Ling Ruan

Power apparatus insulation diagnosis through partial discharge in a smarter grid

Insulation diagnosis based on partial discharge signals from power apparatus is widely accepted as a condition bases maintenance strategy in the smart power grid operation. Field applications show that the amplitude of partial discharge may or may not increase with the severity. Lab investigation was carried out to study the behavior of two major kinds of partial discharges in transformer, i.e., the surface discharge and the internal discharge. The lab tests identify the difference in the amplitude distribution of above two discharges. This characteristic can be used to infer the discharge model in field measurement. The recorded partial discharge signals show that the amplitude of the surface discharge increases with the severity of defect, but the internal discharge shows a different pattern.

Calculation of Electrical Parameters for Studies on Propagation Characteristic of PD along Transformer Winding

In order to investigate the propagation of partial discharge pulses in transformer winding, the simulation model of a 180 turns continuous disc type transformer winding based on multi-conductor transmission line (MTL) theory is constructed. According to the symmetry of windings, a 2D equivalent finite element model is set up under ANSYS environment. A modified method is proposed to calculate the K matrix that decrease distinctly calculation cost without loss of accuracy. For the evaluation of L and R parameter of transformer with iron core in MHz frequency area, the skin effect of conductors and iron area is taken into consideration. The frequency-dependent parameters are calculated first by time harmonic magnetic field analysis. The proposed methods of calculating parameters are helpful to research on propagation characteristic of partial discharge (PD) pulses in electric equipments.

Solution for Voltage Distribution in Transformer Winding Model

This paper uses multi-conductor transmission line (MTL) to model transformer winding. Firstly, distributed parameters should be computed. According to capacitance, inductance and resistance parameter, transmission line equation can be solved by input terminal impedance method. Thus, voltage distribution in transformer winding can be obtained by solving MTL equation. In this paper, only voltage distribution at single frequency excitation is calculated. Then, the calculating voltage distribution is compared with the experimental result. Because PD signal can be separated into superposition of cosine wave by fast Fourier transform (FFT), research on single frequency voltage distribution has important significance in solving voltage distribution of PD signal.

Solution for Voltage Distribution in Transformer Winding Based on the Model of Multi-Conductor Transmission Line

This paper uses multi-conductor transmission line (MTL) to model transformer winding. According to capacitance, inductance and resistance parameter, transmission line equation can be solved by input terminal impedance method. Thus, voltage distribution in transformer winding can be obtained by solving MTL equation. In this paper, only voltage distribution at single frequency excitation is calculated. Then, the calculated voltage distribution is compared with the experimental result. Because PD signal can be separated into superposition of cosine wave by fast Fourier transform(FFT), research on single frequency voltage distribution has important significance on solving voltage distribution of PD signal.

Frequency effect on calculation for voltage distribution of winding

This paper models simplified transformer winding model by multi-conductor transmission line (MTL) model. Because inductance and resistance of transformer winding are frequency-dependent parameters, frequency effect on parameters should be considered when calculating distributed parameter matrices. Then, when solving for voltage distribution of winding model, the distributed parameter matrices should be selected according to the frequency of signal source. Because of frequency change, voltage distribution of winding model changes very significantly. This phenomenon can be verified by accurate experiment.