ABB 615 series Technical Manual page 378

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Protection functions

GUID-1C8D95FA-FA08-4869-B74B-40D2096F160F V1 EN

Functional module diagram

Neutral admittance calculation

The residual current can be selected from the IG or I0 setting. The setting options are

"Measured IG" and "Calculated I0". If "Measured IG" is selected, the current ratio for IG-

channel is given in Configuration/Analog inputs/Current (IG,CT). If "Calculated I0"

is selected, the current ratio is obtained from phase-current channels given in

Configuration/Analog inputs/Current (3I,CT).

Respectively, the residual voltage can be selected from the Vg or V0 setting. The setting

options are "Measured VG" and "Calculated V0". If "Measured VG" is selected, the

voltage ratio for VG-channel is given in Configuration/Analog inputs/Voltage

(VG,VT). If "Calculated V0" is selected, the voltage ratio is obtained from phase-voltage

channels given in Configuration/Analog inputs/Voltage (3V,VT).

Example 1: VG is measured from open-delta connected VTs (20/sqrt(3) kV : 100/sqrt(3)

V:100/3 V). In this case, "Measured VG" is selected. The nominal values for residual

voltage is obtained from the VT ratios entered in Residual voltage VG: Configuration/

Analog inputs/Voltage (VG,VT): 11.547 kV : 100 V. The residual voltage pickup value

of 1.0 × Vn corresponds to 1.0 × 11.547 kV = 11.547 kV in the primary.

Example 2: V0 is calculated from phase quantities. The phase VT-ratio is 20/sqrt(3) kV :

100/sqrt(3) V. In this case, "Calculated V0" is selected. The nominal value for residual

voltage is obtained from the VT ratios entered in Residual voltage V0 : Configuration/

Analog inputs/Voltage (3V,VT) : 20.000kV : 100V. The residual voltage pickup value

of 1.0 × Vn corresponds to 1.0 × 20.000 kV = 20.000 kV in the primary.

In case, if "Calculated V0" is selected, the residual voltage nominal value

is always phase-to-phase voltage. Thus, the valid maximum setting for

residual voltage pickup value is 0.577 × Vn. The calculated V0 requires

that all three phase-to-ground voltages are connected to the protection

relay. V0 cannot be calculated from the phase-to-phase voltages.

When the residual voltage exceeds the set threshold Voltage pickup value, a ground fault

is detected and the neutral admittance calculation is released.

characteristics

1MAC059074-MB A

615 series ANSI

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