GE M60 UR Series

GE Multilin M60 Motor Protection System 5-185
5 SETTINGS 5.6 GROUPED ELEMENTS
5
b) NEUTRAL INSTANTANEOUS OVERCURRENT (ANSI 50N, IEC PIOC)
PATH: SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  NEUTRAL CURRENT  NEUTRAL IOC1(8)
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 5.29)
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 5–88: 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
3I_0K I_1–= where K 116=
I
op
0.9375 I
injected
=
I
op
3 I
injected
=