ABB Relion REG670, Technical Manual

Page: 246 / 1298

In cases where the fault current infeed is more or less completely lack of zero sequence
nature (all phase currents in phase), the measurement will be performed in the phase-
to-earth loops only for a phase-to-phase-earth fault.
However, should it be desirable to use phase-to-earth (and only phase-to-earth) zone
measurement for phase-to-phase-earth faults, the setting
INReleasePE can be lowered
from its excessive default value to the level above which phase-to-earth measurement
should be activated.
7.4.7.4 Directional element
Several criteria are employed when making the directional decision. The basis is
provided by comparing a sum of positive sequence voltage and memory voltage with
phase currents. This has been the standard method up to now in the 600-series
(ZDRDIR). For extra security, especially in making a very fast decision, this method
is complemented with an equivalent comparison where, instead of the phase current,
the change in phase current is used. Moreover, a basic negative sequence directional
evaluation is taken into account as a reliable reference during high load condition.
Finally, zero sequence directional evaluation is used whenever there is more or less
exclusive zero sequence in-feed.
Fundamentally, the directional sectors that represent forward direction, one per
measuring loop, are defined by the following equations (examples for L1and L1L2
only):
− ° <
−
( )
⋅ + ⋅
( )
< °
15
1 1 1
120
1 1
1
arg
k U k U
I
L L M
L
EQUATION2546 V2 EN
(Equation 46)
− ° <
−
( )
⋅ + ⋅
( )
< °
15
1 1 1
120
1 2 1 2
1 2
arg
k U k U
I
L L L L M
L L
EQUATION2547 V2 EN
(Equation 47)
Where:
U1
L1
is the positive sequence phase voltage in phase L1.
U1
L1M
is the positive sequence memorized phase voltage in phase L1.
I
L1
is the phase current in phase L1.
U1
L1L2
is the voltage difference between phase L1 and L2 (L2 lagging L1).
U1
L1L2M
is the memorized voltage difference between phase L1 and L2 (L2 lagging L1).
I
L1L2
is the current difference between phase L1 and L2 (L2 lagging L1).
k is the factor determining the amount of memory voltage.
The corresponding reverse directional sectors range from 165 to -60 degrees. The
value of the k factor determining the amount of memory voltage used is normally 0.8.
Section 7
1MRK502052-UEN B
Impedance protection
240
Technical manual