GE LPS-O Instruction Manual page 57

2 CALCULATION OF SETTINGS
50G provides direct tripping for single-line-to-ground faults, and its operating quantity is:
×
50G = 3 I - 50GRESTNT x
op
0
where 50GRESTNT = 0 or 0.3
When 50GRESTNT is set to 0.3, positive-sequence current restraint is used to provide secure operation during
steady-state unbalances, error currents, and external faults. The 50G setting is established by first determining
the maximum positive value of the operating quantity listed above (taking into account the 50GRESTNT set-
ting). 50GPICKUP is then this maximum operate signal plus a margin of 25% of the
same maximum operate signal.
×
50GPICKUP = 3 I
0
608: 50GPCKUPFF - Pickup During Fuse Failure
If 50G is made directional and potential is lost to the relay, then directional control will be lost and the 50G func-
tion will not be able to provide any protection. To overcome this drawback, a second setting (50GPCKUPFF)
can be made on the 50G function to provide some backup during a loss of potential. A 50GPCKUPFF setting
must always be made and it must always be set as given above and based on the maximum operating quantity
that can be obtained for a fault at either end of the line.
609: 50GRESTNT - 50G Restraint Setting
50GRESTNT can be set to 0 or 0.3, and it determines whether or not a portion of the positive-sequence cur-
rent, is used to restrain the operating quantity,
make the 50G function more secure during external faults, steady-state unbalances and/or error currents.
610: 51G - Select Ground Time Overcurrent (TOC)
51G can be set to either YES or NO. This setting determines whether the 51G function is in service (YES) or
out of service (NO).
611: 51G_DIRCNL - Select Directional Control of TOC
51G_DIRCNL can be set to either YES or NO. This setting determines whether 51G is directionally controlled
(YES) or not directionally controlled (NO).
612: 51GPICKUP - Ground Time Overcurrent Setting
The 51G function provides time-delayed backup tripping for single-line-to-ground faults. Its operating quantity
is:
×
3 I
0
The curve shape used for 51G is determined by the 51GCURVE setting as described below. The pickup and
time-dial settings should be selected to provide coordination with similar functions in adjacent line sections.
613: 51GPCKUPFF - 51G Pickup During Fuse Failure
If 51G is made directional and potential is lost to the relay, then directional control will be lost and the 51G func-
tion will not be able to provide any protection. To overcome this drawback, a second setting (51GPCKUPFF)
can be made on the 51G function to provide some backup during a loss of potential. A 51GPCKUPFF setting
must always be set as given above and is based on the maximum operating quantity that can be obtained for a
fault at either end of the line.
GE Power Management
×
3 I
1
- 50GRESTNT × × + 0.25 ×
3 I
1
×
I
3
0
LPS-O Line Protection System
2.3 PROTECTION SETTINGS
×
3 I
0
. The effect of positive-sequence current restraint is to
2
×
3 I value from this
0
2-
17