Power-system protection is a branch of electrical power engineering that deals with the protection of electrical power systems from faults through the isolation of faulted parts from the rest of the electrical network. The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of the network as possible still in operation. Thus, protection schemes must apply with very pragmatic and pessimistic approach to clearing system faults. The devices that are used power system switchgear and protection pdf protect the power systems from faults are called protection devices.
Batteries to provide power in case of power disconnection in the system. 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 system, fuses are capable of both sensing and disconnecting faults. Failures may occur in each part, such as insulation failure, 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 ensure continued supply of energy. Switchgear is a combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switches are safe to open under normal load current, while protective devices are safe to open under fault current. A single such device can replace many single-function electromechanical relays, and provides self-testing and communication functions.
While the operating quality of these devices, and especially of protective relays, is always critical, different strategies are considered for protecting the different parts of the system. Very important equipment may have completely redundant and independent protective systems, while a minor branch distribution line may have very simple low-cost protection. Advantages of protected devices with these three basic components include safety, economy, and accuracy. Safety: Instrument transformers create electrical isolation from the power system, and thus establishing a safer environment for personnel working with the relays.
Economy: Relays are able to be simpler, smaller, and cheaper given lower-level relay inputs. Accuracy: Power system voltages and currents are accurately reproduced by instrument transformers over large operating ranges. At a basic level, protection looks to disconnect equipment which experience an overload or a short to earth.