Woodward MRM4, Руководство пользователя

Страница: 310 / 460

Protective Elements
It is recommended to measure the total tripping time instead of the tripping
delay. The tripping delay should be specified by the customer. The total
tripping time is measured at the position signalling contact of the CB (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 operating times from the technical data specified in the
relevant documentation provided by the CB manufacturer.
•
Current source;
•
May be: ampere meters; and
•
Timer.
Procedure
Testing the threshold values (3 x single-phase and 1 x three-phase)
Each time feed a current which 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 CB (CB tripping).
Testing the tripping delay (measuring at the relay output)
Measure the tripping times at the relay output.
Testing the fallback ratio
Reduce the current to 97% below the trip value and check the fallback ratio.
Successful test result
The measured total tripping delays or individual tripping delays, threshold values and fallback ratios correspond
with those values, specified in the adjustment list. Permissible deviations/tolerances can be found under
Technical Data.
I2> - Negative-Sequence Overcurrent [51Q]
For activating this function, the parameter »Measuring Mode« has to be set to » I2« in the parameter set of the
corresponding overcurrent element I[x]. Please refer to chapter „I-Protection Module – Overcurrent Protection“.
The negative-sequence overcurrent element ( 51Q ) is to be seen as an equivalent to the phase overcurrent
protection with the exception that it uses negative-sequence current (I2) as measured quantities instead of the
three phase currents used by phase overcurrent elements. The negative-sequence current used by 51Q is
derived from the following well-known symmetrical component transformation:
I
2
=
1
3

I
L1

a
2
I
L2

a I
L3

The pickup set value of a 51Q element should be set in accordance of the negative-sequence current
occurrence in the protected object.
Page 310 EN MRM4 01/11