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.
As nominal power is the result of the multiplication of the nominal current and the nominal
voltage Pn = Vn × In, the calculation of the setting value for Power pickup value (×Pn)
depends on whether IG and VG or V0 are measured or calculated from the phase
quantities.
Table 398: Measured and calculated IG or I0 and VG or V0
Measured IG Calculated I0
Measured VG Pn = (VG, VT) × (IG, CT) Pn = (VG, VT) × (3I, CT)
Calculated V0 Pn = (3V, VT) × (IG, CT) Pn = (3V, VT) × (3I, CT)
Example 1. IG is measured with cable core CT (100/1A) and VG is measured from open
delta-connected VTs (20/sqrt(3) kV:100/sqrt(3) V:100/3 V). In this case, "Measured IG"
and "Measured VG" are selected. The nominal values for residual current and residual
voltage are obtained from CT and VT ratios.
Residual current IG: Configuration/Analog inputs/Current (IG, CT): 100 A:1 A
Residual voltage VG: Configuration/Analog inputs/Current (VG, VT): 11.547 kV:100
V
Residual Current pickup value of 1.0 × In corresponds then 1.0 × 100 A = 100 A in primary
Residual Voltage pickup value of 1.0 × Vn corresponds then 1.0 × 11.547 kV = 11.547 kV
in primary
Residual Power pickup value of 1.0 × Pn corresponds then 1.0 × 11.547 kV × 100 A =
1154.7kW in primary
Example 2. Both I0 and V0 are calculated from phase quantities. Phase CT-ratio is 100:1
A and Phase VT-ratio 20/sqrt(3) kV:100/sqrt(3) V. In this case "Calculated I0" and
"Calculated V0" are selected. The nominal values for residual current and residual voltage
are obtained from CT and VT ratios entered in:
Residual current I0: Configuration/Analog inputs/Current (3I, CT): 100 A:1 A
Residual voltage V0: Configuration/Analog inputs/Current (3V, VT): 20.000 kV:100
V
Residual Current pickup value of 1.0 × In corresponds then 1.0 × 100 A = 100 A in primary
Section 4 1MAC059074-MB A
Protection functions
416 615 series ANSI
Technical Manual
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