ABB RELION REX640 Technical Manual page 891

1MRS759142 F
t(s)
M
k
Table 843: Parameters a, b and c for different IDMT curves
Operating curve type
setting
OvExt IDMT Crv1
OvExt IDMT Crv2
OvExt IDMT Crv3
Figure 497: 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:
REX640
Technical Manual
Operate time in seconds
Excitation level (U/f ratio or volts/hertz) in pu
Time multiplier setting
Equation 249
The constant "60" in
seconds.
a
2.5
2.5
2.5
Protection functions
converts time from minutes to
b c
115.00 4.886
113.50 3.040
108.75 2.443
891