FIELD OF THE INVENTION

The invention relates to a cooling arrangement for cooling of an electrical synchronous machine.

BACKGROUND OF THE INVENTION

From the doctoral thesis of Rudolf Krall, “ Permanentmagneterregte Mehrphasen-Synchronmaschine in Zahnspulenausfuhrung einschlieiilich des phasendezimierten Betriebs” (16 ^th September 2015), the drawing of a two-layer single coil winding of a multi-phase-synchronous machine is known, see Fig. 4.16 b) in this thesis. A complete machine, having two-layer single coil windings is given in Fig. 6 a) of the patent application WO2012/135964 A1.

The heat generation inside the winding is caused by the resistance Rcoii of the conductor of the coil and the effective current Icon in the conductor of the coil. The heat power Pheat is calculated by:

Pheat ⁼ Rcoii * (Icoil)^

In Fig. 3 of the present invention, the winding turns 4 and 3 of the two coils 14 and 15 (Fig. 2) of phase U and V are together in one stator slot 28 (Fig. 3). The heat of the outer windings of those coils are not directly in contact with the stator core 9, which is cooled by the fluid of the channels 2. The consequence is, those outer windings 3 and 4 in the middle of the coils have the highest temperature in this area 1 , because the heat resistance between cooling channels 2 in Fig. 3 or a cooling at the stator back and this area 1 is the highest in this arrangement.

Newer solutions, like EP 3 955 424 A1 , propose axial ducts inside the winding slot for a liquid cooling media. The effort for tightening this liquid cooling and pumping the liquid through the long axial gap is high.

CN109474113A relates to an electric machine and a wind driven generator set. The electric machine comprises an active cooling circuit and a passive cooling circuit, wherein the active cooling circuitand the passive cooling circuit are mutually isolated; the active cooling circuit is communicated with enclosure space; the passive cooling circuit is communicated with external environment; the active cooling circuit comprises cavities, an air gap and radial channels, wherein the cavities are mutually communicated and are positioned on two axial ends of the electric machine, the air gap is positioned between the rotor and the stator of the electric motor, and the radial channels are distributed at intervals along the axial direction of the electric machine; cooling equipment communicated with the enclosure space is arranged in the active cooling circuit; the stator is fixed on a fixing shaft through a stator bracket; the passive cooling circuit comprises a first axial channel which axially penetrates through the stator, a second axial channel which penetrates through the stator bracket, and the outer surface of the electric surface; and a heat exchanger is further arranged in the electric machine and is independently and mutually communicated with the radial channel and the second axial channel. The electric machine combines the advantages of the active cooling circuit and the passive cooling circuit, the power and the self power consumption of cooling equipment are lowered, and the power generation efficiency of a complete machine is improved.

OBJECT OF THE INVENTION

It is an object of the present invention to overcome or at least alleviate one or more of the above problems of the prior art and/or provide the consumer with a useful or commercial choice.

It is an object of the present invention to provide a cooling arrangement for cooling of an electrical synchronous machine.

It is an object of the present invention to provide an integrated drive, containing a gearbox and motor below a mill in a limited height.

It is further an object of the present invention to provide a vertical roller mill comprising a cooling arrangement for cooling of an electrical synchronous machine according to the present invention.

It is a further object of the present invention to provide an alternative to the prior art.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a cooling arrangement for cooling of an electrical synchronous machine comprising a two-layer single coil winding. The two-layer single coil preferably comprises an airgap between different single coils in a stator slot, the stator slot being preferably open towards the radial air ducts of the rotor core and to be part of an air circuit inside the electrical synchronous machine. The air circuit is preferably configured to be driven by one or more rotating radial air ducts and a fan. In another embodiment of the present invention, the cooling arrangement may comprise two or more fans. The cooling arrangement according to the present invention has the advantage of a more efficient cooling at the warmest area of two-layer single coil windings of electrical synchronous machines. The more efficient cooling method let increase the rated torque of a synchronous machine by increasing the effective coil currents, without exceeding the limit of the insulation material temperature. The more efficient cooling is achieved by a cooling airflow in the gap between the winding turns of the coils.

The cooling arrangement may further comprise cooling fins at a stator back, for cooling the internal air circuit.

The cooling arrangement may further comprise cooling channels inside the stator. The cooling channels preferably comprise an external cooling fluid flow inside. The cooling channels are configured for cooling the stator and stator fins.

The cooling arrangement may further comprise a cooling pipe. The cooling pipe is preferably configured for leading the external cooling fluid inside the stator. The cooling pipe preferably comprises fins at an inner diameter.

In another preferred embodiment of the present invention, the cooling arrangement may further comprise swirling leads inside the cooling channel. The swirling leads preferably build at least one spiral channel inside the cooling pipe.

An electrical synchronous machine may comprise a cooling arrangement according to the first aspect of the present invention.

The advantage of incorporating the cooling arrangement in a synchronous machine is the opportunity of operating with higher current at the equivalent hot spot temperature in the coils, respectively to operate a synchronous machine, which has a decreased size, operating with the equivalent torque.

A vertical roller mill may comprise an electrical synchronous machine further comprising a cooling arrangement according to the first aspect of the present invention.

The advantage of incorporating the cooling arrangement in a synchronous machine, applied in operation having limited space, for example under a vertical roller mill, is that the motor volume is decreased by a more efficient cooling. This is achieved by cooling the warmest area of two-layer single coil windings of an electrical synchronous machine. The more efficient cooling method let increase the rated torque of a synchronous machine by increasing the effective coil currents, without exceeding the limit of the insulation material temperature, respectively decreases the machine volume for equivalent torque. The more efficient cooling is achieved by a cooling airflow in the gap between the winding turns of the coils. In a second aspect, the invention relates to a method for cooling of an electrical synchronous machine comprising a two-layer single coil winding, the method comprising the steps of providing cooling air through radial air gaps of a rotor, pressurize the cooling air into a radial air gap and by this into openings between wedges into an air gap between coils, from where the cooling air is exhausted from a radial fan.

The first and second aspect of the invention may be combined.

BRIEF DESCRIPTION OF THE FIGURES

The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Figure 1 schematically illustrates a rotor, stator, and coils 20 of the electrical synchronous machine, having two-layer single coil windings, according to the present invention.

Figure 2 schematically illustrates a section of one pole pair of an electrical synchronous three-phase machine with three single coil two-layer windings, according to the present invention.

Figure 3 schematically illustrates Detail X of Fig. 2, stator slot having winding turns of two single coils of two phases inside, according to the present invention.

Figure 4 schematically illustrates a stator (motor without rotor) with the external cooling fluid 13, according to the present invention.

Figure 5 schematically illustrates an internal air circuit 20, according to the present invention.

Figure 6 schematically illustrates a removal of spacer 31 , according to the present invention.

Figure 7 schematically illustrates a cooling pipe with fins 34 and spiral 32 inside, according to the present invention.

Figure 8 schematically illustrates an electrical machine, according to the present invention, under a vertical roller mill. DETAILED DESCRIPTION OF THE INVENTION

The geometry structure of the electromagnetic components of a synchronous machine, having two-layer single coil windings 20 is given in Fig. 1 . The term of two-layer windings is generally known in the field of electrical machines to have winding turns of two different phases in one stator slot 28 (see Fig. 3). The machine is excited by permanent magnets 11 (Fig. 1). Those magnets are arranged between the poles 10a of the rotor core 12 and the intermediate poles 10b.

In a preferred embodiment, the cooling arrangement according to the present invention, comprises a two- layer single coil winding 28. The two-layer single coil comprises an airgap 17 between different single coils 22 in a stator slot. The stator slot is open towards a radial air duct 24 of a rotor core and to be part of an air circuit 20 inside the electrical synchronous machine. The air circuit 20 is configured to be driven by one or more rotating radial air ducts 24 and a fan 21. In another embodiment of the present invention, there are additional axial fans arranged at the opposite rotor side delivering the air into the rotor.

The cooling arrangement further comprises cooling fins 27 at a stator back, for cooling the internal air circuit 20, as illustrated in figure 2.

In another embodiment, the cooling arrangement further comprises cooling channels 2 inside the stator, also illustrated in figure 2. The cooling channels 2 comprise an external cooling fluid 13 flow inside. The cooling channels 2 are configured for cooling the stator and stator fins 34.

In yet another preferred embodiment, the cooling arrangement further comprises a cooling pipe 29, schematically illustrated in figure 7. The cooling pipe 29 is configured for leading the external cooling fluid inside the stator. The cooling pipe 29 comprises fins at an inner diameter.

As illustrated in figure 3, the cooling arrangement further comprises swirling leads inside the cooling pipe 29. The swirling leads build at least one spiral channel inside the cooling pipe 29.

The challenge is to cool the hot area 1 (Fig. 3) directly by a fluid without high effort.

The solution is to force the air flow through radial air ducts 24 (Fig. 5) of the rotor into the air gap 17 between the neighbor coils, for example 15 and 16, see Fig. 4. The air flow is forced by the rotation of radial air ducts in the rotor core 24 (see Fig. 5) of the rotor. For this function, the rotor core 12 (Fig. 1) is separated in rotor discs 50 (Fig. 5), and the wedges 18 (Fig. 4) do not cover the winding slot at the radial ducts 24. Additionally, this airflow is forced by the fan 21 (Fig. 5), which is already available for the cooling of the winding over hangs. The coils are fastened by the wedges 18 only partially. The coils are made of litz wires which are flexible before the vacuum pressure impregnation (VPI). During the impregnation and during the curing of the resin spacers 31 (Fig. 6), pressing the coils (for example 15 and 16 in Fig. 6) to the surfaces of the stator slot and the hardened resin ensure an adhesive bond between the insulation 30 (Fig. 3) and the stator core 9. After the litz coils have become a stiff block by the hardened resin and are adhesively bonded to the stator core, the spacers 31 (Fig. 6) are removed by the force F (Fig. 6).

The adhesion to the spacer is avoided by using a spacer made of polytetrafluoroethylene or wrapping a non-adhesive foil around the spacer. The removal of the spacers is additionally enabled, after the cooling down of stator, after the oven curing process, by the higher thermal shrinkage of the copper-resin coil in comparison of the shrinkage of the steel of the stator core.

Fig. 5 shows the internal airflow 20, which is driven by radial air ducts 24 of the rotor and the fan 21 . The internal airflow 20 is cooled down at the fins 27 (Fig. 2) at the stator back. Those fins are cooled by the external cooling fluid 13 (Fig. 4).

The internal air flow 20 (Fig. 5) must be effectively cooled, which is achieved by the cooling fins 27 (Fig. 2) at the stator back. Those fins must be cooled effectively by an external cooling fluid 13 (Fig. 2). For the avoidance of a destruction of the machine in case of leakage, for example by cooling water in the lubricating oil of the machine, the same oil, which is used for the lubrication of the bearings and for the lubrication of a gearbox, which could be assembled with the motor, is used to be the cooling fluid. This also minimizes the duty, by the avoidance of a separate pump and a separate cooler. The high viscosity of oil increases the convective heat resistance in the cooling channels 2 (Fig. 3) because there is no turbulent flow under acceptable circumstances. For increasing the heat conductivity between the cooling pipe 29 and the high viscos oil, the inner diameter of the cooling pipes has fins 34 (Fig. 7), which are manufactured by bar extrusion of aluminum. Inducted currents in the stator core are avoided by the electrical insulation between the aluminum pipe 29 and the stator core 9, given by anodization of the aluminum pipe.

A further measure for increasing the heat conductivity of the convection inside the cooling pipes is to swirl the oil inside the cooling pipe by spiral channels 33 (Fig. 7). Those are achieved by spiral elements 32 (Fig. 7) inside the cooling pipes 29. The cooling pipes are filled up along the complete length with those elements 32.

The cooling arrangement according to the present invention is preferably installed in an electrical synchronous machine, which is configured to be inserted in a vertical roller mill. The present invention also relates to a method for cooling of an electrical synchronous machine comprising a two-layer single coil winding. The method comprises the steps of providing cooling air through radial air ducts 24 in the rotor core, pressurize the cooling air into a radial air gap 50 and by this into openings 24 between wedges 18 into an air gap 17 between coils, from where the cooling air is exhausted from a radial fan 21 .

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. It should also be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.

References:

(1) Hot area

(2) Cooling channels

(3) Outer winding-turn of the coil of phase U

(4) Outer winding-turn of the coil of phase V

(5) Part of Coil U-

(6) Part of Coil V+

(7) Part of Coil W+

(8) Part of Coil W-

(9) Stator core

(10) Rotor pole

(11)Permanent magnets

(12) Rotor core

(13) External cooling fluid

(14) Coil of phase U

(15) Coil of phase V

(16) Coil of phase W

(17) Air gap between two coils

(18) Wedges

(19) Outer cover of the internal air flow

(20) Internal air circuit

(21) Fan

(22) Coil

(23) Air gap between two coils

(24) Radial air ducts in the rotor core

(25) Axial air channel inside the rotor core

(26) Shaft

(27) Cooling fins at the stator back

(28) Winding slot having winding turns of phase U and of phase V inside

(29) Cooling pipes

(30) Electrical insulation

(31) Spacer

(32) Spiral

(33) Double spiral channels

(34) Fins

(35) Cross section without oil flow

(36) Air flow between coils

(37) Electrical motor

(38) Gearbox and axial bearing

(39) Mill table

(40) Table liner

(41) Nozzle of louvre ring

(42) Dam ring

(43) Material scraper

(44) Roller

(45) Discharge flap

(46) Mill exhaust

(47) Feed gate

(48) Hydraulic cylinder

(49) Radial airgap between rotor and stator

(50) Rotor disk

(F) Force removing the spacer (31)