Modified Slot Opening for Reducing Shaft-to-Frame Voltage of AC Motors

Manje Yea,Ki Jin Han

doi:10.3390/en13030760

Manje Yea, Ki Jin Han

Open Access

https://doi.org/10.3390/en13030760

Copy DOI

Abstract

This paper presents a method to reduce the winding-to-rotor capacitance of electrical machines for the purpose of suppressing shaft-to-frame voltage, which causes reliability issues, such as electromagnetic interference (EMI) and bearing current. The proposed method is based on the modification of slot opening shape of the stator core, including the variation of slot opening width and the use of oblique slot opening. For the verification of the suggested method, six different slot opening shapes, including a reference design, are analyzed and compared using finite element analysis, and the results show that the proposed method can reduce the shaft-to-frame voltage by 98%, compared to the reference design.

Highlights

Recent electrical machine drive systems generally include pulse-with-modulation (PWM)inverters
Drive signals of the inverters may have a significant amount of common-mode voltage that can be coupled to various parts of electrical machine systems through parasitic capacitances
These coupled voltages can be the origin of various harmful phenomenons, such as ground current, shaft voltage, and bearing current

Summary

Introduction

Recent electrical machine drive systems generally include pulse-with-modulation (PWM). Drive signals of the inverters may have a significant amount of common-mode voltage that can be coupled to various parts of electrical machine systems through parasitic capacitances. These coupled voltages can be the origin of various harmful phenomenons, such as ground current, shaft voltage, and bearing current. The EDM bearing current is a result of partial discharges between the bearing’s inner and outer races by the development of shaft-to-frame voltage above a threshold. Until now, reported solutions to mitigate the shaft-to-frame voltage include, for example, inserting electro-static shields between the windings and the rotor, using common-mode filters, modifying the modulation schemes of inverter control signals, and electrically shorting the shaft and the frame of machines [5–7]. This paper proposes a method to reduce winding-to-rotor capacitance by modifying slot opening shape of stator core, while not affecting the mechanical and electrical performances of machines

Shaft-to-Frame Voltage and Parasitic Capacitances

Slot Opening Shape Modification

Verification by Finite Element Analysis

Effect of Skewed Rotor

Discussion