Effect of 3D Unidirectional and Hybrid SAGE on Electromagnetic Torque Fluctuation Characteristics in Synchronous Generator

Yu-Ling He,Ming-Xing Xu,Gaurang Vakil,Yue-Xin Sun,Jing Xiong,David Gerada,Xiao-Long Wang

doi:10.1109/access.2019.2929868

Abstract

This paper presents a comprehensive study on the variation laws of electromagnetic torque (EMT) under static air-gap eccentricity (SAGE) conditions in synchronous generators. Different from other studies, this paper focuses on not only the impact of radial SAGE, but also the effect of axial and hybrid SAGE, on the EMT fluctuation characteristics, i.e., we actually study the 3D static rotor eccentricity. The theoretical analysis model is first set up to study the influence of SAGE on the magnetomotive force (MFD) and EMT. Then, the finite element calculation and the experimental study on the CS-5 prototype generator which is of two poles and 3000 rpm are carried out to validate the theoretical analysis. It is shown that the radial SAGE will increase the dc component of MFD and shift the whole MFD curve and the phase current upwardly, while the axial SAGE will reduce the dc component as well as the amplitudes of both the MFD and the phase current like a compressing operation. In general, no matter in unidirectional or hybrid SAGE cases, the radial SAGE will intensify the EMT ripple and increase each harmonic of EMT, while axial SAGE will play the opposite role. The research conclusion obtained in this paper is potential to be applied as a supplement criterion for the condition monitoring and control of the eccentricity faults.

Highlights

Since it is very hard to keep the rotor center in strict accord with respect to the stator center, the static air-gap eccentricity (SAGE) which is called static rotor eccentricity by many scholars [1], [2], exists in almost every motor/generator due to many factors [3]
We propose a comprehensive study on electromagnetic torque (EMT) fluctuation characteristics in radial SAGE, axial SAGE, and hybrid SAGE cases
2D FEA model is only qualified for radial SAGE, while it does not meet the requirement of axial SAGE and hybrid SAGE

Summary

SAGE RSAGE ASAGE HSAGE EMT EMF MMF PPUA MFD

0, δs z ω, ωr normal and RSAGE radial air-gap length permeability of the air Constant and variable PPUA relative SAGE in radial direction relative SAGE in axial direction electrical and mechanical angular frequency t time αm mechanical circumferential angle

Stator phase current

INTRODUCTION

Then MFD can be further obtained by

CONCLUSION