GE t60 Instruction Manual page 304

5.6 GROUPED ELEMENTS
c) NEUTRAL INSTANTANEOUS OVERCURRENT (ANSI 50N)
PATH: SETTINGS GROUPED ELEMENTS
NEUTRAL IOC1
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-
5
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 = 0.9375 I
op injected
SETTING
NEUTRAL IOC1 FUNCTION:
Disabled=0
Enabled=1
SETTING
NEUTRAL IOC1 BLOCK:
Off=0
SETTING
NEUTRAL IOC1 SOURCE:
I_0
5-172
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 K I_1
= –
op
; three-phase pure zero-sequence injection:
SETTING
NEUTRAL IOC1 PICKUP:
RUN
AND
3( _0 - K _1 ) PICKUP I I
Figure 5–93: 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
⋅ ) ⁄
where K 1 16
=
×
I = 3 I
op injected
SETTINGS
NEUTRAL IOC1
PICKUP DELAY :
NEUTRAL IOC1
RESET DELAY :
t
PKP
t
5 SETTINGS
NEUTRAL IOC1(8)
).
FLEXLOGIC OPERANDS
NEUTRAL IOC1 PKP
NEUTRAL IOC1 DPO
NEUTRAL IOC1 OP
RST
827035A4.CDR
(EQ 5.37)
GE Multilin