Parametric Optimization and Harmonic Analysis on Damper Winding with Direct Time-Step Field and Circuit Coupling Finite Element Method

Traditional magnetic circuit methods conclude that slot magnetic conductivity harmonics modulates main magnetic field in air gap to form additional magnetic field, which generates induced potentials in damper winding. However, slot magnetic conductivity harmonics and additional magnetic field can not be accurately calculated. Direct time-step field and circuit coupling finite element method is proposed to solve the problem, which considers more details of the constraint of damper winding. Parametric optimization is further used to establish damper winding equivalent circuit. Two types of simulations are executed including damper materials and slot pitch angle variation. The proposed method can attain parameters such as flux density and spectrogram diagram on fundamental and high order harmonics. Analysis of simulation results gives the best scheme in the example. It also offers good reference for asynchronous generator squirrel cage structure optimization.

I. Introduction

Damping windings on aeronautic AC synchronous generator act as an important role in preventing stator and rotor from relative motion. Furthermore, it can eliminate open slot influence, which effectively suppresses generator vibration. It can also improve AC voltage waveform and reduce its harmonic content. However, the tooth frequency current generated by the additional magnetic field will produce harmonic potential in stator windings which distorts stator potential waveform. Free-load high times harmonic potential of salient-pole synchronous generator depends on not only airgap magnetic field of harmonic, stator slot size, air-gap size, but also relevant damper winding material and slot pitch angle. Previous damper winding parameters acquisition methods include sudden short-circuit, load rejection and DC Attenuation [1]–[2], which believe that slot magnetic conductivity harmonics modulates main magnetic field in air gap to form additional magnetic field and generates induced potentials in damper winding. But slot magnetic conductivity harmonics and additional magnetic field can not be accurately calculated.