Circuit breakers are used in a wide range of applications.  They are used in many environments and can handle currents and voltages of different ranges.

Circuit breakers are classified on the basis of different criteria.  Some of the classifications are below

Based on the interrupting medium
  1. Air circuit breaker
  2. Oil circuit breaker
  3. SF6 circuit breaker
Based on type of action
  1. Automatic circuit breakers
  2. Non-automatic circuit breakers
Based on the method of control
  1. Locally controlled circuit breakers
  2. Remotely controlled circuit breakers (remote control can be mechanical, pneumatic or electrical)
Based on the type of mounting
  1. Panel mounted circuit breakers
  2. Remote from panel mounted circuit breakers
  3. Rear of panel mounted circuit breakers
Based on location
  1. Outdoor circuit breakers
  2. Indooor circuit breakers
Based on voltage
  1. Low voltage circuit breakers
  2. Medium voltage circuit breakers
  3. High voltage circuit breakers




A reliable and effective protection system is a crucial part of any power system.  The protection system protects the equipment in the power system, such as generators, motors, transformers, etc from damage to faults.

The protection system also ensures reliability by localizing and isolating the fault and minimizing its impact on the rest of the power system.

The requirements of a power system are as follows

1. To isolate the equipment or component in which the fault has occurred.  The isolation should be quick enough to prevent damage to the component itself.  For instance, a short circuit inside can severely damage a transformer.  The differential relay, in such a situation, should immediately act and trip the transformer.

2. To isolate the smallest possible section of the power system to minimize the interruption.

3. To prevent disturbance or disruption to other parts of the power system.  The fault, if not isolated in time, can cause the upstream breakers to trip.

A well-designed protection system will greatly increase the reliability and performance of a power system.


The faults in a power system can be caused by a wide range of causes.  Below is a list of some of the most probable causes for electrical faults.

Overvoltage is caused due to surges such as lightning or due to switching loads on and off.  In generators, it can be caused due to the failure of the field controller.

Heavy winds which can cause lines to snap or trees to fall on them. This can cause open circuits, earth faults and short circuits.

Ageing which can result in weakening of insulation and failure. This can result in short circuits and earth faults.

Chemical pollution and deposition on the insulators that can result in flash overs

Faults due to wildlife, such as birds, snakes, mice, etc which can cause short circuits and earth faults.

Collision of vehicles on towers and transmission poles can cause the towers to fall.

The table below will give an idea of the percentage of the types of faults in the different equipment in a power system

Overhead lines                      50%
Transformers                         12%
Switch gear                            15%
Cables                                   10%
Miscellaneous                         8%
Instrument Transformers        2%
Control Equipment                 3%