Characteristic Analysis Of Rotor Winding And Research Of Equivalent Slot Combination In Dual Skew Induction Motor

Level of an acoustic noise and vibration is an important index to measure the quality of electrical machines. There is a great demand of quiet electrical machines in industrial production and social life. Dual skew rotor induction motor has the advantages, such as low acoustic noise and vibration. And it also has not the defects which axial endplay problems and synchronous additional torque often occur in conventional skew rotor induction motors. The performance effected when the unique topological structure of dual skew rotor adopted is analyzed in this paper. The phasor relationship of rotor winding current, stator and rotor slot number and synchronous additional torque are analyzed. Major works are listed as follows:The circuit diagram of dual skew rotor winding is different with conventional skew rotor winding. To study the phasor relationship between bar current, end ring current and intermediate ring current, the circuit diagram is established according to basic electrical machines principle. The modal of dual skew induction motor is built in the three dimensional finite element method (FEM). And the simulation work on two of conditions which rotor locked and rated operation. The bar current, end ring current and intermediate ring current are calculated by a calculator in simulation software. The phasor relationship of dual skew rotor winding current is established.The electrical motor will resonate and be noisy, when the orders and frequency of radial electromagnetic force match with the natural resonant orders and frequency.Radial electromagnetic forces which act on stator inner surface are calculated by Maxwell stress tensor. And the orders and frequencies of radial electromagnetic force of four kinds of stator and rotor slot numbers are analyzed. Natural resonant orders and frequency of stator are calculated by modal analysis. Spatial and temporal variation characteristics of radial electromagnetic stress wave of the motor are calculated by a finite element method, and analyzed in space and time domains by the 2-D Fourier analysis. The induction motor is quiet when both the vibration mode and the frequency of electromagnetic force wave keep away from the resonant mode and the natural frequency of the stator core. The quietest induction motor is found by means of the comparison with four different slot number combinations.There are lots of merits when the equivalent slot number is adopted in conventional induction motor. But the stator harmonics will interact with the rotor slot harmonics which not induced by the front. Synchronous additional torques are produced by the interaction. And this will make the conventional induction motor can't start with load.The dual skew rotor is recommended to solve this problem in this paper. The rotor slot harmonic fields are deduced by permeance wave and superposition principle, and the saturation of air-gap magnetic flux is ignored. And the rotor winding magnetic motive force induced by stator harmonics can also be analogized. The rotational speed when synchronous additional torque produced by stator and rotor harmonics flux interaction is deduced. The formulas of synchronous additional torques are deduced. The locked rotor torque of straight rotor, skew rotor and dual skew rotor induction motor are simulated.The simulation results show the dual skew rotor induction motor has all the positive locked rotor torque, and it verified by the experiment data.