Electrical power distribution system for various industries comprises of HV/LV Switchgears, MCCs, LT Transformers, Cabling upto motors and other power consuming equipment like heaters, air conditioners, lighting, UPS etc., field switches, instrumentation, electrical interlocks through PLC, lighting, earthing and lightning protection of all plant buildings and equipment. Plant control is generally through PLC HMI.
Indoor substations are generally used for power distribution at lower voltage levels of 33/11/6.6kV. Transformers are located outside and all switchgears are mounted inside substation building. The cabling between various equipment is done either in cable trenches or in cable spreader rooms below the switchgear room. Because of indoor design, maintenance of equipment is easier.
Huge network of HV & LV Power cables are required in large industries to interconnect HV and LV electrical equipment among themselves. These cables are selected based on magnitude of power flow and their short circuit withstand. Control cables connect various actuating devices with their remote control points and provides status feedback from field devices. Extensive amount of engineering is involved in selecting the cable types, length estimations, their routes and method of laying. Cables can be laid in trenches, cable tunnels, cable overhead bridges or directly buried underground based on application.
Proper Earthing of non current carrying metallic parts of all electrical equipment are essential for safety of operating personnel against shock hazard and for operation of earth fault relays at shortest time. An earth mat is laid below ground at a depth of approx. 0.6m to 1m over the entire area of the high voltage substation to limit the step and touch potentials to tolerable values at the time of passage of earth fault current. For medium voltage indoor substations or for LT switchgear/MCC rooms, generally such earth mat is not required, where only a ring conductor around the electrical room interconnects all the earth electrodes to reduce the earth resistance to less than 1 ohm. Treatment of soil in the close vicinity of the earth electrode and earth grid conductors are some times required by salt & charcoal or bentonite or other chemically treated compounds if the resistivity of surronding soil is very high. Riser conductors from this earth mat or earth ring conductor connects body of all electrical equipment and system neutral points to this earthing system.
Proper illumination of all plant buildings, factory sheds, outdoor areas, stockpiles, roads, conveyer galleries are essential for uniterrupted production, safety and efficient operation of any industry. Luminaires with fluorescent tube lights are generally used for low roof plant buildings and indoor substations. Illumination of factory sheds with high roofs are generally done with high pressure mercurry vapour lamps whereas conveyer galleries, outdoor areas, storage areas, roads etc. are illuminated by high pressure sodium vapour lamps. Usage of CFL and LED fittings are also increasing nowadays.
All plant and industries are operated generally from a central control room with the help of a control desk. The control desk comprises of an industrial computer with keyboard, remote control switches, selector switches, push buttons, indication lamps, meters, alarm annunciators, recording instruments, interlocking circuitry and terminals for external cable connections. The circuitry for interlocking and automation purpose can be done in a programmable logic controller (PLC), backed up by hardwired relay logic. Local control stations (LCS) or LPBS are placed near motor and drives for operation in local deinterlocked mode during testing and maintenance.