GE C70 Instruction Manual page 392

GROUPED ELEMENTS
5
Up to three identical neutral voltage unbalance elements, one per each VT bank configured in hardware, are provided.
The element responds to the voltage signal at the neutral point of the capacitor bank. The operating equations are
properly compensated for both the system unbalance such as during close-in external faults, and the inherent bank
unbalance. The bus zero-sequence voltage required for compensation of the system unbalance can be measured
internally to the relay from phase voltages, or delivered as a 3V0 signal from an open-corner-delta VT via an auxiliary
voltage channel of the relay.
Compensation for the inherent unbalance of the protected bank uses the B and C phase voltages, and thus this function
requires wye connected phase VTs. The inherent unbalance is zeroed out using ratios of the reactances between the
reference phase A, and the two other phases. An automatic setting procedure is available under the
calculate the compensating factors automatically when installing the relay, or after repairs of the bank.
To enhance performance under large system unbalances when the neutral-point and system zero-sequence voltages can
become significant, a concept of a restraint is introduced. The slope of the operating characteristic is user adjustable, and
if required, it can be effectively removed yielding a straight compensated overvoltage function.
For information, see the Application of Settings chapter.
5-226
NTRL VOL UNBAL 1

STG 3 PKP: 0.020 pu
NTRL VOL UNBAL 1

STG 3 SLOPE: 5.0%
NTRL VOL UNBAL 1

STG 4 PKP: 0.030 pu
NTRL VOL UNBAL 1

STG 4 SLOPE: 5.0%
NTRL VOL UNBAL 1 STG

1 PKP DELAY: 30.00 s
NTRL VOL UNBAL 1 STG

2 PKP DELAY: 10.00 s
NTRL VOL UNBAL 1 STG

3 PKP DELAY: 1.00 s
NTRL VOL UNBAL 1 STG

4 PKP DELAY: 0.20 s
NTRL VOL UNBAL 1

DPO DELAY: 0.25 s
NTRL VOL 1 BLK STG1:

Off
NTRL VOL 1 BLK STG2:

Off
NTRL VOL 1 BLK STG3:

Off
NTRL VOL 1 BLK STG4:

Off
NTRL VOL UNBAL 1

TARGET: Self-Reset
NTRL VOL UNBAL 1

EVENTS: Disabled
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Range: 0.001 to 1.000 pu in steps of 0.001
Range: 0.0 to 10.0% in steps of 0.1
Range: 0.001 to 1.000 pu in steps of 0.001
Range: 0.0 to 10.0% in steps of 0.1
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: FlexLogic operand
Range: FlexLogic operand
Range: FlexLogic operand
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
COMMAND
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