Directional Earth Fault Protection - Toshiba GRL100-701B Instruction Manual

2.4 Directional Earth Fault Protection

For a high-resistance earth fault for which the impedance measuring elements cannot operate, the
GRL100 uses a directional earth fault element (DEF) to provide the following protections.
• Directional earth fault command protection
• Directional inverse or definite time earth fault backup protection
Figure 2.4.1 shows the scheme logic for the directional earth fault protection. The two kinds of
protection above can be enabled or disabled by the scheme switches [DEFCR], [CRSCM],
[DEFFEN] and [DEFREN]. The DEF command protection or DEF backup protection can be
blocked by the binary input signal (PLC signal) DEF∗_BLOCK or DEFCRT_BLOCK.
CB-DISCR
(from Figure 3.2.1.2.)
[DEFCR]
+
DEFF_BLOCK
1897
611
DEFF
NON VTF
DEFF_INST_TP
1945
DEFR_BLOCK
1899
612
DEFR
DEFR_INST_TP
1947
EFI_BLOCK
1592
72
EFI
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 2.4.2.
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 (3l 0 ) with respect to the residual voltage (−3V 0 ). 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.
&
&
"ON"
[DEFFEN]
&
"ON"
[DEFREN]
&
"ON"
[EFIBT]
" F "
&
" R "
" NOD "
Figure 2.4.1 Directional Earth Fault Protection
 76 
[SCHEME]
Command
Protection
1875 DEFCRT_BLOCK
TDEF
t 0
≥1
0.00 - 10.00s
&
DEFF_TRIP
TDER 810
t 0
811
≥1
DEFR_
TRIP
0.00 - 10.00s
&
EFI_TRIP
117
≥1
&
&
6 F 2 S 0 8 5 0
S-TRIP
&
M-TRIP
18
≥ 1
BU TRIP
(M-TRIP)