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Control voltage transformers


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#1 chaterpilar

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Posted 30 November 2005 - 03:19 PM

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

#2 johnbose

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Posted 02 December 2005 - 12:04 PM

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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