VA
Z1
IA
RFPG
Phase-to-ground
fault in phase A
Phase-to-phase
fault in phase A-B
Three-phase
fault
(Arc + tower
resistance)
0
KN·Z1
IN
VA
Z1
IA
VB
Z1
IB
RFPP
VA
Z1
IA
VC
Z1
IC
0.5·
RFPP
0.5·
RFPP
(Arc resistance)
Phase-to-ground
element
Phase-to-phase
element A-B
Phase-to-phase
element A-C
ANSI09000242_2_en.vsd
ANSI09000242 V2 EN
Figure 34:
Fault loop model
The Z1 in figure
represents the positive sequence impedance from the measuring point
to the fault location. The settings
RFPGx
(where
x
is 1-5 depending on selected zone) and
RFPPx
(where
x
is 1-5 depending on selected zone) are the eventual fault resistances in the
faulty place.
Regarding the illustration of three-phase fault in figure
, there is of course fault current
flowing also in the third phase during a three-phase fault. The illustration merely reflects
the loop measurement, which is made phase-to-phase.
The zone needs to be set to operate in Non-directional, Forward or Reverse direction
through the setting
DirModeZx
(where
x
is 1-5 depending on selected zone). The result
from respective set value is illustrated in figure
. The impedance reach is not symmetric,
in the sense that it conforms for forward and reverse direction (there are different forward
1MRK 506 335-UUS A
Section 6
Impedance protection
103
Technical manual
Содержание REL650 series
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