WO2015075275A2

WO2015075275A2 - Electric machine

Info

Publication number: WO2015075275A2
Application number: PCT/EP2014/075590
Authority: WO
Inventors: Janne Ikonen; Jani KOSONEN
Original assignee: Abb Technology Ag
Priority date: 2013-11-25
Filing date: 2014-11-25
Publication date: 2015-05-28
Also published as: WO2015075275A3

Abstract

The electric machine comprises a frame, a stator arranged inside the frame, and a rotor arranged inside the stator, and a shaft, whereto the rotor has been fixed, wherein the shaft is arranged to rotate supported the bearings. An axial ribbing is arranged onto the outer surface of the frame, the axial ribbing comprising a plurality of axial ribs, which protrude from the frame, and slots between the adjacent ribs, whereby an accessory is installable onto the outer surface of the frame in the ribbed sector. At least two ribs comprises a fixing knob, which are located in a position corresponding to the fixing points of the accessory, whereby axial thickness of the fixing knobs varies as distance from the fixing point increases.

Description

Electric Machine

FIELD OF THE INVENTION

The invention relates to an electric machine as defined on the preamble part of the claim 1 . BACKGROUND ART

An Electric machine normally comprises a frame of the electric machine, whereby the electromagnetic parts of the electric machine are arranged inside the frame and the mechanical parts of the electrical parts are supported to the frame either directly or via the end shields that are attached to the frame. As a rule the frame of the electrical machine is cast iron, especially when the electric machine is designed to have the power range of tens of or even hundreds of kilowatts. The stator of the electric machine is arranged inside the frame and is attached to the frame. The stator has been made of magnetically conductive material like laminated steel plates. The stator windings are installed onto the inner surface of the stator core. The rotor of the electric machine has been arranged inside the stator and the rotor is supported by the shaft of the rotor and by the bearings to the frame of stator or to the end shields of the electric machine. The rotor also has been made of magnetically conductive material. The rotor has rotor windings or permanent magnets for exciting the electric machine or the rotor is constructed in a suitable manner to guide the magnetic flow like in a reluctance machine, for example.

The electric current flowing in the stator windings and/or in the rotor windings of the electric machine as well as the magnetic flux flowing in the magnetic core of the stator and rotor cause warming of the electric machine. This heat energy must be conducted out from the active parts of the electric machine in order to keep the operating temperature of the electric machine within the allowed limits. For this purpose it has been developed several means and methods to achieve the required result. One often used method and structure is a rib cooled electric machine. In this solution the outer surface has cooling ribs which increase the cooling surface of the outer circumference of the electric machine. A fan or fans are used to blow air into the ribs and to the spaces between the adjacent ribs for increasing the heat transfer from the electric machine. In some embodiments there is a need to install auxiliary equipment that are fixed to the frame of the electric machine. These auxil iary equ ipment may be apparatus to supply lubricating oil for a slide bearing or pressurization devices used in the electric machines that are operating in the explosive space, for example. Because of the client related requirements it sometimes arises a need to attach auxiliary devices onto the electric machines. These auxiliary devices may not have been specified or known when the electric machine has been designed and produced.

In order to create and guarantee a sufficient cooling power the air must flow unrestrictedly on the whole area of the circumferential outer surface of the electric machine. The auxiliary equipment could have been installed afterwards only by boring fixing holes in the cast frame between the adjacent cooling ribs.

This will prevent the designed air flow on the outer surface of the electric machine and between the cooling ribs. As a result the electric machine will warm excessively either locally or totally. The efficiency of the electric machine will decrease, and the heating additionally may cause a shortened lifetime, increases nee for maintenance and decreases reliability.

Publication DE3937672 A1 discloses an electric machine wherein a component, a capacitor for example, is attached onto the electric machine by supporting the fixing means of the component between the adjacent cooling ribs. The fixing means prevent the normal air flow between the ribs.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to ach ieve an electric machine with improved means to fix an accessory to a rib cooled electric machine. The electric machine according to the invention is characterized by what is stated in the characterizing portion of claim 1 .

The electric machine comprises a frame, a stator arranged inside the frame, and a rotor arranged inside the stator, and a shaft, whereto the rotor has been fixed, wherein the shaft is arranged to rotate supported the bearings, whereby an axial ribbing is arranged onto the outer surface of the frame, the axial ribbing comprising a plurality of axial ribs, which protrude from the frame, and slots between the adjacent ribs, whereby an accessory is installable onto the outer surface of the frame in the ribbed sector.

The electric machine is characterized in that it further comprises at least two ribs comprises a fixing knob, which are located in a position corresponding to the fixing points of the accessory, whereby axial thickness of the fixing knobs varies as distance from the fixing point increases.

An advantage of the invention is that for the accessories or the equipment there is provided a fixing surface, which does not at all disturb the flow of the cooling air between the cooling ribs on the outer surface of the machine, it disturbs the flow of the cooling remarkably less than in the conventional structures. There exists a channel or space for the axial flow of the cooling air that is sufficient for the machine in question in the fixing points of the accessories or the auxiliary equipment. Further, the mechanical structure of the frame is not damaged because of additional machining. A further advantage is that when the fixing points for accessories and equipment are set, work on the installation site is avoided. This work is usually expensive to plan and to perform. At the same time the designed operation of the machine will be guaranteed.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an axonometric view showing a frame of the electric machine in accordance with the invention.

Figure 2 is a side view of the frame shown in Figure 1 . Figure 3 is an end view of the frame shown in Figure 1 .

Figure 4 shows a schematic horizontal cross section of an electric machine.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

The figures 1 , 2 and 3 show a frame 2 of an electric machine according to the invention. The figure 4 show a schematic horizontal cross section of an electric machine, wherewith the invention is utilized to describe the structure of the electric machine. The stator 21 of the electrical machine is installed into the frame 2 and the rotor 1 1 of the electrical machine is installed inside the stator 21 , whereby there is an air gap G between the rotor and the stator. The stator comprises winding 25 inserted into the slots of the stator 21 . The rotor 1 1 is fixed to the shaft 13 of the machine and the shaft 13 is supported by bearings 43 to the end shields 51 and 52 of the electric machine. The shaft 13 and the rotor 1 1 rotates around the axial rotating axis X1 -X1 . The end shields 51 and 52 are fixed to the ends 4 of the frame 2. The frame 2 is fixed to the basement via the feet 6 with fixing bolts. The stator frame 2 is made of cast iron and its outer surface comprises a plurality of cooling ribs 8 that extend axially, in other word in the direction of the machine's shaft. In the embodiment of figure 1 , there are cooling ribs both on the sides 10 of the machine and under the machine 12. In the upper portion frame there is arranged a terminal box 14 of the electric machine and a service hatch 16.

At one end of the electric machine a fan 32 has been arranged inside a fan cover 45. The fan 32 blows air flow F from the end of the machine in the direction of the cooling ribs. In two cooling ribs 18 and 20 there has been formed fixing knobs 22 for the accessories 24 (figure 3) that are to be installed into connection of the machine. These auxiliary equipment may be apparatus to supply lubricating oil for a slide bearing or pressurization devices used in the electric machines that are operating in the explosive space, for example. Because of the client related requirements it sometimes arises a need to attach auxiliary devices onto the electric machines. These auxiliary devices may not have been specified or known when the electric machine has been designed and produced. The fixing knob 22 has been formed by making a portion of the cooling rib 18 and 20 thicker than the cooling rib in the other portion is. The fixing knob 22 is, advantageously formed when casting the frame 2. There is fixing hole in the center of the fixing knob 22 when viewed towards the cooling rib 18 from outer side of the machine. The fixing hole is a pre-fabricated in order to facilitate the positioning and the attaching the accessories. In a preferred embodiment the fixing hole is threaded. In the embodiment of figure 2 there are fixing knobs 22 in two cooling ribs. In the cooling rib 18 there are five fixing knobs 22 and in the cooling rib 20 there are five fixing knobs 22 resulting ten fixing knobs altogether. The number of the cooling knobs is naturally variable machine by machine. Similarly, the number of the fixing knobs being active, i.e. the fixing knobs used to fix the accessories depends on the requirement of the application in question.

The location of the fixing knobs corresponds to each fixing point of the accessories and of the auxiliary equipment. The thickness of the fixing knob changes linearly as a function of the distance from the fixing point when viewed in the axial direction of the cooling rib. Thus the fixing knob is the thickest in the center of the surface of the fixing knob and evenly becomes thinner when the distance from the center of the surface increases.

According to another embodiment of the invention the thickness of fixing knob changes streamlined. This results streamlined floe of the cooling air between the cooling ribs.

In one preferred embodiment a rib next to the fixing knob is thinned in the axial position of the fixing knob. This results a channel for the cooling air that is as constant as possible also in the area of the fixing knobs. In one preferred embodiment the fixing knob 23 protrudes outside the cooling rib as shown in figure 3. Thereby there is a free space for the cooling air under accessory, too.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1 . An electric machine comprising a frame, a stator arranged inside the frame, and a rotor arranged inside the stator, and a shaft, whereto the rotor has been fixed, wherein the shaft is arranged to rotate supported the bearings, whereby an axial ribbing is arranged onto the outer surface of the frame, the axial ribbing comprising a plurality of axial ribs, which protrude from the frame, and slots between the adjacent ribs, whereby an accessory is installable onto the outer surface of the frame in the ribbed sector, characterized in that at least two ribs comprises a fixing knob, which are located in a position corresponding to the fixing points of the accessory, whereby axial thickness of the fixing knobs varies as distance from the fixing point increases.

2. An electric machine according to claim 1 , characterized in that the thickness of the fixing knob changes linearly as a function of the distance from the fixing point.

3. An electric machine according to claim 1 , characterized in that the thickness of the fixing knob changes streamlined.

4. An electric machine according to claim 1 , characterized in that a rib next to the fixing knob is thinned in the axial position of the fixing knob.

5. An electric machine according to claim 1 , characterized in that the frame is made by casting.

6. An electric machine according to claim 1 , characterized in that the fixing knobs are located under the horizontal level defined by the shaft of the machine.

7. An electric machine according to claim 1 , characterized in that the fixing knob comprises a thread fixing hole for the fixing bolt of the accessory.

8. An electric machine according to claim 1 , characterized in that the fixing knob protrudes outside the cooling rib.