Woodward MRM4, Manual, Page: 320 / 460

Protective Elements
Necessary means:
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Three-phase current source with adjustable current unbalance; and
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Timer.
Procedure:
Check the phase sequence:
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Ensure that the phase sequence is the same as that set in the field parameters.
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Feed-in a three-phase nominal current.
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Change to the »Measuring Values« menu.
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Check the measuring value for the unbalanced current »I2« . The measuring value displayed for » I2«
should be zero (within the physical measuring accuracy).
If the displayed magnitude for I2 is the same as that for the symmetrical
nominal currents fed to the relay, it implies that the phase sequence of the
currents seen by the relay is reversed.
•
Now turn-off phase L1.
•
Again check the measuring value of the unbalanced current » I2« in the »Measuring Values« menu.
The measuring value of the asymmetrical current » I2« should now be 33%.
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Turn-on phase L1, but turn-off phase L2.
•
Once again check the measuring value of the asymmetrical current I2 in the »Measuring Values« menu.
The measuring value of the asymmetrical current » I2« should be again 33%.
•
Turn-on phase L2, but turn-off phase L3.
•
Again check the measuring value of asymmetrical current » I2« in the »Measuring Values« menu.
The measuring value of the asymmetrical current » I2« should still be 33%.
Testing the trip delay:
•
Apply a symmetrical three-phase current system (nominal currents).
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Switch off IL1 (the threshold value » Threshold« for » I2« must be below 33%).
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Measure the tripping time.
The present current unbalance » I2« corresponds with 1/3 of the existing phase current displayed.
Testing the threshold values
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Configure minimum » %I2/I1« setting (2%) and an arbitrary threshold value » Threshold« (I2).
Page 320 EN MRM4 01/11