ABB RELION REX640 Technical Manual page 536

Section 4
Protection functions
530
The direction of MFADPSDE is defined with setting Directional mode as "Forward"
or "Reverse". The operation characteristic is defined by a tilted operation sector as
illustrated in Figure 289. The characteristic provides universal applicability, that is, it
is valid in both compensated and unearthed networks even if the compensation coil is
temporarily switched off. The tilt of the operation sector is defined with setting Tilt
angle to compensate the measurement errors of residual current and voltage
transformers. The typical setting value of 5 degrees is recommended, but it should
always reflect the maximum expected measurement errors.
In case of unearthed network operation, an adequate tilt angle must be
allowed to ensure dependable operation of MFADPSDE.
In Figure 289, phasors 1...4 demonstrate the behavior of the directional phasor in
different network fault conditions.
• Phasor 1 depicts the direction of the accumulated sum admittance phasor in case
of earth fault outside the protected feeder (assuming that the admittance of the
protected feeder is dominantly capacitive). The result is valid regardless of the
fault type (low ohmic, high(er) ohmic, permanent, intermittent or restriking). If
harmonic components are present in the fault quantities, they turn the phasor
alignment to the negative Im(Yo) axis.
• Phasor 2 depicts the direction of accumulated sum admittance phasor in case of
earth fault inside the protected feeder when the network is unearthed. The result
is also valid in compensated networks when there are harmonic components in
the fault quantities (typically low-ohmic permanent, 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 a high degree of overcompensation,
the phasor turns towards the negative Im(Yo) axis (as phasor 4).
1MRS759142 C
REX640
Technical Manual