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Integrated Oil Cooling of Electrical Machines

IP.com Disclosure Number: IPCOM000200022D
Original Publication Date: 2010-Oct-12
Included in the Prior Art Database: 2010-Oct-12
Document File: 2 page(s) / 94K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Inefficiency of electrical machines is mainly caused by electromagnetic losses, released in the form of heat. In permanent magnet generators, these losses mainly come from copper losses in the stator conductors, resulting in high temperature of the coils and especially of the end-windings which are surrounded by air. The stator winding temperature must be kept low to avoid decrease in the insulation lifetime, so an efficient cooling system is of prime importance. The stator stack is generally cooled by circulating air through the end-windings, airgaps and radial ducts in the stator, the rotor or both of them. It can also be liquid-cooled by pipes inserted in slots or hollow copper strands. Some high power generators also use hydrogen as a coolant. High power transformers are directly immerged in oil and cooled by natural convection.

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This is the abbreviated version, containing approximately 51% of the total text.

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Integrated Oil Cooling of Electrical Machines

Idea: Jean Le Besnerais, DK-Brande

Inefficiency of electrical machines is mainly caused by electromagnetic losses, released in the form of heat. In permanent magnet generators, these losses mainly come from copper losses in the stator conductors, resulting in high temperature of the coils and especially of the end-windings which are surrounded by air. The stator winding temperature must be kept low to avoid decrease in the insulation lifetime, so an efficient cooling system is of prime importance.

The stator stack is generally cooled by circulating air through the end-windings, airgaps and radial ducts in the stator, the rotor or both of them. It can also be liquid-cooled by pipes inserted in slots or hollow copper strands. Some high power generators also use hydrogen as a coolant. High power transformers are directly immerged in oil and cooled by natural convection.

In the following a solution is proposed to cool the machine with cooling ducts, which are directly punched into the lamination, using oil as a coolant (Figure 1). These ducts are punched close to the slots, where main heat is released by copper losses (Figure 2). The cooling circuit comprises an inlet and an outlet at the ends of the lamination stack and can be direct or diverted (Figure 3). The ducts can be punched right under the slots, in order to use the magnetic shade and do not disturb the magnetic flux path. To avoid any corrosion problems by using water instead of oil as a coolant, an alternative solution is to plate the lamination of internal ducts, for example with nickel plating.

The use of ducts directly punched into the lamination improves the cooling capacity, because of the lower thermal resistance from coolant to coils. According to an external piping system, this proposal has advantages in terms of weight, cost and serviceability. Furthermore oil does not cause corrosion problems on the stator lamination.

© SIEMENS AG 2010 file: 2010J11623.rtf page: 1


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Figure 1: Sectional view on the proposed stator


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