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5 SETTINGS
b) NEGATIVE SEQUENCE INSTANTANEOUS OVERCURRENT (ANSI 50Q, IEC PIOC)
PATH: SETTINGS
GROUPED ELEMENTS
NEG SEQ IOC1
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
The negative-sequence instantaneous overcurrent element may be used as an instantaneous function with no intentional
delay or as a definite time function. The element responds to the negative-sequence current fundamental frequency phasor
magnitude (calculated from the phase currents) and applies a positive-sequence restraint for better performance: a small
portion (12.5%) of the positive-sequence current magnitude is subtracted from the negative-sequence current magnitude
when forming the operating quantity:
The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious negative-sequence cur-
rents resulting from:
•
system unbalances under heavy load conditions
•
transformation errors of current transformers (CTs) during three-phase faults
•
fault inception and switch-off transients during three-phase faults
The positive-sequence restraint must be considered when testing for pickup accuracy and response time (multiple of
pickup). The operating quantity depends on the way the test currents are injected into the relay (single-phase injection:
I
0.2917 I
; three-phase injection, opposite rotation:
=
op
injected
GE Multilin
SETTING GROUP 1(6)
NEG SEQ IOC1
FUNCTION: Disabled
NEG SEQ IOC1 SIGNAL
SOURCE: SRC 1
NEG SEQ IOC1
PICKUP: 1.000 pu
NEG SEQ IOC1 PICKUP
DELAY:
0.00 s
NEG SEQ IOC1 RESET
DELAY:
0.00 s
NEG SEQ IOC1 BLOCK:
Off
NEG SEQ IOC1
TARGET: Self-reset
NEG SEQ IOC1
EVENTS: Disabled
I
I_2
K I_1
=
–
op
Figure 5–111: NEGATIVE SEQUENCE IOC1 SCHEME LOGIC
L90 Line Current Differential System
NEGATIVE SEQUENCE CURRENT
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4
Range: 0.000 to 30.000 pu in steps of 0.001
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
1 8
where K
=
I
I
).
=
op
injected
5.6 GROUPED ELEMENTS
NEG SEQ OC1(2)
(EQ 5.29)
5-217
5
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