| Permanent magnet direct drive, half direct drive wind power generationsystem adopting full power converter has the advantages of high power density,high output power, high efficiency, high stability for generator and the powergrid, high ability of low voltage across, etc. With the improving of permanentmagnet and high power converter technologys, permanent magnet synchronousgenerator is being widely used in the large wind power generation fields.However, in the operation process, the rotor ndfeb permanent magnet may havethe demagnetization phenomenon of demagnetization and irreversibledemagnetization, subjected to high temperature, armature current and vibration.If the permanent magnet synchronous generator demagnetize seriously, it notonly can make the output power quality drop, but also have big impact for grid.So, it is very important to detect the demagnetization fault in the permanentmagnet synchronous generator, also to make accurately decision.In this paper, the demagnetization fault of the phase fractional permanentmagnet synchronous generator with1.5MW,32poles,4parallel-circuits per slotwere investigated. The two-dimensional transient electromagnetic fieldmathematical model of permanent magnet synchronous generator with differentdemagnetization degree were established. Based on coupled field-circuit model,the mathematical equations were calculated using time-step finite elementmethod. The magnetic field distribution characteristics with differentdemagnetization faults under rated load were analyzed and the change rules ofthe flux density with demagnetization degree on the different positions of thestator core was researched. Besides, every harmonic spectrum in the air gap fluxdensity are analyzed under the different field failure condition. The fault characteristic parameter detection method based on harmonic component willprovides theoretical basis for permanent magnet synchronous generator on-linefault diagnosis system.Based on the time-step finite element method, the counter emf and current indifferent branch are calculated under different demagnetization fault, and thechange rules of no-load back emf waveform, no-load and rated load branchcurrent waveform were compared with that under normal states. The field failurecharacteristics of the generator was found out. The calculation method wasverified by the loss of filed experiment of the small model machine, whichverified the validity of the computing method. Besides, pulse vibration of thestator and vibration unbalanced magnetic pull force of the rotor are studied whenmotor loss magnetism, and conclude that the distribution of the stress is affectedunder the demagnetization on the motor and provide a theoretical basis for thedetection of electromagnetic vibration and noise method to determine whenmotor appears demagnetization.Demagnetization fault of the permanent magnet synchronous generator willlead to the loss changes of the motor, which will directly affect the motortemperature field. Therefore, the temperature field is studied with differentdemagnetization faults in this paper. Considering the normal states, loss ofexcitation with single piece of permanent magnetic and loss of excitation withadjacent two pieces of permanent magnet magnetic, the three-dimensionalsteady-state temperature field mathematical models were established. Accordingto the heat transfer and air dynamics theories, Equivalent thermal conductivity ofthe air was introduced to simplify the convection cooling process between rotorand stator. By the finite element method, the temperature field was solved, andstator temperature distribution of the generator with different demagnetizationfaults under rated speed operation were obtained. Through the analysis of thetemperature field, the influences of copper loss, iron loss and permanent magneteddy current loss with different demagnetization faults on the temperaturedistribution is explored, which will provide a new method to judge thedemagnetization faults by the temperature detection. |
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