CHAPTER 5: SETTINGS
5.7.7.2 Neutral instantaneous overcurrent (ANSI 50N, IEC PIOC)
SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) NEUTRAL CURRENT NEUTRAL IOC1(8)
NEUTRAL IOC1
The neutral instantaneous overcurrent element can 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
phasor 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:
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:
I
=
0.9375
I
; three-phase pure zero-sequence injection:
op
injected
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
NEUTRAL IOC1
FUNCTION: Disabled
NEUTRAL IOC1 SIGNAL
SOURCE: SRC 1
NEUTRAL IOC1
PICKUP: 1.000 pu
NEUTRAL IOC1 PICKUP
DELAY: 0.00 s
NEUTRAL IOC1 RESET
DELAY: 0.00 s
NEUTRAL IOC1 BLOCK:
Off
NEUTRAL IOC1
TARGET: Self-reset
NEUTRAL IOC1
EVENTS: Disabled
I
=
3
I_0
K
I_1
where K
–
op
Figure 5-110: Neutral IOC1 logic
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 16
I
=
3
I
).
op
injected
GROUPED ELEMENTS
5
Eq. 5-29
5-201