Measurement Of Dielectric Loss Angle Research Articles

Sparse Representation Based Dielectric Loss Angle Measurement

Precise measurement of dielectric loss angle is very important for electric capacity equipment in recent power systems. When signal-to-noise is low and fundamental frequency is fluctuating, aiming at the measuring error of dielectric loss angle based on some recent Fourier transform and wavelet transform harmonics analysis method, we propose a novel algorithm based on sparse representation, and improved it to be more flexible for signal sampling. Comparison experiments describe the advantages of our method.

Fast Measurement of Dielectric Loss Angle With Time-Domain Quasi-Synchronous Algorithm

Fast Fourier transform (FFT) algorithm inevitably suffers from spectral leakage and picket-fence effect under asynchronous sampling and nonintegral period truncation. So the FFT-based dielectric loss angle (DLA) measurement needs window functions and spectral lines interpolation algorithm, which requires massive sampled data and high computational cost. Therefore, this paper proposes a DLA measurement method on the basis of time-domain quasi-synchronous sampling technique to achieve fast measurement and high accuracy. First, the fundamental frequencies of the original voltage and current sampled signals were estimated accurately with the time-domain Newton interpolation algorithm. Then, the quasi-synchronous sampled sequences (QSSA) of the original asynchronous sampled signals were reconstructed using cubic spline interpolation algorithm. Finally, the DLA was calculated according to the equivalent circuit model and frequency-domain analysis of voltage and current QSSA based on FFT. The proposed method in this paper can perfectly restrain spectral leakage and picket-fence effect without window functions and spectral lines interpolation algorithm. The results of simulation and the implementation on the embedded system have confirmed the effectiveness of the proposed algorithm in this paper with less sampled data and lower computational cost.

Analysis on the Influence Factors of Capacitor Voltage Transformer Dielectric Loss Measurement

Capacitor voltage transformer (CVT), which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. And its capacitance and dielectric loss Angle measurement is an important test on testing the insulation of the equipment. This paper is mainly to introduce and discuss one of the CVT test methods——the “self excitation method”, combined with the actual situation encountered in the work, sums up and expounds the maintenance of CVT and preventive test of influence factors.

Measurement of Dielectric Loss Angle Based on Wavelet Threshold Denoising and Least Squares

Dielectric loss angle is the effective means to determine the status of the high voltage equipment.Influenced by power grid frequency fluctuation and white noise, the measurement accuracy of traditional method of dielectric loss angle such as harmonic analysis method, cannot meet the demand.A new methodbased on wavelet threshold denoising and least squares is presented in this paper. Firstly, harmonic wave and white noise are eliminated by improved wavelet thresholddenoising, Second, the fundamental wave of voltage and current signal is extracted by mean of least square method, then we can get dielectric loss angle.Simulation and calculation are validated in the different values of frequency fluxion and whtie noise.Comparing with harmonic analysis method,the result show the feasibility and effectiveness of this method.

Application of Synthetic Relative Measuring Method in On-Line Monitoring for Capacitive Equipment

On-line measurement for dielectric loss angle can effectively monitor the insulation condition of capacitive equipment in power system. Synthetic relative measuring method not only markedly overcomes the shortcomings of traditional absolute measuring method but also greatly improves the accuracy of dielectric loss angle measurement. However, the papers nowadays only focus on the application of synthetic relative measuring method based on two or three pieces of capacitive equipment, which does not have the characteristic of generality. In the paper, the principle of synthetic relative measuring method is given. The example of application for synthetic relative method based on three and four pieces of capacitive equipment run in the same phase is taken to present the failure judgment matrices for N pieces of equipment. According to these matrices, the fault condition of N pieces of capacitive equipment can be watched, which is more general. Finally some problems needing attention and two diagnostic methods used in diagnostic system are put forward in the paper to guide the application of synthetic relative measuring method on local.

Dielectric loss-angle measurement of multi-core high-tension cables, with special reference to the Schering bridge

In section (1), the special difficulties of dielectric loss-angle (D.L.A.) measurement on multi-core cables are examined. The conclusion is reached that an iner-admittance, say between one core and another, cannot be considered to have associated with it a definite D.L.A., but will have a varying D. L. A. with different stress distributions. Measurements mede with one stress distribution cannot be used to foretell the D. L. A. with any other; and 3-phase D. L. A. cannot be precisely estimated from measurements made with single phase currents.In section (2), a new method of obtaining the inter-D. L.A. in conformity with the conclusions of section (1) is described. The Schering bridge equations are fully worked out and the corrections for various stray capacitances are given.In section (3), it is shown that the wavelength effect appreciably affects the apparent D.L.A. when the cable exceeds in length a small fraction of the wavelength. Corrections on the apparent D.L.A. are given.