GE L60, Instruction Manual, Page: 220 / 498

5-128 L60 Line Phase Comparison Relay GE Multilin
5.5 GROUPED ELEMENTS 5 SETTINGS
5
c) NEUTRAL INSTANTANEOUS OVERCURRENT (ANSI 50N)
PATH: SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) NEUTRAL CURRENT NEUTRAL IOC1(2)
The Neutral Instantaneous Overcurrent element may be used as an instantaneous function with no intentional delay or as a
Definite Time function. The element essentially responds to the magnitude of a neutral current fundamental frequency pha-
sor calculated from the phase currents. A “positive-sequence restraint” is applied for better performance. A small portion
(6.25%) of the positive-sequence current magnitude is subtracted from the zero-sequence current magnitude when forming
the operating quantity of the element as follows:
(EQ 5.15)
The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious zero-sequence currents
resulting from:
• system unbalances under heavy load conditions
• transformation errors of current transformers (CTs) during double-line and three-phase faults
• switch-off transients during double-line and 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 how test currents are injected into the relay (single-phase injection:
; three-phase pure zero-sequence injection: ).
Figure 5–73: NEUTRAL IOC1 SCHEME LOGIC
NEUTRAL IOC1 NEUTRAL IOC1
FUNCTION: Disabled
Range: Disabled, Enabled
MESSAGE
NEUTRAL IOC1 SIGNAL
SOURCE: SRC 1
Range: SRC 1, SRC 2, SRC 3, SRC 4
MESSAGE
NEUTRAL IOC1
PICKUP: 1.000 pu
Range: 0.000 to 30.000 pu in steps of 0.001
MESSAGE
NEUTRAL IOC1 PICKUP
DELAY: 0.00 s
Range: 0.00 to 600.00 s in steps of 0.01
MESSAGE
NEUTRAL IOC1 RESET
DELAY: 0.00 s
Range: 0.00 to 600.00 s in steps of 0.01
MESSAGE
NEUTRAL IOC1 BLOCK:
Off
Range: FlexLogic™ operand
MESSAGE
NEUTRAL IOC1
TARGET: Self-reset
Range: Self-reset, Latched, Disabled
MESSAGE
NEUTRAL IOC1
EVENTS: Disabled
Range: Disabled, Enabled
I
op
3 I_0 K I_1 ⋅
–
( ) ×
=
where K 1 16 ⁄
=
I
op
0.9375 I
injected
⋅
=
I
op
3 I
injected
×
=
FLEXLOGIC OPERANDS
NEUTRAL IOC1 FUNCTION:
NEUTRAL IOC1 PICKUP:
NEUTRAL IOC1 SOURCE:
NEUTRAL IOC1 BLOCK:
NEUTRAL IOC1 DPO
NEUTRAL IOC1 OP
NEUTRAL IOC1 PKP
RUN
AND
827035A4.CDR
SETTING
SETTING
Enabled=1
Disabled=0
SETTING
SETTING
I
_0
Off=0
SETTINGS
NEUTRAL IOC1
RESET DELAY :
NEUTRAL IOC1
PICKUP DELAY :
t
PKP
t
RST
3( _0 - K _1 ) PICKUP
I I