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Model Of Air Flow In Cooling System Of Induction Machines

Roman Pechánek, University of West Bohemia in Pilsen (20.7.2009, Doc Ing. Josef Červený CSc, University of West Bohemia in Pilsen)

Abstract

This paper deals with cooling system for traction enclosed induction machines from Škoda Electric a.s. A FEM model was designed to improve internal and external air flow systems. The model of a rotor shorting ring was made in internal air flow system. Further the model of complete external air flow system was made too. Software ANSYS WorkBench 11 was used for solving the model. The results of both FEM models are presented and described.

1. Introduction

Thermal analysis of electric machines or their components, are now highly desirable and important. For how to maximize the use of electrical equipment leads to an increase in electrical load of active components. Losses that arise in these parts, have resulted in increasing the temperature of active components, or the whole machine. This issue is important to address simultaneously the electromagnetic and mechanical design tools. For this reason, there is in collaboration with Skoda Electric a.s. software suitable for calculating the temperature rise of traction machines. When creating a replacement blower motor for a closed network (Fig. 1) there were areas that can be very difficult to describe using existing literature and where the

cooling air flow estimate is highly uncertain. The internal cooling system is the ventilation of the area surrounding the balancing ring. Here, first of all to investigate the influence of rotation circle of balancing on the the flow of cooling air entering the rotor. In addition to the entry of cooling air into the ventilation ducts of the rotor. In particular, the components of the velocity vector of flowing air. In the outer ventilation circuit is the output of the fan and the cooling air entry into the stator ventilation ducts. Software Ansys Workbench 11 was used to obtain a picture of the behavior of cooling air in the above areas.

2. Machine parameters MLU 3436 K/4

Nominal power 90kW Nominal voltage 400V Nominal current 163A Speed 1973ot/min Maximum speed 4800ot/min Insulation class 200 Opacity / cooling IP54/IC41

3. Inner cooling circuit On the leeward side of the cooling air after

passing through the stator ends enters the space defined balancing ring, shorting ring, rotor bars, rotor and shaft of the packet. In this area can be expected to influence the balancing ring. This is a rotating component, hence the movement creates pressure effect, which operates in the same direction as the effect of the pressure bars and shorting ring. May also circle around the balancing occur swirl fields that would diminish inline air cooling section. Another uncertain point in creating alternative ventilation networks showed enter to cooling ducts of the rotor. This is the determining components of the velocity vector of flowing air.

3. 1. Without balancing ring

In figure 2 shows the model without the balancing ring. Computational model corresponds to the technical documentation Skoda Electric as. The model is created in SolidWorks software and the environment Ansys transferred as geometry type

XI International PhD Workshop OWD 2009, 17–20 October 2009

Fig. 1: Cross section of the induction machine

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Parasolid. Areas respectful air intake are awarded discharges fronts around the stator and discharges between the stator ends. Boundary condition in the ventilation channels (the output from the model) is specified such as "opening". Other boundary conditions are a type of "wall" and with a rotation speed corresponding to a nominal or no rotation. FEM model is solved for constant temperature. Figure 3 illustrates the flow velocity in the direction of x. In addition to the cooling air nozzles in the field representing the free space between the ends of the stator windings and focal shield. Finally, it shows the progress rate, depending on the x-s coordinate. On entering the rotor ventilation ducts leads to a sharp reduction in the speed increase = 2.4 m/s at v =1.2 m/s.

3. 2. With balancing ring

Geometry of the study area with balancing ring is similar to the previous model. Again it is imported geometry from SolidWorks. Cut the area is shown in Figure 4 The speed of rotation of the balancing ring is entered along with other boundary conditions. The results of simulation calculation is shown in Figure 5 The results indicate a projected vortex field

around and over the balancer ring (Fig. 5.b). The size of the speed in the direction x (Fig. 5.c) is the apparent reduction in speed in the direction of balancing x around the circle. Subsequently, however, the flow velocity increases to the value v = 2 m/s to enter the cooling ducts in the rotor. Flowing through the air passage around the balancing ring gets in the rotation direction of rotation of the rotor.

4. External cooling circuit

Computational model is again based on the design documentation Skoda Electric as. Surveyed area is defined by an internal shield, external ventilation ducts and the outer shield. Air enters the model of free space and passes through the fan. After exit from the fan, the air is divided into separate external ventilation ducts. Computational model is created in the software Solidworks and

Ansys transferred to the environment as the geometry type Parasolid. The fan is modeled as two circular area. Area respects the air intake is given discharges. Boundary condition at the outlet of the cooling ducts is specified, type "opening". Other boundary conditions are a type of "wall" and with the corresponding rotation speed or without rotation. The fan surfaces are specified as boundary condition a higher toughness, the FEM model is solved for constant temperature. The results of simulation calculation is shown in Fig 7. The results illustrate the distribution of cooling air flow. For the nominal speed, the air outlet from the fan divided into the cooling ducts in the circumstances, see Fig 7. For maximum speed of rotation of the cooling air away from extreme cooling ducts figure 8.

Fig. 2: The FEM model of the internal cooling system

Obr. 4: The model with the balancing ring

Fig. 6: The model of the external cooling system

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Fig.3: The results of the calculation model, without balancing circle a) cooling air velocity in x-direction of entry into the ventilation ducts b) streamline of cooling air

c) the course of the speed depending on the x-coordinate

Fig.5: The results of the calculation model, with balancing circle a) cooling air velocity in x-direction of entry into the ventilation ducts b) streamline of cooling air c) the course of the speed depending on the x-coordinate

Fig 7: The distribution of cooling air in the external cooling system for the nominal speed. a) cooling air streamlines

b) pressure distribution in the area before entering the external cooling ducts

Fig 8: The distribution of cooling air in the external cooling system for the maximal speed.

a) cooling air streamlines b) pressure distribution in the area before entering

the external cooling ducts

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5. Conclusion The work performed calculation models are problematic areas in cooling system asynchronous traction motor. In the internal cooling system is evident from the results effect of the balancing ring to the flow cooling air. Balancing ring results in a vortex field around the balancing circle and above it. As Figure 5.c) is the apparent reduction in speed in the direction of x around the balancing ring. Subsequently, however, the flow velocity increases to the value v = 2m/s to enter the ventilation ducts in the rotor. Figure 3.c) shows the course of the speed in x-direction without the balancing ring. On entering the rotor ventilation ducts leads to a sharp decrease in the speed from v = 2.4 m/s to v = 1.2 m/s. The outer cooling system is evident from the results of cooling air diverted from the extremes of cooling ducts, resulting in a reduction in surface cooling machines.

6. Bibliography

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[4] Steinberg D. S.; Cooling Techniques for Electronic Equipment, Wiley-Interscience, 1991, ISBN: 0471524514.

[5] Pechánek, R.; Teplotní analýza trakčního asynchronního motoru pomocí softwaru ANSYS, Elektrotechnika a informatika 2008. Část 1., Elektrotechnika, V Plzni, Západočeská univerzita, 2008. ISBN 978-80-7043-702-5.

[6] Hrabovcová, V; Jokinen; T.; Pyrhönen, J.: Design of rotating electrical machines, Wiley, 2008. ISBN 978-0-470-69516-.

[7] Mellor, P. H.; Roberts, D.R.; Turner, D.R: Lumped Parameter Thermal Model for Electrical Machines of TEFC Design, V zborníku konferencie IEEE Procedings B, Vol.-138, No. 5, Sept. 1991.

[8] Lee, Y.; Hahn, S.; Kauh, S. K.: Thermal Analysis of Induction Motor with Forced Cooling Channels, V časopise IEEE Transactions on Magnetic, Vol. 36, No. 4, 2000. s. 1398 – 1402

[9] Shenkman, A. L.; Chertkov, M.: Experimental Method for Synthesis of Generalized Thermal Circuit of Polyphase Induction Motors, V časopise IEEE Transaction on Energy Conversion, Vol. 15,

Author: Ing.Roman Pechánek

University of West Bohemia in Pilsen, Faculty of electrical engineering, Department of Electromechanics and Power Electronics. Univerzitní 26 306 14 Plzeň email: rpechane@kev.zcu.cz