GE C70 Instruction Manual page 425

CHAPTER 5: SETTINGS
The negative-sequence instantaneous overcurrent element can be used as an instantaneous function with no intentional
delay or as a definite time function. The element responds to the negative-sequence current fundamental frequency
phasor 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 current
magnitude when forming the operating quantity.
The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious negative-sequence
currents 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 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 the test currents are injected into the relay (single-phase injection:
I = 0.2917 x I ; three-phase injection, opposite rotation: I
op injected
5.7.6.4 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

C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
I = |I_2| - K x |I_1| where K = 1/8
op
op
Figure 5-113: Negative sequence IOC1 logic
NEG SEQ DIR OC1

FUNCTION: Disabled
NEG SEQ DIR OC1

SOURCE: SRC 1
NEG SEQ DIR OC1

OFFSET: 0.00 Ω
NEG SEQ DIR OC1

TYPE: Neg Sequence
NEG SEQ DIR OC1 POS-

SEQ RESTRAINT: 0.063
NEG SEQ DIR OC1 FWD

ECA: 75° Lag
NEG SEQ DIR OC1 FWD

LIMIT ANGLE: 90°
NEG SEQ DIR OC1 FWD

PICKUP: 0.050 pu
NEG SEQ DIR OC1 REV

LIMIT ANGLE: 90°
= I ).
injected
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6
Range: 0.00 to 250.00 ohms in steps of 0.01
Range: Neg Sequence, Zero Sequence
Range: 0.000 to 0.500 in steps of 0.001
Range: 0 to 90° Lag in steps of 1
Range: 40 to 90° in steps of 1
Range: 0.015 to 30.000 pu in steps of 0.005
Range: 40 to 90° in steps of 1
GROUPED ELEMENTS
Eq. 5-19
5
5-221