U.S. patent application number 09/194578 was filed with the patent office on 2002-05-02 for rotating electric machine for high voltage.
Invention is credited to HOLLELAND, MONS, IVARSON, CLAES, LEIJON, MATS, TEMPLIN, PETER.
Application Number | 20020050758 09/194578 |
Document ID | / |
Family ID | 20402760 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050758 |
Kind Code |
A1 |
LEIJON, MATS ; et
al. |
May 2, 2002 |
ROTATING ELECTRIC MACHINE FOR HIGH VOLTAGE
Abstract
The present invention relates to a rotating electric high
voltage machine comprising a stator (8), a rotor (7; 37; 47) and at
least one winding. The machine is characterized in that said
winding comprises at least one current-carrying conductor (2), that
a first layer (3) having semiconducting properties is provided
around said conductor, that a solid insulating layer (4) provided
around said first layer, and that a second layer (5) having
semiconducting properties is provided around said insulating layer.
Alternatively, the rotating electric machine according to the
invention is provided with a magnetic circuit for high voltage
comprising a magnetic core and a winding, and is characterized in
that said winding is formed of a cable (1; 11) comprising at least
one current-carrying conductor (2), that each conductor comprises a
number of strands (18), that an inner semiconducting layer (3) is
provided around each conductor, that an insulating layer (4) of
solid insulating material is provided around said inner
semiconducting layer, and that an outer semiconducting layer (5) is
provided around said insulating layer.
Inventors: |
LEIJON, MATS; (VASTERAS,
SE) ; TEMPLIN, PETER; (VASTRA FROLUNDA, SE) ;
HOLLELAND, MONS; (VASTERAS, SE) ; IVARSON, CLAES;
(VASTERAS, SE) |
Correspondence
Address: |
DYKEMA GOSSETT PLLC
FRANKLIN SQUARE, THIRD FLOOR WEST
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Family ID: |
20402760 |
Appl. No.: |
09/194578 |
Filed: |
August 11, 1999 |
PCT Filed: |
May 27, 1997 |
PCT NO: |
PCT/SE97/00892 |
Current U.S.
Class: |
310/180 |
Current CPC
Class: |
H02K 1/165 20130101;
Y10S 174/28 20130101; H02K 3/48 20130101; H01F 29/14 20130101; Y10S
174/29 20130101; H01F 27/34 20130101; H01F 2027/329 20130101; H01F
27/288 20130101; H01F 2027/2833 20130101; H02K 3/14 20130101; H01F
3/14 20130101; H02K 3/28 20130101; Y10S 174/14 20130101; H02K 15/00
20130101; H02K 9/19 20130101; Y10S 174/22 20130101; Y10S 174/26
20130101; H01F 27/323 20130101; Y10S 174/17 20130101; Y10S 174/25
20130101; H02K 15/12 20130101; Y10S 174/20 20130101; H02K 3/40
20130101; Y10S 174/15 20130101; H01F 2029/143 20130101; H02K 11/048
20130101; H02K 2203/15 20130101; Y10S 174/19 20130101; H02H 3/025
20130101; Y10S 174/13 20130101; Y10S 174/24 20130101; H01F 3/10
20130101 |
Class at
Publication: |
310/180 |
International
Class: |
H02K 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 1996 |
SE |
9602079-7 |
Claims
1. A rotating electric high voltage machine comprising a stator
(8), a rotor (7;37;47) and at least one winding, characterized in
that said winding comprises at least one current-carrying conductor
(2), that a first layer (3) having semiconducting properties is
provided around said conductor, that a solid insulating layer (4)
is provided around said first layer, and that a second layer (5)
having semiconducting properties is provided around said insulating
layer.
2. A rotating machine according to claim 1, characterized in that
the potential of said first layer is substantially equal to the
potential of the conductor.
3. A rotating machine according to claim 1 or 2, characterized in
that said second layer is arranged to constitute a substantially
equipotential surface surrounding said conductor.
4. A rotating machine according to claim 3, characterized in that
said second layer is connected to a predetermined potential.
5. A rotating machine according to claim 4, characterized in that
said predetermined potential is ground potential.
6. A rotating machine according to any one of the preceding claims,
characterized in that at least two adjacent layers have
substantially equal thermal expansion coefficients.
7. A rotating machine according to any one of the preceding claims,
characterized in that said current-carrying conductor (2) comprises
a number of strands (18), only a minority of said strands being
uninsulated from each other.
8. A rotating machine according to any one of the preceding claims,
characterized in that each of said three layers (3,4,5) is solidly
connected to the adjacent layer along substantially the whole
connecting surface.
9. A rotating electric machine having a magnetic circuit for high
voltage comprising a magnetic core and a winding, characterized in
that said winding is formed of a cable (1;11) comprising at least
one current-carrying conductor (2), that each conductor comprises a
number of strands (18), that an inner semiconducting layer (3) is
provided around each conductor, that an insulating layer (4) of
solid insulating material is provided around said inner
semiconducting layer, and that an outer semiconducting layer (5) is
provided around said insulating layer.
10. A rotating electric machine according to claim 9, characterized
in that it comprises a stator (8) and a rotor (7;37;47).
11. A rotating electric machine according to claim 10,
characterized in that the stator comprises a laminated core (8)
provided with winding slots (10) and that said winding is arranged
in said slots.
12. A rotating electric machine according to any one of the
preceding claims, characterized in that said cable also comprises a
metal shield and a sheath.
13. A rotating electric machine according to any one of claims 1-8,
10-12, characterized in that the rotor (7) comprises salient poles
(20).
14. A rotating electric machine according to claim 13,
characterized in that the rotor includes strip coils.
15. A rotating electric machine according to claim 13,
characterized in that the rotor includes wire coils.
16. A rotating electric machine according to claim 13,
characterized in that the rotor is provided with a damper winding
(27).
17. A rotating electric machine according to claim 13,
characterized in that the poles are laminated poles.
18. A rotating electric machine according to claim 13,
characterized in that the poles are solid poles.
19. A rotating electric machine according to claim 13,
characterized in that the poles are mounted on the rotor by means
of bolts.
20. A rotating electric machine according to claim 13,
characterized in that the poles which are mounted on the rotor by
means of a dovetail arrangement.
21. A rotating electric machine according to claim 13,
characterized in that the rotor includes a rotor rim made of thin
steel sheet.
22. A rotating electric machine according to claim 13,
characterized in that the rotor includes a rotor rim made of thick
steel plate.
23. A rotating electric machine according to claim 13,
characterized in that the rotor includes a rotor rim made of solid
steel.
24. A rotating electric machine according to claim 13,
characterized in that the rotor includes an armature spider, and
that the poles and said armature spider are made in one piece and
with pole shoes bolted to the poles.
25. A rotating electric machine according to claim 13,
characterized in that the rotor is provided with an armature
spider, a shaft and bearings.
26. A rotating electric machine according to claim 13,
characterized in that the rotor is provided with a shaft and that
the poles are provided directly on said shaft.
27. A rotating electric machine according to any one of claims 1-8,
10-12, characterized in that the rotor is a turbo type rotor
(37).
28. A rotating electric machine according to claim 27,
characterized in that the rotor includes a shaft (32) and a body
and that said shaft and said body are forged.
29. A rotating electric machine according to claim 27,
characterized in that the rotor includes a body and that said body
is provided with winding slots (35).
30. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with a winding made of
copper strips.
31. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with a winding and that
said rotor is designed with a direct ventilation of said
winding.
32. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with a winding and that
said rotor is designed with an indirect ventilation of said
winding.
33. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with grooves for a
cooling medium.
34. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with ventilation
ducts.
35. A rotating electric machine according to claim 27,
characterized in that the rotor is provided with bearings.
36. A rotating electric machine according to any one of claims 1-8,
10-12, characterized in that the rotor is a cylindric rotor
(47).
37. A rotating electric machine according to claim 36,
characterized in that the rotor is made of laminated steel sheet
compressed by means of steel rings.
38. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a three-phase
winding.
39. A rotating electric machine according to claim 38,
characterized in that the winding is a diamond winding.
40. A rotating electric machine according to claim 38,
characterized in that the winding is a bar winding.
41. A rotating electric machine according to claim 38,
characterized in that the winding is a flat winding.
42. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a single-phase
winding.
43. A rotating electric machine according to claim 42,
characterized in that the winding is a flat winding.
44. A rotating electric machine according to claim 42,
characterized in that the winding is a diamond winding.
45. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a damper
winding.
46. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a squirrel cage
winding made of aluminium.
47. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a squirrel cage
winding made of copper.
48. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a squirrel cage
winding made of brass.
49. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with an armature
spider.
50. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with a shaft (42).
51. A rotating electric machine according to claim 36,
characterized in that the rotor is provided with bearings.
52. A rotating electric machine according to any one of claims 1-8,
10-51, characterized in that the rotor is designed for horizontal
mounting.
53. A rotating electric machine according to any one of claims 1-8,
10-51, characterized in that the rotor is designed for vertical
mounting.
54. A rotating electric machine according to any one of claims 1-8,
10-53, characterized in that the rotor is provided with slip
rings.
55. A rotating electric machine according to any one of claims 1-8,
10-53, characterized in that the rotor is provided with a brushless
exciter.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a rotating electric machine
in accordance with the introductory part of claim 1 and a rotating
electric machine in accordance with the introductory part of claim
9.
[0002] The rotating electric machines which are referred to in this
context comprise synchronous machines which are substantially used
as generators for connection to distribution and transmission
networks, commonly referred to below as power networks. Synchronous
machines are also used as motors and for phase compensation and
voltage control, in that case as mechanically idling machines. The
technical field also comprises asynchronous machines, double-fed
machines, alternating current machines, asynchronous converter
cascades, external pole machines and synchronous flux machines.
[0003] The magnetic circuit referred to in this context comprises a
magnetic core of laminated, non-oriented or oriented, sheet or
other material, for example amorphous or powder-based, or any other
arrangement for the purpose of allowing an alternating magnetic
flux, a winding, a cooling system, etc., and which may be arranged
in the stator of the machine, in the rotor or in both.
BACKGROUND OF THE INVENTION
[0004] In order to explain and describe the machine, a brief
description of a rotating electric machine will first be given,
exemplified on the basis of a synchronous machine. The first part
of the description substantially relates to the magnetic circuit of
such a machine and how it is composed according to conventional
technique. Since the magnetic circuit referred to in most cases is
arranged in the stator, the magnetic circuit below will normally be
described as a stator with a laminated core, the winding of which
will be referred to as a stator winding, and the slots in the
laminated core for the winding will be referred to as stator slots
or simply slots.
[0005] Most synchronous machines have a field winding in the rotor,
where the main flux is generated by direct current, and an A.C.
winding in the stator. Synchronous machines are normally of
three-phase design and the invention substantially relates to such
machines. Sometimes, synchronous machines are designed with salient
poles. However, cylindrical rotors are used for two- or four-pole
turbogenerators and for double-fed machines. The latter have an
A.C. winding in the rotor.
[0006] The stator body for large synchronous machines are often
made of sheet steel with a welded construction. The laminated core
is normally made from lacquered 0.35 or 0.5 mm electrical steel
sheet. For radial ventilation and cooling, the laminated core, at
least for medium-large and large machines, is divided into stacks
with radial and axial ventilation channels. For larger machines,
the sheet is punched into segments which are attached to the stator
body by means of wedges/dovetails. The laminated core is retained
by pressure fingers and pressure plates. The stator winding is
disposed in slots in the laminated core where the slots normally
have a cross section in the form of a rectangle or a trapezoid.
[0007] Polyphase A.C. windings are designed either as single-layer
or two-layer windings. In the case of single-layer windings, there
is only one coil side per slot, and in the case of two-layer
windings there are two coil sides per slot. By coil side is meant
one or more conductors brought together in height and/or width and
provided with a common coil insulation, i.e. an insulation intended
to withstand the rated (test) voltage towards ground. Two-layer
windings are usually designed as diamond windings, whereas the
single-layer windings which are relevant in this connection may be
designed as a diamond winding or as a concentric winding. In the
case of a diamond winding, only one coil span (or possibly two coil
spans) occurs, whereas flat windings are designed as concentric
windings, i.e. with a greatly varying coil span. By coil span is
meant the distance in arc measure between two coil sides belonging
to the same coil, either in relation to the relevant pole pitch or
in the number of intermediate slot pitches. Usually, different
variants of cording are used, for example fractional pitch, to give
the winding the desired properties.
[0008] The type of winding substantially describes how the coils in
the slots, i.e. the coil sides, are connected together outside the
stator, i.e. at the coil ends. A typical coil side is formed from
so-called Roebel bars, wherein certain bars have been made hollow
for a coolant. A Roebel bar comprises a plurality of rectangular,
parallel-connected copper conductors, which are transposed 360
degrees along the slot. Ringland bars with transpositions of 540
degrees and other transpositions also occur. The transposition is
necessary to avoid circulating currents. Between each strand there
is a thin insulation, for example epoxy/glass fibre. The main
insulation between the slots and the conductors is made, for
example, of epoxy/glass fibre/mica and has at its outermost end a
thin semiconducting ground-potential layer which is used to
equalize the electric field. Outside the sheet stack of the stator,
on the other hand, there is no external semiconducting
ground-potential layer, but an electric field control in the form
of so-called corona protection varnish intended to convert a radial
field into an axial field, which means that the insulation on the
coil ends occurs at a high potential relative to ground. The field
control is a problem which sometimes gives rise to corona in the
coil-end region, which may be destructive.
[0009] Normally, all large machines are designed with a two-layer
winding and equally large coils. Each coil is placed with one side
in one of the layers and the other side in the other layer. This
means that all the coils cross each other in the coil end. If more
than two layers are used, these crossings render the winding work
difficult and deteriorate the coil end.
[0010] What is mentioned above can be said to be part of
conventional technique relating to current rotating electric
machines.
[0011] During the last decades, there have been increasing demands
for rotating electric machines with higher voltages than what has
previously been possible to design. The maximum voltage level
which, according to the state of the art, has been possible to
achieve for synchronous machines with a good yield in the coil
production is around 25-30 kV. It is also commonly known that the
connection of a synchronous machine/generator to a power network
must take place via a .DELTA./Y-connected so-called step-up
transformer, since the voltage of the power network normally lies
at a higher level than the voltage of the rotating electric
machine. Thus, this transformer, and the synchronous machine,
constitute integral parts of an installation. The transformer
constitutes an extra cost and also has the disadvantage that the
total efficiency of the system is reduced. If it were possible to
manufacture machines with considerably higher voltages, the step-up
transformer could thus be omitted.
[0012] Attempts to develop the generator with higher voltages have,
however, been in progress for a long time. This is obvious, for
instance from "Electrical World", Oct. 15, 1932, pages 524-525.
This describes how a generator designed by Parson 1929 was arranged
for 33 kV. It also describes a generator in Langerbrugge, Belgium,
which produced a voltage of 36 kV. Although the article also
speculates on the possibility of increasing voltage levels still
further, the development was curtailed by the concepts upon which
these generators were based. This was primarily because of the
shortcomings of the insulation system where varnish-impregnated
layers of mica oil and paper were used in several separate
layers.
[0013] Certain attempts at new approach as regards the design of
synchronous machines are described, inter alia, in an article
entitled "Water-and-oil-cooled Turbogenerator TVM-300" in J.
Elektrotechnika, No. 1, 1970, pp. 6-8, in U.S. Pat. No. 4,429,244
"Stator of Generator" and in Russian patent document CCCP Patent
955369.
[0014] The water- and oil-cooled synchronous machine described in
J. Elektrotechnika is intended for voltages up to 20 kV. The
article describes a new insulation system consisting of oil/paper
insulation, which makes it possible to immerse the stator
completely in oil. The oil can then be used as a coolant while at
the same time using it as insulation. To prevent oil in the stator
from leaking out towards the rotor, a dielectric oil-separating
ring is provided at the internal surface of the core. The stator
winding is made from conductors with an oval hollow shape provided
with oil and paper insulation. The coil sides with their insulation
are secured to the slots, made with rectangular cross section, by
means of wedges. As coolant, oil is used both in the hollow
conductors and in holes in the stator walls. Such cooling systems,
however, entail a large number of connections for both oil and
electricity at the coil ends. The thick insulation also entails an
increased radius of curvature of the conductors, which in turn
results in an increased size of the winding overhang.
[0015] The above-mentioned US patent relates to the stator part of
a synchronous machine which comprises a magnetic core of laminated
sheet with trapezoidal slots for the stator winding. The slots are
tapered since the need for insulation of the stator winding is less
towards the interior of the rotor where that part of the winding
which is located nearest the neutral point is disposed. In
addition, the stator part comprises a dielectric oil-separating
cylinder or ring nearest the inner surface of the core which may
increase the magnetization requirement relative to a machine
without this ring. The stator winding is made of oil-immersed
cables with the same diameter for each coil layer. The layers are
separated from each other by means of spacers in the slots and
secured by wedges. What is special for the winding is that it
comprises two so-called half-windings connected in series. One of
the two half-windings is disposed, centred, inside an insulation
sleeve. The conductors of the stator winding are cooled by
surrounding oil. The disadvantages with such a large quantity of
oil in the system are the risk of leakage and the considerable
amount of cleaning work which may result from a fault condition.
Those parts of the insulation sleeve which are located outside the
slots have a cylindrical part and a conical termination reinforced
with current-carrying layers, the purpose of which is to control
the electric field strength in the region where the cable enters
the end winding.
[0016] From CCCP 955369 it is clear, in another attempt to raise
the rated voltage of the synchronous machine, that the oil-cooled
stator winding comprises a conventional high-voltage cable with the
same dimension for all the layers. The cable is placed in stator
slots formed as circular, radially disposed openings corresponding
to the cross-section area of the cable and with the necessary space
for fixation and for coolant. The different radially disposed
layers of the winding are surrounded by and fixed in insulated
tubes. Insulating spacers fix the tubes in the stator slot. Because
of the oil cooling, an internal dielectric ring is also needed here
for sealing the coolant against the internal air gap. The design
shown shows no tapering of the insulation or of the stator
slots.
[0017] The design exhibits a very narrow radial waist between the
different stator slots, which means a large slot leakage flux which
significantly influences the magnetization requirement of the
machine.
[0018] In machine designs according to the documents described
above, the electromagnetic material in the stator is not optimally
utilized. From a magnetic point of view, the stator ends shall
connect as closely as possible with the casing of the coil sides.
It is most desirable to have a stator tooth with a maximum width at
each level, since the width of the tooth significantly influences
the losses and the magnetization requirement of the machine. This
is especially important for machines for higher voltage since the
number of conductors per slot there becomes large.
[0019] With reference to a report from the Electric Power Research
Institute, EPRI, EL-3391 from April 1984, an account is given of
generator concepts for achieving higher voltage in an electric
generator with the object of being able to connect such a generator
to a power network without intermediate transformers. Such a
solution is assessed in the report as offering good gains in
efficiency and considerable financial advantages. The main reason
that it was deemed possible in 1984 to start developing generators
for direct connection to power networks was that a supra-conducting
rotor had been developed at that time. The considerable excitation
capacity of the supra-conducting field enables the use of
airgap-winding with sufficient thickness to withstand the
electrical stresses.
[0020] By combining the concept deemed most promising according to
the project, that of designing a magnetic circuit with winding,
known as "monolith cylinder armature", a concept in which two
cylinders of conductors are enclosed in three cylinders of
insulation and the whole structure is attached to an iron core
without teeth, it was assessed that a rotating electric machine for
high voltage could be directly connected to a power network. The
solution entailed the main insulation having to be made
sufficiently thick to withstand network-to-network and
network-to-earth potentials. Obvious drawbacks with the proposed
solution, besides its demand for a supra-conducting rotor, are that
it also requires extremely thick insulation, which increases the
machine size. The coil ends must be insulated and cooled with oil
or freons in order to control the large electric fields at the
ends. The whole machine must be hermetically enclosed in order to
prevent the liquid dielectric medium from absorbing moisture from
the atmosphere.
SUMMARY OF THE INVENTION
[0021] The object of the present invention is to solve the above
mentioned problems and to provide a rotating electric machine which
permits direct connection to all types of high-voltage power
networks. This object is achieved by providing the machine defined
in the introductory part of claim 1 with the advantageous features
of the characterizing part of said claim.
[0022] Accordingly, the winding comprises at least one
current-carrying conductor and the machine is further characterized
in that a first layer having semiconducting properties is provided
around said conductor, that a solid insulating layer is provided
around said first layer, and that a second layer having
semiconducting properties is provided around said insulating
layer.
[0023] A very important advantage of the present invention, as
defined in claim 1, is that the use of the described insulated
conductor for the winding makes it possible to obtain a rotating
electric machine with a considerably higher voltage than machines
according to the state of the art. In fact, a rotating electric
machine as defined in claim 1 has the advantage that it is possible
to have at least one winding system of conductors suitable for
direct connection to distribution or transmission networks.
Consequently, the voltage level in question is 36 kV-800 kV, and
preferably 72,5 kV-800 kV.
[0024] This also entails the further important advantage that the
.DELTA./Y-connected step-up transformer mentioned above can be
omitted. Consequently, the solution according to the present
invention represents major savings both in economic terms and
regarding space requirement and weight for generator plants and
other installations comprising rotating electric machines.
[0025] In order to cope with the problems which arise in the case
of direct connection of rotating electric machines to all types of
high-voltage power networks, a machine according to the invention
may have a number of features which significantly distinguishes it
from the state of the art both as regards conventional mechanical
engineering and the mechanical engineering which has been published
during the last few years. Some features will follow below.
[0026] As mentioned, the winding is manufactured from one or more
insulated conductors with an inner and an outer semiconducting
layer, preferably an extruded cable of some sort. Some typical
examples of such conductors are a cable of crosslinked polyethylene
(XLPE) or a cable with ethylene propylene (EP) rubber insulation,
which, however, for this purpose and according to the invention,
has an improved design both as regards the strands of the conductor
and as regards the outer layer.
[0027] The use of an insulated conductor with an outer
semiconducting layer has the advantage that it permits the outer
layer of the winding, in its full length, to be maintained at
ground potential. Consequently, the claimed invention may have the
feature that the outer semiconducting layer is connected to ground
potential. As an alternative, the outer layer may be cut off, at
suitable locations along the length of the conductor, and each
cut-off part length may be directly connected to ground
potential.
[0028] A considerable advantage with having the outer layer
connected to ground potential is that the electric field will be
near zero in the coil-end region outside the outer semiconductor
and that the electric field need not be controlled. This implies
that no field concentrations can be obtained within the sheet, in
the coil-end region, or in the transition therebetween.
[0029] As another advantageous feature at least two, and preferably
all three, of the layers have substantially equal thermal expansion
coefficients. Through this is achieved that thermal movement is
prevented and the occurrence of cracks, fissures or other defects
in the winding due to thermal movement is avoided.
[0030] According to another characterizing feature each of the
three layers is solidly connected to the adjacent layer along
substantially the whole connecting surface. This has the advantage
that the layers are fixed and unable to move in relation to each
other and serves to ensure that no play occurs between the layers.
It is very important that no air is allowed to enter in-between the
layers since that would lead to disturbances in the electric
field.
[0031] As yet another advantageous feature the present invention is
characterized in that the current-carrying conductor comprises a
number of strands, only a minority of said strands being
uninsulated from each other. The uninsulated strand or strands in
the outer layer of the conductor defines the potential on the inner
semiconducting layer and thereby ensures a uniform electric field
within the insulation. By using uninsulated strands instead of
insulated strands a less expensive insulated conductor for a
winding is obtained. Theoretically, every second strand may be
uninsulated, but for practical reasons the number of uninsulated
strands is less than the insulated strands.
[0032] As an alternative, the object may be achieved by providing
the machine defined in the introductory part of claim 9 with the
advantageous features of the characterizing part of said claim.
Accordingly, the winding is formed of a cable comprising at least
one current-carrying conductor and the machine is further
characterized in that each conductor comprises a number of strands,
that an inner semiconducting layer is provided around each
conductor, that an insulating layer of solid insulating material is
provided around said inner semiconducting layer, and that an outer
semiconducting layer is provided around said insulating layer.
[0033] Naturally, the cable according to claim 9 may be provided
with any one of the features of claims 2-8 regarding the
winding.
[0034] Preferably, cables with a circular cross section are used.
However, in order to obtain, among other things, better packing
density, cables with a different cross section may be used.
[0035] The use of an insulated conductor or cable according to the
invention has the additional advantage that it permits the
laminated core, both with respect to slots and teeth, to be
designed in a new and optimal way.
[0036] As a further advantageous feature, the winding may be
designed with tapered insulation to utilize the laminated core in
the best way.
[0037] To continue, the shape of the slots may advantageously be
adapted to the cross section of the cable of the winding in such a
way that the slots are formed as a number of cylindrical openings,
extending axially and radially outside one another, with a
substantially circular cross section, and with an open waist
extending between the layers of the stator winding. The shape of
the slots may also be adapted to the tapered insulation of the
winding. As an additional feature, the substantially circular cross
section may, counting from the ridge portion of the laminated core,
be designed with a continuously decreasing radius, or, as an
alternative, with a discontinuously decreasing radius.
[0038] A particular advantage with the tapered insulation is that a
reasonably constant tooth width can be obtained, independently of
the radial extension.
[0039] Furthermore, the winding is preferably designed as a
multi-layer concentric cable winding to reduce the number of
coil-end crossings.
[0040] As a further feature, the machine according to the invention
may be characterized in that the cable also comprises a metal
shield and a sheath.
[0041] The rotor of the rotating electric machine according to the
present invention may be designed in a number of different ways,
known per se. In brief it may be mentioned that the rotor may be a
rotor comprising salient poles and including a number of different
features related to that configuration. For example, it may be
designed with or without a damper winding, with or without an
armature spider.
[0042] Alternatively, the rotor may be a turbo type rotor and
include a number of different features related to that particular
configuration. For example, it may be designed with or without
grooves for a cooling medium, with or without ventilation
ducts.
[0043] As yet an alternative, the rotor may be configured as a
cylindric rotor and, naturally, include a number of different
features related to such a configuration. For example, it may be
designed with or without a damper winding, with or without an
armature spider, with or without a shaft, with or without bearings.
In general, as applicable, the winding may be made of copper
strips, it may be a single-phase or three-phase winding, it may be
a diamond winding, a bar winding, a flat winding or a squirrel cage
winding, etc.
[0044] The rotor may further be designed for horizontal or vertical
mounting, it may be provided with slip rings, it may be provided
with a brushless exciter etc. The rotor may also be made of
different materials. Other configurations and features are also
possible.
[0045] Further features and advantages will be apparent from the
remaining dependent claims.
[0046] As a summary, thus, a rotating electric machine according to
the invention results in a considerable number of important
advantages in relation to corresponding prior art machines. First
of all, it can be connected directly to a power network at all
types of high voltage. Another important advantage is that ground
potential may be consistently provided along the whole winding,
which implies that the coil-end region can be made compact and that
bracing means at the coil-end region can be applied at practically
ground potential. Still another important advantage is that
oil-based insulation and cooling systems will disappear. This means
that no sealing problems will arise and that the dielectric ring
previously mentioned is not needed. Another important feature is
that all forced ventilation can be made at ground potential. In
addition, a considerable space and weight saving from the
installation point of view is obtained with a rotating electric
machine according to the invention, since it replaces a previous
installation design with both a machine and a step-up
transformer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a detailed perspective view of an insulated
conductor or cable according to the present invention,
[0048] FIG. 2 shows a schematic axial end view of a sector/pole
pitch of a magnetic circuit according to one embodiment of the
invention,
[0049] FIG. 3 shows a schematic axial end view of a sector/pole
pitch of a magnetic circuit according to another embodiment of the
invention, and
[0050] FIG. 4 shows a schematic axial end view of a part of a
sector/pole pitch of a magnetic circuit according to yet another
embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0051] An important condition for being able to manufacture a
rotating electric machine in accordance with the disclosure of the
invention is to use, for the winding, an insulated conductor or a
conductor cable with an electrical insulation with a semiconducting
layer both at the conductor and at the casing. Such cables are
available as standard cables for other power engineering fields of
use. As described under the summary of the invention, however, an
improved embodiment of such a standard cable is preferably used as
a stator winding.
[0052] In order to describe an embodiment, initially a short
description of a standard cable will be made. The internal
current-carrying conductor comprises a number of uninsulated
strands. Around the strands there is a semiconducting inner layer.
Around this semiconducting inner layer, there is an insulating
layer of extruded insulation. An example of such an extruded
insulation is XLPE or, alternatively, so-called EP rubber. This
insulating layer is surrounded by an external semiconducting layer
which, in turn, is surrounded by a metal shield and a sheath. Such
a cable will be referred to below as a power cable.
[0053] A preferred embodiment of the improved cable or insulated
conductor is shown in FIG. 1. The insulated conductor or cable 1 is
represented in the figure as comprising a current-carrying
conductor 2 which comprises a number of strands 18. The strands are
transposed both uninsulated and insulated strands. Transposed,
insulated strands are also possible. Around the conductor there is
an inner semiconducting layer 3 which, in turn, is surrounded by an
extruded insulation layer 4. This layer is surrounded by an
external semiconducting layer or layer 5. The cable used as a
winding in the preferred embodiment has no metal shield and no
external sheath. In order to avoid induced currents and losses, the
external semiconducting layer has such a high resistivity that the
induced voltage does not provoke any appreciable losses. As an
alternative to avoid induced currents and losses associated
therewith in the outer semiconductor, this is cut off, preferably
in the coil end, i.e. in the transitions from the sheet stack to
the end windings. Each cut-off part is then connected to ground,
whereby the external semiconductor will be maintained at, or near,
ground potential for the whole cable length. This means that,
around the extruded insulated winding at the coil ends, the
contactable surfaces, and the surfaces which are dirty after some
time of use, only have negligible potentials to ground, and that
they also cause negligible electric fields.
[0054] As regards the geometric dimensions of the insulated
conductor or cable the conductor area is comprised in the
approximate interval of 80-3000 mm.sup.2 and the outer diameter is
in the approximate interval of 20-250 mm.
[0055] To optimize a rotating electric machine, the design of the
magnetic circuit as regards the slots and the teeth, respectively,
are of decisive importance. As mentioned above, the slots should
connect as closely as possible to the casing of the coil sides. It
is also desirable that the teeth at each radial level are as wide
as possible. This is important to minimize the losses, the
magnetization requirement, etc., of the machine.
[0056] With access to the above described insulated conductor or
cable for the winding, there are great possibilities of being able
to optimize the laminated core from the above mentioned points of
view. In the following, a magnetic circuit in the stator of the
rotating electric machine is referred to. FIG. 2 shows an axial end
view of a sector/pole pitch 6 of a magnetic circuit according to
one embodiment of the invention, namely an embodiment including a
rotor 7 with salient poles 20. In a conventional manner, the stator
is composed of a laminated core of electric sheets successively
composed of sector-shaped sheets. From a rear portion of the stator
core 8, located at the radially outermost end, a number of teeth 9
extend radially inwards towards the rotor. Between the teeth there
are a corresponding number of slots 10. The slots have a cross
section tapering towards the rotor, since the need for cable
insulation decreases for each winding layer in the direction
towards the air gap. As is clear from the figure, the slot
substantially consists of a circular cross section 12 around each
layer of the winding with narrower waist portions 13 between the
layers. With a certain justification, such a slot cross section may
be referred to as a "bicycle chain slot". However, it need not be
symmetric. In a high-voltage machine, a relatively large number of
layers will be needed and, if a continuous tapering of the cable
insulation and the stator slot, respectively, is desired, a large
number of cable dimensions are required. However, it will neither
be practical nor economic to use more than a certain number of
cable dimensions. Therefore, as shown in the embodiment of FIG. 2,
cables 11 with three different dimensions of the cable insulation
are used, arranged in three correspondingly dimensioned sections
14, 15 and 16, i.e. in practice a modified bicycle chain slot is
obtained. The rotor 7 represented in FIG. 2, which is only partly
shown, is as mentioned a rotor with salient poles 20. It comprises
a rotor rim 21, a pole body 23 with a pole plate 24 and a field
winding 26. The illustrated pole is also provided with a damper
winding 27.
[0057] FIG. 3 shows a schematic axial end view of a sector/pole
pitch of a magnetic circuit according to another embodiment of the
invention, namely an embodiment including a turbo type rotor 37,
only partly shown. The different parts of the stator and the stator
winding are essentially the same as in FIG. 2 and have accordingly
been given the same reference numerals. The rotor includes a body
and a shaft 32 forged from solid steel. It is provided with milled
slots 35 for the rotor winding 36. The represented turbo rotor is
also provided with poles 30.
[0058] FIG. 4 shows a schematic axial end view of a part of a
sector/pole pitch of a magnetic circuit according to yet another
embodiment of the invention, namely an embodiment including a
cylindric rotor 47, only partly shown. The 30 illustrated rotor is
a laminated rotor with a regular field winding. The rotor includes
a shaft 42 and a rotor rim 41 provided with slots 45 for the rotor
winding 46. The rotor is also provided with poles 40.
[0059] As an alternative, the cable which is used as a winding may
be a conventional power cable, like the one described above. The
grounding of the external semiconducting shield then takes place by
stripping the cable of the metal shield and the sheath at suitable
locations.
[0060] It should be noted that the scope of the invention
accommodates a large number of alternative embodiments of a
modified cycle chain slot, depending on the available insulated
conductor or cable dimensions as far as insulation and the external
semiconductor layer etc. are concerned.
[0061] As winding, a winding is preferably used which may be
described as a multilayer, concentric cable winding. Such a winding
implies that the number of crossings at the coil ends has been
minimized by placing all the coils within the same group radially
outside one another. This also permits a simpler method for the
manufacture and the threading of the stator winding in the
different slots.
* * * * *