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Operating time check for IDMT curve
The testing circuit is shown in Figure 6.5.2.
Single-phase
current
source
+
DC
power
−
supply
Start
Time
counter
Stop
OV
One of the inverse time characteristics can be set, and the output signal numbers of the IDMT
elements are as follows:
Fix the time characteristic to test by setting the scheme switch MOC1 or MOC2 on the "OC"
screen.
"Settings" sub-menu → "Protection" screen → "Group ∗ " screen → "OC" screen
The test procedure is as follows:
•
Enter the signal number to observe the operating time at the monitoring jack A as shown in
Section 6.5.1.
•
Apply a test current and measure the operating time. The magnitude of the test current should
be between 1.2 × I s to 20 × I s , where I s is the current setting.
•
Calculate the theoretical operating time using the characteristic equations shown in Section
2.1.1. Check that the measured operating time is within IEC 60255-3 class 5.
A
Figure 6.5.2 Testing IDMT
Element
Signal No.
OC1I-A
20
24
OC2I-A
⎯
⎯
255
6 F 2 S 0 8 4 2
GRD150
TB1
1
-
2
-
A
Monitoring
jack
0V
TB4 -18
-19
-20
(E)
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