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Practical Power Cabling & Earthing

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Role of Power Cables in Electrical Power Systems

• An electrical cable - A bundle of electrical conductors used for carrying electricity

• Cables classification depends on their application

• Applications:

Electric cables

Overhead transmission lines

Power transmission Underground cables

Overhead lines

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Role of Power Cables in Electrical Power Systems

Typical view of an overhead transmission line terminating at a substation

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Role of Power Cables in Electrical Power Systems

Typical view of a 33kV, cross-linked polyethylene cable

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Trouble-free Operation of Cables

• Trouble causing factors:– Mechanical activities in the vicinity – Accessories– Improper selection of the cable– Overvoltages arising from system operation or due

to external factors – Installation problems causing excessive stresses

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Earthing and its Importance

A typical earth electrode used in electrical installations

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Earthing and its Importance

A metal chassis being used as earth reference

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Earthing

• Provides an electrical supply system with an electrical reference to the earth mass

• Earthed metallic surface ensures that it stays at earth potential always and thus remains safe to persons who may come into contact with it

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Earthing and its Importance

(a) Fault in unearthed system, (b) Effect of earthing the neutral

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Fault current flow in a earthed system

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System Earthing and Protective Earthing

• Well designed earthing systems:

• Provide a low impedance return path for earth fault currents back to the power source so that the occurrence of fault can be sensed by the circuit protective devices and faulty circuit can be safely isolated.

• Minimize fire or explosion hazard by providing an earth path of adequate rating, matching the let through energy by circuit protective devices.

• To dissipate accumulated static charges on machinery parts and electronic assemblies containing sensitive circuits to avoid damage or accidents

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