5-208 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
GROUPED ELEMENTS CHAPTER 5: SETTINGS
5
The neutral directional overcurrent element provides both forward and reverse fault direction indications for the NEUTRAL
DIR OC1 FWD and NEUTRAL DIR OC1 REV operands, respectively. The output operand is asserted if the magnitude of the
operating current is above a pickup level (overcurrent unit) and the fault direction is seen as forward or reverse,
respectively (directional unit).
The overcurrent unit responds to the magnitude of a fundamental frequency phasor of either the neutral current
calculated from the phase currents or the ground current. There are separate pickup settings for the forward-looking and
reverse-looking functions. If set to use the calculated 3I_0, the element applies a positive-sequence restraint for better
performance: a small user-programmable portion of the positive-sequence current magnitude is subtracted from the
zero-sequence current magnitude when forming the operating quantity.
I
op
= 3 x (|I_0| - K x |I_1|) Eq. 5-18
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 the way the test currents are injected into the relay (single-phase injection:
I
op
=(1–K)× I
injected
; three-phase pure zero-sequence injection: I
op
= 3 × I
injected
.
The positive-sequence restraint is removed for low currents. If the positive-sequence current is below 0.8 pu, the restraint is
removed by changing the constant K to zero. This facilitates better response to high-resistance faults when the unbalance
is very small and there is no danger of excessive CT errors as the current is low.
NEUTRAL DIR OC1
SOURCE: SRC 1
Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6
NEUTRAL DIR OC1
POLARIZING: Voltage
Range: Voltage, Current, Dual, Dual-V, Dual-I
NEUTRAL DIR OC1 POL
VOLT: Calculated V0
Range: Calculated V0, Measured VX
NEUTRAL DIR OC1 OP
CURR: Calculated 3I0
Range: Calculated 3I0, Measured IG
NEUTRAL DIR OC1 POS-
SEQ RESTRAINT: 0.063
Range: 0.000 to 0.500 in steps of 0.001
NEUTRAL DIR OC1
OFFSET: 0.00 Ω
Range: 0.00 to 250.00 Ω in steps of 0.01
NEUTRAL DIR OC1 FWD
ECA: 75° Lag
Range: –90 to 90° in steps of 1
NEUTRAL DIR OC1 FWD
LIMIT ANGLE: 90°
Range: 40 to 90° in steps of 1
NEUTRAL DIR OC1 FWD
PICKUP: 0.050 pu
Range: 0.006 to 30.000 pu in steps of 0.001
NEUTRAL DIR OC1 REV
LIMIT ANGLE: 90°
Range: 40 to 90° in steps of 1
NEUTRAL DIR OC1 REV
PICKUP: 0.050 pu
Range: 0.006 to 30.000 pu in steps of 0.001
NEUTRAL DIR OC1 BLK:
Off
Range: FlexLogic operand
NEUTRAL DIR OC1
TARGET: Self-reset
Range: Self-reset, Latched, Disabled
NEUTRAL DIR OC1
EVENTS: Disabled
Range: Disabled, Enabled
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