Earth Fault Protection - Toshiba GRL150-100 Series Instruction Manual

2.4 Earth Fault Protection

The standard earth fault protection is available in models 110/410, and provides four independent
overcurrent thresholds EF1 to EF4. Protection functionality is the same as for the phase fault
elements, only with more sensitive current thresholds.
For models 110/410, the earth fault quantity is measured directly by connecting the input in the
residual circuit of the phase CTs.
2.4.1 Scheme Logic
Figure 2.4.1.1 to Figure 2.4.1.4 show the scheme logic of the earth fault protection EF1 to EF4.
The EF1 protection provides selective definite time or inverse time characteristic as shown in
Figure 2.4.1.1. The definite time protection is selected by setting [MEF1] to "DT", and the trip
signal EF1 TRIP is given through the delayed pick-up timer TEF1. The inverse time protection is
selected by setting [MEF1] to any one of "IEC", "IEEE", "US" or "CON" and then setting
[MEF1C] according to the required IDMT characteristic, and the trip signal EF1 TRIP is given.
Figure 2.4.1.2 to Figure 2.4.1.4 show the scheme logic of the definite time earth fault protection
EF2 to EF4. The EF2 to EF4 give trip and alarm signals EF2 TRIP, EF3 TRIP and EF4 ALARM
through the delayed pick-up timers TEF2, TEF3 and TEF4 respectively.
The signal EF1-INST to EF4-INST are available to trip instantaneously for a fault.
The EF1 to EF4 protection can be disabled by the scheme switches [EF1EN] to [EF4EN] or the
binary input signals EF1 BLOCK to EF4 BLOCK respectively.
ICD is the inrush current detector ICD, which detects second harmonic inrush current during
transformer energisation, and can block the EF elements by the scheme switch [OC-ICD]. See
Section 2.10. The logic logic sequence is configured by the PLC.
EF1
EF1
(INST)
EF1_INST_TP
1624
+
373
ICD
1683
By PLC
EF1_BLOCK
1560
112
≥1
128
&
≥1
[MEF1]
"IEC"
"IEEE"
"US"
"CON"
"DT"
EF1-EN
+
"ON"
OC_IC_BLK 1
&
[OC-ICD]
(+)
" "
BLK
1
Figure 2.4.1.1 EF1 Earth Fault Protection
&
&
⎯ 28 ⎯
6 F 2 S 0 8 2 8
TEF1
t 0 292
&
≥1
0.00 - 300.00s
&
EF1_TRIP