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6.5.1.5 Restricted earth fault element REF
The restricted earth fault element is checked on the following items.
• Operating current value
• Percentage restraining characteristic
Note: Set all the CT ratio matching settings (1kct1 - 1kct3 to 3kct1 - 3kct3) to "1", because the
operating value depends on the settings.
Operation current value
The testing circuit is shown in Figure 6.5.7.
Single-phase
current
source
A
TB1
DC
voltmeter
TB4
-7
-8
-
A
16
-
A
17
E
GRT100
DC
power
supply
+
−
Monitoring
j
ack
A
0V
+
−
+
−
I
N
Figure 6.5.7 Operating Current Value Test of REF_DIF element (Model 100s, 200s)
The test current input terminal number and output signal number of the REF_DIF element is as
follows:
Element Input terminal
number
Output signal
number
1REF_DIF TB1-7 and –8 29
2REF_DIF TB1-15 and –16
30
3REF_DIF TB1-23 and –24
31
• Press 4 (= Logic circuit) on the "Test" sub-menu screen to display the "Logic circuit"
screen.
• Enter the signal number 29 to observe the 1REF_DIF output at monitoring jack A and press
the
ENTER
key.
• Apply a test current to TB1-7 and -8 and change the magnitude of the current applied and
measure the value at which the element operates.
Check that the measured value is within 15% of the theoretical operating value.
Theoretical operating value = (CT secondary rated current) × (1ik setting)