GE C70 Instruction Manual page 351

CHAPTER 5: SETTINGS
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):
— This setting enables and disables the neutral instantaneous overcurrent protection element.
NEUTRAL IOC1 FUNCTION
NEUTRAL IOC1 SIGNAL SOURCE
element.
— This setting specifies the neutral instantaneous overcurrent pickup level in per-unit values.
NEUTRAL IOC1 PICKUP
— This setting delays the assertion of the
NEUTRAL IOC1 PICKUP DELAY
coordination with other elements and relays.
— This setting specifies a delay for the reset of the neutral instantaneous overcurrent element
NEUTRAL IOC1 RESET DELAY
between the operate output state and the return to logic 0 after the input passes outside the defined pickup range. This
setting is used to ensure that the relay output contacts are closed long enough to ensure reception by downstream
equipment.
— Assertion of the operand assigned to this setting blocks operation of the neutral instantaneous
NEUTRAL IOC1 BLOCK
overcurrent element.
— This setting enables and disables the logging of neutral instantaneous overcurrent events in the
NEUTRAL IOC1 EVENTS
sequence of events recorder.
5.7.4.4 Neutral directional overcurrent (ANSI 67N, IEC PDEF/PTOC)
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  NEUTRAL CURRENT  NEUTRAL DIRECTIONAL OC1
 NEUTRAL
 DIRECTIONAL OC1
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
I = 3 x (|I_0| - K x |I_1|) where K = 1/16
op
— This setting selects the signal source for the neutral instantaneous overcurrent protection
Figure 5-93: Neutral IOC1 logic
NEUTRAL DIR OC1

FUNCTION: Disabled
operands. It is used to achieve timing
NEUTRAL IOC OP
Range: Disabled, Enabled
GROUPED ELEMENTS
Eq. 5-16
Eq. 5-17
5
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