60
6
F
2
S
0
8
3
4
2.4.4 High-Resistance
Earth Fault Protection
For a high-resistance earth fault for which the impedance measuring elements cannot operate, the
GRZ100 uses a directional earth fault element (DEF) to provide the following protections.
•
Directional earth fault command protection
•
Directional inverse or definite time earth fault protection
Figure 2.4.4.1 shows the scheme logic for the directional earth fault protection. The four kinds of
protection above can be enabled or disabled by the scheme switches [SCHEME], [CRSCM],
[DEFFEN] and [DEFREN]. The DEF and EF protections issue an alarm individually for the
backup trip for earth fault. The DEF protection can be blocked by the binary input signal (PLC
signal) DEF_BLOCK.
NON VTF
Command
Protection
&
CB-DISCR
&
M-TRIP
DEFR
DEFF
&
&
≥
1
[DEFFEN]
TDEF
t
0
0.00 - 10.00s
"ON"
DEF_ALARM
[SCHEME]
S-TRIP
(from Figure 3.2.1.2.)
59
58
186
DEF_BLOCK
1629
≥
1
[DEFREN]
TDER
t
0
0.00 - 10.00s
"ON"
[CRSCM]
"ON"
+
&
DEF_INST_TP
1705
&
DEFR_INST_TP
1707
[DEFBTAL]
"ON"
"
[DEFI]
NOD "
" R "
F "
EFI
&
61
EFI_BLOCK
1628
&
&
"
≥
1
BU TRIP
(M-TRIP)
677
763
194
≥
1
DEF_TRIP
DEFR_
TRIP
184
EFI_TRIP
DEFF_BLOCK
1849
DEFR_BLOCK
1851
Figure 2.4.4.1 Directional Earth Fault Protection
The directional earth fault command protection provides the POP, UOP and BOP schemes using
forward looking DEFF and reverse looking DEFR elements. All schemes execute three-phase
tripping and autoreclose.
The command protection is disabled during a single-phase autoreclosing period (CB-DISCR=1).
The directional earth fault protection as backup protection is described in Section 2.4.4.2.
The directional earth fault element DEF provides selective protection against a high-resistance
earth fault. The direction of earth fault is determined by the lagging angle (
θ
) of the residual
current (3l0) with respect to the residual voltage (
−
3V0). The residual voltage and residual current
are derived from the vector summation of the three-phase voltages and three-phase currents inside
the relay.
The phase angle
θ
in the event of an internal fault is equal to the angle of the zero-sequence
impedance of the system and in the directly-earthed system this value ranges approximately from
50
°
to 90
°
.
θ
of the DEF can be set from 0
°
to 90
°
. The minimum voltage necessary to maintain
directionality can be set from 1.7 to 21.0 V.
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