Undercurrent Unit - GE Multilin MIGII Instruction Manual

9 RELAY COMMISSIONING

9.19UNDERCURRENT UNIT (37)

This unit will trip when the current level is between two thresholds, being the upper limit Tap 37, and the lower limit 5% of
FLA.
Enable only Unit 37.
Set (for In=5 A):
FLA = 1.2 * In = 1.2 * 5 A = 6 A
Upper limit: TAP 37 = 0.27 ⇒ 0.27*6 A = 1.62 A
Lower limit: 5% FLA = 5% 6 A = 0.3 A
t = 1 s
Check the following for the lower limit:
• Apply 90% of the lower limit; 90% 0.3 A = 0.27 A; the relay should not trip.
Apply 110% of the lower limit; 110% 0.3 A = 0.333 A. Acceptable time range is between 1.00 and 1.06 sec. ±500ms
•
• Apply 90% of the lower limit; 90% 0.3 A = 0.27 A; the unit will drop out.
Check the following for the upper limit:
• Apply 110% of the lower limit; 110% 1.62 A = 1.78 A; the relay should not trip.
Apply 90% of the lower limit; 90% 1.62 A = 1.46 A. Acceptable time range is between 1.00 and 1.06 sec. ±500ms
•
• Apply 110% of the lower limit; 110% 1.62 A = 1.78 A; the unit will drop out.
GEK-113188A MIGII Digital Protection for Electrical Machines
9.19 UNDERCURRENT UNIT (37)
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