Part Winding Start Motors 2

[viperone]

I am having a disagreement with another electician over the size of internal windings in a part winding start motor. He claims the start windings are wound with larger wire since they experience a higher current inrush. All my literature says the motor draws approximately 65% inrush at start up and cannot find any information on the windings. Can you help me settle this.
Thank you in advance,
viperone.

 

[motorsdirect]

Hi.
Part start windings normally use the same size conductors, but only use a % of the winding on start up.....i.e. 60/40....using 60% of the windings for a softer, or lower current start up.
hope this is of some help
Jeff

http://www.motors-direct.co.uk

 

[aolalde]

“A standard Part-Winding-Start induction motor is arranged so that one-half of its primary winding can be energized initially and, subsequently, the remaining half can be energized, both halves then carrying equal current (NEC 430-3).”

In general part-winding-start motors have the standard type and the winding almost that of a standard dual voltage motor.

Special applications could have variations of this “50% standard array”. Motors with two poles could develop cusps in the speed-torque curve when part-winding started.

 

[jraef]

Inrush current is not the primary determining factor in deciding on conductor size for motor windings. Continuous current is more relevant, inrush is used in a "double check" of sorts once the continuous current requirements are satisfied. It is also incredibly impractical for a motor manufacturer to switch wire sizes when winding a stator so they will be the same size, selected based on the worst-case continuous current application.

Your buddy is wrong. He buys the next beer.

"Venditori de oleum-vipera non vigere excordis populi"

 

[acmotorengineer]

to viperone:

There is one case where the part winding start leads are larger. For 9-lead, delta connected, dual voltage, suitable for PWS on the low voltage, the 1-2-3 leads are normally larger than the remaining 6 leads. However this is for cost reasons rather than current sizing

Also some modern motors do not use true "part" windings anymore. They use a center tapped delta -- which uses the whole winding to start, but has the characteristics of a true "part" winding. This confuses some electricans who expect a split winding and find continuity on all leads.

to jrael:

There are some special application motors which must be sized for starting --- high inertia centrifuges comes to mind.

to aolalde:

There are other fractional part winding starts -- i.e. 2/3 part winding, where the current balance is unequal.

to motorsdirect:

I would be interested in seeing a 60/40 connection.