Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K9/00—Arrangements for cooling or ventilating
  • H02K9/19—Arrangements for cooling or ventilating for machines with closed casing and closed-circuit cooling using a liquid cooling medium, e.g. oil

Definitions

• the present invention relates to an electric machine. More specific, the present invention relates to electric machines filled with fluid that is used to lubricate the bearings and cool and protect the electric parts from ingress of unwanted chemicals and particles. Such motors are often used in subsea applications but can also be used topside.
• the Norwegian patent application 20071861 describes a fluid pump system for subsea applications comprising an electric motor where the volume between the rotor and stator is filled with fluid. The fluid is circulated for cooling and lubricating the different parts of the fluid pump system.
• the object of the present invention is to reduce the overall losses of electric machines filled with fluid such that a maximum output power and a maximum overall efficiency can be achieved for a given machine.
• the present invention utilizes the design principle that instead of optimizing the electric efficiency only, all the electrical, mechanical and hydraulic losses are calculated separately in dependence on a variation of the gap between the stator and the rotor. The total efficiency is then calculated and an optimum gap between the stator and the rotor is calculated.
• the present invention relates to an electric machine, comprising a rotor and a stator provided inside a housing, the housing comprises a fluid inlet opening and a fluid outlet opening, where a fluid is circulated inside the housing from the fluid inlet opening to the fluid outlet opening via a gap between the rotor and the stator, and where the rotor is rotating at 1.800-6.000 rounds per minute during normal operation, characterized in that the width of said gap is approximately 2 - 6 times as large as a width of a gap that is optimized to provide an optimal electromagnetic efficiency for the machine, for optimizing the total energy efficiency for the electric machine.
• the width of said gap is approximately 4.5 times as large as the electromagnetic optimal gap width for the machine.
• the electromagnetic design of the motor is optimized for the highest possible electric efficiency at the increased gap width.
• Fig. 1 illustrates a cross sectional view of one embodiment of the invention
• Fig. 2 illustrates the relative losses and the relative power efficiency with respect to relative gap width.
• Fig. 1 shows an electric machine 1, comprising a substantially cylindrical rotor 2 and a stator 3 provided inside a housing 4.
• the rotor 2 fixed to a shaft 5 rotatably supported by means of bearing devices 6 and 7 near the respective ends of the shaft 5.
• the central axis of the shaft 5 defines the rotation axis for the shaft and rotor.
• electrical cables/connectors (not shown) are guided through the housing by means of pressure/fluid resistant penetrators (not shown), which also is considered known for a skilled person.
• the shaft is further connected to an energy consumer or supplier (not shown) depending on whether the electric machine is a motor or a generator respectively.
• the electric machine is a motor used for driving a hydraulic fluid pump system in subsea applications, for example as described in the above- mentioned Norwegian patent application 20071861.
• the housing 4 is at least partially filled with fluid.
• the fluid is lubricating the moving parts of the machine 1, moreover, the fluid is cooling the moving parts.
• the liquid is also used as a protection fluid to prevent ingress of unwanted liquid or particles from ambient surroundings by keeping it at a pressure higher than the surrounding pressure. At larger water depths the external pressure can be considerable and in the order of 100 bar per 1.000 meter water depth and installations in 2-3.000 meter water depth is today considered.
• the fluid inside the motor housing is normally kept at a pressure 10-30 bar above the surrounding water pressure, typically at 210-230 bar at 1.000 meter water depth.
• the rotor has a typical rotating speed of 1.800 - 6.000 rounds per minute during normal operation.
• the rotor is rotating in the fluid inside the motor and as the viscous losses are (somewhat simplified said) proportional to volume of the rotor and proportional to the 3rd power of the speed, the losses are high in absolute values (several 100 KW).
• a gas can be used as fluid inside the motor, as the pressure of the gas increases with increasing depth if the internal pressure shall be higher than the external, the losses using a gas will approach the losses using a liquid in very deep water.
• the housing comprises one or several fluid inlet openings 8 and one or several fluid outlet openings 9, where the fluid is circulated inside the housing from the fluid inlet opening to the fluid outlet opening.
• the fluid inlet openings 8 and the fluid outlet openings 9 are parts of a fluid circulation system generally denoted with number 10.
• the fluid circulation system 10 transports the fluid on the outside of the housing, hence the fluid can be cooled by means of the surrounding sea water.
• the fluid circulation system 10 can for example comprise a pumping device for circulating the fluid, or the fluid can be circulated by the rotation of the machine 1 itself.
• the fluid is also circulated via a gap G between the rotor and the stator.
• the gap G has a width L defined as the distance between the outer diameter of the rotor and inner diameter the stator, as indicated in fig. 1.
• the width L is very small when optimization is done with respect to the electric/magnetic power efficiency.
• Curve A shows the viscous losses in the motor. It can be seen that the viscous losses are decreasing as the gap width L increases.
• Curve B shows the electromagnetic losses. It can be seen that the electromagnetic losses increases as the gap width L increases. However, these losses are relatively low when compared with the viscous losses.
• Curve C shows the total losses, i.e. the sum of curve A and curve B.
• Curve D shows the total power efficiency for the machine.
• the optimal gap width L is a little above 60 on the relative scale, which is far beyond the gap width L where the electromagnetic losses are at its minimum, i.e. below ca 15 on the same scale.
• the housing comprises a fluid inlet opening and a fluid outlet opening, where a fluid is circulated inside the housing from the fluid inlet opening to the fluid outlet opening via a gap between the rotor and the stator, and where the rotor is rotating at 1.800-6.000 rounds per minute during normal operation, the width of said gap should be approximately 2 - 6 times as large as the width of a gap that is optimized to provide an optimal electromagnetic efficiency for the machine, for optimizing the total energy efficiency for the electric machine.
• the width of said gap should be approximately 4.5 times as large as the electromagnetic optimal gap width for the machine.
• the specific optimization will vary from one motor size to another.
• the optimization be dependent on the fluid properties, such as density, viscosity and heat capacity.
• it is achieved an electric machine where the heat generation is reduced during operation, and hence, the total energy efficiency has been improved.
• the pipes or cooler on the outside of the housing that is used for removing the heat from the fluid may be reduced considerably in size due to the reduced generation of heat due to the increase in gap between the stator and rotor.
• the power output to the shaft is increased due to the increase in overall efficiency, the power that is required to be sent to the motor can be reduced and the size and cost of the power supply system is thereby reduced.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Motor Or Generator Frames (AREA)
• Iron Core Of Rotating Electric Machines (AREA)
• Motor Or Generator Cooling System (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=41506404

Family Applications (1)

Country Status (2)

Citations (3)

Family Cites Families (1)

• 2008
  • 2008-10-27 NO NO20084506A patent/NO328758B1/no unknown
• 2009
  • 2009-10-27 WO PCT/NO2009/000373 patent/WO2010050824A1/en active Application Filing

Patent Citations (3)

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