SINUS PENTA
PROGRAMMING
INSTRUCTIONS
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42.2.3.
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A X IMUM
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NHA NCE D
If a more precise calculation is required, when the ratio between LRC and FLC is different from 7.2, you can refer to the
graph below, where the x axis shows the LRC/FLC ratio, and the y axis shows the multiplicative constant to be applied
to the LRT to calculate the value of parameter
C267
:
Figure 61: Set up of parameter C267 depending on the LRC/FLC ratio.
Example 1b:
When using a 7.5kW motor, the multiplicative constant corresponding to an LRC/FLC=8.2 is approx. 46
if referring to the graph above.
As a result, the motor thermal time constant that you would select is 27.3 x 46,
C267
= 1257s, which is a more
accurate value than 1080s computed in Example 1a.
Example 2:
The 250kW motor in Table 106 can be approximated to have a trip class of:
690 x 79
IEC Class = ------------- = 90.85
100 x 6
Because this value is not given in Table 105, the motor thermal time constant that you would select is directly
C267
=
90.85 x 36 = 3260s, or 90.85 x 33 = 2998s if the value “33” is considered, resulting from Table 106 with a ratio between
LRC/FLC=6.9.
