The document discusses the design of the stator in an electric motor. It covers key aspects of stator design including the stator lamination material and patterns, winding methods, insulation techniques, and manufacturing processes. Design considerations like reducing cogging torque, maintaining a small air gap, effective stator cooling, and robust stator construction are also addressed to optimize motor performance and reliability.

1. STATOR DESIGN
of an
ELECTRIC MOTOR
S.VARUN
M.Tech[EST]
SRM UNIVERSITY
1

2. MOTOR PARTS
2

3. AREAS OF DESIGN
• Stator
• Rotor
• Shaft
• Frame & Bearing
3

4. STATOR
• The stator is an static part of the motor which acts as
outer body to house the driven windings on a laminated
steel core for creating a rotating magnetic field.
• The stator core is made up of a stack of pre punched
laminations assembled into a motor housing that is
made of aluminum or cast iron or no separate housing
designs.
4

5. STATOR SIZES
5

6. STATOR DESIGN CONSTRAINTS
• Stator Lamination.
• Magnet Wire.
• Stator Insulation.
6

7. STATOR LAMINATION
• Lamination Material
• Lamination Pattern
a)One Piece Lamination
b)T-Shaped Segmented Lamination
c)Connected Segmented Lamination
d)Two-Section Stator Lamination
e) Stator Lamination Integrated by Individual Teeth.
f)Slot less Stator core
g)Slinky Lamination Stator Core.
7

8. ONE PIECE LAMINATION
• One-piece lamination is
fabricated from an undivided
piece of steel sheet and
continuous in the 360°
circumference.
• The one-piece lamination
method offers the advantage
of fabrication and assembly
simplicity.
8

9. T-SHAPED SEGMENTED LAMINATION
• Segmented stator laminations are
frequently encountered in large-size
motors.
• The recent trend toward using
segmented laminations in small
motors is a means to not only
increase the slot-filling rate and
facilitate automated fabrication of
electric motors.
9

10. TWO-SECTION STATOR LAMINATION
• A stator lamination is
integrated by two lamination
pieces: a section of teeth and
a section of yoke.
• The stator windings are
wound on the section of
teeth.
10

11. STATOR LAMINATION INTEGRATED BY
INDIVIDUAL TEETH AND A YOKE SECTION
• Each tooth is individually
positioned in the concave slot
made at the inner surface of
the yoke.
• This design can use the
grain-oriented material to
make the teeth, arranging the
grain orientation in the radial
direction.
11

12. SLOT LESS STATOR CORE
• Slot less stator designs have
emerged as a solution to zero
cogging in conventional PM
motors.
• The slot less stators totally
eliminate the cogging torque,
simplify the lamination
process, and smooth the
motor performance.
12

13. SLINKY LAMINATION STATOR CORE
• A stator core is built up from a
continuous slotted strip of silicon
steel rather than cross-sectional
laminations in a conventional
manufacturing process.
• The strip is wound edgewise in a
helical configuration by a coiling
machine that consists of three
flanged rolls.
13

14. MAGNET WIRE
• Regular Magnet Wire
• Self-Adhesive Magnet Wire
• Litz Wire
14

15. REGULAR MAGNET WIRE
• Regular magnet wire consists of a base metal, commonly
copper or aluminum, and coated one or multilayer of
insulation materials, such as enamel, fibrous polyester,
fiberglass yarn, and polyamide.
• Several cross-sectional shapes of magnetic wires are
available in stator windings, including round, square,
and rectangular.
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16. SELF-ADHESIVE MAGNET WIRE
• When activated by heat or solvent, the bond coating
cements the winding turn-to-turn to create a self-
supporting coil.
• This type of wires opens up new avenues for some
special applications, especially where regular magnetic
wires are not suitable.
16

17. SELF-ADHESIVE MAGNET WIRE
17

18. LITZ WIRE
• Litz wire is basically used for high-frequency
applications. It contains many thin wire strands that are
individually insulated and twisted together.
• Litz wire utilizes the full cross-sectional area of the wire
to carry current.
• A size of a Litz wire is often expressed in abbreviated
format of N/XX, where N is the number of strands and
XX is the AWG size of each strand.
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19. STATOR INSULATION
• Injection Moulded Plastic Insulation
• Slot Liner
• Glass Fibre Reinforced Mica Tape
• Powder Coating on Stator Core
19

20. INJECTION MOULDED PLASTIC
INSULATION
• Injection Moulded Plastic insulation provides highly
insulating properties to laminated stator stacks.
• The use of moulded plastic insulation prior to winding
assures consistent & durable insulation of wound
winding to stator cores.
20

21. Main Body & End
Cap
Insulator applied
to Stator
Windings
21

22. SLOT LINER
• Heat Resistant & mechanically stable insulation papers
or thermoplastic materials are inserted in stator slots for
preventing coils from shorting from stator core.
• The typical thickness of an insulator material may have a
range of 0.1-0.65mm.
22

23. GLASS FIBER REINFORCED MICA TAPE
• For large size motors, stator windings are often made of
conducting bars which are continuously wrapped with
mica tape.
• The taped winding bars are placed in a vacuum
impregnation tank & flooded with a epoxy resin.
23

24. POWDER COATING ON STATOR CORE
• The motor stators are often shaped cylindrically with
inwardly facing slots configured to receive stator
windings.
• It is required to insulate the copper windings from stator
metal surfaces which can also be achieved by applying
powder coating techniques to provide uniform insulating
coating layers on stator slot surfaces as well as partially
on stator end surfaces.
24

25. MANUFACTURING PROCESS OF
STATOR
• Stator Lamination Cutting
• Lamination Fabrication Process
• Lamination Annealing
• Lamination Stacking
• Stator Winding
25

26. STATOR LAMINATION CUTTING
• Laser cutting machine is often used for the cutting the
laminations with extra large dimensions or complex
geometrics.
• The design information is loaded into the machine & a
high energized laser beam is focussed in a tiny spot so
that the local temperature rises extremely high to melt
lamination sheets.
26

27. LAMINATION FABRICATION PROCESS
• This method uses a sequence of stamping operation on
strip materials to generate first the rotor sheet piece &
then the stator sheet piece.
• The stamping operation starts to punch pilot holes, shaft
holes, rotor ventilating holes & rotor teeth to complete
the rotor lamination fabrication.
27

28. 28

29. LAMINATION ANNEALING
• During lamination cutting process, residual stresses are
introduced in processed laminations, leading to
degradation of material magnetic properties near the
edges of the laminations.
• The smaller the rotor size, the larger the cut effected
zone relative to whole lamination area.
• So Annealing is necessary step for stress relief & for
optimum properties of laminations with temperature of
730-790 deg C
29

30. LAMINATION STACKING
• The stator stack is formed by stacking laminations into a
pack. There are several methods to assemble stack
laminations into stator cores.
• With the automation, the lamination stacking becomes
more important which increases production efficiency &
reduces the requirement for storage capacity, especially
for rotor stacking.
30

31. LAMINATION STACKING TECHNIQUES
• Welding
• Bonding with Adhesive Materials
• Riveting
• Fastened by pins
• Lamination Interlocking
• Using Slot-Liners
• Using Thin Sleeves
• Bolting
31

32. WELDED STATOR STACK
32

33. SPOT BONDED STATOR WITH EPOXY
ADHESIVE
33

34. THIN SLEEVE STATOR CORE
34

35. STATOR WINDING
• One of the important parameters in stator winding is the
slot fill ratio, which is defined as the percentage of the
space occupied by magnet wires to the total available
space of the slot.
• In order to lower the wire resistive loss and increase the
power density, it is highly preferable to have the
maximum copper fill, that is, maximum slot fill ratio.
35

36. STATOR WINDING Contd..
• A winding end turn refers to the amount of the winding
extending beyond each end of the stator’s magnetic core
structure.
• Though the end turns are necessary to complete the
electrical path within the winding, they contribute little
to the motor torque output.
• Motor torque is only generated by the winding that lies
within the stator’s magnetic core structure.
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37. STATOR WINDING Contd..
• So it is highly desired to minimize the length of the
winding end turns.
• This can not only save the wiring material and lower the
material cost but also reduce the copper loss and
increase the motor efficiency.
• The shorter the winding stack length, the greater the
impact of the end turn length on motor efficiency.
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38. WINDING METHODS
• Random Winding.
• Distributed Winding by Hand.
• Concentrated Winding.
• Conductor Bar
38

39. Distributed
Winding
Concentrated
Winding
39

40. STATOR ENCAPSULATION &
IMPREGNATION
• Encapsulating and impregnating stators can strengthen
stator winding electrical insulation, provide reliable
protection to chemicals and harsh environments,
enhance thermal dissipation, promote stator structure
integrity, and stabilize motor operation.
• Partial encapsulation is basically applied to the stator
end windings for integrating them with other stator
components against vibration and for enhancing heat
transfer.
40

41. ENCAPSULATION
• Entire encapsulation is applied to the whole stator
assembly for achieving better protection of the stator
from moisture, dirt, debris, and erosions caused by
chemicals.
• A wide variety of encapsulation materials are available
for electric machines.
• Thermoset plastics such as epoxies, phenolics, and
thermoset polyesters, have long been applied to electric
machines as encapsulation materials.
41

42. ENCAPSULATION MATERIALS
• E88 epoxy.
• C89 hardener
• Araldite CW 229-3.
• Aradur HW 229-1
• Araldite XB 2252
• Araldite CW 1312
• Aratherm CW 2731
• EP 234
• EP 1282
• EP 1285
42

43. VARNISH DIPPING
• Varnishing dipping is an effective way of securing stator
windings. In this method, a stator is immersed into an
open varnish tank.
• After a certain time, the stator is removed from the
varnish tank to allow excess varnish dipping. Then, place
the stator in an oven to dry off solvent.
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44. ENCAPSULATED STATOR
44

45. TRICKLE IMPREGNATION
• Trickle impregnation is extensively used in many motor
manufacturers. In practice, a trickle varnish machine is
usually used to impregnate the stator winding with a
varnish that rigidly secures the wires.
• The varnish improves heat transfer within the winding
and between its surrounding magnetic core structure.
This improves motor cooling and in turn increases the
motor’s continuous torque and power density.
45

46. VACUUM PRESSURE IMPREGNATION
• The characteristic of this technology is to use a VPI tank
that is vacuumed first and then pressurized to achieve
the best insulation effect on stators.
• This method can provide the highest industrial
standards for electric machines. By driving out voids
from the electric winding through the VPI process, the
thermal conductivity of the winding is remarkably
enhanced so that the hot spots are eventually eliminated.
46

47. VPI Contd..
•It also reduces the risk of partial
discharge in the winding. In fact,
the VPI can make the high stator
mechanical integration to reduce
vibration of the motor.
•It can achieve complete
penetration of resin throughout
turns, coils, slots, and insulation
and thus is primarily applied on
heavy-duty applications.
47

48. VPI Contd..
48

49. STATOR DESIGN CONSIDERATIONS
• Cogging Torque
• Air Gap
• Stator Cooling
• Robust Design of Stator
49

50. COGGING TORQUE
• Cogging torque is one of inherent characteristics of PM
motors, resulted from the interaction of the PM MMF
harmonics and the air gap permeance harmonics due to
slotting.
• As cogging torque can cause speed ripples, induce motor
vibration, and deteriorate motor performance, it is one
of the major design goals for motor engineers to reduce
cogging torque. Electromagnetic design primarily
determines the level of cogging torque.
50

51. AIR GAP
• The radial distance between the rotor and stator in a
motor is defined as the air gap. Normally, a smaller air
gap provides a more efficient and powerful motor.
• Hence, it is highly desired to maintain the air gap
dimension as small as possible and within a small
variation in operation. The control of the air gap
dimension involves the design of several components
such as the stator, rotor, motor housing, and end bells.
51

52. AIR GAP Contd..
• An important factor that affects the air gap dimension is
the accuracy of the coincidence of the stator and rotor
axes.
• To provide a motor with a small air gap dimension
within only a small tolerance, preciseness in
manufacturing of these parts is required.
52

53. STATOR COOLING
• An important objective in motor design is to control the
motor temperature below its allowable value. Increased
motor temperature often reduces motor efficiency and
affects bearing life. The Thermal Engineers focus on
cooling for following reasons.
• The stator winding is usually the main heat source in a
motor. Test data show that in most applications heat
generated in a motor is primarily attributed to the stator.
53

54. STATOR COOLING Contd..
• Cooling in the stator end-winding region is particularly
difficult and still remains a challenge due to various
factors.
• As a stationary component, the stator is much easier to
be cooled compared with the rotor. In fact, the stator
often serves as a heat sink for the motor.
• For some electric motors, the pumping effect, which is
resulted from the rotor rotation, is strong enough to
generate turbulent circulating flows for making the
motor self-cooling.
54

55. ROBUST DESIGN OF STATOR
• The root causes of motor failure are often related to
mechanical deterioration such as vibration, static and
cyclic loads, insulation fracture, and bearing lubricant
contamination and leakage.
• Because the rotor is supported on bearings located at the
end bells of the machine, the stator design is significantly
impacted by the dynamic behaviour of the rotor.
• Motor vibration is greatly influenced by its base. A weak
motor base usually results in high vibration.
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