Protection Engineering Basics and Schemes Protection Engineering | Page 20

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pg. 20
you are the person removing cover you can be acted
as earth.
Check Voltage on all secondary output from Test
block, it must be zero. Then take CT one of contact
you need to test, the other contact is the return path
or star point if you have CT connected in star.
Now your CT is in Dead state , place your ammeter in
series and voltmeter in parallel with your at test CT
connection,
Complete your connection by connecting them with
power supply of 250V (from variable Transformer-
VARIAC) and have capability of injecting 8A current in
circuit.
Now start raising voltage slowly and kept eyes on
Voltmeter and ammeter, the point at which you
observe the slight raise in voltage will result in spike
in current value, note that voltage is knee point
voltage.
After conducting test and note values , reduce
voltage to zero level and observe current at zero
value then wait for some time , make this duration
more when you are conducting test on remnant flux
CTs(TCX,TCY and TCZ)
In case of any CT with 1A secondary current , we
must use one step transformer with our VARIAC,