Lv Fangcheng

Pulse propagation model of partial discharge in transformer winding

Based on multi-conductor transmission lines (MTLs) theory, a new model of partial discharge pulse propagating in single phase transformer is established. The parameter matrices C in the model are calculated based on static-steady electromagnetic field theory, and other parameters R, L, and G result from the relationship between the parameters. The transformation of mode voltages and mode currents is applied in order to obtain MTL general solution, and the transfer functions of transformer winding are obtained, then scattering parameter method for measuring the transfer characteristics of transformers winding are presented. The experimental results tested on 180-turn single winding and 400 kV transformer winding consistent with the simulation results derived from their MTL model.

A new method for ultrasonic array location of PD in power transformer based on FastDOA

The precise partial discharge(PD) locating in power transformer has important significance for the steady and safe operation. The Multiple Signal Classification Method (MUSIC) is an classical algorithom in DOA of ultrasonic array location. However,the estimation of the compelete covariance matrix and the subsequent eigendecomposition are computationally intensive and time consuming. A new fast subspace algorithom is adopted in this paper. The algorithom of FastDOA can rapidly obtain the signal subspace from a submatrix of the array covariance matrix without eigendecomposition and it only needs estimating the submatrix instead of estimating the whole covariance matrix. With the same direction-finding precision, the new algorithom has a low computational complexity and a faster operation speed. Based on this, crossover location principle is used to realize the space position of the PD source. Computer simulation results show the correctness and superiority of the new method.

Breakdown characteristics of transformer oil insulation under impulse voltage with different waveform parameters

This paper conducts an experimental investigation about the breakdown in transformer oil under the action of impulse voltages with different waveform parameters for the insulation of the transformer in field may be subjected to the lightning and switching overvoltage. In the paper, an impulse voltage generator is built based on the solid state switch and it can produce different kinds of impulse voltage. Five different impulse voltage waveforms are used: 1.4/50µs, 11/210µs, 60/700µs, 130/1700µs and 250/2600µs. Then the breakdown tests are carried out under these impulse voltages. Specifically, a needle plate electrodes immersed in the bulk of the transformer oil is used to form a nonuniform electric field gap. The different radii of curvature and different gap distances of the needle plate electrodes are also taken into consideration in order to determine the properties of breakdown electric field strength. The impulse voltage is increased step by step with a step increment of 2 kV for positive polarity (1 shot/step) until the oil gap breakdown takes place. The description of discharge and breakdown in the oil gap is obtained by the measurement of impulse voltage, transient currents and the emitted light. Meanwhile, the breakdown voltage and breakdown time for impulse voltages with different waveform parameters are obtained. And the average velocity of streamer propagation is deduced. The results show that the breakdown voltage is closely related to the front time of the impulse voltage, the gap distance and the radii of curvature of the needle electrode. The propagation time of the streamer increases with the increase of the impulse front time, also the breakdown time delay has the same characteristic. The factors that influence the gap breakdown voltage are finally analyzed and discussed.

Volt-time characteristics of transformer oil under impulse voltage with different waveforms

This paper conducts an experimental investigation about the breakdown in transformer oil under the action of impulse voltages with different waveforms for the insulation of the transformer in field may be subjected to lightning and switching overvoltage. In the paper, an impulse voltage generator is built based on the solid state switch and it can produce different kinds of impulse voltage. Then the breakdown tests are carried out under the standard lightning, the standard switching and the nonstandard impulse voltage. Specifically, the planeplane electrodes immersed in the bulk of the transformer oil are used to form a quasi-uniform electric field gap. The clean oil samples (oil samples were filtered, degassed and dehydrated) are used to avoid the effect of particles and moisture on the breakdown strength of transformer oil. The electric field strength of the parallel-plate electrodes is taken into consideration in order to determine the properties of breakdown. The impulse voltage is increased step by step following standard IEC 60060 with a step increment of 2 kV for positive polarity (15 shot/step) until the oil gap breakdown takes place every shot. The description of discharge and breakdown in the oil gap is obtained by the measurement of impulse voltage. Meanwhile, the breakdown voltage and breakdown time for impulse voltages with different waveform parameters are obtained and then mathematically analyzed the obtained data. The influence of wave front/tail time on the Volttime characteristics of oil insulation is experimentally studied. The results show that the breakdown voltage is closely related to the front time of the impulse voltage. The factors that influence the gap breakdown voltage are finally analyzed and discussed.