5-248 D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUALGROUPED ELEMENTS CHAPTER 5: SETTINGS5The negative-sequence instantaneous overcurrent element can be used as an instantaneous function with no intentionaldelay or as a definite time function. The element responds to the negative-sequence current fundamental frequencyphasor magnitude (calculated from the phase currents) and applies a positive-sequence restraint for better performance:a small portion (12.5%) of the positive-sequence current magnitude is subtracted from the negative-sequence currentmagnitude when forming the operating quantity.I op = |I_2| - K x |I_1| where K = 1/8 Eq. 5-21The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious negative-sequencecurrents resulting from• System unbalances under heavy load conditions• Transformation errors of current transformers (CTs) during three-phase faults• Fault inception and switch-off transients during 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 the test currents are injected into the relay (single-phase injection:Iop = 0.2917 x Iinjected ; three-phase injection, opposite rotation: Iop = I injected ).Figure 5-138: Negative sequence IOC1 logic5.7.11.4 Negative sequence directional overcurrent (ANSI 67Q, IEC PDEF/PTOC)SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) NEGATIVE SEQUENCE CURRENT NEG SEQ DIROC1(2) NEG SEQ IOC1 PICKUPDELAY: 0.00 sRange: 0.00 to 600.00 s in steps of 0.01 NEG SEQ IOC1 RESETDELAY: 0.00 sRange: 0.00 to 600.00 s in steps of 0.01 NEG SEQ IOC1 BLOCK:OffRange: FlexLogic operand NEG SEQ IOC1TARGET: Self-resetRange: Self-reset, Latched, Disabled NEG SEQ IOC1EVENTS: DisabledRange: Disabled, Enabled NEG SEQ DIR OC1 NEG SEQ DIR OC1FUNCTION: DisabledRange: Disabled, Enabled NEG SEQ DIR OC1SOURCE: SRC 1Range: SRC 1, SRC 2 NEG SEQ DIR OC1OFFSET: 0.00 ΩRange: 0.00 to 250.00 ohms in steps of 0.01
