5-214
L90 Line Current Differential System
GE Multilin
5.6 GROUPED ELEMENTS
5 SETTINGS
5
The equation above brings an advantage of generating the restraining signal of twice the external ground fault current,
while reducing the restraint below the internal ground fault current. The negative-sequence component of the restraining
signal (IR2) is meant to provide maximum restraint during external phase-to-phase faults and is calculated as follows:
(EQ 5.27)
The multiplier of 1 is used by the relay for first two cycles following complete de-energization of the winding (all three phase
currents below 5% of nominal for at least five cycles). The multiplier of 3 is used during normal operation; that is, two cycles
after the winding has been energized. The lower multiplier is used to ensure better sensitivity when energizing a faulty
winding.
The positive-sequence component of the restraining signal (IR1) is meant to provide restraint during symmetrical condi-
tions, either symmetrical faults or load, and is calculated according to the following algorithm:
1 If
of phase CT, then
2
If ,
then
3
else
4 else
Under load-level currents (below 150% of nominal), the positive-sequence restraint is set to 1/8th of the positive-sequence
current (line 4). This is to ensure maximum sensitivity during low-current faults under full load conditions. Under fault-level
currents (above 150% of nominal), the positive-sequence restraint is removed if the zero-sequence component is greater
than the positive-sequence (line 3), or set at the net difference of the two (line 2).
The raw restraining signal (Irest) is further post-filtered for better performance during external faults with heavy CT satura-
tion and for better switch-off transient control:
(EQ 5.28)
where k represents a present sample, k – 1 represents the previous sample, and
is a factory constant (
1). The equa-
tion above introduces a decaying memory to the restraining signal. Should the raw restraining signal (Irest) disappear or
drop significantly, such as when an external fault gets cleared or a CT saturates heavily, the actual restraining signal (Igr(k))
will not reduce instantly but will keep decaying decreasing its value by 50% each 15.5 power system cycles.
Having the differential and restraining signals developed, the element applies a single slope differential characteristic with a
minimum pickup as shown in the logic diagram below.
Figure 5–109: RESTRICTED GROUND FAULT SCHEME LOGIC
IR2
I_2
=
or IR2
3
I_2
=
I_1
1.5 pu
I_1
I_0
IR1
3
I_1
I_0
–
=
IR1
0
=
IR1
I_1 8
=
Igr k
max Irest k
Igr k 1
–
=
SETTING
SETTING
SETTING
SETTING
SETTINGS
SETTING
FLEXLOGIC OPERANDS
ACTUAL VALUES
RESTD GND FT1
FUNCTION:
RESTD GND FT1
BLOCK:
RESTD GND FT1
SOURCE:
RESTD GND FT1
PICKUP:
RESTD GND FT1 RESET
DELAY:
RESTD GND FT1 PICKUP
DELAY:
RESTD GND FT1
SLOPE:
RESTD GND FT1 OP
RESTD GND FT1 DPO
RESTD GND FT1 PKP
RGF 1 Igd Mag
RGF 1 Igr Mag
Off=0
Enabled=1
AND
828002A3.CDR
RUN
RUN
Igd > PICKUP
IN
IG
I_0
I_1
I_2
AND
>
SLOPE
*
Igd
Igr
Differential
and
Restraining
Currents
tPKP
tRST
Summary of Contents for UR Series L90
Page 652: ...A 16 L90 Line Current Differential System GE Multilin A 1 PARAMETER LISTS APPENDIX A A ...
Page 772: ...B 120 L90 Line Current Differential System GE Multilin B 4 MEMORY MAPPING APPENDIX B B ...
Page 802: ...C 30 L90 Line Current Differential System GE Multilin C 7 LOGICAL NODES APPENDIX C C ...
Page 812: ...D 10 L90 Line Current Differential System GE Multilin D 1 IEC 60870 5 104 APPENDIX D D ...
Page 824: ...E 12 L90 Line Current Differential System GE Multilin E 2 DNP POINT LISTS APPENDIX E E ...
Page 834: ...F 10 L90 Line Current Differential System GE Multilin F 3 WARRANTY APPENDIX F F ...
Page 846: ...xii L90 Line Current Differential System GE Multilin INDEX ...
