7/22/2019 Electrical Machines and Drives III - Assignment 1

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Electrical Machines & Drives IIIAssignment 1

Name: W.N.L. Weerakkody Index No: 100573H Semester: 5

a. Sketch the coil-side arrangement of a 4 pole, 3 phase AC elementary winding

b. Show options available in connections

a. No of layers = 1

No of poles = 4

No of phases = 3

Let the no of slots = 12

No of slots per pole per phase = 12/ (4x3) = 1 slots

Pole pitch = no of slots/no of poles = 12/4 = 3 slots

Front pitch = (2/3)*3 = 2 slots

Coil pitch = pole pitch

a1 c1 b1 a1

c1

b1

a2 c2

b2 a2

c2

b2

Options available in connections

Series

Parallel

Delta

Wye

b.

Elementary three phase winding This type of windings has one slot per pole per phase Windings are wound together in series to form one multi-turn coil All the turns have the same magnetic axis Examples

Salient-pole synchronous machines (Field windings) Transformers (Primary and secondary windings) D.C. machines

Distributed three phase winding

This type of windings has more than one slot per pole per phase There can be single layer or double layer windings In double layer windings turns are arranged in full-pitch or fractional-pitch coils

7/22/2019 Electrical Machines and Drives III - Assignment 1

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Examples Stator and rotor of induction machines The armatures of both synchronous and D.C. machines

Coil pitch

The distance between the two coil-sides of a coil in terms of slotsPole pitch

The peripheral distance between identical points on two adjacent poles. Pole pitch is alwaysequal to 180 electrical degrees. It can be found by taking the ratio of no of slots to the no of

poles.

Front pitch

Separation between similar coil sides of successive phases in terms of no of slots. It can befound by taking 2/3 times of the pole pitch.

c.

No of layers = 2

No of slots per pole per phase = 24/(4x3) = 2 slots

Pole pitch = no of slots/no of poles = 24/4 = 6 slots

Front pitch = (2/3)*6 = 4 slots

Coil pitch = 5 (< pole pitch)

Shift the bottom layer by 1 slot

a1 a1 c1

c1

b1 b1 a1

a1

c1

c1 b1

b1

a2 a2 c2

c2

b2 b2 a2

a2

c2

c2 b2

b2

a1 c1

c1 b1 b1 a1

a1

c1

c1 b1

b1

a2 a2 c2

c2

b2 b2 a2

a2

c2

c2 b2

b2

a1