# Current vs. Voltage Transformer - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Kent
Post subject: Current vs. Voltage Transformer
Unread postPosted: Thu Dec 23, 2004 11:06 am

I've been looking around the internet and have so far been unsuccessful in finding info on the differences between current and power transformers (3-phase).
My guess is that a current transformer steps-up current by having less secondary windings... and a power transformer steps-up voltage by increasing the number of secondary windings when compared to the primary windings.

This explanation seems a little too simple!

Another thing i was wondering about, is that a superior of mine was telling me that when dealing with current transformers, it's important not to short circuit the terminals (or open circuit them, i can't remember which one)... when i asked why this was the case, he said he wasn't sure, but that it caused arcing between the terminals.

Would there be a similar issue to consider in power transformers?

Does this make any sense!? I would really appreciate a response.

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Eric R.
Post subject:
Unread postPosted: Mon Jan 24, 2005 2:31 am

A voltage transformer is used to either step up or step down a voltage.
That is usually what people refer to when talking transformers.

A current transformer, or "CT" as it is sometimes called, is usually used when measuring large currents. A good example of this is a clamp on ammeter. When measuring a 150 amp current there is no way that 150 amps is flowing in the meter. The meter steps the current down proportionally to the current you are measuring in the wire the meter is clamped around. CT's are designed to operate with the secondary shorted.

The book I have(Delmar's Standard Textbook of Electricity) says that...

"The secondary winding of a CT should never be opened when there is power applied to the primary. This will cause the transformer to produce a step-up voltage that could be high enough to kill anyone who comes in contact with it."

When CT's are used 1 loop of wire goes through the core of the CT. Remember, the CT secondary is designed to be used short circuited. The secondary of the CT has several windings.....when disconnected, the CT turns into a step up transformer. If the voltage you are measuring is 480 and the CT secondary has 50, 100, or even 200 turns.....you now have a 1:50, 1:100, or 1:200 step up transformer. That is going to hurt if you get across it.

Basicly, if you disconnect the secondary of a CT, be prepared to get the heck knocked out of you. :wink:

Posted  11/12/2012

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