Directional reverse
-90° > [ (angle(V2) +180°) - angle(I2) - RCA) ] > 90°
where RCA is the relay characteristic angle set in the DEF Char. Angle setting.
This is represented in the following figure:
V03523
For a forward direction, -V2 hs to be in the shaded area
For a reverse direction, -V2 has to be in the unshaded area
I2
I2 angle -RCA
Figure 114: Directional criteria for residual voltage polarization
5.4
AIDED DEF SETTING GUIDELINES
To use Aided DEF protection you need to set the polarization and the thresholds. Polarization can be achieved
using either zero sequence signals or negative sequence signals.
For zero sequence polarized Aided DEF, the typical zero sequence voltage on a healthy system can be as high as
1% (i.e.: 3% residual), and the voltage transformer (VT) error could be 1% per phase. A VNpol Set setting between
1% and 4%.Vn is typical, to avoid spurious detection on standing signals. The residual voltage measurement
provided in the MEASUREMENTS 1 column may assist in determining the required threshold setting during
commissioning, as this will indicate the level of standing residual voltage present. The Virtual Current Polarizing
feature will create a polarizing voltage, which is always large regardless of whether actual VN is present.
With Aided DEF, the residual current under fault conditions lies at an angle lagging the polarized voltage. Hence,
negative characteristic angle settings are required for Aided DEF applications. This is set in cell DEF Char. Angle in
the EARTH FAULT settings.
The following angle settings are recommended for a residual voltage polarized device:-
● Solidly earthed distribution systems: -45°
● Solidly earthed transmissions systems: -60°
If Virtual I Pol is set to ‘Disabled’ it prevents checking of the faulted phase and subsequent removal of the faulted
phase voltage. The aided DEF protection is then polarized by the residual voltage only.
For negative sequence polarization, the relay characteristic angle settings (DEF Char. Angle) must be based on the
angle of the upstream negative phase sequence source impedance. A typical setting is -60°.
Chapter 8 - Carrier Aided Schemes P543i/P545i
230 P54x1i-TM-EN-1
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