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Control voltage transformers


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Why is that all electrical panels come with control voltage transformers.


Say a panel has 380 V 3 phase incomer...then 2 phases are taken into a 380v to 220 v transformer, and this voltage is used in control circuits.


What is the advantage of this system?


Can we put a 13.8 kv/ 220/110 volts dyn11 transformer and use 220 volts supply ( phase to phase ) for control voltage in 33/13.8kv substations?



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Control transformers are provided mainly for following reasons

1. To have isolation from the Main supply

2. To limit fault levels in control ciruit

3. To have a safer and lower control voltage


As far as second part of the question is concerned if u are planning to take secondary of the MAin transformer it msy not be a good idea ( Sl No 2 above )


It is also a good practice to use secondary centre tap earthed control transformers so that those working on the system are subjected to a lesser voltage w.r.t ground

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