ABB RELION REX640 Technical Manual page 560

Protection functions
Y
osum CPS
Y
osum CPS
Figure 321: 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 an unstable fault
type such as a restriking or intermittent earth fault. This is also true for harmonic
components included in the sum admittance phasor. Harmonics typically have a
highly fluctuating character.
Harmonic components provide a more distinctive directional determination in
compensated networks than the fundamental frequency component. With higher
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 opposite
directions in the faulty and healthy feeder.
The direction of MFADPSDE is defined with setting
or "Reverse". The operation characteristic is defined by a tilted operation sector as
illustrated in
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.
Figure 322
In
different network fault conditions.
560
( ) t Y ( ) t Y
= +
_ osum
4 1
( ) t Y ( ) t Y
= +
_ osum
5 1
Figure 322
. The characteristic provides universal applicability, that is, it
In case of unearthed network operation, adequate tilt angle must be
allowed to ensure dependable operation of MFADPSDE.
, phasors 1...4 demonstrate the behavior of the directional phasor in
( ) t Y ( ) t Y
+ +
osum osum
2 3
( ) t Y ( ) t Y
+ +
osum osum
2 3
1MRS759142 F
( ) t
osum
4
( ) t Y t ( )
+
osum osu m m
4 5
Directional mode as "Forward"
Technical Manual
(Equation 94)
(Equation 95)
REX640