This specific configuration is not a traditional design, as slot wedges are typically made of insulating or magnetic material, but it's an advanced technique employed for specific electromagnetic performance enhancements, primarily to reduce rotor losses and suppress harmonics.
Function and Benefits
The primary function of incorporating a closed-circuit copper coil (or a copper bar/ring) as a slot wedge is to generate eddy currents that oppose the changing magnetic flux near the stator slot opening. This action helps to mitigate undesirable motor effects:
1. Reduction of Rotor Eddy Current Losses
- The permanent magnets on the rotor pass by the stator teeth and slots, creating a time-varying magnetic field (flux density distribution) that is rich in space harmonics.
- These harmonics can penetrate the rotor's surface and permanent magnets, inducing eddy currents within them. These currents lead to energy loss (heat) and reduced motor efficiency.
- The closed copper coil acts as a shielding element. The coil's closed-circuit nature allows the induced voltage from the changing slot flux to drive a circulating current (eddy current) in the coil itself.
- By Lenz's Law, the magnetic field produced by this induced current in the copper coil opposes the original change in flux. This opposition effectively dampens the high-frequency harmonics of the air-gap flux density, preventing them from reaching and inducing losses in the rotor magnets.
2. Cogging Torque and Torque Ripple Reduction
- The air-gap magnetic field is not uniform due to the presence of stator slots, which causes a phenomenon called cogging torque (detent torque) when the rotor magnets align with the slots. This results in vibration and noise.
- By smoothing out the magnetic flux distribution at the slot opening, the copper coil slot wedge can help reduce cogging torque and torque ripple, leading to quieter and smoother motor operation, especially at low speeds.
3. Reduced Pulsation of Air Gap Flux
- The copper ring acts as a short-circuited turn that intercepts the flux pulsations caused by the rotor's movement relative to the slots, creating a counter-field that stabilizes the magnetic flux density in the air gap.
Why hasn't Dr Okon done this if he leads US? Where is Bayern in this?
File back a few 100 pages because I know the wundermotor experts missed it! You need to study with the IEEE!










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