ABB 615 Series - Page 654

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:
t s e
ak b M
c
( ) = ⋅
+ −






60
100
GUID-5D74EA35-03AD-44D1-9EE0-0B1999C55BF1 V1 EN (Equation 122)
t(s)
Trip time in seconds
M Excitation level (V/f ratio or volts/hertz) in pu
k Time multiplier setting
The constant "60" in Equation 122 converts time from minutes to seconds.
Table 557: 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
Section 4 1MAC059074-MB A
Protection functions
648 615 series ANSI
Technical Manual