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Unformatted text preview: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 2, MARCH/APRIL 2008 555 An Advanced Stator Winding Insulation Quality Assessment Technique for Inverter-Fed Machines Jinkyu Yang, Student Member, IEEE , Jintae Cho, Student Member, IEEE , Sang Bin Lee, Senior Member, IEEE , Ji-Yoon Yoo, and Hee Dong Kim Abstract —The lifetime of the stator winding insulation is re- duced when operated with pulsewidth-modulation inverters, since insulation degradation is accelerated due to increased thermal and electrical stresses on the motor. This paper focuses on a new approach for monitoring the condition of the stator insula- tion for failure-prone inverter-fed machines. The main concept of the proposed technique is to apply a dc and/or variable- frequency ac test voltage to the stator insulation using the inverter and to perform standard offline insulation tests whenever the motor is not operating. This allows the stator insulation to be tested more frequently as compared to offline tests performed once every three to six years during periodic maintenance. Two methods for testing the insulation with minimal modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low-cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. This does not only helps prevent forced outages and safety risks due to insulation breakdown but also helps perform maintenance in an efficient manner, since individual motor maintenance can be prioritized and scheduled based on its present condition. Index Terms —AC electric machines, capacitance ( C ) test, condition monitoring, diagnostics, dissipation factor (DF), insu- lation resistance (IR), inverters, predictive maintenance, stator insulation. I. INTRODUCTION T HE TECHNOLOGICAL advances made in power semiconductor devices since the 1990s has enabled high- frequency switching operation, which has significantly en- Paper IPCSD-07-067, presented at the 2006 Industry Applications Society Annual Meeting, Tampa, FL, October 8–12, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Elec- tric Machines Committee of the IEEE Industry Applications Society. Manu- script submitted for review February 17, 2007 and released for publication September 6, 2007. This work was supported by the Ministry of Commerce, Industry, and Energy (MOCIE) through the Electrical Industry Research Center (EIRC) program with the Advanced Power Systems Research Center at Korea University. J. Yang, S. B. Lee, and J.-Y. Yoo are with the Department of Electrical Engineering, Korea University, Seoul 136-701, Korea (e-mail: [email protected]; [email protected]; [email protected])....
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.
- Spring '11