Switchboards
A switchboard is a distribution board (DB) that receives a large amount of power and dispatches it in small packets to various electrical equipments.
It has power-controlling devices such as breakers, switches along with protection devices such as fuses, etc.
Switchboards in general are divided into the following four classes:
• Direct-control panel-type
• Remote mechanical-control panel-type
• Direct-control truck-type
• Electrical-operated.
Direct-control panel-type switchboards
With the direct-control panel-type, switches, rheostats, bus bars, meters, and other apparatus are mounted on the board or near the board and the switches and rheostats are operated directly by operating handles if they are mounted on the back of the board. For both AC and DC, voltages are limited to 600 V or lower, but with oil circuit breakers, they may operate up to 2500 V. Such panels are not recommended for capacities of more than 3000 kVA.
Remote mechanical-control panel-type switchboards
Remote mechanical-control panel-type boards are the AC switchboards with the bus bars and connections removed from the panels and mounted separately away from the load. The oil circuit breakers are operated by levers and rods. This type of board is designed for a heavier duty than the direct-control type switchboards and is used up to 25 000 kVA.
Direct-control truck-type switchboards
Direct-control truck-type switchboards are used for 15 000 V or lower and consist of equipment enclosed in steel compartments completely assembled. The high-voltage parts are enclosed and the equipment is interlocked to prevent any operational mistakes. This type of a switchboard is designed for low- and medium-capacity plants and for auxiliary power in large generating stations.
Electrically operated switchboards
Electrically operated switchboards employ solenoid or motor-operated circuit breakers. Rheostats, etc. are controlled by small switches mounted on panels. Electrically operated switchboards make it possible to locate high-voltage and other equipment independent of the location of the switchboard.
Switchboards should be erected at least 1–2 m (3–4 ft) from the walls. Switchboard frames and structures should be grounded. For low-potential equipment, the conductors
on the rear of the switchboard are usually made of a flat copper strip known as a copper bus bar. Aluminum bus bars are also used due to its low cost. Switchboards must be individually adapted for each specific electrical equipment/system.
Motor control center
In large plants, a number of electrical motors are placed offsite. To conveniently locate all supply cables, control circuitry, and various protections at one location, there is a Motor Control Center (MCC).
The size of an MCC depends on the number of electrical circuits and motors it controls. An MCC consists of a number of cubicles or compartments in a compact, floor-mounted assembly. The cubicles are sized differently for starters depending on the rating of the motor it controls.