Torque Required At Maximum Speed; Continuous Power Rating - Sevcon Gen4 Applications Reference Manual

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;
T

max
T
 

   

 
rated
In the high speed region;
T

max
T
2
 

   

 
rated
This is shown in Figure 11. Select a motor with a torque rating greater than the peak torque
required.
3.5
3
2.5
2
1.5
1
0.5
0
0 0.5
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.
Doc. # 177/52701
Rev. 3.3
Torque speed curve for a typical induction motor
constant power region
1 1.5 2
Speed (pu)
breakdown torque
System design
high speed region
2.5 3 3.5
rated torque
4 4.5
5-3