• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.335-339
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• 2001

The recent advancements in power electronic switching devices have enabled high frequency switching operation and have improved the performance of pulse-width modulated (PWM) inverters for driving induction motors. But, the insulation failures of stator winding have attracted much concern due to high dv/dt of IGBT PWM inverter. In this paper, the test results for evaluation on the stator winding insulation of low-voltage induction motors for IGBT PWM inverter applications are presented. The insulation characteristics are analyzed with partial discharge and dissipation factor tests. Also, insulation breakdown tests by switching pulse voltage are performed. An effective insulation technique to enhance the insulation strength is suggested from the test results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.10
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• pp.965-975
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• 2005

In the case of the fault in stator windings of a high voltage motor. it facilitates certain destructive characteristics in insulations. This will result in a decreased reliability in power supplies and will prevent the generation of electricity, which will result in huge economic losses. This study simulates motor windings using normal windings and four faulty windings for an actual fault in stator winding of a high voltage motor. The partial discharge signals produced in each faulty winding were measured using an 80 PF epoxy/mica coupler sensor. In order to quantified signal waves its a way of feature extraction for each faulty signal, the signal wave of winding was quantified to measure the degree of skewness shape and kurtosis, which are both types of statistical parameters, using a discrete wavelet transformation method for each faulty type. Wave types present different types lot each faulty type, and the skewness and kurtosis also present different quantified values. The result of feature extraction was used as a preprocessing stage to identify a certain fault in stater windings. It is evident that the type of faulty signals can be classified from the test results using faulty signals that were randomly selected from the signal, which was not applied in the training after the training and learning period, by applying it to a back-propagation algorithm due to the supervising and learning method in a neural network in order to classify the faulty type. This becomes an important basis for studying diagnosis methods using the classification of faulty signals with a feature extraction algorithm, which can diagnose the fault of stator windings in the future.

• Journal of Power Electronics
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• v.16 no.2
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• pp.675-684
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• 2016

This paper presents a new stand-alone wind-based induction generator system with constant frequency and adjustable output voltage. The proposed generator consists of a six-phase cage-rotor induction machine with two separate three-phase balanced stator windings and a three-phase space vector pulse width modulation inverter that operates as a static synchronous compensator (STATCOM). The first stator winding is fed by the STATCOM and used to excite the machine while the second stator winding is connected to the generator external load. The main frequency of the STATCOM is determined to be constant and equal to the load-requested frequency. The generator output frequency is independent of the load power demand and its prime mover speed because the frequency of the induced emf in the second stator winding is the same as this constant frequency. A sliding mode control (SMC) is developed to regulate the generator output voltage. A second SMC is used to force the zero active power exchanged between the machine and the STATCOM. Some simulation and experimental results are presented to prove the validity and effectiveness of the proposed generator system.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1526-1529
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• 1994

In hydro-generator, a groundwall insulation of stator windings gradually deteriorates due to mechanical, thermal, electrical and environmental stresses. These stresses combine to result in loose windings, delamination of the stator insulation and/or electrical tracking of the end winding, all of which can lead to stator insulation failures. Conventionally, off-line tests such as partial discharge measurement, DC/AC current test and ${\Delta}tan{\delta}$ test has been used for estimation of winding condition. However, off-line test requires large power supply and generator outage. In addition, major cause of insulation problems such as loose wedges and slot discharges may not be found with off-line diagnoses. This paper describes the on-line partial discharge measurement techniques in the generator stator windings. The experimental results from the UIAM #1 hydro-generator confirms a optimistic application of on-line generator diagnosis method as a reliable tool for evaluation of winding condition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.7
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• pp.645-649
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• 2007

Partial discharge(PD) test for simulated insulation defects of used hydro generator stator winding was conducted to analyze the PD Parameters. Simulated insulation defects are classified by 5 types corona, slot, internal, multi and aging defect. Phase resolved partial discharge, statistical parameter (skewness, kurtosis), PD magnitude as a function of the test voltage(Q-V curve) and PD magnitude change under test voltage for 2 minutes are used as PD parameters. The analysis of PD parameters by 4 types are proved to be useful methods. In particular, PD parameter characteristics of aging defect could help to assess the aging condition of stator winding because aging defect has more weak insulation strength than other insulation defects : PD distribution is wide and flat, PD rises rapidly near $0^{\circ}\;and\;180^{\circ}$ and Q-V curve rises sharply and then gently drops.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.571-575
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• 2008

Stator insulation quality assessment for high voltage motors is a major issue for the reliable maintenance of industrial and power plants. To assess the condition of stator insulation, nondestructive tests were performed on the sixty coil groups of twelve motors. After completing the nondestructive tests, the AC voltage applied to the stator winding was gradually increased until insulation failure in order to obtain the breakdown voltage. The stator winding of each motor was classified into five coil groups; one group with healthy insulation and four groups with four different types of artificial defects. To analyze the breakdown voltage statistically, Weibull distribution was employed for the tests on the fifty coil groups of ten motors. The 50th percentile values of the measured breakdown voltages based on the statistical data of the five coil groups of ten motors were 26.1kV, 25.0kV, 24.4kV, 26.7kV and 30.5kV, respectively. Almost all of the failures were located in the line-end coil at the exit of the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of dissipation factor and ac current. It is shown that the condition of the motor insulation can be determined from the relationship between the probability of failure and the type of defect.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2145-2149
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• 2007

This paper deals with optimum design criteria to minimize the torque ripple of a concentrated winding Synchronous Reluctance Motor (SynRM) using Response Surface Methodology (RSM). The feasibility of using RSM with the finite element method (FEM) in practical engineering problem is investigated with computational examples and comparison between the fitted response and the results obtained from an analytical solution according to the design variables of stator and rotor in concentrated winding SynRM (6slot).

• Journal of Power Electronics
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• v.9 no.2
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• pp.243-258
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• 2009

Bearingless centrifugal pump systems are employed in the semiconductor, pharmaceutical and medical industries due to their facility for pumping high purity fluids without particle contamination. Two types of forces have to be generated by the stator units, namely bearing forces for achieving magnetic levitation, and drive forces for producing the needed pump torque. The generation of these forces requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, combined coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, whereby the copper losses, the power electronics losses, and the achievable pump output pressure are evaluated for both concepts. For each criterion a ratio of improvement is calculated analytically which allows evaluation of the performance of the two winding concepts for any given pump operating point and design. Finally, also practical features such as control complexity, cabling effort and manufacturability are discussed and measurements on prototype systems are carried out to validate the considerations.

• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.369-374
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• 2011

An induction motor operated with high voltage source generally generates high current in starting mode and has a long transient time after being started. This large and sustaining starting current causes the end windings of the stator to have excessive electromagnetic force. This force is the source of vibration and has a negative and serious influence on the insulation of end windings. Therefore, designing the end winding part with an appropriate support system is needed. To design the support ring enclosing the end windings, we analyze the distribution of electromagnetic force on the end windings by applying the Biot-Savart's law and the 3D finite element method (FEM), and comparing two simulation methods. Finally, we verify the safety of the support structure of the end winding part using stress analysis, which is analyzed with the electromagnetic forces from the 3D FEM simulation.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.1
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• pp.1-9
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• 2002

This paper describes for new design method to improve respones characteristics of moving-magnet type LDM with volume reduction of slider back iron. To achieve the constant thrust of LDM through restraining saturation at the center core of stator excitation coil, double sided stator winding of LDM is proposed. We constructed new type LDM to prove the validity of design process. Analysis results through measurement and simulation of proposed multi-separated winding LDM were proved excellent in response characteristics and static thrust.