Thermal Overload Protection; 50/51 Phase Overcurrent - Siemens Reyrolle 7SR5 Manual

Functional Tests
9.10 Protection Functional Tests

49 Thermal Overload Protection

9.10.10
The current can be applied from a 3P balanced supply or phase by phase from a 1P supply. Alternatively the 3
phase current inputs can be connected in series and injected simultaneously from a single 1P source.
The Thermal Overload setting and Time Constant setting can be considered together to calculate the
operating time for a particular applied current.
The following table lists operate times for a range of Time Constant settings for an applied current of 2
times the Thermal Overload setting. Ensure that the thermal rating of the relay is not exceeded during this
test.
Time Constant (min)
1
2
3
4
5
10
15
20
25
30
50
100
The Thermal State must be in the fully reset condition in order to measure the operate time correctly. This
can be achieved by setting change in the Thermal Protection settings menu or by pressing the Test/
Reset button when the Thermal Meter is shown in the Instruments mode.
Reset the thermal state then apply 2 times the Overload setting current.
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 instru-
ment to be accurate.
Capacity Alarm Setting
Element Blocking
The thermal element can be blocked by Binary Input Inhibit. This functionality should be checked.
Element
49
9.10.11

50/51 Phase Overcurrent

Some other current protection functions may overlap with these functions during testing, it may be useful to
disable some functions to avoid ambiguity. It should be particularly noted that if the function is enabled, the
51C Cold Load settings may modify the normal 50-n and 51-n settings if the CB is open during testing.
Voltage inputs may not be required for this function if the Phase Overcurrent functions are not directional
but it may be advantageous to apply balanced 3 phase nominal rated voltage to the VT inputs during testing
430
Operate Time (s)
17.3
34.5
51.8
69
86.3
173
259
345
432
51.8
863
1726
Measured Operate Time (s)
Measured
BI Inhibits
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019