Sevcon Gen4 - Torque Required at Maximum Speed; Continuous Power Rating

System design
Doc. # 177/52701
Rev. 3.3
5-3
Torque required at maximum speed
Calculate the torque as above. As speed increases beyond base speed the maximum torque an
induction motor can supply falls as defined by the following two equations:
In the constant power region;









rat ed
T
T


max
In the high speed region;
2
max









rated
T
T


This is shown in Figure 11. Select a motor with a torque rating greater than the peak torque
required.
Figure 11 Torque speed curve
Continuous power rating
The required continuous power rating of the motor is governed by the application load cycle over
a shift. Use the maximum RMS current over a period of one hour to determine the motor rating
required. The motor manufacturer will typically specify a 1 hour or continuous rating. Select a
motor whose ratings are equal to or greater than your calculated load over 1 hour.
Torque speed curve for a typical induction motor
0
0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Speed (pu)
Torque (pu)
breakdown torque rated torque
constant power region
high speed region