Control transformer


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Could anybody explain what is control transformer and how it is used in MCC? What could be the design criteria? The system is 6.6 kv, 50 hz, and I have to take 220 vac from that.

The control transformer provides low voltage power to activate the starter contactors. In a high voltage MCC such as yours it's usual to have one transformer to supply all the starter contactors. Usually in lower voltage MCCs, e.g. 400 Volt each starter has its own control transformer. Often in a high voltage MCC the contactor coils are large requiring lots of current to activate. It's usual to have an interposing relay so that your control system only has to switch a low current. Ask for a schematic of the MCC before you buy your I/O cards so you can pick the right output type.