In short: concentrated winding places all the coil turns of a phase in a single slot pair per pole, giving a simple, low-cost construction with a lower winding factor and higher harmonic content, while distributed winding spreads the same phase turns across several slots per pole to raise the winding factor, smooth out the MMF waveform, and cut torque ripple and losses - the trade-off being more complex tooling and longer winding time.
Motor and transformer designers pick between the two (and fractional slot winding, which sits between them) based on how much they need to balance manufacturing cost against electromagnetic performance.
I. What is concentrated winding?
a. how the coils are arranged
In concentrated winding, every turn belonging to one phase of one pole is wound into a single slot (or a single slot pair). There is no spreading of the phase across adjacent slots - the coil is literally "concentrated" around one tooth or pole. This is the classic arrangement used in small transformers, single-layer stator windings, and many BLDC motors, where q (slots per pole per phase) equals 1.
b. where concentrated winding is used
Concentrated winding shows up in cost-sensitive, compact designs: ceiling fan motors, small BLDC/PMSM drives, control transformers, and single-phase induction motors. Coil ends are shorter, copper usage per turn is lower, and the winding process on a coil winding machine is faster because each coil is a repeatable, single-slot unit - which is exactly why high-volume, low-torque-ripple-tolerant applications default to it.
Example: A customer producing small ceiling fan stators asked us to compare concentrated tooth winding against a distributed layout for a 24-slot, 16-pole motor. Switching to concentrated winding on our stator winding line cut cycle time per stator by roughly 30% because each tooth could be wound independently before assembly, without threading wire across the stack. The trade-off was a winding factor drop from about 0.95 (distributed) to around 0.87, acceptable given the motor's low-speed, cost-driven application.
Considering a concentrated tooth-winding setup for a similar high-volume motor line? Contact our engineering team - we can review your slot/pole combination and recommend the right winding machine configuration.
II. What is distributed winding?
a. how the coils are arranged
Distributed winding spreads the turns of one phase across multiple slots per pole (q > 1) rather than concentrating them in one slot. Each coil group only occupies a fraction of the total phase turns, and the groups are connected in series or parallel across the stator or transformer core. This is the standard configuration in industrial induction motors, generators, and most medium-to-large three-phase transformers.
b. where distributed winding is used
Because the MMF (magnetomotive force) waveform produced by a distributed winding more closely approximates a sine wave, this arrangement is preferred wherever torque smoothness, low harmonic content, and efficiency matter more than manufacturing simplicity - traction motors, industrial three-phase induction motors, generators, and precision toroidal transformers.
Example: An industrial motor OEM was seeing excessive torque ripple and audible noise in a 36-slot, 4-pole induction motor wound with a concentrated layout. Re-winding the stator with a double-layer distributed winding (q = 3) on a programmable coil winding machine raised the winding factor from about 0.87 to 0.955 and measurably reduced the 5th and 7th harmonic content in the back-EMF waveform, resolving the noise complaint without changing the lamination stack.
Working through a torque-ripple or harmonic issue on your own winding design? Reach out to our team with your slot/pole/phase data - we can help you model the winding factor before you commit to tooling.
III. What is the difference between concentrated and distributed winding?
| Parameter | Concentrated Winding | Distributed Winding |
|---|---|---|
| Slots per pole per phase (q) | q = 1 | q > 1 (typically 2–6) |
| Winding factor (kw) | Lower (~0.85–0.90) | Higher (~0.92–0.96) |
| MMF waveform | More stepped, higher harmonics | Closer to sinusoidal, fewer harmonics |
| Coil end length | Shorter | Longer |
| Copper usage per turn | Lower | Slightly higher (longer end turns) |
| Manufacturing complexity | Simple, faster winding | More complex, longer winding time |
| Torque ripple / cogging | Higher | Lower |
| Typical applications | Small BLDC motors, fan motors, control transformers | Industrial induction motors, generators, large transformers |
| Cost per unit (small volume) | Lower | Higher |
The core trade-off is electromagnetic quality versus manufacturing cost and speed - concentrated winding vs distributed winding is ultimately a decision about which one your application can afford to give up.
IV. How do you calculate the winding factor for each type?
a. the winding factor formula
The winding factor (kw) combines two components - the distribution factor (kd) and the pitch factor (kp):
kw = kd × kp
A winding factor closer to 1.0 means the winding converts a larger share of the theoretical MMF into useful, sinusoidal flux linkage - which is why distributed windings, with their higher kw, generally run cooler and quieter for the same electrical loading.
b. the distribution factor formula
kd = sin(q × α / 2) / [q × sin(α / 2)]
Where:
q = slots per pole per phase
α = slot angle in electrical degrees = (P × 180°) / S
P = number of poles, S = total number of slots
For concentrated winding, q = 1, and the formula reduces to kd = 1 - there is no distribution loss because all turns sit in one slot.
c. the pitch factor formula
kp = sin(β / 2)
Where β is the coil pitch expressed in electrical degrees relative to full pitch (β = 180° for a full-pitch coil). Short-pitching a coil (β < 180°) is a common technique in distributed windings to suppress specific harmonics, at a small cost to fundamental winding factor.
d. worked example comparison
| Winding type | Slots (S) | Poles (P) | q | α (elec. deg) | kd | kp (full pitch) | kw = kd × kp |
|---|---|---|---|---|---|---|---|
| Concentrated | 12 | 4 | 1 | 60° | 1.000 | 1.000 | 1.000* |
| Distributed | 36 | 4 | 3 | 20° | 0.960 | 0.966 (5/6 pitch) | 0.927 |
*Concentrated windings can show kd = 1 in this simplified single-slot model, but real-world concentrated designs (especially fractional-slot tooth windings) often carry additional winding-factor penalties from coil overlap and end-turn geometry not captured by this basic q = 1 case - always verify against the specific slot/pole combination.
V. What is fractional slot winding and how does it relate to concentrated winding?
Fractional slot winding is a special case where the number of slots per pole per phase (q) is not a whole number - for example, q = 1.5 or q = 0.4. This is common in modern PMSM and BLDC designs using concentrated coils wound around individual teeth (single-layer or double-layer tooth winding), such as a 12-slot/10-pole or 9-slot/6-pole combination.
Fractional slot concentrated winding (FSCW) is popular because it shortens end turns further than integer-slot concentrated winding, improves copper fill factor, and allows each tooth to be wound off-line on automated equipment before stator assembly - a major manufacturing advantage on high-volume production lines. The trade-off is a more complex harmonic spectrum that requires careful electromagnetic design (often finite-element analysis) to control unwanted torque ripple and rotor losses.
VI. Which winding type should you choose for your motor or transformer application?
| Decision factor | Favor concentrated winding | Favor distributed winding |
|---|---|---|
| Production volume | High volume, cost-sensitive | Lower volume, performance-driven |
| Torque smoothness requirement | Tolerant of some ripple | Requires low ripple/noise |
| Efficiency target | Standard efficiency acceptable | Premium (IE3/IE4-class) efficiency needed |
| Automation goal | Independent tooth winding on automated lines | Needle or flyer winding across multiple slots |
| Machine size | Small motors, control transformers | Medium-to-large industrial motors, generators, power transformers |
Case in point: A generator manufacturer initially specified concentrated winding for a mid-size alternator to shorten lead time. After reviewing efficiency targets tied to IEC 60034-1 performance ratings, they switched to a distributed, double-layer design produced on our automatic coil winding machine - raising rated efficiency enough to meet the contract's IE3-equivalent requirement.
Not sure which winding configuration fits your efficiency class or production volume? Talk to our sales engineers - we'll help you match the winding type to the right machine before you finalize your design.
VII. Which KIOXIA machines support concentrated and distributed winding production?
Both winding types are common on our production floor, and the right machine depends on coil geometry rather than winding type alone. For concentrated, single-slot tooth coils, our winding machines handle high-speed, repeatable single-coil winding well suited to fan motors and small BLDC stators.
For distributed, multi-slot windings - including short-pitched coils used to suppress harmonics - programmable indexing places coil groups accurately across multiple slots. For toroidal transformer and CT applications where winding factor and space factor both matter, fine wire and flat copper wire winding with precise tension control meets the demands of distributed toroidal designs.
If your production line runs concentrated single-tooth coils at volume - ceiling fan motors being the most common example - our ceiling fan winding machine is purpose-built for that geometry. Send us your slot/pole/phase configuration and target winding factor, and our engineering team can confirm fit and tooling.
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