I am totally lost in a question, how can be derived the friction losses of a induction machine based on this equation (It wasn’t given explication about these nor the bibliography/source of this equation and I don’t find it in the Chapman,Stevenson,Sen, Beaty among others)

Im guessing that

  • \$T_{e}\$ is the motor torque

  • \$J\$ is work in Joules

  • \$\frac{2}{P}\$ 2 divided by the nominal power

  • \$\frac{d\omega_r}{dt}\$ the instant angular speed

  • \$T_{L}\$ The torque of the load

    But I dont have a idea how to justify the friction losses of a induction machine based on these equation

  • 1
    \$\begingroup\$ What is the context in which you found the equation? Why do you think it can be used to derive friction losses? \$\endgroup\$
    – user80875
    Commented May 27, 2018 at 17:45
  • \$\begingroup\$ Because I have found it unsolved in an old notebook in the "Induction Machines" theme. \$\endgroup\$
    – riccs_0x
    Commented May 27, 2018 at 18:09
  • 1
    \$\begingroup\$ Without some context, it is difficult to interpret. It could be used to determine the required motor rating for a load. With no load and known motor rotor inertia, it could be used in a coast-to rest test to determine the motor friction and aerodynamic drag. \$\endgroup\$
    – user80875
    Commented May 27, 2018 at 18:36
  • \$\begingroup\$ Thats the weird thing, I remember this one was told us just like that, with no more context. \$\endgroup\$
    – riccs_0x
    Commented May 27, 2018 at 21:20

1 Answer 1


I think that formula just says that the torque delivered to the load is equal to the load inertia, J, multiplied by the rotational acceleration, dw/dt plus the torque required to turn the load without acceleration. The 2/P term may be an adjustment for units of measure. If there is no external load, the torque developed by the rotor is equal to the torque required to accelerated the rotor inertia plus the torque losses consisting of friction and aerodynamic drag.


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