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16, 1708
A
17, 1709
OC4
B
18, 1710
C
OP. BLOCK
[OC4-2F]
+
&
"BLK"
ICD
[OC4EN]
+
"ON"
1539
OC4 BLOCK
Figure 2.1.12
Earth fault overcurrent protection
Figure 2.1.13 and Figure 2.1.14 show the scheme logic of the earth fault overcurrent protection
EF1 and EF2 with selective definite time or inverse time characteristic.
The definite time protection is selected by setting [MEF1] and [MEF2] to "DT". Definite time
overcurrent elements EF1D and EF2D are enabled for EF1 and EF2 earth fault protection
respectively, and trip signal EF1 TRIP and EF2 TRIP are given through the delayed pick-up timer
TEF1 and TEF2.
The inverse time protection is selected by setting [MEF1C] and [MEF2C] to any one of "IEC",
"IEEE", "US" or "CON" according to the IDMT characteristic to employ. Inverse time
overcurrent elements EF1I and EF2I are enabled for EF1 and EF2 earth fault protection
respectively, and trip signal EF1 TRIP and EF2 TRIP are given.
ICD is the inrush current detector ICD, which detects second harmonic inrush current during
transformer energisation, and can block the EF1D and EF2D elements by the scheme switches
[EF1-2F] and [EF2-2F] respectively. See Section 2.1.7.
EFHS element is used for blocked overcurrent protection. See Section 2.1.1.9.
The EF1 and EF2 protections can be disabled by the scheme switches [EF1EN] and [EF2EN] or
PLC logic signals EF1 BLOCK and EF2 BLOCK.
Figure 2.1.15 and Figure 2.1.16 show the scheme logic of the definite time earth fault protection
EF3 and EF4. The EF3 and EF4 give trip and alarm signals EF3 TRIP and EF4 ALARM through
delayed pick-up timers TEF3 and TEF4.
The EF3 and EF4 protections can be disabled by the scheme switches [EF3EN] and [EF4EN] or
PLC logic signals EF3 BLOCK and EF4 BLOCK.
The EF3 and EF4 can also be blocked by the ICD.
&
&
&
0.00 - 300.00s
1
OC4 Definite Time Phase Overcurrent Protection
⎯
⎯
21
TOC4
0
t
0
t
0
t
≥ 1
6 F 2 S 0 8 4 2
398
OC4-A ALARM
399
OC4-B ALARM
400
OC4-C ALARM
397
OC4 ALARM
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