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Ultrasonic method is a non-invasive partial discharge (PD) detection method for power equipment, which plays a more and more important role in partial discharge location. The propagation characteristics of ultrasonic in converter transformer can be effectively analyzed by using numerical method. In this paper, according to the actual size of a 110kV converter transformer, the 3-D finite element simulation model of converter transformer is established to simulate the propagation of ultrasonic signals in the tank. A 2-D model is then established to simulate the influence of windings on the propagation of ultrasonic signals. The simulation results show that when the partial discharge is generated, it will spread around in the form of a spherical wave, which spreads over the entire converter transformer space within 2000μs. The sound pressure amplitude is exponentially decreased with the increase of distance between PD sources and prbes, and the drastic attenuation is caused by the windings and core. When the discharge source is located between the winding and the core or between the windings, the wave arrival time from the partial discharge source to the ultrasonic sensor will be increased. The analysis can provide the basis for the detection and localization of partial discharge in converter transformer.

Deterioration of insulation materials caused by partial discharge is one of the important reasons for the failure of power equipment. The noise caused by the interference of the external electromagnetic environment seriously affects the accuracy of partial discharge detection. Aiming at the problem of partial discharge noise suppression, this paper proposed a partial discharge signal noise suppression method based on adaptive window singular value decomposition. This method first randomly generated a series of windows with different positions and lengths on the noisy partial discharge signal; Then singular value decomposition method was employed to denoise the signals in each window; Finally, the denoising index was chosen as the fitness function, through the particle swarm algorithm to obtain the optimal solution of the window position and length. The noise signals obtained by simulation and experiment were verified, and the method was compared with adaptive singular value decomposition, wavelet denoising, and other methods. The results showed that this method could achieve a better denoising effect.

Traditional methods cannot detect hot spot temperature, mechanical vibration and partial discharge signal and other state parameters of the transformer in real time. Optical fiber sensing technology has a wide range of application prospects due to its high accuracy, strong anti-interference ability and distributed measurement. However, the premise for its application is that the embedded optical fiber does not affect the safe operation of the transformer. This paper explores the interact between embedded fibers and transformers. In this paper, four different types of optical fibers were initially selected to prepare fiber-oil composite insulation. Samples under different aging time were obtained through accelerated thermal aging experiments. The mechanical strength and optical loss characteristics of fibers with different aging degrees were tested separately. At the same time, moisture content, acid value, oil chromatogram, dielectric loss factor and volume resistivity of insulating oil were tested. The results show that the mechanical strength of the PVC tight fiber decreases significantly as the aging time increases. PVC tight fiber significantly improves the dielectric loss factor, CO 2 /CO and total hydrocarbon content in insulating oil. The mechanical properties of the other three optical fibers remain basically unchanged and have little effect on the insulating oil. Thermal stress does not affect the optical transmission characteristics of all optical fibers. The PVC tight fiber is not suitable as the embedded optical fiber in transformers, while the other three optical fibers meet the basic requirements of the embedded optical fiber. The experimental results provide solutions for the safety risk assessment of the embedded optical fiber in transformers.

The insulation diagnosis method based on frequency domain dielectric spectrum is widely used in field test because of its nondestructive testing, rich insulation information and so on. FDS measurement results are easy to be affected by many factors. However, interpretation on the dielectric properties of oil paper insulation with moisture content, impurity ion concentration influence mechanism of the current research is not very ideal, so it is necessary to determine more appropriate and effective dielectric response simulation and experimental analysis of characteristics. In addition, moisture content (m.c.) is an extremely important factor which can determine the insulation state of Oil-immersed paper. Therefore, the evaluation of moisture content of oil-immersed paper has obvious significance. In this paper, based on the experimental results, the extended Debye model parameters of the field transformer are obtained. Then, the influence of the insulation resistance value in the Debye model on the FDS curve is simulated by MATLAB modeling. The simulation and experimental verification show that the regularity of the change of the FDS conductance process is obviously different from the moisture content influenced by the impurity ions. The impurity ions mainly affect the low frequency section of the imaginary part of the complex capacitor. A non-linear phenomenon in dielectric response with different moisture contents under different is observed. We found that the non-linear phenomenon has relationship with the hindrance effect of cellulose (m.c.

Partial discharge (PD) in power transformer degrades the dielectric insulation and results in insulation failure and breakdown after a long period. In fact, a partial discharge detector can gather signals from two or more PD sources which increase the difficulty on pattern recognition and insulation state assessment. How to separate multiple PD signals is meaningful to subsequent data processing. In this paper, a PD separation algorithm based on cumulative energy (CE) function is introduced. The CE functions in time domain (TCE) and frequency domain (FCE) are calculated from PD waveforms and their FFT spectra, respectively. By using an oblique line to cross the CE curves, width features are extracted from the intersection points between them. Through the mathematical morphology gradient (MMG) operation, sharpness features are extracted to characterize the rise steepness of CE. A clustering algorithm is adopted to discover different clusters in feature space and separate PD signals. After that, a transformer experiment platform is introduced and some different defects are placed at different places in this transformer to produce PD signals. The pulse current method is applied to gather their PD waveforms and to record phase resolved partial discharge (PRPD) which can be used to analyse discharge characteristics of different defects. The separation algorithm is examined with mixed PD current pulses acquired from experiments. The results prove the feasibility of separation algorithm with different PD defects.

So as to adapt to the condition-based maintenance of power equipment and to overcome the disadvantages and deficiencies of traditional condition evaluation model in data acquisition approaches, component classifications, performance indicators and scoring model, a comprehensive condition evaluation model (CCEM) was proposed in this paper based on multi-source information. Combined with the offline test, online detection, online monitoring, inspection and operating environment, equipment criteria, undesirable service condition (USC) and family defects were reclassified in this model. Practice example verified that the proposed model can describe the power transformer state more comprehensively and immediately. The evaluation results provide scientific guidance for front-line operation and maintenance staffs to develop equipment maintenance strategy, and also practical basis for the condition evaluation of other power equipment.

A particular Cathode-like luminescence (CLL) phenomenon occurring on vacuum-dielectric interface under high DC electrical field before or accompanied with flashover is reported, which is widely existed in vacuum-dielectric system. It is considered that the CLL presented in this paper is initialized by field electron emission at Cathode Triple Junction (CTJ) and finally generated by a process of radiative recombination due to the self-stabilizing secondary electron emission (SSEE) and collision on surface of insulator. The spectrum of CLL is measured and analyzed, and it shows that there are not any characteristic spectrums of C, O, N, which means that the CLL is not produced by discharge of desorption gas. In addition, simulation results also approved that the SSEE process in fact exists. Finally, its relevance to flashover is also discussed. It shows that flashover seldom occurs on the channels of CLL, which seems that the CLL has an inhibition effect on flashover. However, the exact mechanism is still unclear. This work will be researched in near future.

Surface flashover phenomena in vacuum restrict the overall performance of vacuum solid insulation system. Since accidents caused by surface flashover in vacuum occur constantly, it is always the international highlight to study some new insulating materials and insulation structure with high electric withstanding for vacuum insulation. On the basis of the novel low melting temperature machinable glass ceramics for vacuum insulation system, which has excellent machinable performance and good electrical properties, the samples of embedded electrode into machinable ceramics are machined, and then the samples' flashover voltage of different embedded mode and embedded depth are investigated under nanosecond pulse voltage in vacuum. The electric field distributions and electric field of cathode triple junction (CTJ) are simulated to explain the experimental results. The experimental results indicate embedded electrode in cathode can increase the surface flashover voltage of the sample; with increasing of the embedded depth, the surface flashover voltage tends to be increased. The simulation results indicate embedded electrode in cathode can decrease the electric field of CTJ, and with increasing of the embedded depth, the electric field of CTJ tends to be decreased.

Summary form only given. Flashover phenomena in vacuum restrict the performance of insulation system, which has been paid much attention by many researchers. However, due to the rapidity and complexity of flashover development process, the mechanism of surface flashover phenomena is still not fully understood. In this paper, an ICCD camera is adopted to observe the dynamic process of surface flashover on alumina ceramic in vacuum under impulse voltage. A needle as the HV electrode and a round-shaped steel as ground electrode are placed on the alumina ceramic, which forms an asymmetric electrodes configuration. Negative and positive impulse high voltages are applied on needle electrode, respectively. And the development processes of surface flashover are investigated. The results show that when negative voltage is applied on needle electrode, light emission always starts from cathode and then move to the anode, while positive voltage is applied on needle electrode, due to high electric field near needle electrode, light emission can be observed both at cathode and anode. But at the anode, the light emission region is limited in a small scale. It can also be seen that light emission near the cathode is developing to anode with applied voltage increasing, and the light branches are only developed in the direction of anode.

Surface flashover in vacuum is a kind of complicated surface and interface phenomena, which seriously restricts the development of high voltage electro-vacuum devices. Introducing a kind of machinable ceramic with excellent machinable performance and good surface electrical capability into vacuum insulation system, and considering the commonly used truncated cone structure, machinable ceramic samples with different coning angles are machined. Their surface flashover voltage are investigated under pulsed voltage in vacuum, and the electric field distributions and surface charge density of different coning angles are numerically simulated. The experimental results indicate that, the flashover voltage of cone insulators is higher than that of cylindrical insulators, the flashover voltage of truncated cone samples with positive coning angle is much higher than that of with negative coning angles, and the flashover voltage with ∼45°conical frustum is highest. It is considered that, the coning angle plays an important role on the electric field of cathode triple junction (CTJ) and surface charge distribution. When the coning angle is positive, the electric field of CTJ and surface charge distribution is smaller, and when the coning angle is negative, these values are bigger, so its higher CTJ electric field and surface charge result in a lower flashover voltage than that with positive angle, and also the short free path of electrons and decreased energy of electrons colliding with insulator surface lead to a higher flashover voltage than that of cylindrical insulators.