Winding pitch

Issue #WP105: Technical Information from Cummins Generator Technologies

AC Generators with 2/3rd and 5/6th winding pitch

White Paper
Dr Jawad Al-Tayie
Chris Whitworth
Dr Andreas Biebighaeuser

Abstract
Cummins Generator Technologies has

in case of parallel operation and also will

a wide range of AC generator products

impact on the type of neutral grounding

covering many applications, from prime

method. Paralleling generators with

power to marine, oil and gas to name

different winding pitch will require careful

a few. The stator of the AC generator

consideration if interconnecting star

is manufactured with either a 2/3rd

points of all running generators should be

or a 5/6th winding pitch. Winding pitch

necessary. Both winding pitch (2/3rd and

of AC generators has influence on the

5/6th) have some pros and cons, correct

shape of waveform (harmonic contents)

selection for any proposed application

and on the level of the fundamental

is the key for ensuring a cost effective

voltage. The winding pitch will have

power supply solution.

an influence on neutral circulating current

I. Introduction
The stator winding pitch of a generator is a design parameter that can be used to optimise the generator waveform shape and minimise the generator cost, because shorter pitch (lower pitch ratios) use the generator stator less effectively and require the use of more electrical steel and copper for the same kW output than higher pitch machines.
For example: n  /6th pitch windings suppress 5th and 7th voltage
5
harmonics but may enhance the triple harmonics
(third, ninth etc.) n  /3rd pitch windings suppress the triple
2
harmonics but may enhance the 5th and 7th.
In addition, 2/3rd pitch wound machines generally have lower zero sequence reactances that can increase the single phase fault current.
When comparing generator specifications, the listed value for output voltage total