Re: What is a single phase electric motor and how does it work?

Hello Siew: The major difference between DC and AC motor design is 
the “type” of electricity used. Direct current flows from one polarity to 
the other whereas alternating current produces a stationary electron 
standing wave as the polarity periodically changes from positive to 
negative. Good starting references for you are found at Britannica on the 
Internet where ac and dc motors are explained with graphical references:
www.britannica.com/bcom/eb/article/2/0,5716,108542+17,00.html
www.britannica.com/bcom/eb/article/3/0,5716,32843+1+32282,00.html?
query=electric%20motor
www.britannica.com/bcom/eb/article/index/7/0,8377,108497,00.html

DC motors produce high initial torque by maximizing the magnetic pole 
repulsion. In order to do so, commutator and carbon brushes are used to 
switch the power to the windings at each pole. Single-phase induction 
motors require coercing to spin-up. That is accomplished by a similar 
commutation as used in the dc machines, or more often the rotation is 
achieved by introducing a capacitor driven winding.
www.britannica.com/bcom/eb/article/7/0,5716,108497+1+106019,00.html 

Single-phase simply means a two wire (plus safety wire earth ground) 
alternating current (AC) circuit. Power plants generate three phase 
alternating power, usually in a “Y” configuration. This circuit is 
composed of three high potential terminals (phases) separated by 120 
degrees of rotation angle. The low potential terminals are tied together 
and called the “neutral” conductor. Under ideal circumstances the neutral 
carries no current because the return currents from the three high 
potential phases cancel each other out. One Internet resource to explore 
is:
www.elec-toolbox.com/frames.html

Three phase systems can also be supported by a delta arrangement, a three-
wire system without a neutral. There are certain advantages and drawbacks 
in either configuration, and the architecture is defined to best 
accommodate the needs of users.

Transformers are devices that convert not only voltage (by the ratio of 
primary/secondary) turns but also reconfigure Y circuits into Delta 
circuits as well as single phase circuits. Graphical explanation can be 
found at:
www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm

If you have specific questions don’t hesitate to contact me through the 
MAD SCI organization. I will be happy to be of further assistance. Your 
MAD.SCI Micro.