Restricted Ground Differential Current (87R) - GE Multilin MIGII Instruction Manual

9 RELAY COMMISSIONING

9.18RESTRICTED GROUND DIFFERENTIAL CURRENT (87R)

NOTE: Before doing neutral currents differential test (87R), it is necessary to wire the relay as shown in section 3.2.1.
Special Wiring Diagram for unit 87R, from chapter 3 Hardware.
The trip condition for this protection element is as follows:
Id > S + K x Ipaso = Trip, being Ipaso the largest of phase currents
If the calculated differential current is larger than the sensitivity setting plus the K * I. Max value, the 87R element will
produce an internal output, which after the set timing will activate the tripping contact enabled for this purpose.
Set the relay as follows:
Apply the current values shown on table 2 through phase A and through the neutral. Increase gradually the neutral current
until the unit trips starting from a current value equal to the value in the "In trip" column of the table. The permitted error will
not exceed 3%.
Table 9–1: FOR A RATED CURRENT OF 1 AMP. IN PHASES AND 1 AMP. IN NEUTRAL
IA@0º
1
2
3
1
2
3
GEK-113188A
9.18 RESTRICTED GROUND DIFFERENTIAL CURRENT (87R)
87R Enable Yes
87R Trip Yes
87R K According to table 2
87R S 0.3 In
87R Time Delay 0
IN@0º
1,4
2,6
3,8
1,6
3,0
4,4
MIGII Digital Protection for Electrical Machines
K IN TRIP
20% 1,5
20% 2,7
20% 3,9
40% 1,7
40% 3,1
40% 4,5
9
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