49 Thermal Overload Protection
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)
Operate Time (s)
1
17.3
2
34.5
3
51.8
4
69
5
86.3
10
173
15
259
20
345
25
432
30
51.8
50
863
100
1726
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)
Measured 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
Measured
Element Blocking
The thermal element can be blocked by
Binary Input Inhibit
. This functionality should be checked.
Element
BI Inhibits
49
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
9.10.10
9.10.11
Functional Tests
9.10 Protection Functional Tests
430
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019