Woodward MRM4, Manual, Page: 313 / 460

Protective Elements
Commissioning: Negative Sequence Overcurrent]
Object to be tested
Signals to be measured for each current protection element: the threshold values, total tripping time
(recommended), or alternatively tripping delays and the dropout ratios.
It is recommended to measure the total tripping time instead of the tripping
time. The tripping delay should be specified by the customer. The total
tripping time is measured at the position signalling contacts of the CBs (not
at the relay output!).
Total tripping time: = tripping delay (please refer to the tolerances of the
protection stages) + CB operating time (about 50 ms)
Please take the CB switching times from the technical data, specified in the
relevant documentation, provided by the CB manufacturer.
Necessary means:
•
Current source;
•
Current meters; and
•
Timer.
Procedure:
Testing the threshold values
In order to get a negative-sequence current, please change the phase sequence at the terminals of the current
source (in case of ABC sequence to ACB – in case of a ACB sequence to ABC).
For each test performed, feed a current that is about 3-5% above the threshold value for activation/tripping.
Then check the threshold values.
Testing the total tripping delay (recommendation)
Measure the total tripping times at the auxiliary contacts of the breakers (breaker tripping).
Testing the tripping delay (measuring at the relay output contact)
Measure the tripping times at the relay output contact.
Testing the dropout ratio
Reduce the current to 97% below the trip value and check the dropout ratio.
Successful test result
The measured total tripping delays or individual tripping delays, threshold values, and dropout ratios correspond
with those values specified in the adjustment list. Permissible deviations/tolerances can be found under
Technical Data.
EN MRM4 01/11 Page 313