How to select a electrical circuit breaker for your application?


#1

Electrical Circuit Breakers Requirement

1.Circuit breaker breaker should be a perfect conductor in the closed position.

2.Circuit breaker should be a insulator in the open position

3.Should be fast when closing.Slow closure can damage contact.

4.Should be fast when opening.

Must not extinguish before its zero crossing and must not produce over voltages

Most Important operation of a circuit breaker is the interruption of high short circuit current.

Circuit Breaker selection

Circuit breaker selection is based on its ability to perform the following functions.

1.Carry the required full load current without overheating.

2.Switch and isolate or disconnect the load from the source at the system voltage.

  1. Interrupt any possible abnormally high operating current or short circuit current likely to be encountered during operation.

These all must be performed over an acceptable period of time and under actual operating/environmental conditions.

Selection -

1.Voltage rating - Specifies the maximum voltage level of the line that the breaker can be used on.

2.Current rating -

Ensuring the breaker can carry the systems full load current

Ensure the breaker’s rated current is capable of breaking the maximum amount faulted current.

Ensure the breaker is capable of carrying the faulted current for a period of one second.

3.Operating time -

The time the breaker takes to open short circuit current after it is activated.

Time between operations

4.Temperature range -

Under extreme cold condition,some material may tend towards brittleness

Under extreme heat physical and electrical strength of material may be reduced to marginal levels.

5.Altitude -

Transfer properties of higher altitude,less dense air require circuit breakers to be de-rated for voltage withstand and current carrying capacity.

Current de-rating can be compensated if the temperature is lower at a higher altitude.

Voltage withstand capability is unaffected by lower temperature at higher altitude.

  1. Insulation level

2 electrical conditions require the insulation to operate:

Electrically exposed

Non-Exposed

7.Trip and Coils

The number of trip and close coils depends on whether the application is intended for single or three pole closing.

Single pole closing - Each breaker will require two trip and two coils

Three pole closing - Six trip and six close coils

8.Life Span

The type of arcing contact material determine the life and the number of breaking operations a circuit breaker can perform in its life span.

Each circuit breaker will be specified with the number of operation in its life-time before maintenance is required.