5-204 C60 BREAKER PROTECTION SYSTEM – INSTRUCTION MANUALGROUPED ELEMENTS CHAPTER 5: SETTINGS5The neutral instantaneous overcurrent element can be used as an instantaneous function with no intentional delay or as adefinite time function. The element essentially responds to the magnitude of a neutral current fundamental frequencyphasor 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 whenforming the operating quantity of the element as follows:I op = 3 x (|I_0| - K x |I_1|) where K = 1/16 Eq. 5-16The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious zero-sequence currentsresulting 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 faultsThe positive-sequence restraint must be considered when testing for pickup accuracy and response time (multiple ofpickup). The operating quantity depends on how test currents are injected into the relay (single-phase injection):Eq. 5-17NEUTRAL 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 protectionelement.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 timingcoordination with other elements and relays.NEUTRAL IOC1 RESET DELAY — This setting specifies a delay for the reset of the neutral instantaneous overcurrent elementbetween the operate output state and the return to logic 0 after the input passes outside the defined pickup range. Thissetting is used to ensure that the relay output contacts are closed long enough to ensure reception by downstreamequipment.NEUTRAL IOC1 BLOCK — Assertion of the operand assigned to this setting blocks operation of the neutral instantaneousovercurrent element.NEUTRAL IOC1 EVENTS — This setting enables and disables the logging of neutral instantaneous overcurrent events in thesequence of events recorder. NEUTRAL IOC1PICKUP: 1.000 puRange: 0.020 to 30.000 pu in steps of 0.001 NEUTRAL IOC1 PICKUPDELAY: 0.00 sRange: 0.00 to 600.00 s in steps of 0.01 NEUTRAL IOC1 RESETDELAY: 0.00 sRange: 0.00 to 600.00 s in steps of 0.01 NEUTRAL IOC1 BLOCK:OffRange: FlexLogic operand NEUTRAL IOC1TARGET: Self-resetRange: Self-reset, Latched, Disabled NEUTRAL IOC1EVENTS: DisabledRange: Disabled, Enabled
