Optimization of double-layer stress grading system for high voltage rotating electrical machines by electric field and thermal coupled analysis

Umemoto, Takuya; Otake, Yasutomo; Yoshimura, Manabu; Nada, Takashi; Miyatake, Ryoji

doi:10.1109/tdei.2019.008535

Cited by 9 publications

(7 citation statements)

References 19 publications

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“…Due to the nonlinear conductivity of SiC particle-loaded materials, the distribution of surface potential on the layer was almost straight. However, in the case of AC dielectric strength test, the test voltage frequently exceeded the limit of the SiC layer and results in a large current pass through, which may cause joule losses and temperature rise at the surface of SiC layer [96] . To solve this problem, a novel double-layer stress grading system for high voltage rotating machines was proposed by Umemoto et al, as shown in Figure 4 [97] .…”

Section: Power Apparatus and Devices Based On Sadsmentioning

confidence: 99%

Smart dielectric materials for next-generation electrical insulation

Huang

Han

Yang

et al. 2022

iEnergy

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Smart dielectric materials with bioinspired and autonomous functions are expected to be designed and fabricated for next-generation electrical insulation. Similar to organisms, such dielectrics with self-adaptive, self-reporting, and self-healing capabilities can be employed to avoid, diagnose, and repair electrical damage to prevent catastrophic failure and even a blackout. Compared with traditional dielectrics, the utilization of smart materials not only increases the stability and durability of power apparatus but also reduces the costs of production and manufacturing. In this review, researches on self-adaptive, self-reporting, and self-healing dielectrics in the field of electrical insulation, and illuminating studies on smart polymers with autonomous functions in other fields are both introduced. The principles, methods, mechanisms, applications, and challenges of these materials are also briefly presented.

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Section: Power Apparatus and Devices Based On Sadsmentioning

confidence: 99%

Smart dielectric materials for next-generation electrical insulation

Huang

Han

Yang

et al. 2022

iEnergy

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“…The nonlinear transient electric field and thermal coupled simulation [10,12,13] was introduced to evaluate the timeaveraged power density and the temperature rise distributions at the SG system. Figure 2 shows a schematic of a 2-D axisymmetrical simulation model and its dimensions.…”

Section: Simulation Model and Meterial Propertiesmentioning

confidence: 99%

“…However, in this study, the high conductivity of CAT, such as 10 S/m, can maintain the CAT to the ground potential, even when voltage pulses with 1 μs-rise time are applied, therefore the potential drop and the Joule heating at the CAT are negligible. The other material properties are described in [12]. In the thermal conduction analysis, the emissivity and convective heat transfer coefficient at an interface between the coil and surrounding air are set to 0.8 and 15 W/m 2 K, respectively.…”

Section: Simulation Model and Meterial Propertiesmentioning

confidence: 99%

Power Density and Temperature Rise Estimation at End-turn Stress Grading System of Large Rotating Machines under PWM Waveform

Umemoto

Nakamura

2021

IEEE Trans. Dielect. Electr. Insul.

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In this paper, the time-averaged power densities as well as the resulting temperature rise, on an end-turn stress grading (SG) system under PWM waveforms as functions of the carrier and the fundamental frequencies are systematically investigated by finite element method-based computations. A novel analytical approximation method to estimate the power densities and the temperature rises without time-consuming numerical computations are proposed. As a result, the maximum power density and the temperature rise increase nearly linearly with increasing fundamental and the carrier frequencies. It is suggested that power dissipations in the SG layer by the fundamental frequency component of a PWM waveform and those by the carrier frequency component can be clearly separated. Moreover, the estimated power densities and temperature rises based on the analytical approximations show reasonable agreement with the numerically computed ones, which indicates the validity of the proposed estimation method.

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“…The resistive field grading is applied as e.g. wrapped tape or paint, and the conductive filler is mainly silicon carbide (SiC) [3]- [6]. The electric conductivity of SiC is nonlinearly dependent on the applied electric field [7], and therefore provides better field grading properties than alternative filler materials with constant or linear conductivity [8].…”

Section: Introductionmentioning

confidence: 99%

Frequency Dependence of the Electric Field Grading of End-Winding of Generator Bars

Aakre

Enoksen

Eberg

et al. 2023

IEEE Trans. Dielect. Electr. Insul.

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To reduce the electric field stresses in the endwinding in hydropower generator bars, a field dependent grading tape is applied in the transition zone from outer corona protection to bare insulation. The design is typically optimized for 50/60 Hz with both low heat generation and optimal electric field distribution. The introduction of power electronic converters with high switching frequencies and dU/dt for controlling the generators changes the optimal design requirements. This work investigated experimentally the effect of higher voltage-frequencies on the conductivity in three field grading tapes from the same manufacturer with different field grading properties. The experimentally determined material parameters were then applied as inputs to finite element method (FEM) models to evaluate the electric field distribution at different voltage-frequencies. Measurements showed that the DC conductivity was highly nonlinear and strongly dependent on the electric field. This strong nonlinearity decreased at low electric fields as the frequency increased. The AC conductivity had a transition from a strong nonlinear material at line frequency to a less nonlinear material at 10 kHz. Simulations of the surface electric field and temperature using the DC conductivity for different voltage frequencies showed minor differences from simulations using the apparent AC conductivity. This indicates that the low field conductivity is of minor importance as it varied by two decades between DC and 10 kHz without resulting in a significant difference in either electric field, or temperature. The measured and simulated surface temperature increased linearly with applied voltage frequency. The simulated surface electric field was well distributed at line frequency, whereas it was greatly enhanced above 1 kHz.

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Optimization of double-layer stress grading system for high voltage rotating electrical machines by electric field and thermal coupled analysis

Cited by 9 publications

References 19 publications

Smart dielectric materials for next-generation electrical insulation

Smart dielectric materials for next-generation electrical insulation

Power Density and Temperature Rise Estimation at End-turn Stress Grading System of Large Rotating Machines under PWM Waveform

Frequency Dependence of the Electric Field Grading of End-Winding of Generator Bars

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