Temperature and electric field distributions along a form wound coil of an inverter-fed rotating machine with micro-varistor stress grading system

Naeini, Alireza; Cherney, E.A.; Jayaram, S.

doi:10.1109/tdei.2019.008344

Cited by 5 publications

(3 citation statements)

References 14 publications

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“…While the temperature would also have an effect to conductivity and electric field distribution [13]. [39], studies on the effect of different temperature conditions are to be explored in further work.…”

Section: A Modeling For Electrical Field Analysismentioning

confidence: 99%

“…The voltage applied to the conductor was simulated with a 60 Hz AC. In many previous studies, pulse waveforms were applied to consider the electric field distribution by pulse width modulation (PWM) signals [3], [8], [20], [39]. Because the PWM is a power source for operating a rotating machine, it is suitable for the condition monitoring of a rotating machine and reviewing its lifespan, whereas AC power is suitable for reviewing a factory acceptance test or type test for certification [40].…”

Section: A Modeling For Electrical Field Analysismentioning

confidence: 99%

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Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

Kim

2022

IEEE Access

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In rotating machines, the approach of applying nonlinear conductive stress grading tape (SGT) has been applied to reduce the electric field stress in the coil's overhang region. To characterize and verify the electric field grading effect of SGT in electric machines, electric field analysis using the nonlinear conductivity of SGT as a boundary condition must be considered. However, previous studies have shown limitations in the characterization and application of SGT materials in insulation system design for various reasons, such as lack of conductivity measurement standards for nonlinear materials or not considering possible changes in material properties during the manufacturing procedure. In this study, the nonlinear conductivity of SGT was measured by considering the rotating machine's manufacturing procedure. A finite element method (FEM) electric field analysis was performed using the measured nonlinear conductivity. Based on the improved conductivity measurement method of SGT and FEM analysis, the effects of changing several insulation design parameters in the field grading performance were studied on a 13.8 kV stator coil. Moreover, the effect of preheating on the SGT conductivity was also examined. Based on analysis results, we realized the possibility of more precise insulation design of the stator coil. Our findings supplement the insufficient insulation design guide on the SGT part and contribute to establishing a systematic approach for insulation design. Furthermore, the proposed methods enable design optimization and detection of the cause of insulation failure.

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Section: A Modeling For Electrical Field Analysismentioning

confidence: 99%

Section: A Modeling For Electrical Field Analysismentioning

confidence: 99%

Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

Kim

2022

IEEE Access

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“…In recent years, using the technology has developed the meaning of electric stress control. Applications of microvaristor for electrical machines and transmission lines and their performance improvement have been presented in [9,10]. In research [4], improvement due to the microvaristor layer reported a 21% increase in flashover voltage in breakdown tests.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Electrical Characteristics of Composite Insulators with the Presence of Optimum Layer of ZnO Microvaristors

Darmiani

Shariatinasab

Najafi

et al. 2023

International Journal of Energy Research

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The electric field distribution of insulator surface is nonuniform, and the maximum electric field is visible around two terminals of the insulator. Using a microvaristor layer is one of the methods of field control that can reduce the electric field stresses to prevent an extension of discharges on the insulator surface and a complete flashover caused by the subsequent development of arcing. This study targets the effect of zinc oxide (ZnO) microvaristors on the electric field distribution along the contaminated and clean composite insulators that have been investigated. In addition, the impact of the insertion of microvaristor layers on the critical flashover voltage (CFO) of the insulators through a mathematical formula has been presented for the first time. The estimation of electric field distribution is conducted through finite element method (FEM) on a 400 kV insulator using COMSOL Multiphysics, in which the optimal dimensions of the microvaristor layer were obtained using the accelerated particle swarm optimization (APSO) algorithm. Then, for the first time, the analysis of the influence of the ZnO insertion on the transient performance of the insulator, i.e., the outage rate of the network, is performed in EMTP software for the insulator with the optimized insertion of the microvaristor layer. Modelling techniques were used to simulate the components of a transmission network according to the valid models. Finally, by setting different values for CFO, Monte Carlo simulation, and linking EMTP and MATLAB software, the lightning flashover rate (LFOR) and the failure risk (F.R.) of the different insulator models are calculated. It is shown that the proposed method reduces the maximum electric field of the inside and outside of the insulator, which in turn leads to a reduction in the outage rate of the power network and the insulation risk of the insulator, and an increase in CFO of the insulator.

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Experiment of electrothermal stress for different types of end turn grading in the inverter‐fed form‐wound windings

Zhao,

Wang,

Zhu

et al. 2024

High Voltage

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End turn grading with resistive–capacitive coupling experiences severe electrothermal stress when subjected to pulse width modulation (PWM) voltage. In this paper, several experiments and simulations were carried conducted for four types of end turn grading. First of all, the temperature rise in the end turn grading increased with a decrease in rise time. When the rise time was less than 500 ns, the temperature rise at the terminal was higher owing to the increased capacitive current coupled from the main wall insulation. Further, the current in the linear region exhibited minimal variation at different fundamental frequencies resulting in synchronized the temperature rise at the terminal and overlap. Furthermore, the jump voltage was the key factor influencing temperature rise in end turn grading, confirmed by comparing different voltage magnitudes. Finally, the transient behaviour of the maximum field in the stress grading material was determined at rise time. The experimental and simulation results indicate that balancing and interdependently addressing the electrical and thermal stress protection in end turn grading is crucial. The study aims to provide an experimental and theoretical foundation for an insulation system of inverter‐fed rotating machinery operating under PWM voltage.

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Temperature and electric field distributions along a form wound coil of an inverter-fed rotating machine with micro-varistor stress grading system

Cited by 5 publications

References 14 publications

Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

Analysis of Electrical Characteristics of Composite Insulators with the Presence of Optimum Layer of ZnO Microvaristors

Experiment of electrothermal stress for different types of end turn grading in the inverter‐fed form‐wound windings

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