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CHAPTER 5: SETTINGS GROUPED ELEMENTS

C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 5-213

Up to three identical neutral current unbalance elements, one per each installed CT/VT module.

The neutral current unbalance element responds to a differential current signal measured as a vectorial current difference

between neutral currents of parallel banks. In case of ungrounded banks, regular, preferably low-ratio CT can be used. In

case of grounded banks, a window or core-balance CT shall be used for increased accuracy/sensitivity.

The function applies simplified compensation for the inherent bank unbalance. Accurate compensation requires three

balancing factors that are difficult to measure in practical situations. Instead, a simple and practical compensation

responding to both the positive-sequence current and negative-sequence current is applied. This method is easy to apply

and remains accurate as long as the zero-sequence bank currents are relatively small. Under large zero-sequence bank

currents, the applied method of compensation for the inherent bank unbalance is less accurate. The solution to this

problem is to use a small portion of the zero-sequence current at the bank terminals to produce extra restraint and

preserve high sensitivity of this protection method.

By setting both the slope and the inherent unbalance compensating factor to zero, one can apply the function as a plain

overcurrent element responding to the split-phase neutral current.

The relay allows manual setting of the inherent unbalance factor or automatic setting via a dedicated command. For more

information, see the Application of Settings chapter.



NTRL CUR UNBALCE 1

STG 2 PKP: 0.030 pu

Range: 0.001 to 5.000 pu in steps of 0.001



NTRL CUR UNBALCE 1

STG 2 SLOPE: 2.0%

Range: 0.0 to 10.% in steps of 0.1



NTRL CUR UNBALCE 1

STG 3 PKP: 0.040 pu

Range: 0.001 to 5.000 pu in steps of 0.001



NTRL CUR UNBALCE 1

STG 3 SLOPE: 2.0%

Range: 0.0 to 10.% in steps of 0.1



NTRL CUR UNBALCE 1

STG 4 PKP: 0.050 pu

Range: 0.001 to 5.000 pu in steps of 0.001



NTRL CUR UNBALCE 1

STG 4 SLOPE: 5.0%

Range: 0.0 to 10.% in steps of 0.1



NTRL CUR UNBALCE 1

STG 1 DEL: 30.00 s