Control voltage transformers

[chaterpilar]

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?

 

chaterpilar

[johnbose]

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