Power system protection

Power protection is a branch of  power engineering that deals with the protection of power systems from faults through the disconnection of faulted parts from the rest of the  .

The objective of a protection scheme is to keep the power stable by isolating only the components that are under fault, whilst leaving as much of the as possible still in operation.

Thus, protection schemes must apply a very pragmatic and pessimistic approach to clearing faults. The devices that are used to protect the power systems from faults are called protection devices.


Protection systems usually comprise five components:

  • Current and voltage transformers to step down the high voltages and currents of the power to convenient levels for the relays to deal with
  • Protective relays to sense the fault and initiate a trip, or disconnection, order
  • Circuit breakers to open/close the based on relay and autorecloser commands
  • Batteries to provide power in case of power disconnection in the
  • Communication channels to allow analysis of current and voltage at remote terminals of a line and to allow remote tripping of equipment.

For parts of a distribution , fuses are capable of both sensing and disconnecting faults

Failures may occur in each part, such as insulation , fallen or broken transmission lines, incorrect operation of circuit breakers, short circuits and open circuits.

Protection devices are installed with the aims of protection of assets and ensuring continued supply of .

Switchgear is a combination of disconnect switches, fuses or circuit breakers used to control, protect and isolate equipment.

Switches are safe to open under normal load current (some switches are not safe to operate under normal or abnormal conditions), while protective devices are safe to open under fault current.

Very important equipment may have completely redundant and independent protective systems, while a minor branch distribution line may have very simple low-cost protection. 

Last Updated on 3 years by pinc