ABB RELION 620 Series Technical Manual page 308

Section 4
Protection functions
302
GUID-47898DF5-3AC0-4EFC-AC30-23A0BBECE133 V1 EN
Figure 136: An example of a delayed reset in the inverse time characteristics. When
the pickup becomes active during the reset period, the trip time counter
continues from the level corresponding to the drop-off (reset time = 0.50 ·
Cooling time)
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
 
( ) = 60 ⋅
t s e
GUID-5D74EA35-03AD-44D1-9EE0-0B1999C55BF1 V1 EN
t(s) the trip time in seconds
M excitation level (V/f ratio or volts/hertz) in pu
Time multiplier setting
k the
The constant "60" in Equation 10 converts time from minutes to seconds.
1MAC504801-IB E
(Equation 10)
620 series ANSI
Technical Manual