Substations, switchyards and switch rooms are hazardous areas but only become dangerous if procedures are not strictly followed. The safety of personnel is the paramount consideration in the operation of any power system.

Substations are therefore designed to ensure that people can work safely within this extremely hazardous environment. The making dead, isolation and earthing of any part of the substation must therefore be able to be done safely.

When working in an outdoor substation, all equipment must be carried below shoulder height. It is also essential to barricade the safe working area (to restrict access to non-essential personnel) and to be aware of any live equipment.

Given the high fault currents likely to flow when safety measures are called into action, the earthing system within a substation becomes the most crucial part of the installation.

Frequently, earthing is overlooked compared to the more visible transformers, switchgear and lines, but should any of these fail, the integrity of the earthing is the last line of defence to ensure personal safety. The earthing system must therefore always be comprehensive. The earthing electrodes and connections to all metalwork must be sound and kept in good condition.

The requirement for safe working arrangements tends to restrict the operational flexibility of substations and given system reliability and security considerations there may be some conflict of objectives. The next sections look at the arrangement of the transmission and zone substations and then the substation equipment.

By Craig Hagan,
Electrical and High Voltage Training Specialist

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