Effect of conductivity on the thermal and electrical properties of the stress grading system of an inverter-fed rotating machine

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.

Section: Temperature Rise Estimationsupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

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

Umemoto

Nakamura

2021

“…The relative permittivity in all layers was set equal to ε r = 2, which reflects a typical value found for many polymeric insulators commonly used in engineering applications. The geometry and signal attributes remained the same as before, with the exception that now the electrical conductivity was graded following the profiles described by ( 24) and ( 25), with σ min = 10 −14 S/m (approximate range for common engineering polymers) and σ max = 10 −4 S/m (possible range attained by commercially-available conductive grading tapes [37]). Once again, the analytical field distributions and transient responses using the linear profile are shown in Fig.…”

Section: B Graded Conductivitymentioning

confidence: 99%

Modeling of the Transient Electric Field in Multilayer Dielectric Composites Under Impulsive HV Energization

Wong

Timoshkin

MacGregor

et al. 2023

This article presents the theoretical analysis of composite electrical insulation, formed from layered dielectric materials and subjected to impulsive energization. One-dimensional planar and cylindrical geometries were considered, consisting of an arbitrary number of layers with arbitrary relative permittivity and electrical conductivity. Analytical solutions have been succesfully derived for the time-dependent electric field inside the i-th layer. To demonstrate the usage of the model under complex multilayer topologies where analytical solutions are nontrivial, the characteristics of a 20-layer graded composite under microsecond and sub-microsecond impulses were analyzed and validated against a finite-element solver. Results indicate that the transient electric field response under impulsive energization is strongly dependent on the interplay between the composite relaxation time constants and the characteristic timescales associated with the applied impulse. The model is a further development for the design and coordination of functionally graded materials (FGMs) and composite insulation for high voltage system design. This is particularly relevant under fast-rising impulsive conditions as often encountered in many pulsed power applications.

“…in [7]. The available measured data on the resistive nonlinear properties of FGMs for medium voltage rotating electrical machines are depicted in Figure 3 [1, [7][8][9][10][11][12][13][14][15][16][17]. The data was reproduced from respective references at temperatures close to 80 C for comparative purposes.…”

Section: Existing Commercial Nonlinear Resistive Field Grading Materi...mentioning

confidence: 99%

One-Dimensional Model for the Nonlinear Resistive Electric Field Control in Medium-Voltage Rotating Electrical Machines

Egorov

Pyrhönen

2021

This study provides an insight in the analytical estimation of the electric field along the surface of a stress grading system (SGS) in the end-winding region of an electrical machine. An analytical approach is derived for the field grading materials (FGMs) having power-law electric-field-dependent conductivity. Despite some limitations, the introduced model can be used for the preliminary analysis of SGS with specific geometric and dielectric parameters both during sinus and pulsed voltage condition. The analytical considerations are verified with finite element simulations for 15 markedly different nonlinear FGMs, which were previously reported in the applications related to the medium voltage rotating electrical machines.