g)Control Xmer guidelines

Control Xmer guidelines

Q)Is there any guidelines available to determine the correct size of control teansformers?

To determine the size of auto control transformer, the following guidelines may be used.

For switching on contactors, the control rating of the transformer should be:
0.33 times the sum of the pick up VAs of the contactors which are to be switched on simultaneously

For Example: If 3x contactors of 3TF43 & 2x contactors of 3TF 55 are to be switched on simultaneously then the total pickup VA is 3064. Required control

transformer rating: 3064/3 = 1.021 kVA. With 5% regulation.Note: In general, as control transformers have poorer regulation, usage of higher VA of transformer is recommended


Fig:Control transformer


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