.

What are the functions and requirements of an isolator

Isolator must be capable to withstand the dynamic and thermal effects of the maximum possible short circuit current of their system in their closed position. It should be constructed in a way that it must not open under the influence of short circuit current. There must be constructional interlocks in the construction of isolator and it must be an addition to electrical interlocks. All of these interlocks must be fail-safe type. Individual interlocking coil arrangement must be provided.

What are the applications of isolator

  • Isolators are used in high voltage devices such as transformers
  • Isolators are used in the substation, so when a fault occurs in a substation then the isolator will cut out the portion of the substation.
  • These are protected with a locking system on the external or with a lock to stop the accidental usage.
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Great content. Very informative. Thanks for sharing.

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