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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. Thanks for your help Top
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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