CHAPTER 5: SETTINGS GROUPED ELEMENTSC70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 5-2215The 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. 5-19The 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 5-113: Negative sequence IOC1 logic5.7.6.4 Negative sequence directional overcurrent (ANSI 67Q, IEC PDEF/PTOC)SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) NEGATIVE SEQUENCE CURRENT NEG SEQ DIR OC1 NEG SEQ DIR OC1 NEG SEQ DIR OC1FUNCTION: DisabledRange: Disabled, Enabled NEG SEQ DIR OC1SOURCE: SRC 1Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6 NEG SEQ DIR OC1OFFSET: 0.00 ΩRange: 0.00 to 250.00 ohms in steps of 0.01 NEG SEQ DIR OC1TYPE: Neg SequenceRange: Neg Sequence, Zero Sequence NEG SEQ DIR OC1 POS-SEQ RESTRAINT: 0.063Range: 0.000 to 0.500 in steps of 0.001 NEG SEQ DIR OC1 FWDECA: 75° LagRange: 0 to 90° Lag in steps of 1 NEG SEQ DIR OC1 FWDLIMIT ANGLE: 90°Range: 40 to 90° in steps of 1 NEG SEQ DIR OC1 FWDPICKUP: 0.050 puRange: 0.015 to 30.000 pu in steps of 0.005 NEG SEQ DIR OC1 REVLIMIT ANGLE: 90°Range: 40 to 90° in steps of 1
