ABB 615 Series ANSI, Technical Manual

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Section 4
1MAC050144-MB C
Protection functions
254 615 series ANSI
Technical Manual
Equation 8
t(s) the Trip time in seconds
M
the excitation level (‘V/f ratio’ or ‘Volts/Hertz’) in pu
k the setting
Time multiplier
The IDMT curve parameters a, b and c are according to the following .
Table 255: Parameters a, b and c for different IDMT curves
Figure 120: Trip 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:
The constant “60” in converts time from minutes to seconds..
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

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



 
 
c
M b ak
e s t
100
60 ) (