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6.5.1.8 Thermal overload element THR
The testing circuit is shown in Figure 6.5.12.
Single-phase
current
source
A
TB1
-1
-2
I
a
GRT100
Monitoring
j
ack
A
0V
TB4
-
A
16
-
A
17
E
DC
power
supply
+
−
Time
counter
Start
Stop
OV
+
−
Figure 6.5.12 Testing THR (Model 100s, 200s)
The output signal of testing element is assigned to the monitoring jack A.
The output signal numbers of the elements are as follows:
Element Signal No.
THR-S 83
THR-A
87
To test easily the thermal overload element, the scheme switch [THMRST] in the "Switch" screen
on the "Test" menu is used.
• Set the scheme switch [THMRST] to "ON".
• Enter the signal number to observe the operation 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 10 × I
s
, where I
s
is the current setting.
CAUTION
After the setting of a test current, apply the test current after checking that the THM% has
become 0 on the "Metering" screen.
• Calculate the theoretical operating time using the characteristic equations shown in Section
2.10.6. Check that the measured operating time is within 5%.