# Induction motor higher starting torque

After a refresher about basic principle of Induction motor, I realized that the torque developed by induction motor is
$$\tau$$ = P$${gap}_$$ / $$\omega$$$${s}_$$

Where P$${gap}_$$ is amount of power crossing air gap from the stator to the rotor.

In case of wound rotor motors, starting torque can be increased by temporarly connecting external resistors in the rotor winding. However no such method is available in case of squiral cage.
I am currently thinking that keeping in view the above equation, it should be possible to increase the starting torqe by decreasing $$\omega$$$${s}_$$. So, it decrease it, no of poles should be increased. Although I haven't currently thought of specific winding and switching mechanisim, do you think it might be possible to achieve higher starting by say temporarly switching a 2-pole machine to 4-pole machine during starting?

Edit: sorry for the misaligned 'latex'. I tried but couldn't make it work. Why do you call it latex? Because you use latin words? And also isn't the admin reasearching on more intutive and easier method for 'latex'. Sorry, if I questioned things out of my business.

I am using a 1/4 HP 4-pole repulsion-start, induction-run motor on a buffer/grinder, and a 1/2 HP repusion start, induction run motor on a 14" bandsaw. One (Century Electric, patent date 1915) has a radial commutator (see picture). It has higher torque and lower starting current than a similar capacitor-start motor. The repulsion-start motors have a second squirrel cage that is selectively shorted by the brushes on the repulsion-start commutator.

RE Latex- I think it stands for Los Alamos tex. Test your equations at

test Latex equations here http://www.equationsheet.com/textoimage.php

Is this what you mean?

$$\tau = \frac{P_g_a_p}{\omega s}$$

Is P the power per pole (the total power divided by the number of poles)?

Bob S

#### Attachments

• Motor Repulsion 010.jpg
51.2 KB · Views: 1,201
Last edited:
P is the TOTAL power crossing the air gap from stator to the rotor i.e. Total input power less the stator losses.