Protection Engineering Basics and Schemes Protection Engineering | Page 28

1.1.9.1 Method:
 1 st off the breaker
 Check zero Voltage status by high voltage tester, also
earthed dead circuit
 Place short on incoming side of primary red, yellow
and blue phase conductor
 Place your 250V supply operated Primary injection
set and connects it with any two primary conductors,
and places your optional ammeter in series
connection of under ratio test CT via test block. I said
it optional because in new injection sets the
secondary and primary side metering is available in
test sets.
 Now start injecting current, if you have CT of 400/1,
you need to inject up to 25% of primary current
means 100A, and observe the reading on secondary
side. If secondary side reading is around 0.25A,if
there is slight reduction in secondary reading it is just
because of composite errors. But let suppose if you
get output secondary of 0.10A or 0.15A, then its
means your CT secondary windings are deteriorating
and CT need to be replace.
pg. 28