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Chapter 6) 7SR17 Commissioning and Maintenance Guide
Calculated Operate Time (s)
If the Thermal Overload Capacity Alarm is used, this can be tested by monitoring the Thermal Capacity in the
instruments menu. If the Thermal time constant is longer than a few minutes, this can be assessed during the
timing test above. If the Time Constant is less than a few minutes, a lower multiple of current will be required such
that the rate of capacity increase is slowed to allow monitoring of the instrument to be accurate.
Capacity Alarm Setting
Element Blocking
The Thermal element can be blocked by Binary Input Inhibit. This functionality should be checked.
Element
The cooling characteristic can be checked by timing the rate of reduction of the thermal capacity. A sufficiently
accurate check can be made using the restart inhibit feature. Programming this to operate an output contact and
to reset at 50% of thermal capacity. Start external timer at 100% (trip) level and stop the timer when 50% is
reached.
Depending on the selected cooling time constant (Gn 49 TauC Cooling Constant) the re-start inhibit, with setting
of 50% thermal capacity, should reset in the following times assuming the initial thermal state = 100%
Gn 49 TauC Cooling Constant
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49
1
2
3
4
5
10
15
20
25
30
50
100
Measured Operate Time (s)
Measured
BI Inhibits
Operate Time (sec)
41.6
83.2
124.8
166.4
207.9
415.9
623.8
831.8
1039.7
1247.7
2079.4
4158.9
©2014 Siemens Protection Devices Limited
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