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The pulse current signal generated by partial discharge in the transformer winding will be affected by the winding structure during the process from the discharge source through the winding to the external measurement device, which is manifested as signal attenuation, distortion or delay, which is affected by the signal propagation path and distance, and it has a great relationship with the propagation characteristics of the windings. The simulation analysis method was used in this paper to establish a multi-conductor transmission line model of a 180-turn transformer single winding with simplified distribution parameters, and the transformer winding head and interior were obtained Propagation characteristics of the winding, then simulated partial discharge current pulses are injected into the winding ends of different turns, and the changes of the pulse signal after propagating to the winding first end are observed.

Current carrying capacity of power cable should be determined by the maximum operating temperature which the insulation can withstand. The temperature rise in cable is mainly due to Joule's loss in conductor and induced eddy loss in sheath. In this paper, based on the coupled electromagnetic-thermal theory, the power losses calculated in electromagnetic field analysis are used as the input data of thermal analysis to predict the temperature rise in different layers of cable. Using the simplified cable model, the temperature distributions in single phase and three phases cable with different arrangements are calculated and compared. The results show that three phases cable get the higher temperature distribution according to the proximity effects between the different phases compared to the single phase cable. As a result, in application, the optimized arrangement of cable can be applied to make the temperature rise of cable as low as possible.

Partial discharge (PD) in transformer can be detected on-line by UHF technique. However, the relationship between the UHF signal received by UHF sensors and the PD sources is not very clear. It is very important studying the propagation properties of the PD signal. In this paper, the electromagnetic waves emitted by PD sources are investigated. The finite difference time domain (FDTD) technique is used to model wave transients. The model consists of a tank and a PD source. The wave transients at different time and position are simulated. The results show the propagation transients of the PD signal in the tank and wave propagation attenuates with distance between the source and the sensors.

A test system with UHF and UWB detection technologies developed to measure PD under DC voltage is introduced in this paper. According to the typical defects in oil-paper insulation of converter transformer, six corresponding PD models are designed. The test results of PD UWB detection under DC voltage show that the PD current pulses have a very short rise-time, which are capable of radiating UHF signals at frequencies up to at least 300 MHz, and these electrical magnetic waves can be picked up by the UHF sensor. The DBM spectrum analysis is made for all UHF signals of the models, which shows that they differ with various defects, and the maximum amplitudes of the energy distribution against the UHF are also different. These indicate the on-line monitoring for the UHF PD signal under DC voltage should be realized utilizing the narrowband filter with adaptive center frequency.

Feature extraction methods for time-frequency energy distribution (TFED) using moment, marginal and Renyi information are studied in this paper. They are developed by combination of TFEDpsilas own characteristics with mathematic statistic and information entropy. The Wigner-Ville distribution (WVD) of a simulated PD pulse is chosen as the subject investigated to illustrate those methods, which gives the result of time and frequency moments, time and frequency marginals and Renyi information for the TFED. The results show that those methods can exactly and easily make feature extraction for the TFED of PD pulse, which can be used to PD pattern recognition and in-depth study of PD mechanism in the electrical insulation system.

In the UHF detection of power transformers, the main method is detecting the UHF signals through UHF sensor in the transformer. The sensibility of this method is high but mounting way is trouble. Field detection and lab testing show that the UHF signals can diffract from the transformerpsilas joint. Some PD detector using external detection has used in field. But, the difference of signals in transformer and external transformer is not clear. In this paper, the feasibility of using external UHF sensor for detecting partial discharge activities is discussed, and then external propagation characteristic of UHF E-M wave is studied by lab experiments. Wavelet packet analysis of signals show the high frequency of external signals is bigger than inside signals. The relationship of distance of joint and UHF sensor is studied in this paper. The results show that UHF signals could leak outside the transformer through the joints after multiple refraction and reflection in the transformer tank. An antenna outside the tank could receive the signals. Study result will supply some signal acquisition direction for the UHF detection transformer PD.