is also valid in compensated networks when there are harmonic components
present in the fault quantities (typically low ohmic permanent or intermittent or
restriking fault). In this case, the result is valid regardless of network’s actual
compensation degree. Harmonics would turn the phasor align to the positive
Im(
)
Yo
axis.
• Phasors 3 and 4 depict the direction of accumulated sum admittance phasor
in case of higher-ohmic earth fault in the protected feeder without harmonics
in the fault quantities when the network is compensated. As no harmonic
components are present, the phase angle of the accumulated phasor is
determined by the compensation degree of the network. With high degree
of overcompensation, the phasor turns towards the negative
Im(
)
Yo
axis (as
phasor 4).
Figure 249: Directional characteristic of MFADPSDE
The residual current is recommended to be measured with accurate
core balance current transformer to minimize the measurement errors,
especially phase displacement. This is especially important, when high
sensitivity of protection is targeted.
Protection functions
1MRS757644 H
486
620 series
Technical Manual