U.S. patent application number 17/474793 was filed with the patent office on 2021-12-30 for metal coil fabrication.
This patent application is currently assigned to ROLLS-ROYCE plc. The applicant listed for this patent is ROLLS-ROYCE plc. Invention is credited to Geraint W. JEWELL, Alexis LAMBOURNE, Iain TODD.
Application Number | 20210408859 17/474793 |
Document ID | / |
Family ID | 1000005840030 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210408859 |
Kind Code |
A1 |
LAMBOURNE; Alexis ; et
al. |
December 30, 2021 |
METAL COIL FABRICATION
Abstract
A 3D printed metal coil for an electrical machine. The 3D
printed coil has a plurality of turns and is configured to fit
within a slot in an electrical machine. A portion of each turn
forming an end winding of the coil has a flat plate-like shape for
dissipating heat from the end winding.
Inventors: |
LAMBOURNE; Alexis; (Belper,
GB) ; TODD; Iain; (Sheffield, GB) ; JEWELL;
Geraint W.; (Sheffield, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROLLS-ROYCE plc |
London |
|
GB |
|
|
Assignee: |
ROLLS-ROYCE plc
London
GB
|
Family ID: |
1000005840030 |
Appl. No.: |
17/474793 |
Filed: |
September 14, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16269152 |
Feb 6, 2019 |
11177712 |
|
|
17474793 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 41/04 20130101;
H02K 15/02 20130101; H02K 3/26 20130101; H02K 3/12 20130101; H02K
15/0435 20130101; H02K 15/00 20130101; H02K 15/045 20130101; H01F
5/06 20130101; H02K 3/32 20130101; H02K 3/18 20130101; B05D 5/12
20130101; H02K 3/28 20130101; B33Y 80/00 20141201; H02K 19/02
20130101; H02K 15/0407 20130101; B33Y 10/00 20141201 |
International
Class: |
H02K 3/28 20060101
H02K003/28; H01F 41/04 20060101 H01F041/04; H02K 3/12 20060101
H02K003/12; H02K 3/32 20060101 H02K003/32; H02K 15/02 20060101
H02K015/02; H02K 15/04 20060101 H02K015/04; H02K 19/02 20060101
H02K019/02; H02K 3/26 20060101 H02K003/26; B33Y 80/00 20060101
B33Y080/00; H02K 15/00 20060101 H02K015/00; H02K 3/18 20060101
H02K003/18; H01F 5/06 20060101 H01F005/06; B33Y 10/00 20060101
B33Y010/00; B05D 5/12 20060101 B05D005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2018 |
GB |
1802534.6 |
Claims
1. A 3D printed metal coil for an electrical machine, the 3D
printed coil having a plurality of turns and being configured to
fit within a slot in an electrical machine, wherein a portion of
each turn forming an end winding of the coil has a flat plate-like
shape for dissipating heat from the end winding.
2. The 3D printed metal coil of claim 1, wherein a cross-sectional
shape of the turns transition from a rectangular cross-section in
the slot to the flat plate-like shape at the portion of the turn
that forms the end winding of the coil.
3. The 3D printed metal coil of claim 2, wherein, while the
cross-sectional shape of the turns transition from the rectangular
cross-section to the flat plate-like shape, a cross-sectional area
of the turns remains constant.
4. The 3D printed metal coil of claim 1, wherein each turn has a
square or rectangular cross-section in the slot.
5. The 3D printed metal of claim 1, wherein a cross-sectional shape
of the turns varies for successive turns.
6. The 3D printed metal coil of claim 5, wherein, while the
cross-sectional shape of the turns varies for successive turns, the
cross-sectional area of the successive turns remains constant.
7. The 3D printed metal coil of claim 5, wherein a cross-sectional
area of the turns of the coil varies for successive turns.
8. The 3D printed coil of claim 1, being further configured such
that a portion of each turn forms a part of an external surface of
the metal coil, the external surface forming an interface with a
side of the slot.
9. The 3D printed metal coil of claim 1, comprising one or more 3D
printed pockets for thermocouples or other sensors.
10. The 3D printed metal coil of claim 1, comprising 3D printed
termination features at the ends of the coil.
11. The 3D printed metal coil of claim 1, further comprising
insulation between the turns to electrically insulate the turns
from each other.
12. The 3D printed metal coil of claim 11, wherein the insulation
incorporates spacers physically separating successive turns from
each other.
13. The 3D printed metal coil of claim 11, wherein the insulation
comprises a dielectric resin.
14. The 3D printed metal coil of claim 1, wherein the metal is
copper.
15. An electrical machine comprising: a plurality of teeth forming
a plurality of slots; a plurality of 3D printed metal coils within
said plurality of slots, wherein, for each 3D printed metal coil, a
portion of each turn forming an end winding of the coil has a flat
plate-like shape for dissipating heat from the end winding.
16. The electrical machine of claim 15, wherein, for each 3D
printed metal coil, a cross-sectional shape of the turns transition
from a rectangular cross-section in the slot to the flat plate-like
shape at the portion of the turn that forms the end winding of the
coil.
17. The electrical machine of claim 16, wherein, while the
cross-sectional shape of the turns transition from the rectangular
cross-section to the flat plate-like shape, a cross-sectional area
of the turns remains constant.
18. The electrical machine of claim 15, wherein each 3D printed
coil is further configured such that a portion of each turn forms a
part of an external surface of the metal coil, the external surface
forming an interface with a side of the slot.
19. The electrical machine of claim 15, wherein, for each 3D
printed metal coil, a cross-sectional shape of the turns varies for
successive turns.
20. The 3D printed metal coil of claim 19, wherein, while the
cross-sectional shape of the turns varies for successive turns, the
cross-sectional area of the successive turns remains constant.
Description
[0001] This is a Continuation of application Ser. No. 16/269,152
filed Feb. 6, 2019, which claims priority to British Application
No. 1802534.6 filed Feb. 16, 2018. The entire disclosures of the
prior applications are hereby incorporated by reference herein
their entirety.
FIELD OF THE PRESENT DISCLOSURE
[0002] The present disclosure relates to a method for fabricating a
metal coil for an electrical machine.
BACKGROUND
[0003] A typical electrical motor comprises a rotor, which is
mounted on a shaft, and a stator. The rotor is supported by
bearings, which allow the rotor to turn on its axis, thereby
allowing the rotor to turn the shaft relative to the stator in
order to deliver mechanical power. The stator comprises a plurality
of thin metal sheets, or laminations, of a soft magnetic material,
such as silicon steel or cobalt-iron. The laminations of the stator
are shaped such that they form alternating teeth and slots in the
stator. Each slot is filled with turns of a metal wire coil. When
the coils are energised, i.e. when a current flows through the
turns, each tooth acts as a magnetic pole of the electrical
machine. By energising the coils in sequence, magnetic poles are
turned on and off in sequence, which induces the rotor to rotate on
its axis.
[0004] A typical electrical generator is similarly configured, but
instead of delivering mechanical power, it converts mechanical
power in the form of rotation of the rotor to electrical power
generated in the coils of the stator.
[0005] The power density of an electrical machine (whether a motor,
a generator, or another type of machine such as an actuator)
depends on two factors; the magnetic loading (i.e. how much
magnetic flux each tooth can carry), and the electrical loading
(i.e. how much electrical load the coil in each slot can carry).
Increasing the magnetic loading and/or the electrical loading of
the electrical machine increases the power density of the
electrical machine.
[0006] In conventional electrical machines, each slot has an
approximately rectangular cross section, and the wire of the metal
coils has a circular, or round, cross-section. Regardless of the
size of the cross-section and the packing arrangement of the wire
in the slot, there are always spaces between different turns of the
wire and between the turns of the wire and the sides of the slot.
In other words, there are always spaces in each slot which are not
filled with metal wire. Instead, these spaces are filled with a
combination of air and insulating material. Insulating material is
required between the turns of the coil in order to prevent short
circuits, and ultimately to prevent failure of the coil. In
conventional electrical machines, as little as 45% of the cross
sectional area of each slot may be filled with metal wire, the
remaining 55% of the cross sectional area being filled with a
combination of air and insulating material.
[0007] Thus in order to increase the electrical load, the turns of
the metal coils must be more densely packed in the slots so that
there are fewer and/or smaller spaces between the turns of the
metal coil. In other words, the packing factor of the wire in the
slots of the stator must be increased.
[0008] One approach to increasing the packing factor is to use
metal wire with a rectangular cross section. However, such wires
can be more difficult to bend or manipulate into coils as they are
stiffer than wires with a circular cross section. Furthermore,
kinking or creasing at the sharp edges of wire with a rectangular
cross section can result in damage to insulating material
surrounding the metal coil. This in turn can lead to corona
discharge and failure of the coil.
[0009] Another approach to increasing the packing factor is to use
multi stranded wire, commonly known as Litz wire. Thin strands of
metal wire can be compressed, twisted and woven together into high
packing factor bundles which are then wound to form the turns of a
coil. Litz wire is generally easier to manipulate than solid
rectangular metal wire. Moreover, because of the low
cross-sectional area of the individual strands, Litz wire bundles
also reduce the increase in resistance of a metal wire that takes
place at higher frequencies, and therefore reduce electromagnetic
losses at higher frequencies compared to conventional metal
wire.
[0010] However, each individual thin strand of metal wire woven
into the Litz wire bundle is coated in a layer of insulating
material. Therefore, although the wire bundles can be packed
efficiently, a substantial proportion of the cross sectional area
of each slot is still filled with insulating material. In other
words, although there may be fewer spaces between the metal wires
that are filled with air, these spaces have simply been replaced
with spaces filled with insulating material. The insulating
material of Litz wire bundles can also be easily damaged during the
manipulation of the bundles into metal coils.
SUMMARY OF THE DISCLOSURE
[0011] The present disclosure aims to provide a metal coil that can
better fit within the slots of a stator, for example so that the
packing factor of the turns of the coil is increased. Such a coil
can result in a higher electrical loading, and therefore an
increased power density of an electrical machine.
[0012] Accordingly, the present disclosure provides in a first
aspect a method for fabricating an insulated metal coil for an
electrical machine including: 3D printing a metal coil having a
plurality of turns; and subsequently infiltrating insulating
material between the turns of the metal coil to electrically
insulate the turns from each other.
[0013] By 3D printing the metal coil, the configuration of the coil
can be modelled and defined for its specific application. The turns
of wire in the coil can be densely packed in a slot of a stator
such that the total cross-sectional area of the wire in the slot is
increased. Therefore, the packing factor is increased and the
electrical loading and power density of the electrical machine is
increased. Furthermore, the cross-sectional shape and/or area of
the turns of the metal coil can be varied within the coil itself.
Also, rather than printing the coil and the insulating material
simultaneously in a combined 3D printing process, the metal coil is
printed before infiltrating the insulating material. This helps to
prevent the metal coil from picking up impurities from the
insulating material.
[0014] Optional features of the method of the first aspect will now
be set out. These are applicable singly or in any combination.
[0015] The method may further include locating spacers between the
turns of the metal coil to space the turns from each other before
infiltrating the insulating material. Locating spacers between the
turns of the coil helps to prevent turn-to-turn short circuits.
[0016] The method may further include curing the infiltrated
insulating material.
[0017] The method may further include modelling a coil geometry
based on an intended electrical loading of the metal coil and/or a
thermal analysis of the electrical machine, the metal coil being 3D
printed to the modelled coil geometry. Modelling the coil geometry
based on the intended electrical loading of the metal coil allows
factors such as slot depth, slot-to-tooth ratio, cross sectional
area of wire and packing factor of wire in the slot to be defined.
Modelling the coil geometry based on the thermal analysis of the
electrical machine allows factors such as heat dissipation area,
peak coil temperature, contact area of the coil to the slot and end
winding geometry to be defined and modelled. Advantageously, the
combination of thermal and electrical requirements can then be used
to define the coil geometry.
[0018] The metal coil may be a copper coil. For example, copper
powder having a diameter within the range of 50-100 .mu.m may be
used for 3D printing the coil. Copper powder having a diameter
within this range is particularly suitable for the flow and
handling characteristics of a 3D printer. However, it should be
noted that the wire could formed of another electrically conductive
metal, such as aluminium.
[0019] The 3D printing may be performed in an oxygen free
environment. Maintaining an oxygen free environment by means of an
inert gas or vacuum reduces the risk of oxygen contamination, which
can impair the electrical conductivity of the wire. Therefore, the
electrical conductivity of the wire can be improved.
[0020] The method may further include annealing the metal coil to
reduce or remove residual stresses in the coil before infiltrating
the insulating material.
[0021] The method may further include heat treating the metal coil
in an inert atmosphere to improve the electrical conductivity of
the coil before infiltrating the insulating material. The heat
treating can be performed using a hot isostatic pressure (HIP)
furnace. The combination of an increased temperature and increased
pressure in the HIP furnace can enhance the electrical conductivity
of the wire. Generally, the increased pressure contributes to
healing, or closing up, of residual porosity, and the increased
temperature results in grain crystallization and grain growth.
[0022] The insulated metal coil may be configured to fit within a
slot in the electrical machine, and the plurality of turns of the
metal coil may have configurations such that a portion of each turn
forms a part of an external surface of the metal coil, the external
surface of the metal coil forming an interface with a side of the
slot. In this way, thermal management of the coil can be improved.
In other words, each turn can have an external heat sink to the
side of the slot.
[0023] The cross-sectional shape of the turns of the coil may vary
for successive turns, typically with the cross-sectional area
remaining the same for successive turns. This shape variation is
known as grading. As an example, the cross-sectional shape of the
turns may transition from square-like to more rectangular, and vice
versa. As the portions of the coil exiting a slot and turning to
re-enter another slot, also known as end-windings, are not
positioned within a slot but are instead exposed to air or coolant,
it is beneficial to extract heat from the coils at the
end-windings. Therefore, each turn may be graded to transition at
the end windings from having e.g. a rectangular cross sectioned
bar-like shape within a slot to having e.g. a flat plate-like shape
at the end winding, thereby increasing the surface area of the end
windings while maintaining the cross sectional area for current
flow. Heat dissipation can therefore be improved in the end
windings while the current-carrying capacity of the coil remains
the same.
[0024] The metal coil may be 3D printed with termination features
at the ends of the coil. Termination features may include threaded
fittings or spade connectors. By 3D printing the termination
features, a manufacture stage may be removed when compared to a
conventional process for fabricating insulated metal coils.
Accordingly, efficiency of fabricating the insulated metal coil may
be improved.
[0025] The present disclosure provides in a second aspect a process
for fabricating a stator of an electrical machine, the process
including: performing the method of the first aspect; and fitting
the fabricated insulated metal coil into slots of the stator of the
electrical machine.
[0026] The present disclosure provides in a third aspect an
insulated metal coil fabricated according to the method of the
first aspect.
[0027] The present disclosure provides in a fourth aspect, an
insulated metal coil having a plurality of turns and being
configured to fit within a slot in an electrical machine, the coil
being further configured such that a portion of each turn forms a
part of an external surface of the metal coil, the external surface
forming an interface with a side of the slot. For example, by
varying the cross-sectional shapes of the turns of the coil, each
turn can form an interface with a side of the slot in order to
improve thermal management of the coil. In other words, each turn
can have an external heat sink to the side of the slot.
[0028] The present disclosure provides in a fifth aspect, an
insulated metal coil for an electrical machine, the coil having a
plurality of turns, and the cross-sectional shape of the turns of
the coil varying for successive turns, preferably with the
cross-sectional area of the turns remaining the same for successive
turns.
[0029] The insulated metal coil of the fourth or fifth aspect may
be fabricated according to the method of the first aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Embodiments of the present disclosure will now be described
by way of example with reference to the accompanying drawings in
which:
[0031] FIG. 1 shows a metal coil with a high packing factor;
[0032] FIG. 2 shows a flow chart of a method of fabricating an
insulated metal coil;
[0033] FIG. 3 shows grading of a metal coil to form improved end
windings;
[0034] FIG. 4A shows a cross section through a metal coil with a
constant cross sectional shape;
[0035] FIG. 4B shows a cross section through a metal coil having a
varied cross sectional shape; and
[0036] FIG. 5 shows a cross section through another metal coil
according.
DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES
[0037] 3D printing, also known as direct laser deposition (DLD),
selective laser melting (SLM), additive layer manufacture (ALM) and
direct metal deposition (DMD), is a process which uses a directed
energy source such as a laser or electron beam to create 3D objects
from a powder. The directed energy source melts, sinters or fuses
together the powder into a 3D object based on a geometry
predetermined by a computer generated CAD (computer aided design)
model file, a 3D scanner or a digital camera and photogrammetry
software.
[0038] It is possible to 3D print metal, such as copper, into a
metal coil having a plurality of turns, such as the metal coil 50
shown in FIG. 1. More specifically, it is possible to 3D print a
copper coil using a blown powder or powder bed and an electron beam
or laser process.
[0039] A 3D printed metal coil can be designed using a
computer-aided design (CAD) package to have a particular shape and
configuration. In this way, 3D printed metal coils can be
configured to suit a particular slot geometry in an electrical
machine such that a high packing factor of the coil within the slot
is achieved.
[0040] FIG. 2 shows a flow chart of a method of fabricating an
insulated metal coil using 3D printing. In this example, an
insulated copper coil is fabricated, although a similar method
could be used to fabricate a coil made from a powder of another
metal, such as aluminium.
[0041] At step 1a, an intended electrical loading of the insulated
copper coil is defined and modelled to produce an electrical
machine model. Software such as Flux 3D.TM. from Altair.TM.
HyperWorks.TM. or Opera.TM. from Cobham.TM. can be used for the
modelling of electrical loading of the coil into an electrical
machine model. Factors such as slot depth, slot-to-tooth ratio,
cross section of copper, and packing factor of the copper coil are
defined in the electrical machine model.
[0042] At step 1b, an analysis of heat inputs from the environment
and/or self-heating of the electrical machine is carried out in a
thermal analysis of the electrical machine, and a thermal model is
produced. Self-heating may result from resistive losses and/or eddy
current losses in the coil. Factors such as heat dissipation area,
peak coil temperature, contact area of the coil to the slot and end
winding geometry are defined in the thermal model.
[0043] The electrical machine model and the thermal model may be
separate or integrated models.
[0044] At step 2, a coil geometry is modelled and generated based
on the electrical machine model and the thermal model using a CAD
package to produce a CAD model file. The generated coil geometry
can be modelled to increase the packing factor of the coil within
the slot. Specifically, the cross sectional area of the wire in the
slot can be increased, and the cross sectional area of the space
containing a combination of air and insulating material is
decreased.
[0045] At step 3, integration and/or termination features may be
added to the generated coil geometry in the CAD model file.
Specifically, connectors such as spade connectors, pockets for
thermocouples or other sensors, coolant channels, heat sinks, heat
dissipation surfaces and threaded fittings may be added to the CAD
model file. Such integration and/or termination features are added
to the CAD model file so that they can be 3D printed as part of the
metal coil. For example, FIG. 1 shows integral terminal connectors
20 at the ends of the coil 50, and in FIG. 3 heat dissipation
surfaces 10 are shown integrated with the end windings of the coil
50. More particularly, in FIG. 3, each turn is graded to transition
at the end windings from having a rectangular cross sectioned
bar-like shape, to a flat plate-shaped heat dissipation surface 10,
thereby increasing the surface area of the end winding exposed to
air or motor coolant, whilst maintaining the same cross-sectional
area for current flow. Therefore, heat dissipation is improved in
the end windings, but the current carrying capacity of the coil
remains the same.
[0046] The integration and/or termination features can improve the
thermal management of the copper coil such that changes in
electrical resistance can be reduced, and therefore the efficiency
of the electrical machine is improved. Advantageously, these
features do not need to be added to the coil later on in the
fabricating process, thereby improving the efficiency of the
fabrication of the insulated metal coils.
[0047] At step 4, the generated coil geometry in the CAD model file
is tested in the electrical machine model to check that the
intended electrical loading is achieved. If the intended electrical
loading is not achieved, further optimization cycles may be carried
out by repeating steps 1a, 1b, 2 and 3 until the intended
electrical loading is achieved. If the intended electrical loading
is achieved, the calculated coil geometry becomes the final coil
geometry which is used for the 3D printing.
[0048] At step 5, the final coil geometry in the CAD model file is
converted into a 3D print format to be 3D printed. The 3D print
format depends on the 3D printing machine used to fabricate the
coils. Typically the 3D print format is an .stl file.
[0049] At step 6, the copper coil is 3D printed using the 3D
printing machine. The copper powder used should be suitable for the
flow and handling characteristics required by the 3D printing
machine. Super pure copper powder having a diameter in the range of
50-100 .mu.m is generally suitable. The 3D printing can be
performed in an oxygen free environment in order to reduce the risk
of oxygen contamination, which impairs the electrical conductivity
of the wire. An oxygen free environment is achieved by means of an
inert gas or vacuum.
[0050] Rapid cooling of the copper as it is deposited by the 3D
printer results in residual stresses. In step 7, the copper coil is
annealed within the 3D printing machine in an in situ stress
release process in order to reduce or eliminate these residual
stresses. The annealing temperature of copper is within the range
of 250-750.degree. C. An oxygen free environment is maintained.
[0051] 3D printing can result in a fine grained copper coil with
some residual porosity. Both porosity and small grain sizes may
lead to an increased electrical resistance. This effect is reduced
at step 8, by heat treatment of the copper coil in a hot isostatic
pressure (HIP) furnace. Increased temperature, increased pressure,
and an inert environment in the HIP furnace enhances the electrical
conductivity of the copper wire. Specifically, the increased
temperature (usually >850.degree. C.) results in grain
recrystallization and grain growth, and the increased pressure aids
in closing up, or healing, the porosity.
[0052] An insulating process begins at step 9. Here, each turn of
the coil is separated from one another in order to prevent
turn-to-turn short circuits. Specifically, spacers are inserted
between each turn. Masking is added to some areas, such as
interconnects, which do not require a coating of insulation
material.
[0053] At step 10, the insulating material is infiltrated between
each turn such that each turn is coated in insulating material. The
insulating material should reach and coat all turns of the copper
coil. Examples of suitable insulating materials include dielectric
resins such as polyester, epoxy, PVC, polyimide Kapton, PTFE or
silicone. The insulating material can be infiltrated by a number of
techniques, including dipping, spraying, vacuum infiltration or
powder coating. The spacers inserted at step 9 become incorporated
into the insulating material to form an overall insulating system.
Preferably, the spacers inserted at step 9 are fabricated from the
same material as the insulating material. The insulating material
is then cured. Curing can be carried out by cooling, UV curing,
condensation curing, polymerisation, cross-linking or other types
of polymer curing processes.
[0054] At step 11, the insulated copper coil is complete and can be
inserted into slots of an electrical machine.
[0055] The design flexibility of 3D printing allows the
cross-section of each turn to be varied, or different from one
another. Therefore, as well as integration and/or termination
features discussed above in respect of FIGS. 1 and 3, the cross
section of each turn of metal wire in the coil may be a different
configuration, size or shape. FIG. 4A shows a coil with wire of
constant cross-sectional shape. In contrast, 3D printing the coil
allows the cross-sectional shape of the wire to be varied for
successive turns of the coil, as shown in FIG. 4B.
[0056] In particular, the cross-sectional shape of the wire may be
varied to allow each turn to have access to a side of the slot in
order to improve thermal management of the coil. An example of a
cross section of an insulated metal coil 50, the insulated metal
coil 50 being configured to fit within a slot 60 in a stator core
70 of an electrical machine, is shown in FIG. 5. The plurality of
turns 80 have different cross-sectional shapes such that a portion
of each of the turns 80 forms a part of an external surface of the
metal coil, the external surface forming an interface with a side
of the slot 60.
[0057] As each of the turns 80 can be in contact with a side of the
slot 60, each turn has an external heat sink to the stator core 70.
Therefore, in-slot cooling can be improved. However, in this
example, the cross sectional area of each turn is not varied so
that the current-carrying capacity of each turn is maintained.
[0058] Even if it is not possible to configure the turns such that
they all form an interface with a side of the slot, a substantial
proportion of the turns may form such an interface.
[0059] One or more of the following benefits can follow from the
improved packing factor obtainable by 3D printing the coil. [0060]
If the dimensions of the slot are unchanged, due to the improved
packing factor there can be an increase in the amount of wire in
each slot and so a reduction in the current density in the wire.
Therefore, there are less electrical losses, resulting in an
improved efficiency of the electrical machine. [0061] If the slot
depth is reduced such that the metal density in the slot is
unchanged, an outer diameter of the stator can be reduced.
Therefore, the mass and volume of the stator is reduced, and so
losses in the stator core are reduced. Again, this results in an
improved efficiency of the electrical machine. [0062] If the width
of the slot is reduced whilst maintaining both the slot depth and
overall cross sectional area of metal in the slot, the teeth of the
stator increase in volume. Therefore, the tooth flux density
decreases and there is a reduction in electrical losses from the
teeth of the stator. Again, this results in an improved efficiency
of the electrical machine. [0063] If the slot width is reduced,
leaving the tooth width unchanged, this can also result in a
reduction of stator losses, and therefore an improvement in
efficiency of the electrical machine.
[0064] In general reducing the slot depth is the most effective
option for improving the efficiency of the electrical machine.
Furthermore, there are additional benefits in reducing the slot
depth, such as a reduction of outer diameter of the stator and a
reduction of weight of the stator.
[0065] The insulated metal coil may be used in a motor, a
generator, an actuator or another type of electrical machine.
[0066] While the invention has been described in conjunction with
the exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given this disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Moreover, in determining extent of
protection, due account shall be taken of any element which is
equivalent to an element specified in the claims. Various changes
to the described embodiments may be made without departing from the
spirit and scope of the invention.
* * * * *