ABB 615 series Technical Manual page 654

Section 4
Protection functions
648
Overexcitation IDMT curves 1, 2 and 3
The base equation for the IDMT curves "OvExt IDMT Crv1", "OvExt IDMT Crv2" and
"OvExt IDMT Crv3" is:
ak b 100 M
+ −
 
 
c
 
t s ( ) = 60 e
⋅
GUID-5D74EA35-03AD-44D1-9EE0-0B1999C55BF1 V1 EN
t(s) Trip time in seconds
M Excitation level (V/f ratio or volts/hertz) in pu
Time multiplier setting
k
The constant "60" in
Table 557: Parameters a, b and c for different IDMT curves
Operating curve type a
setting
OvExt IDMT Crv1 2.5
OvExt IDMT Crv2 2.5
OvExt IDMT Crv3 2.5
Equation 122 converts time from minutes to seconds.
b
115.00
113.50
108.75
1MAC059074-MB A
(Equation 122)
c
4.886
3.040
2.443
615 series ANSI
Technical Manual