Motor control switchgear

Application domain Motor control, switchgear system, arc protection... 

For most plants, 01001 110 distribution systems start at the power company s service point on the plant s property. The choice of an electrical system will depend on many fartors relating to the particular projecl . A wide range of items, from switchgear, transformers, and motor control centers to cabling, earthing, and lighting, are required. Normally, competitive quotations would be obtained to take an estimate beyond the study stage. 

Frequently switchgear is used for motor control, particularly for large high-voltage motors. Switchgear (Fig, 29-6) must be used for motors... 

This chapter introduces the basic items of design and specification for the principal systems and components of an electrical industrial installation. Electrical supply systems are discussed with regard to interface with the supply authorities and the characteristics. Salient features of switchgear, transformers, protection systems, power factor correction, motor control equipment and standby supplies are identified and discussed together with reference to the relevant codes of practice and standards. The equipment and systems described are appropriate to industrial plant installations operating at typically 11 kV with supply capacities of around 20MVA. 

When connected as switchable banks the rating of each step of the capacitor bank must be selected with care. It is important that the control relay settings are matched to the ratings of each capacitance step in order to prevent hunting (i.e. continuously switching in and out at a particular load point). When capacitors are connected to one particular load (usually a motor) the capacitor bank can be located at the motor, adjacent to but separate from the control switchgear or within the control switchgear itself. 

Layout of power cables and specific requirements for switchgear and motor control centers, including mounting details. 

Feeders originating in switchgear, panelboards, and motor control centers provide power to electrical distribution equipment within the pharmaceutical plant. Branch circuits originating in panelboards and motor control centers provide power to pharmaceutical equipment, lighting, motors, and other equipment. 

Individual motor controllers are sometimes connected to the main switchgear when they serve large motors but are more often connected to motor branch circuits originating in the distribution panelboards or MCCs. Individual motor... 

Switchgear tends to be operated infrequently, whereas motor control centres operate frequently as required by the process that uses the motor. Apart from the incomers and busbar section circuit breakers, the motor control centres are designed with contactors and fuses (or some types of moulded case circuit breakers in low voltage equipment) that will interrupt fault currents within a fraction of a cycle of AC current. Circuit breakers need several cycles of fault current to flow before interruption is complete. Consequently the components within a circuit breaker must withstand the higher forces and heat produced when several complete cycles of fault current flow. 

Switchgear is available up to at least 400 kV, whereas motor control centres are only designed for voltages up to approximately 15 kV because this is the normal limit for high voltage motors. 

The following description of integrated motor control systems (IMCS) is based upon Reference 7, for which permission to use the material therein was kindly given by Switchgear and Instrumentation Ltd. The principles described can be used for low and high voltage switchgear that contain plain feeders, interconnectors, incomers and busbar section circuit breakers, in addition to... 

Integrated motor control system Recommended technical specification. Rev B-November 1998. Switchgear Instrumentation Ltd. Ripley Road, Bradford, BD4 7EH, UK. 

The system receives its main power from a circuit breaker (6) or contactor in the upstream switchboard or motor control centre. This switchgear will contain the main power protective relays... 

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