Current
Transformers (CT) and Potential Transformers (PT) are used to measure the
current and voltage in a circuit of the order of hundreds of amperes and volts
respectively.
A CT has
large number of turns on its secondary winding, but very few turns on its
primary winding. The primary winding is connected in series with the load so
that it carries full load current. A low voltage range ammeter (0-5A) is
connected across the secondary winding terminals. Secondary of the CT is
practically short circuited since the ammeter resistance is very low. It should
be remembered that secondary of the CT should not be made open as it draws
heavy current and damages the primary winding of the CT.
A PT has
large number of turns in the primary and fewer turns in the secondary and hence
it steps down the voltage. The primary winding is connected across the supply
voltage and low range voltmeter (0-110V) is connected across the secondary
winding terminals
Some of the
main difference between current transformers (CT) and potential transformers
(PT) are given below:
- The
secondary of the CT is almost short circuit, whereas the secondary of the
PT is practically a open circuit
- The
primary winding of the CT is connected in series with the load so that it
carries the full line current, but there is only a small voltage across
it. However the primary winding of the PT has the full supply voltage
applied across it
- In
CT the excitation current I0 and
flux density vary over a wide range whereas in PT, they vary over a
limited range only.
As secondary of current transformer that can not be open circuited on any circumstance when it was under service and this current transformer may be considered as a series transformer.
ReplyDeleteAs secondary of a potential transformer which can be open circuited without any damage being caused either to the operator or the transformer and this potential transformer may be considered as a parallel transformer.
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