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5-248 C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL

GROUPED ELEMENTS CHAPTER 5: SETTINGS

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

COMMAND menu to

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.



NTRL VOL UNBAL 1

STG 3 PKP: 0.020 pu

Range: 0.001 to 1.000 pu in steps of 0.001



NTRL VOL UNBAL 1

STG 3 SLOPE: 5.0%

Range: 0.0 to 10.0% in steps of 0.1



NTRL VOL UNBAL 1

STG 4 PKP: 0.030 pu

Range: 0.001 to 1.000 pu in steps of 0.001



NTRL VOL UNBAL 1

STG 4 SLOPE: 5.0%

Range: 0.0 to 10.0% in steps of 0.1



NTRL VOL UNBAL 1 STG

1 PKP DELAY: 30.00 s