J Electr Eng Technol Vol. 8, No. 4: 938-944, 2013 http://dx.doi.org/10.5370/JEET.2013.8.4.938 938 Suppression of Shaft Voltage by Rotor and Magnet Shape Design of IPM-Type High Voltage Motor Kyung-Tae Kim*, Sang-Hoon Cha**, Jin Hur*, Jae-Sun Shim*** and Byeong-Woo Kim † Abstract – In this paper, we propose a method for suppressing shaft voltage by modifying the shape of the rotor and the permanent magnets in interior permanent magnet-type-high-voltage motors. Shaft voltage, which is induced by parasitic components and the leakage flux in motor-driven systems, adversely affects their bearings. In order to minimize shaft voltage, we designed a magnet re- arrangement and rotor re-structuring of the motor. The shaft voltage suppression effect of the designed model was confirmed experimentally and by comparative finite element analysis. Keywords: Shaft voltage, Bearing fault, Common mode voltage, Parasitic parameter, V-shaped motor, Interior permanent magnet motor 1. Introduction The electric vehicle is used many motors. Also, the heavily equipped vehicle is used high-voltage motor. So, shaft voltage has become a serious problem in interior permanent magnet (IPM)-type motors. In addition, the lifetime and the reliability of such motors are greatly reduced by bearing faults, which are caused by the induced voltage on the shaft’s surface. These bearing faults create motor vibration and noise, which are the main causes of motor faults. There are four causes of shaft voltage in a motor: electrostatic shaft voltage, magnetic unbalanced shaft voltage, electromagnetic shaft voltage and shaft voltage from the external power supply. Among these four causes, electromagnetic shaft voltage and external power- supply are the primary causes of shaft voltage. Magnetic unbalanced shaft voltage is caused by modification of the stator core and eccentricity between the stator and rotor. Shaft voltage from the external power supply is caused by the common mode voltage, which is due to a parasitic component as well as leakage flux from the high input voltage and high frequency of the inverter. Shaft voltage can be suppressed with insulated bearings, shaft grounding rings, grounding brushes, Faraday shields, conductive grease, insulated rotors, etc. [1, 2]. There are many ways to suppress shaft voltage, but they cannot be used in special circumstances. For example, a motor with the fragile insulating material cannot be high- temperature parts and cannot be used in the deep sea because of high hydraulic pressure. The magnetic circuit technique of modifying the permanent magnet and rotor shape in an IPM motor to suppress shaft voltage has not yet been described in detail in the literature. Therefore, in order to suppress shaft voltage, we propose an improved shape for permanent magnets that will not affect the torque characteristics. Consequently, in this paper, we propose suppressing shaft voltage by modifying the magnet and rotor shape, taking the common mode voltage into consideration. The shaft voltage suppression in IPM-type high-voltage motors was confirmed through experiments. In addition, the proposed method was validated by the finite element method (FEM). 2. The Cause of Shaft Voltage 2.1 Electrostatic shaft voltage An electrostatic shaft voltage is induced by friction static electricity in motor-driven systems of shaft included electrostatic capacity. This shaft voltage in motor driven- system mostly occurs in the drive belt, and is the direct current component. 2.2 Magnetic unbalanced shaft voltage Magnetic unbalanced shaft voltage is induced by structure, material, and work deviation such as the commissure of the segmented stator core, the segment-contact of the core, transformation of the stator core and the eccentricity between the rotor and stator. Thus, the linkage magnetic flux of the shaft occurs because by magnetic unbalance. 2.3 Shaft voltage from the external power supply Shaft voltage from the external power supply occurs † Corresponding Author: Dept. of Electrical Engineering, Ulsan University, Korea. (bywokim @ulsan.ac.kr) * Dept. of Electrical Engineering, Ulsan University, Korea. (jinhur@ ulsan.ac.kr, kkt2782@nate.com) ** Korea Marine Equipment Research Institute, Korea. (sang3806@ komeri.re.kr) *** Dept. of Electrical Engineering, Kangwon National University, Korea. (namsuk6645@daum.net) Received: May 27, 2013; Accepted: June 7, 2013 ISSN(Print) 1975-0102 ISSN(Online) 2093-7423