Woodward MRM4, Manual

Page: 419 / 460

Supervision
Current Transformer Supervision Signals (Outputs States)
Name Description
active Signal: active
ExBlo Signal: External Blocking
Alarm Signal: Alarm Current Transformer Measuring Circuit Supervision
Commissioning: Current Transformer Failure Supervision
Precondition:
1. Measurement of all three phase currents (are applied to the
measuring inputs of the device).
2. The earth current is detected via a cable-type transformer (not in
Holmgreen connection).
Object to be tested
Check of the CT supervision (by comparing the calculated with the measured earth current) .
Necessary means:
•
Three-phase current source.
Procedure, part 1:
•
Set the limiting value of the CTS to »delta I=0.1*In« .
•
Feed a three-phase, symmetrical current system (approx. nominal current) to the secondary side.
•
Disconnect the current of one phase from one of the measuring inputs (the symmetrical feeding at
secondary side has to be maintained).
•
Make sure that the signal »CTS.A
LARM
« is generated now.
Successful test result, part 1:
•
The signal »CTS.A
LARM
« is generated.
Procedure, part 2:
•
Feed a three-phase, symmetrical current system (approx. nominal current) to the secondary side.
•
Feed a current that is higher than the threshold value for the measuring circuit supervision to the earth
current measuring input.
•
Ascertain that the signal »CTS.A
LARM
« is generated now.
Successful test result, part 2
The signal »CTS.A
LARM
« is generated.
EN MRM4 01/11 Page 419