Shield Ring Research Articles

Novel Structure of Shield Ring to Reduce Shaft Voltage and Improve Cooling Performance of Interior Permanent Magnet Synchronous Motor

Novel Structure of Shield Ring to Reduce Shaft Voltage and Improve Cooling Performance of Interior Permanent Magnet Synchronous Motor

Reduction of Shaft Voltage of IPMSM According to the Shape of the Novel Shield Ring

Reduction of Shaft Voltage of IPMSM According to the Shape of the Novel Shield Ring

Study on the mechanism and rapid treatment method of leakage disease at the junction between the shaft and shield tunnel

Tunnel leakage disease will seriously affect the metro operation and threaten the safety of passengers. Therefore, this study investigates the mechanism of structural leakage disease at the junction between the shaft and shield tunnel through the operational tunnel in the Beijing area. Firstly, the characteristics and intrinsic cause of the leakage are analyzed by ground penetrating radar, endoscope detection, and total station. The field inspection indicates that the water-rich cavity caused by the rise of groundwater is the main external environmental factor inducing structural leakage. The uneven deformation of the junction between the shield segments and ring beam and the deterioration of the ring beam structure are the main reasons for the waterproof layer failure, which further lead to structural leakage. In addition, numerical simulations are carried out to study the leakage mechanism of the junction structure under the effects of structural uneven deformation and ring beam deterioration. The numerical results show that the leakage caused by uneven deformation of tunnel junction is significant. Especially, the water-rich cavity near the ring beam will aggravate structural leakage. Furthermore, the deterioration of the ring beam structure has a more significant effect on the structural leakage, and the leakage mainly occurs in the ring beam and ring beam-segment joints. This finding is basically consistent with the actual leakage situation. In addition, the rapid treatment method for plugging water-rich cavities and structural defects is proposed, and a new cement-based material with good non-dispersible underwater properties is developed. The surface observation and internal detection show that the rapid treatment method effectively controls structural leakage. This research can provide a reference for future similar leakage and disease control projects of metro subways in operation.

Rail transit shield tunnel deformation detection method based on cloth simulation filtering with point cloud cylindrical projection

Subway shield tunnels are important components of urban infrastructure. To maintain the safety of a tunnel during operation, tunnel deformation must be detected in a timely manner. The large quantities of metal brackets, electrical equipment, and other ancillary facilities installed along the lining of subway shield tunnels, along with bolt holes in the shield ring plate, significantly affect the detection accuracy of tunnel deformation. To increase deformation detection accuracy, a filtering method for tunnel ancillary facilities based on cloth simulation filtering with point cloud cylindrical projection is proposed. In this method, a cylindrical projection of the original point cloud of the tunnel cross-section is created. In this projection, each tunnel lining point corresponds to a projection onto the horizontal plane and the tunnel ancillaries are expanded onto the lining surface. The cloth simulation filtering algorithm is then used to separate the point clouds of the tunnel lining and ancillaries. The filtered tunnel section curves are fitted with an ellipse model based on the direct least squares method and the deformation of the tunnel is analyzed using the ellipse parameters. The repeatability values of tunnel measurements of the overall and local deformation are 0.41 and 0.66 mm, respectively. Indicating that the proposed filtering method can effectively obtain a tunnel lining point cloud from the original point cloud of the tunnel and meet the accuracy requirements of subway tunnel deformation detection.

Radiation Damage Analysis of FNSF Components Using McCad and MCNP

The Fusion Energy System Studies Fusion Nuclear Science Facility (FESS-FNSF) concept represents a transitional step between ITER and a commercial fusion power plant. The FNSF is a conceptualized D-T fueled tokamak with 518 MW of fusion power that has been extensively used to explore and optimize design features. The energetic 14.1-MeV neutrons can produce significant localized heating and activations, and can cause damage to plasma-facing components, which can determine maintenance/outage scheduling needs and also impact the lifetime of the device as a whole. This study illustrates a neutronics analysis that was conducted on a 22.5-degree symmetric sector of the FNSF with the goal of understanding the neutron heating and radiation damage that can be characterized by quantifying the displacements per atom (dpa). Concurrently, this study also focused on the development of analysis capabilities by converting a three-dimensional computer-aided design model of the FNSF into MCNP6.2 input using the McCad code. Accordingly, some confirmatory results on tritium production and the tritium breeding ratio (TBR) are provided to support model validation. The results produced by MCNP6.2 simulations showed that the highest heating and damage occurred in the outboard region, which concentrated approximately 290 MW of the total nuclear heating, in contrast to 97 MW within the inboard region. These results are consistent with previous studies that employed earlier versions of the FNSF concept and different modeling approaches. This study also provides additional details on neutron wall loading, as well as total heating from neutrons and gammas, results which show the total heating of the device (16 sectors) is approximately 477.83 ± 0.80% MW, indicating a neutron energy multiplication factor of 1.15. Additionally, the capability to calculate hydrogen and helium production, as well as dpa, is illustrated. Finally, the neutronics effects of using alternative materials to tungsten carbide were evaluated for the vacuum vessel, low-temperature shield, and structural ring components, which showed that compounds like YH2, Mg(BH4)2, and ZrH2 could reduce the total heating on the magnet and also reduce the TBR.

Research on the Time Drift Stability of Differential Inductive Displacement Sensors with Frequency Output.

An edge displacement sensor is one of the key technologies for building large segmented mirror astronomical optical telescopes. A digital interface is one novel approach for sensor technologies, digital transformation and the Internet of Things (IoT) in particular. Frequency output sensors and inductance-to-digital converter (LDC) demonstrated significant advantages in comparison with conventional sensors with analog-to-digital converter (ADC) interfaces. In order for the differential inductive frequency output displacement (DIFOD) sensor to meet the high-stability requirements of segmented mirror astronomical telescopes, it is important to understand the factors for time drift of the sensor. This paper focuses on the investigation of key factors of sensor structure and material, signal conditioning and interface, and fixtures for time drift to permanently installed applications. First, the measurement principle and probe structural characteristics of the sensor are analyzed. Then, two kinds of signal conditioning and digitalization methods using resonance circuits and LDC chips are implemented and compared. Finally, the time drift stability experiments are performed on the sensors with different signal conditioning methods and fixtures under controlled temperature. Experimental results show that the magnetic shield ring effectively improves the sensitivity and quality factor of the sensors, the time drift stability of the sensor using the signal conditioning based on resonance circuits is better than that of the sensors using LDC chips, and the root mean square (RMS) of the sensor time drift meets the requirement of 0.01 μm/24 h. This study will help further development of high-stability of frequency output sensors and IoT-based systems for scaled-up applications in the future.

Electrostatic Field Calculation and Structure Optimization of New Shield Ring of 1000 kV Nan-Jing Loop Transmission Line

Considering the frequent breakage of the hard jumper shield ring in the strain tower of ultra-high voltage alternating current 1000 kV Nan-Jing Transmission Line, the theoretical and experimental studies on new shield ring were carried out in terms of mechanical properties; however, due to the structural changes of shield ring, the field characteristics should be calculated and analyzed. In accordance with the theory that there is no electric field in a metal conductor under electrostatic equilibrium, if there is any metal conductor in the 3D model of the computational domain, there will be no need to subdivide the metal conductor. In this paper, a 3D model load applying method with metal conductors was proposed to calculate the field intensity of Tuned mass damper (TMD) shield ring after improving the mechanical properties of the strain tower, which saved the total number of mesh subdivisions by 48.02%, reduced the computational time by 76.47%, and increased the computational efficiency of 3D numerical electric field. The calculation results validated the correctness and effectiveness of this method. The new TMD shield ring with the field intensity meeting the relevant requirements was adopted in 1000 kV Nan-Jing Loop Transmission Line in December 2016, which has been operating in good condition so far.

Movement Behavior and Partial Discharge of the Single Metallic Particle in GIS at Operated Voltage

At operated voltage, the movement behavior, partial discharge, and harmfulness of linear particle in different positions of GIS (high-voltage bus, shield ring, and insulator) are still not clear now. In order to study and solve this urgent engineering problem, the discharge signals, ultrasonic signal, and movement locus of linear particles were recorded and observed. The movement behavior, partial discharge characteristics, and harmfulness of metallic particle in different positions are analyzed and compared. The results suggest that: 1) at operated voltage, the movement behavior of linear particle has a great difference in different positions of GIS. The particle jumps with small height under the high-voltage bus, but the jumping frequency is very high and the time series of discharge signal has one-to-one correspondence with that of the ultrasonic signal. When the particle moves to the shielding ring, particle instantly jumps to the high-voltage electrode. At this time, the consistency between the discharge signal and the ultrasonic signal becomes worse. In addition, when the particle touches the insulator, it can attach to the insulator, never move, and become a fixed metallic particle. 2) When the metallic particle freely jumps under the high voltage bus and the shielding ring, the breakdown voltage of the GIS is still very high. However, when the particle attaches to the insulator, the creeping discharge of the particle will make it has serious harmfulness.

3D response analysis of a shield tunnel segmental lining during construction and a parametric study using the ground-spring model

In this research, an analysis method aiming as a tool to investigate the behavior of a tunnel lining during construction is developed based on a nonlinear ground-spring model in conjunction with a finite element method. A nonlinear ground-spring model that considers yield pressures is proposed and implemented into the numerical analysis. All relevant components of the shield tunnel construction process including the TBM, jack thrust force, shield tail wire brush, segmental lining, key-segment and ring and segment joints and proper interactions are considered in the analysis model. The reliability of the developed method is verified by comparing the analysis results with the full-scale test and field measurements of a previous study. The developed analysis method could reasonably reproduce the responses of a segmental lining at various stages with special attention during construction. A series of parametric analyses are conducted to highlight the robustness of the developed method to capture the effect of the key factors on the structural behavior of the segmental lining during construction. The effects of the tunnel depth, forces from eccentric jack thrust together with shield tail wire brush and position of key segment on the induced lining stresses can be well captured.

Fracture Mechanism Analysis and Structural Improvement for 1000-kV UHV Shield Ring

Some fracture failures of multiple shield rings on a 1000-kV ultra-high voltage transmission line have been found in succession. The method of reinforcing and welding at the fracture site were used to avoid crack enlargement. However, the reinforced shield rings were damaged again after half a year's use. A new approach is proposed to extract the root cause. The finite-element method is employed to calculate the static performance of shield ring for determining that the cause of the crack is not the ultimate strength failure of the material. And after acquiring the wind vibration frequency by vibration image recognition method, the critical vibration wind speed is obtained by the vortex-induced resonance analysis. And based on the critical speed, the lift force function is formed. According to the historical load simulated by lift force function, the displacement and stress response under the vortex-induced resonance are acquired by transient dynamic calculation. With the regional meteorological data of the transmission line, the probability of the wind direction and velocity within the critical vibration wind speed range is calculated out. Then, with the probability, the displacement and stress response and the vibration frequency of shield ring, the fatigue life assessment is conducted. Inspired by the idea of the energy dissipation-seismic reduction, a new type shield ring is designed. After testing the mechanical and electrical performance, the new one runs perfectly without emerging crack from November 2016, that verified the effectiveness of the design scheme for the new type shield ring.

Coupling-Shielded Inductor for High Isolation Between PA and <italic>LC</italic>-Based DCO

This letter presents a novel coupling-shielded inductor. The inductor has a magnetic coupling shield ring (CSR), designed with an Al pad metal. The CSR has an electromotive force-induced current, which flows in such a direction as to oppose the magnetic field from an aggressor. As a result, the proposed inductor can be protected from the attack of a power amplifier (PA) with a strong magnetic field. The inductor is applied in an $LC$ -based digitally controlled oscillator (DCO) to verify the enhancement of isolation. It was fabricated by a 55-nm 1P6M CMOS process. Using the CSR, the isolation between the DCO and PA is increased by about 11 dB without degradation of the DCO performance. The DCO with CSR has a low phase noise of −114.5 dBc/Hz at 1 MHz with 0.74-mW power consumption.

TUNNEL POINT CLOUD FILTERING METHOD BASED ON ELLIPTIC CYLINDRICAL MODEL

The large number of bolts and screws that attached to the subway shield ring plates, along with the great amount of accessories of metal stents and electrical equipments mounted on the tunnel walls, make the laser point cloud data include lots of non-tunnel section points (hereinafter referred to as non-points), therefore affecting the accuracy for modeling and deformation monitoring. This paper proposed a filtering method for the point cloud based on the elliptic cylindrical model. The original laser point cloud data was firstly projected onto a horizontal plane, and a searching algorithm was given to extract the edging points of both sides, which were used further to fit the tunnel central axis. Along the axis the point cloud was segmented regionally, and then fitted as smooth elliptic cylindrical surface by means of iteration. This processing enabled the automatic filtering of those inner wall non-points. Experiments of two groups showed coincident results, that the elliptic cylindrical model based method could effectively filter out the non-points, and meet the accuracy requirements for subway deformation monitoring. The method provides a new mode for the periodic monitoring of tunnel sections all-around deformation in subways routine operation and maintenance.

TUNNEL POINT CLOUD FILTERING METHOD BASED ON ELLIPTIC CYLINDRICAL MODEL

Abstract. The large number of bolts and screws that attached to the subway shield ring plates, along with the great amount of accessories of metal stents and electrical equipments mounted on the tunnel walls, make the laser point cloud data include lots of non-tunnel section points (hereinafter referred to as non-points), therefore affecting the accuracy for modeling and deformation monitoring. This paper proposed a filtering method for the point cloud based on the elliptic cylindrical model. The original laser point cloud data was firstly projected onto a horizontal plane, and a searching algorithm was given to extract the edging points of both sides, which were used further to fit the tunnel central axis. Along the axis the point cloud was segmented regionally, and then fitted as smooth elliptic cylindrical surface by means of iteration. This processing enabled the automatic filtering of those inner wall non-points. Experiments of two groups showed coincident results, that the elliptic cylindrical model based method could effectively filter out the non-points, and meet the accuracy requirements for subway deformation monitoring. The method provides a new mode for the periodic monitoring of tunnel sections all-around deformation in subways routine operation and maintenance.

FDTD Analysis of the Electric Field of a Substation Arrester Under a Lightning Overvoltage

The electric field in and around a 2.6-m-long substation arrester, on which a 1 MV lightning impulse is imposed, has been analyzed using the finite-difference time-domain (FDTD) method. The arrester is represented as a combination of 10 mm × 10 mm × 10 mm cubic cells, each of which has a nonlinear resistivity (or conductivity) in each of the x-, y- , and z -directions, dependent on the electric field in each direction. This simple representation requires no iterative procedure, and is suitable and useful for the FDTD simulation of an overvoltage-imposed arrester. The transient electric field in and around the overvoltage-imposed arrester, and the spatial distributions of vertical and radial electric fields along the surface of the arrester are shown. The influence of a shield ring is also shown.

Development of 300-kV Air-Insulation Standard Impulse Measurement System

This paper describes the development of a 300-kV standard full lightening impulse measurement system. The high-voltage (HV) arm of the impulse resistive divider was constructed with an air-insulation frame wound with nichrome alloy resistance wire using the Ayrton-Perry winding method. The winding inductances of different frame cross-sectional shapes were studied. The result showed that the rectangular shape gives the least winding inductance compared with the circular and square cross sections under the condition of the same circumference. The HV arm was divided into 10 sections, and the stray parameters were subtracted with Finite Element Method method; the step response of the system is simulated with Simulink of MATLAB to optimize shield ring design. The low-voltage arm is composed of 24 low-inductance metal film resistors, which is similar in design to that developed by a Russian national metrology institute. The step response measurement result showed that the partial response time was less than 5 ns. The convolution method is used to evaluate uncertainty due to different waveform shapes based on the normalized step response. The expanded uncertainty evaluation of peak value gives 0.5% ( $k =2$ ), and the time parameter $T_{1}$ is 2.6% ( $k=2$ ) and $T_{2}$ is 1.3% ( $k =2$ ).

Electrochemical evaluation of the corrosion resistance of cup-yoke-type dental magnetic attachments.

The corrosion resistance of different magnetic assemblies—Magfit DX800 (Aichi Steel), Gigauss D800 (GC), Hyper Slim 4013, and Hicorex Slim 4013 (Hitachi Metals)—were electrochemically evaluated using anodic polarization curves obtained in 0.9% NaCl solution at 37°C. Stainless steels (444, XM27, 447J1, and 316L) composing the magnetic assemblies were also examined as controls. This revealed that all of the magnetic assemblies break down at 0.6-1.1 V; however, their breakdown potentials were all still significantly higher (p<0.05) than that of 316L. The distribution of elements in the laser welding zone between the yoke and shield ring was analyzed using EPMA; except with Magfit DX800, where the Cr content of the shield ring weld was greater than that of 316L. These magnetic assemblies are expected to have good corrosion resistance in the oral cavity, as their breakdown potentials are sufficiently higher than the 316L commonly used as a surgical implant material.

Parametric Study on Unit Step Responses of Impulse Voltage Measuring Systems Based on FDTD Simulations

Unit step responses (USRs) of a USR-measuring system recommended by the International Electrotechnical Commission have been computed using the finite-difference time-domain (FDTD) method for various conditions of grounding and shield ring. The USR measuring system subject to analysis has a resistor divider of height 3.3 m and resistance 9 k <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\Omega$</tex></formula> . It follows from FDTD-computed results that USR parameters are not much influenced by either the laboratory-floor conductivity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sigma$</tex> </formula> or its relative permittivity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\varepsilon_{r}$</tex></formula> if <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sigma$</tex></formula> is higher than or equal to 10 mS/m, and they are close to the USR parameters for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sigma=\infty$</tex></formula> . When <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sigma$</tex></formula> is lower than about 0.1 mS/m, USR parameters are more influenced by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sigma$</tex> </formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\varepsilon_{r}$</tex> </formula> . Variations in the partial response time <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$T_{\alpha}$</tex></formula> , the experimental response time <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{n}$</tex></formula> , the settling time <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{s}$</tex> </formula> , and the overshoot <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\beta$</tex> </formula> , due to the differences of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sigma$</tex> </formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\varepsilon_{r}$</tex> </formula> , are 8 ns, 14 ns, 150 ns, and 50%, respectively. Even if the width of a horizontal metal sheet is extended from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$w_{g}=$</tex></formula> 2 to 3 m, these variations are not much reduced. The extension of the width of a vertical metal sheet from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$w_{v}=$</tex></formula> 1 to 2 m does not influence the USR parameters much, either. The installing height of a shield ring <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$h$</tex> </formula> influences the USR parameters: with decreasing <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$h$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{\alpha}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$T_{n}$</tex></formula> decrease while <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\beta$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$T_{s}$</tex></formula> increase. Note that the FDTD-computed USR for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sigma=$</tex> </formula> 0.1 S/m and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\varepsilon_{r}=$</tex> </formula> 10 agrees well with the corresponding measured USR.

Effect of configuration on magnetic field in cold crucible using for continuous melting and directional solidification

To improve the power efficiency and optimize the configuration of cold crucible using for continuous melting and directional solidification (DS), based on experimental verification, 3D finite element (FE) models with various configuration-elements were developed to investigate the magnetic field in cold crucible. Magnetic flux density (B) was measured and calculated under different configuration parameters. These parameters include the inner diameter (D2), the slit width (d), the thickness of crucible wall, the section shape of the slit and the shield ring. The results show that the magnetic flux density in z direction (Bz) both at the slit and at the midpoint of segment will increase with the decrease of D2 or with the increase of the width of the slit and the section area of wedge slit or removing the shield ring. In addition, there is a worst wall thickness that can induce the minimum Bz for a cold crucible with a certain outer diameter.

Renovation Design of Coal Powder Conveyor Bearing Support

The bearing support breakage of screw coal powder conveyor in power plant boiler went through four stages: axial displacement of shaft sleeve, shaft sleeve wearing by shield ring and by bearing, and the wearing of skeleton seal rings and dustproof felts by shaft sleeve. By analyzing the wearing characters of each part, the renovation structure was designed. The bearing settled style was changed from using shield ring to using locknut by designing convex sidestep on the shaft sleeve, preventing the axial from drifting. Substituting for the welding assembly, the bolt connecting between the covers and the bearing support body was selected to replace the worn sealing materials easily in dismantling and installing. Good operating effects were achieved after the renovation of the coal powder conveyor bearing support, in the screw coal powder manufacturing line of 100MW power plant boiler, there was no line vibrating, coal leaking, noising and line locking, having decreased the repairing cost greatly and insuring the safety and stable electric power producing.

An analytical model for the surface electrical field distribution of LDMOSFETs with shield rings

An analytical model of an LDMOSFET with a shield ring is established according to the 2D Poisson equation. Surface electrical field distribution along the drift region is obtained from this model and the influence of shield length and oxide thickness on the electrical field distribution is studied. The robustness of this model is verified using ISE TCAD simulation tools. The breakdown voltage of a specific device is also calculated and the result is in good agreement with experimental data.