Neutral Instantaneous Overcurrent (Ansi 50N, Iec Pioc); Neutral Ioc1 Scheme Logic - GE T60 Instruction Manual
Transformer protection system ur series
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5.6 GROUPED ELEMENTS
c) NEUTRAL INSTANTANEOUS OVERCURRENT (ANSI 50N, IEC PIOC)
PATH: SETTINGS
NEUTRAL IOC1
5
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:
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
0.9375xI
=
op
injected
5-236
GROUPED ELEMENTS
SETTING GROUP 1(6)
NEUTRAL IOC1
FUNCTION: Disabled
NEUTRAL IOC1 SIGNAL
MESSAGE
SOURCE: SRC 1
NEUTRAL IOC1
MESSAGE
PICKUP:
NEUTRAL IOC1 PICKUP
MESSAGE
DELAY:
NEUTRAL IOC1 RESET
MESSAGE
DELAY:
NEUTRAL IOC1 BLOCK:
MESSAGE
Off
NEUTRAL IOC1
MESSAGE
TARGET: Self-reset
NEUTRAL IOC1
MESSAGE
EVENTS: Disabled
I
3
I_0
=
op
; three-phase pure zero-sequence injection:
Figure 5–112: NEUTRAL IOC1 SCHEME LOGIC
T60 Transformer Protection System
NEUTRAL CURRENT
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6
Range: 0.000 to 30.000 pu in steps of 0.001
1.000 pu
Range: 0.00 to 600.00 s in steps of 0.01
0.00 s
Range: 0.00 to 600.00 s in steps of 0.01
0.00 s
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
Kx I_1
where K
1 16
–
=
I
3 I
=
op
injected
5 SETTINGS
NEUTRAL IOC1(8)
(EQ 5.37)
).
GE Multilin
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