The windings of motors are available in many different forms. This article will discuss 3-phase

distributed wound AC motors. These are the most common 

AC motors used in industry. This discussion is applicable equally to 

induction motors and permanent magnet synchronous engines.

This distributed winding creates a smooth sinusoidal magneto-motive 

force (MMF) that flows through the motor's air gap. The MMF forms 

when balanced three-phase AC currents flow through the windings. 

The motor's magnetic design creates a traveling wave in the air, 

producing the torque needed for the motor to work.

The windings consist of several coils made from copper wire or, in certain cases, aluminium. Multiple 

strands can be connected parallel to create a single conductor. This is then wound up into a coil with 

multiple turns. Number of turns depends on the design.

A distributed winding is made up of multiple coils that are inserted into 

slots on the stator of the motor. Number of coils depends on number of slots in the stator, number of 

phases (3 for us) and number motor poles.

Each coil spans several slots. The average coil span of a full-pitch will be equal to 360deg/p or the number 

slots in the winding. A short-pitch will only have fewer slots. This figure shows the full-pitch for a 4 pole motor.

A 4-pole motor stator with a 3-phase distributed winding

The rest will go in the end windings which do not contribute to the motor torque. Rest of 

the winding will be placed in end winds which does not affect motor torque. To avoid unnecessary copper waste, 

careful design is required. 

Achieving good thermal performance also drives the requirement for high slot-fill and thermal end-winding 

management. The manufacturing processes often limit these 

factors. An ideal distributed winding would have infinite coils in infinite slots, so that the MMF distribution space 

is perfect. In practice, this is not 

feasible so the best compromise to achieve performance requirements must be made.

To avoid failures or short-circuits, coils of different phases must be isolated from one 

another and the core of the stator. The insulation will act as a thermal barrier, limiting the transfer of heat from 

inside the machine to outside. 

There will be air voids between winding cables and the insulation. The voids between the winding wires 

and insulation, as well as between the stator core and winding are filled using a resin by an impregnation 

procedure. This improves heat transmission while also improving winding insulation.

There are many different applications for electric motors. Motor design is affected by different applications. 

The winding will impact on several of these requirements.

• Maximisation of efficiency by minimising harmonic losses

• Reduce torque pulsations

• Reducing acoustic and vibration noise

There are several winding arrangements that can achieve the same performance. These layouts are 

determined by production constraints, which in turn is influenced heavily by the automation level 

used for winding.

This table shows some common configurations of winding as well as the key selection criteria.

There are clear compromises to be made when it comes to the technical requirements, automation, 

and costs. Motor designers must work with the manufacturing engineers to determine the best solution.