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High Voltage

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.

Many items of equipment are very expensive, and so the complete power system represents a very large capital investment. To maximise the return on this outlay, the system must be utilised as much as possible within the applicable constraints of security and reliability of supply. More fundamental, however, is that the power system should operate in a safe manner at all times. No matter how well designed, faults will always occur on a power system, and these faults may represent a risk to life or property. The destructive power of a fault arc carrying a high current is very great; it can burn through copper conductors or weld together core laminations in a transformer or machine in a very short time – some tens or hundreds of milliseconds. Even away from the fault arc itself, heavy fault currents can cause damage to power plant if they continue for more than a few seconds. The provision of adequate protection to detect and disconnect elements of the power system in the event of fault is therefore an integral part of power system design. Only by doing so can the objectives of the power system be met and the investment protected. This is the measure of the importance of protection systems as applied in power system practice and of the responsibility vested in the Protection Engineer.

Protection Equipment

The definitions that follow are generally used in relation to power system protection:

a) Protection System: a complete arrangement of protection equipment and other devices required to achieve a specified function based on a protection principal (IEC 60255-20)
b) Protection Equipment: a collection of protection devices (relays, fuses, etc.). Excluded are devices such as CT’s, CB’s, Contactors, etc.
c) Protection Scheme: a collection of protection equipment providing a defined function and including all equipment required to make the scheme work (i.e. relays, CT’s, CB’s, batteries, etc.)
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