t(s) Operate time in seconds
M Excitation level (U/f ratio or volts/hertz) in pu
k
Time multiplier
setting
The constant "60" in
Equation 135
converts time from minutes to
seconds.
Table 639: Parameters a, b and c for different IDMT curves
Operating curve type
setting
a b c
OvExt IDMT Crv1 2.5 115.00 4.886
OvExt IDMT Crv2 2.5 113.50 3.040
OvExt IDMT Crv3 2.5 108.75 2.443
Figure 352: Operating time curves for the overexcitation IDMT curve ("OvExt IDMT
Crv1") for parameters a = 2.5, b = 115.0 and c = 4.886
Overexcitation IDMT curve 4
The base equation for the IDMT curve "OvExt IDMT Crv4" is:
Protection functions
1MRS757644 H
678 620 series
Technical Manual
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