GE C70

CHAPTER 5: SETTINGS GROUPED ELEMENTS
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 5-207
5
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:
I
op
= 3 x (|I_0| - K x |I_1|) where K = 1/16 Eq. 5-16
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):
Eq. 5-17
NEUTRAL IOC1 FUNCTION — This setting enables and disables the neutral instantaneous overcurrent protection element.
NEUTRAL IOC1 SIGNAL SOURCE — This setting selects the signal source for the neutral instantaneous overcurrent protection
element.
NEUTRAL IOC1 PICKUP — This setting specifies the neutral instantaneous overcurrent pickup level in per-unit values.
NEUTRAL IOC1 PICKUP DELAY — This setting delays the assertion of the NEUTRAL IOC OP operands. It is used to achieve timing
coordination with other elements and relays.
NEUTRAL IOC1 RESET DELAY — This setting specifies a delay for the reset of the neutral instantaneous overcurrent element
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.a
NEUTRAL IOC1 BLOCK — Assertion of the operand assigned to this setting blocks operation of the neutral instantaneous
overcurrent element.
NEUTRAL IOC1 EVENTS — This setting enables and disables the logging of neutral instantaneous overcurrent events in the
sequence of events recorder.
Figure 5-105: Neutral IOC1 logic
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

NEUTRAL DIR OC1
FUNCTION: Disabled
Range: Disabled, Enabled