74 TM1700-SERIES ZP-BL16E BL1448GE
6 APPLICATION EXAMPLES
6.3 External clamp-on CT
input
Coil current measurement
Measurement in X/Y-relay configuration
With the traditional (internal) coil current measure-
ment method just the current through the X-relay
would be recorded. The external current clamp allows
the real close coil current to be recorded.
Individual measurements when close
command are ganged
With the traditional (internal) coil current measure-
ment method the sum of all three close coils would
be recorded. The external current clamps allow the
individual close coil currents to be recorded.
Measurement at First trip / First close
test
The circuit breaker is in service during first trip test.
Thus, it is not allowed to put the breaker in local
mode or break up the circuit in order to measure the
coil current. The only way to measure coil currents in a
safe way is to use current clamps.
Individual spring charge motor
current measurements
The clamp-on CTs enables non-invasive, individual mo-
tor current measurement.
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