Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations IFRs on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

two speed motor

Status
Not open for further replies.

sparkknock

Electrical
Mar 21, 2007
1
how does a two speed motor work? does the motor start on half the windings and runs on all the windings or is the motor really split into two motors. the first motor start it and then both run it?
 
Replies continue below

Recommended for you

The windings are installed in groups. With a motor rated 1750/3500 RPM the groups will be connected so as to form 4 magnetic poles (2 north and 2 south) for 1750 RPM operation and connected to form 2 magnetic poles for 3500 RPM operation.
There is another technique called subsequent pole where the windings will be connected so as to form 4 poles, N, S, N, S.
The motor will approach a synchronous speed of 1800 RPM. (1750 more or less)
Half of the windings are then reversed to form N, N, N, N.
South poles are subsequently developed between the north poles and the motor approaches a synchronous speed of 900 RPM.
Depending on the winding pitch, not all motors are suitable for consequent pole operation.
The conventions "North" and "South" apply to instanteneous conditions. One half cycle later all the north poles will be south poles and vice versa.
respectfully
 
For single winding motors, the terminal leads are arranged for connections that allow reverse polarity on half of the winding groups, that way the poles could be doubled reducing the speed in one half (2/4 , 4/8, 6/12 etc, See NEMA MG1 for typical connections ). For two winding motors the stator has physically two independent windings assembled into the stator slots. The winding on idle condition is kept with the terminals open to avoid unwanted circulating currents.
 
Hello sparkknock,

Adding to the others comments note the Synch RPM = 120 F/P,
Where F is the line frecuency and P the pairs of poles, then the speed is dependant on the numbers of pair of poles and line frecuency.

You can find three kinds of two speed motors:

1. Dahlander conected, very well explained above.With only one winding making external conection you can obtain one speed or the double due to a P change, in this motors High Speed/Low Speed = 2.
2. PAM(pole amplitude modulation) With only one winding too the speed change is possible because the stator is windded with one special internal connection ,when the stator is energized, in one external connection, two differents magnetic field are produced, the superimposition of the two-fields result in an specific speed, in this motors the High speeed/Low speed is different than 2. (4/6 poles) or (2/8 poles).

3.Two separate windings or Dual wound: In this case, the simplest, the motor has two different windings windded in the same stator.

I hope this can help you

Best regards

Petronila
 
Hi Keith,

Three phase motors : you could have two or three windings windded in the same stator.

For two windings: one is dahlander and the other is normal = 3 speeds or two dahlanders= 4 speeds.

For three windings: two are dahlander and one normal= 5 speeds, Three dahlander= 6 speeds. One dahlander and two normal= 4 speeds.

The dahlander winding could be replaced with PAM winding.

For Single phase you can find one start winding with two run windings (4/6 poles) others single phase used in air conditioned matters change the speed adding turns by taps on the Run winding this cause a very slight speed change.

Regards

Petronila
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor