Power-system protection

 

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 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 electrical power system to convenient levels for the relays to deal with them.
• Protective relays to sense the fault and initiate a trip, or disconnection, order.
• Circuit breakers to open/close the system based on relay and auto re-closer commands.
• 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.

 

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