GE Power Management LPS-O Line Protection System 2-
17
2 CALCULATION OF SETTINGS 2.3 PROTECTION SETTINGS
2
50G
provides direct tripping for single-line-to-ground faults, and its operating quantity is:
50G
op
= -
50GRESTNT
x
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 value from this
same maximum operate signal.
50GPICKUP
= -
50GRESTNT
×
+ 0.25
×
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, . The effect of positive-sequence current restraint is to
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:
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.
3
I
0
×
3
I
1
×
3
I
0
×
3
I
0
×
3
I
1
×
3
I
0
×
3
I
0
×
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