ABB RELION 620 Series Technical Manual page 466

Section 4
Protection functions
460
calculated continuously and it is available in the monitored data view. The power is
given in relation to nominal power calculated as Pn = Un × In, where Un and In are
obtained from the entered voltage transformer and current transformer ratios entered,
and depend on the Io signal Sel and Uo signal Sel settings.
Level detector
Level detector compares the magnitudes of the measured operating quantity (residual
current Io), polarizing quantity (residual voltage Uo) and calculated residual power to
the set Current start value (×In), Voltage start value (×Un) and Power start value
(×Pn) respectively. When all three quantities exceed the limits, Level detector enables
the Timer module.
When calculating the setting values for Level detector, it must be considered that the
nominal values for current, voltage and power depend on whether the residual
quantities are measured from a dedicated measurement channel or calculated from
phase quantities, as defined in the Io signal Sel and Uo signal Sel settings.
For residual current Io, if "Measured Io" is selected, the nominal values for primary
and secondary are obtained from the current transformer ratio entered for residual
current channel Configuration/Analog inputs/Current (Io, CT). If "Calculated Io"
is selected, the nominal values for primary and secondary are obtained from the
current transformer ratio entered for phase current channels Configuration/Analog
inputs/Current (3I, CT).
For residual voltage Uo, if "Measured Uo" is selected, the nominal values for primary
and secondary are obtained from the voltage transformer ratio entered for residual
voltage channel Configuration/Analog inputs/Voltage (Uo, VT). If "Calculated
Uo" is selected, the nominal values for primary and secondary are obtained from the
voltage transformer ratio entered for phase voltage channels Configuration/Analog
inputs/Voltage (3U, VT).
Calculated Uo requires that all three phase-to-earth voltages are
connected to the protection relay. Uo 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 = Un × In, the calculation of the setting value for Power start value
(×Pn) depends on whether Io and Uo are measured or calculated from the phase
quantities.
Table 460: Measured and calculated Io and Uo
Measured Uo
Calculated Uo
Example 1. Io is measured with cable core CT (100/1A) and Uo is measured from
open delta-connected VTs (20/sqrt(3) kV:100/sqrt(3) V:100/3 V). In this case,
Measured Io
Pn = (Uo, VT) × (Io, CT)
Pn = (3U, VT) × (Io, CT)
1MRS757644 F
Calculated Io
Pn = (Uo, VT) × (3I, CT)
Pn = (3U, VT) × (3I, CT)
620 series
Technical Manual