Compare and contrast of C.T and PT - 2 Mins Read

Current Transformers

a. A current transformer is a step down instrument for measuring the high value current in L.T

/H.T/ E.H.T lines

b. It has one or two windings or a bus bar or a heavy line conductor surmounted by a core

having large number of thin wires.

c. In a C.T the number of turns is inversely proportional to the current and it is connected in

series in the line

d. C.T is used for metering, recording and relay circuits for different requirements.

e .C.T must have its secondary always closed through relays/short circuited and no fuse should

be used. However the fuses can be used in shunt circuits while in service.

f. Never open a secondary circuit of a C.T which may have high potential due to high impedance

and endanger to personnel operating.

g. Polarity is important in connecting a C.T in the circuit

h. In calibrating a C.T’s impedance burden the configuration of different coil connection in

series or in parallel is to be kept in mind. For safety purposes one of the secondary of a C.T

needs to be earthed.

Potential Transformers

P.T is a step down instrument from higher value to a lower value to measure the H.T/E.H.T

Volts

a. A Potential transformer has turns per volt on the secondary side nearly equal to the that

in the primary

b. It has a primary with large number of thin wire and secondary with small number of

thick wires

c. In a P.T the number of turns is directly proportional to the voltage and it is connected

across the line

d. P.T secondary side must not be short circuited and a fuse has to be there on primary and

secondary sides

e. P.T is used for metering, recording and relay circuits for different requirements.