Aging Characterization of Medium Voltage Groundwall Insulation Intended for PWM Applications

A two dimensional self-consistent fluid model has been established to investigate the discharge dynamics of double-ring electrode He atmospheric pressure plasma jet (APPJ) driven by high frequency AC voltage. The difference of the internal stream and external jet and the influence of the change of applied voltage polarity on plasma discharge characteristics has been discussed. It has been discovered that the capacitive breakdown characteristic of the double ring electrode significantly enhances the intensity of the APPJ. The discharge intensity of the external jet is stronger than that of the internal stream and the propagation speed of the external jet is faster than that of the internal stream due to the ionization and Penning ionization of N2 and O2. Therefore, the density of reactive species in the external jet is greater than that in the internal stream. When the negative voltage is applied to the downstream electrode, the propagation direction of the internal stream changes to the downstream electrode. The ionization of the external jet is also concentrated near the downstream electrode and in the streamer head. The radial propagation distance of the external jet on the dielectric surface continues to increase and the peak value of the radial electric field is concentrated at the streamer head. When the applied voltage changes from negative to positive, the propagation direction of the internal stream turns to the upstream electrode and the upstream jet is formed above the electrode. At the beginning of the positive cycle, the radial propagation distance of the external jet is shortened due to the effects of the electron attachment of O2 and the radial electric field. With the increase of applied voltage, the ionization in the streamer head gradually increases, which promoted the radial propagation of external jet.

Insulation aging in large generators is one of critical fault sources for machines. About 1/3 of generator faults are caused by critical temperature under stator winding insulation faults, especially stator ground-wall insulation shelling fault. To determine stator ground-wall insulation aging mechanism under influences of electric-thermal-mechanical stresses, the 3-D temperature field mathematic models considering different stator ground-wall insulation shellings are established. Based on calculated additional copper losses, turbulent movement in the ventilation ducts and boundary conditions of the model, stator temperature field in the generator normal operating is calculated via finite volume method (FVM). The obtained results are compared with the measurements to verify the accuracy of the calculation method. Then, the stator temperature field considering ground-wall insulation non-transfixion shelling, 1/4 lamination stacking in axial direction and 0.5 mm in circular direction, is calculated. Next, stator temperature fields under multiple ground-wall insulation shelling faults are also investigated. Moreover, the heat transfer laws within the stator components such as strands, ground-wall insulation both in shelling side and non-shelling side, row insulation, and air in the shelling gap, etc., are analyzed. The comparative analysis on the heat transfer laws under different shellings are addressed to provide practical reference in insulation failure diagnosis.

In this paper the results from a prototype low voltage DC input (<30 VDC) kilowatt class high frequency parallel-loaded resonant AC-link inverter is described. This system delivers utility grade voltage-source power at electronically selectable 50, 60, or 400 Hz. Cycle-by-cycle bidirectional current flow reduces the need for intermediate energy storage and allows for operation in a wide range of power factor with passive stability. The high frequency AC link and voltage boost stage is comprised of a zero voltage, zero current switching full-bridge inverter. This soft switching high frequency inverter is well suited for handling the large currents expected from a low voltage source. The output inverter is connected directly to this high frequency AC-link and zero voltage switching is employed in the output inverter to eliminate switching loss. A discretized sinusoidal carrier wave modulation (DSCWM) algorithm is used to control the high frequency boost inverter. The switching frequency of the DSCWM algorithm is fixed in relation to the frequency of the resonant high frequency AC link. The discretization of the modulation algorithm allows for the high frequency link to be discontinuous thus improving the zero voltage switching of the inverter. The elimination of a rectifier stage and reduction of the intermediate energy storage delivers a high power density design when compared to conventional dc-dc-ac methods. While switching loss has been greatly minimized, AC resistance due to high frequency operation and large peak currents present must be addressed in the interconnections and magnetic design.

In gamma irradiated cable specimen, increase in harmonics, generates predominantly a tree like tree/fibrillar type of electrical trees. Weibull studies concludes that the life time of cable insulation failure due to electrical trees gets drastically reduced under high frequency AC voltage and with harmonic AC voltage with increased total harmonics distortion. The results of shape parameter indicate that increase in total harmonic distortion can cause exponential reduction in life of cable due to treeing. The fractal dimension of electrical trees generated under harmonic AC voltages lies in the range of 1.55-1.7.

Introduction. Switched reluctance motor (SRM) is a type of electric motor featuring nonlinear magnetic characteristics. The flux linkage or inductance profile of SRM is usually required for the purpose of high control performance, and can be normally obtained through conventional static test by using DC or AC method when the rotor is locked. Problem. However, it is not practical to use the conventional method of measurement when the specific apparatus for locking the rotor is unavailable. Besides, due to the magnetic nonlinearity of SRM, the saturation effect makes it difficult to obtain the saturated magnetic characteristics, and the conventional static AC test fails to address this problem. Novelty. In this paper, a dynamic measurement method of the magnetization curves of SRM is proposed which allows the measurement take place while the motor is running with load. Methodology. Based on the conventional static AC test, the proposed measurement handles the saturation problem successfully by introducing a DC offset in the high frequency AC voltage. Phase inductance with different rotor positions and currents can be obtained by analyzing simple equivalent circuit. Practical value. Simulation is conducted in MATLAB/Simulink environment and the results have verified that the proposed dynamic measurement can effectively obtain the magnetic characteristics of SRM.

It is difficult to verify the reliability of a new type of ammunition components through traditional statistical testing methods. And the accelerated life test of ammunition components at the present often requires a large amount of sample size. The calculation model for minimum sample size of the Inertial Gyro has been established by clearing the accelerated life test method of Inertial Gyro, considering the Weibull distribution is assumed to product life, and taking advantage of a priori information. And the minimum sample size of the Inertial Gyro that step-stress accelerated life-test required has been calculated out.

In Malaysia, PILC cable has been used for more than 25 years. Based on the cable manufacturers' recommendation, the chronological lifetime of PILC is 40 years. However, the physical age of the cable may be lower due to various stresses experienced by the cables. Since there are 41,911 km of PILC cables in the system (more than 50% population), there must be a strategy to prioritize the replacement of PILC cables. Therefore the aim of this study is to determine the remaining life of the existing PILC in Malaysia. Based on the literature review, a well-known method to estimate remaining life is to use Accelerated Life Testing (ALT). ALT is a method used in this project to accelerate the aging of the samples to fail faster than normal aging. The data collected from the ALT are analyzed using Weibull Distribution and Inverse Power Law formula to predict remaining life of the PILC cables.

Combined with the actual project, a grating ruler accelerated life test device is designed, which can simulate the actual loads, including temperature, humidity and speed stress. An accelerated life test scheme based on stepped stress loading is proposed, and 6 grating rulers are tested based on time-censored test method. An accelerated life model based on Weibull distribution used for evaluating the lifetime is established. Related experimental techniques also can be typical application cases for innovative practical teaching.

In addition to conventional censoring schemes such as Type-I or Type-II censoring, progressively censoring is a useful method to reduce cost and obtain additional reliability information in accelerated life testing. Statistical inference for accelerated life testing (ALT) with Weibull distribution and progressively censoring is found to be difficult. This paper develops generalized fiducial inference techniques for the constant-stress ALT model with Weibull distribution and progressively Type-II censoring. Simulation studies reveal the good performance of the proposed inference methods. An example is given for illustration.

Decomposition of hexane and benzene by dielectric barrier discharge plasma and reaction temperature: Comparison of performance of DC nano-second pulsed power supply and AC high voltage power supply

Gyroscopes are widely applied in weapon system and other high precision system. During the using course, the reliability and performance of gyroscope are influenced by environment and using condition. The performance of gyroscope degenerates periodically, and the remaining useful life (RUL) is payed close attention by engineers in order to monitor the whole systems steadily and safely during life-cycle. Traditionally, researchers used the reliability test and statistic method to estimate RUL. But it’s difficult to get enough samples in the test because the gyroscope cost much. In this paper, we mainly discussed the life prediction of gyroscopes, designed the accelerated life testing(ALT), and used Path Classification and Estimation(PACE) to predict the RUL of gyroscopes. In addition, we analyzed the theory of life prediction for gyroscopes, mainly about the relationship of gyroscope’s fault, nature element and useful life. Then the method is researched based on PACE method. At last, the prediction algorithms is illustrated by the practical accelerate life test data. The methods discussed in this paper was applied in a practical equipment maintenance support project, which can provide technical support for the product life prolong research work in the future. Keywords-component; gyroscopes; remaining useful life; accelerated life testing; path classification and estimation

Accelerated life tests are used to explore the lifetime of extremely reliable items by subjecting them to elevated stress levels from stressors to cause early failures, such as temperature, voltage, pressure, and so on. The alpha power inverse Weibull (APIW) distribution is of great significance and practical applications due to its appealing characteristics, such as its flexibilities in the probability density function and the hazard rate function. We analyze the step stress partially accelerated life testing model with samples from the APIW distribution under adaptive type II progressively hybrid censoring. We first obtain the maximum likelihood estimates and two types of approximate confidence intervals of the distributional parameters and then derive Bayes estimates of the unknown parameters under different loss functions. Furthermore, we analyze three probable optimum test techniques for identifying the best censoring under different optimality criteria methods. We conduct simulation studies to assess the finite sample performance of the proposed methodology. Finally, we provide a real data example to further demonstrate the proposed technique.

Pneumatic cylinders, as a long lifetime product, are used continuously under normal conditions. So Accelerated Life Testing is an important tool to get information quickly on lifetime which is achieved by subjecting the test cylinders to conditions that are more severe than the normal ones. This paper firstly analyze the failure mechanism of pneumatic cylinder, then based on the General Log-Linear relationship and Weibull distribution, describes a model for multiple stress-type accelerated life data analysis. The paper gives the parameter statistical method of the mode by using likelihood theory. Based on the test data from ALT of pneumatic cylinders which adopt four test stresses including air temperature, motion frequency, working pressure and operation velocity, the parameter of the model are fitted. According to the test data and the estimated model, the paper extrapolates the pneumatic cylinder’s lifetime information under the normal user level.

Optimal design of accelerated life tests for the Weibull distribution under periodic inspection and type I censoring

This article describes Bayesian methods for accelerated life test planning with one accelerating variable, when the acceleration model is linear in the parameters, based on censored data from a log-location-scale distribution. We use a Bayesian criterion based on estimation precision of a distribution quantile at a specified use condition to find optimum test plans. We also show how to compute optimized compromise plans that satisfy practical constraints. A large-sample normal approximation provides an easy-to-interpret yet useful simplification to this planning problem. We present a numerical example using the Weibull distribution with type I censoring to illustrate the methods and to examine the effects of the prior distribution, censoring, and sample size. The general equivalence theorem is used to verify that the numerically optimized test plans are globally optimum. The resulting optimum plans are also evaluated using simulation.