ABB Relion REC615, Техническое руководство

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Y t Y t Y t Y t Y t Y
osum CPS osum osum osum osum osu _
( ) ( ) ( ) ( ) ( )
5 1 2 3 4
= + + + +
m m
t ( )
5
(Equation 39)
Figure 196: Principle of Cumulative Phasor Summing (CPS)
The CPS technique provides a stable directional phasor quantity despite individual
phasors varying in magnitude and phase angle in time due to a non-stable fault
type such as restriking or intermittent earth fault. This is also true for harmonic
components included in the sum admittance phasor. Harmonics have typically a
highly fluctuating character.
Harmonic components provide a more distinctive directional determination in
compensated networks than the fundamental frequency component. The higher
the frequencies, the compensation coil appears as very high impedance and the
harmonics are not affected by compensation coil and degree of compensation.
When harmonics are present, they cause the sum admittance phasor to behave as
in case of an unearthed network, where directional phasors point in fully opposite
directions in the faulty and healthy feeder.
The direction of the MFADPSDE function is defined with setting
Directional mode as
“Forward” or “Reverse”. The operation characteristic is defined by tilted operation
sector as illustrated in
Figure 197
. The characteristic provides universal applicability,
that is, it is valid both in compensated and unearthed networks, also 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 actual maximum expected
measurement errors.
In case of unearthed network operation, adequate tilt angle must be
allowed to ensure dependable operation of MFADPSDE.
In
Figure 198
, phasors 1...4 demonstrate the behavior of the directional phasor in
different network fault conditions.
• Phasor 1 depicts the direction of 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). In
1MRS758755 C Protection functions
REC615 & RER615
Technical Manual
393