Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K3/00—Details of windings
  • H02K3/46—Fastening of windings on the stator or rotor structure
  • H02K3/48—Fastening of windings on the stator or rotor structure in slots
  • H02K3/487—Slot-closing devices
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K1/00—Details of the magnetic circuit
  • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
  • H02K1/12—Stationary parts of the magnetic circuit
  • H02K1/16—Stator cores with slots for windings
  • H02K1/165—Shape, form or location of the slots
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K2203/00—Specific aspects not provided for in the other groups of this subclass relating to the windings
  • H02K2203/15—Machines characterised by cable windings, e.g. high-voltage cables, ribbon cables

Definitions

• the present invention relates to a device for increasing the mechanical rigidity and natural frequency of the stator in a rotating electric machine, which stator is provided with stator teeth between the slots holding the winding, the free ends of the teeth being situated at the air gap between stator and rotor.
• the invention also relates to such a rotating electric ma- chine.
• High-voltage electric alternating current machines such as generators in a power station for generating electric power, dual-fed machines, outer pole machines, synchronous machines and asynchronous static current converter cascades, have hitherto been designed for voltages in the range 15-30 kV, and 30 kV has normally been considered to be an upper limit.
• the object of the present invention is to provide a new solution to the problem of vibrations in the stator te- eth in the type of alternating current machines under discussion, that is not encumbered with the drawbacks of the previous solution.
• the yoke is formed at the top of the slot. This localisation of the yoke provides the best mechanical bracing of the stator teeth.
• the yoke may be formed across the slot at a distance from the top of the slot, or alternatively a plurality of yokes may be formed across the slot at different distances from the top of the slot.
• the width in the direction of the slot shall not be less than a lower li- it of typically 2-3 mm.
• Closing the slots also reduces slot harmonics in the air gap flux so that only a fraction remains, typically 5-15%, of the harmonics obtained with an open slot. Thus substantially all noise caused magnetically by slot harmonics disappears.
• the yoke is constructed so that its magnetic properties deviate from the magnetic properties of the stator teeth.
• the yoke may thus be constructed so that the relative magnetic permeability in the yoke material is close to the value 1, by the yoke being perforated, for instance, or by the material in the yoke being worked, e.g. laser-worked, in order to lower its relative magnetic permeability, preferably to a value in the vi- cinity of 1.
• the invention is in the first place intended for use with a rotating electric machine in which the stator windings are drawn through slots in the stator and the windings are wound from high-voltage cable of a type comprising a core with a plurality of strand parts, an inner semiconducting layer surrounding the core, an insulating layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the insulating layer.
• high-voltage insulated electric conductors in the following termed high- voltage cables, with solid insulation similar to that used in cables for transmitting electric power (e.g. XLPE cables) the voltage of the machine can be increa- sed to such levels that it can be connected directly to the power network without an intermediate transformer. The transformer can therefore be eliminated.
• the slots in which the cables are placed in the stator are generally deeper than with con- ventional technology, since thicker insulation is required due to higher voltage and more turns in the winding. This increases the problems of mechanical natural vibrations in the stator teeth between the stator slots. In a stator with deep slots damaging vibrations easily occur, generated by electro-magnetic forces and as a result of resonance phenomena, typically with a frequency of twice the network frequency. The advantages of the device according to the invention are therefore particularly pronounced for this kind of machines.
• the windings are preferably composed of cables of a type having solid, extruded insulation, such as those used nowadays for power distribution, e.g. XLPE-cables or cables with EPR-insulation .
• Such cables are flexible, which is an important property in this context since the technology for the device according to the invention is based primarily on winding systems in which the winding is formed from cable which is bent during as- sembly.
• the flexibility of a XLPE-cable normally corresponds to a radius of curvature of approximately 20 cm for a cable 30 mm in diameter, and a radius of curvature of approximately 65 cm for a cable 80 mm in diameter.
• the term "flex- ible” is used to indicate that the winding is flexible down to a radius of curvature in the order of four times the cable diameter, preferably eight to twelve times the cable diameter.
• the cable may preferably have a diameter within the interval 20-200 mm and a conducting area within the interval 80-3000mm 2 .
• windings are constructed to retain their properties even when bent and when subjected to thermal stress during operation. It is vital that the layers retain their adhesion to each other in this context.
• the material properties of the layers are decisive here, par- ticularly their elasticity and relative coefficients of thermal expansion.
• the insulating layer consists of cross-linked, low-density polyethylene
• the semiconducting layers consist of polyethylene with soot and metal particles mixed in.
• the insulating layer may consist, for example, of a solid thermoplastic material such as low-density polyethylene (LDPE) , high-density polyethylene (HDPE) , polypropylene (PP), polybutylene (PB) , polymethyl pentene (PMP), cross-linked materials such as cross-linked po- lyethylene (XLPE) , or rubber such as ethylene propylene rubber (EPR) or silicon rubber.
• LDPE low-density polyethylene
• HDPE high-density polyethylene
• PP polypropylene
• PB polybutylene
• PMP polymethyl pentene
• XLPE cross-linked po- lyethylene
• EPR ethylene propylene rubber
• the inner and outer semiconducting layers may be of the same basic material but with particles of conducting material such as soot or metal powder mixed in.
• Ethylene-vmyl-acetate copolymers/nitrile rubber, butyl graft polyethylene, ethylene-butyl-acrylate-copolymers and ethylene-ethyl-acrylate copolymers may also constitute suitable polymers for the semiconducting layers .
• the materials listed above have relatively good elasticity, with an E-modulus of E ⁇ 500 MPa, preferably ⁇ 200 MPa.
• the elasticity is sufficient for any minor differences between the coefficients of thermal expansion for the materials m the layers to be absorbed m the radial direction of the elasticity so that no cracks appear, or any other damage, and so that the layers are not released from each other.
• the material in the layers is elastic, and the adhesion between the layers is at least of the same magnitude as the weakest of the materials.
• the conductivity of the two semiconducting layers is sufficient to substantially equalize the potential along each layer.
• the conductivity of the outer semiconducting layer is sufficiently great to enclose the electrical field m the cable, but sufficiently small not to give rise to significant losses due to currents induced in the longitudinal direction of the layer.
• each of the two semiconducting layers essentially constitutes one equipotential surface and the winding, with these layers, will substantially enclose the electrical field within t. There is, of course, nothing to prevent one or more additional semiconducting layers being arranged in the insulating layer.
• FIG. 1 shows a slot division in the stator with an open slot
• Figure 2 a slot division designed according to the present invention
• Figure 3 shows an alternative embodiment according to the invention
• Figure 4 shows a cross section through the high-voltage cable used according to the invention.
• Figure 1 shows a slot division of the sheet iron core in the stator, comprising a slot 2 and a part of the stator teeth 4, 6 on each side of the slot 2.
• the slot
• stator 2 is arranged to receive winding cables 12 running axi- ally through the stator and the slots 2 are normally deeper in this type of alternative current machine than in conventional machines. This incurs the drawbacks of the stator having low natural frequencies and of oscillations easily occurring in the stator 4, 6, as mentioned above .
• the slots 2 in this type of machine contrary to conventional generators, resemble a bicycle chain with protrusions 10 between each cable 12 in the teeth 4, 6 located between the slots 2, so that the cable is secured radially.
• This type of slot is thus often known as "semi-closed", to differentiate it from conventional, open, rectangular slots with perfectly straight sides all the way out to the air gap.
• the slot 2 is open to the air gap at the slot top, to the left in Figure 1.
• the opposite end of the slot is termed the slot bottom.
• yokes 14 are provided across the slots ac- cording to the invention, see Figure 2.
• a yoke is arranged at the slot top and another yoke is arranged at approximately the middle of the slot 2. The most efficient localisation of the yoke from the mechanical aspect is at the top of the slot.
• the yoke (or yokes) 14 is made in one pi- ece with the adjacent stator teeth 4, 6.
• the tangential stability achieved by the yokes 14 increases the natural frequency and provides considerably increased rigidity in each individual tooth, as well as increased flexural rigidity in the entire stator body.
• Another important advantage is that the tangential, electromagnetic forces at the air gap, deriving from the rotor poles, are distributed uniformly between the teeth.
• the yokes cause increased slot lea- kage.
• the increased leakage flow limits the short- circuit currents in the case of any short-circuiting, and eliminates, or at least reduces, slot harmonics in the air gap flux.
• the increased slot leakage causes increased excitation losses.
• the yoke or yokes 14 should preferably be constructed so that their magnetic properties deviate from the mag- netic properties of the stator teeth 4, 6.
• the yoke is preferably constructed so that the relative magnetic permeability in the yoke material is in the vicinity of the value 1. This can be achieved by perforation of the yokes, as shown in Figure 6 at 13.
• the magnetic permeability in the yoke material can be reduced by suitable treatment of the materi- al, e.g. laser treatment.
• FIG. 4 shows a cross section through a high-voltage cable 29 used in the rotating electric machine according to the present invention.
• the high-voltage cable 29 is composed of a number of strand parts 31 having circular cross section and made of copper, for instance. These strand parts 31 are arranged in the middle of the high-voltage cable 29 and around the strand parts 31 is a first semiconducting layer 32.
• a first semiconducting layer 32 Around the first semiconducting layer 32 is an insulating layer 33, e.g. XLPE-insulation, and around the insulating layer 33 is a second semiconducting layer 34.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Iron Core Of Rotating Electric Machines (AREA)
• Insulation, Fastening Of Motor, Generator Windings (AREA)

Applications Claiming Priority (5)

Publications (1)

Family

ID=26662885

Family Applications (1)

Country Status (13)

Families Citing this family (4)

Family Cites Families (3)

• 1997
  • 1997-11-28 SE SE9704433A patent/SE9704433D0/xx unknown
• 1998
  • 1998-02-02 BR BR9807542-0A patent/BR9807542A/pt not_active IP Right Cessation
  • 1998-02-02 KR KR1019997006932A patent/KR20000070683A/ko not_active Application Discontinuation
  • 1998-02-02 JP JP53281798A patent/JP2001510019A/ja active Pending
  • 1998-02-02 EP EP98902372A patent/EP1016193A1/en not_active Withdrawn
  • 1998-02-02 NZ NZ337068A patent/NZ337068A/xx unknown
  • 1998-02-02 CN CN98802268A patent/CN1246977A/zh active Pending
  • 1998-02-02 PL PL98334996A patent/PL334996A1/xx unknown
  • 1998-02-02 AU AU58926/98A patent/AU725272B2/en not_active Ceased
  • 1998-02-02 TR TR1999/01801T patent/TR199901801T2/xx unknown
  • 1998-02-02 WO PCT/SE1998/000175 patent/WO1998034325A1/en not_active Application Discontinuation
  • 1998-02-02 CA CA002278602A patent/CA2278602A1/en not_active Abandoned
• 1999
  • 1999-07-29 NO NO993688A patent/NO993688L/no not_active Application Discontinuation

Non-Patent Citations (1)

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