[Default] On Tue, 12 Feb 2013 13:48:56 -0800,"Frank Shields" <[email protected]> wrote:
>I wonder what they consider ?full load? when rating the motor. Must be some >torque percentage of the HP value or something Frank The no load speed of an induction motor is near enough the supply frequency for a 2 pole motor( double the number of poles and the synchronous rpm halves), so 60Hz is 60 x 60 rpm or 3600. At this speed the motor is only drawing enough power from the grid to overcome frictional losses. The voltage you apply to the motor is matched by a back electromotive force, a sort of opposing voltage, that is induced in the windings by the magnetic force induced in the rotor. As soon as you put a load on the motor it slows and the back emf is reduced but the applied voltage is the same, the difference between these voltages is what drives a current through the motor and produces power. The rated power of an induction motor is thus developed when there is an optimum slip, say about 10% which would give a speed of 3240rpm. If you reduce the forward voltage below the designed voltage for the same load the slip would increase beyond 10%, the motor would slow but the current would not reduce as much, so the heating effect would increase and ultimately the motor would burn out. AJH _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://www.bioenergylists.org/
