Power system protection

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Power system protection is that part of electrical power engineering that deals with protecting the electrical power system from faults by isolating the faulted part from the rest of the network.

The main 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 a very pragmatic and pessimistic approach to clearing system faults. For this reason, the technology and philosophies utilized in protection schemes are often old and well-established because they must be very reliable.

Protection systems usually comprise five components:

1. 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;
2. Relays to sense the fault and intiate a trip, or disconnection, order;
3. Circuit breakers to open/close the system based on relay and autorecloser commands;
4. Batteries to provide power in case of power disconnection in the system.
5. 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.