Advanced Materials Research Vols. 614-615

Abstract: Under the condition of Baader aging, the chemical composition variation and the effect of transformer oil aging on electrical properties such as dielectric loss factor and physic-chemical properties such as kinematic viscosity were studied during aging. Moreover, the correlation between hydrogenated transformer oil electrical and physic-chemical properties and its chemical composition variation were investigated.

Abstract: The Axial Magnetic Field (AMF) applied to the arc vacuum column in the vacuum tube can make the vacuum arc keeping in diffusion state, provided that the short circuit current to be interrupt is within a critical value. In the results, the breaking ability of Vacuum Interrupters can be highly improved with the help of the AMF. The experimental study has proved that the AMF should be sufficient strong and have optimum distribution, in order to improve the breaking capacity of vacuum circuit breaker. This paper presents a novel axial magnetic contact with the concave axial magnetic field distribution and its 3-d simulation.

Abstract: The partial discharge direction of arrival (DOA) estimation based on ultrasonic array sensor is the basic of partial discharge’s accurate positioning. The precision and searching success rate of traditional MUSIC direction finding algorithm is low. So this paper presented a new method based on ultrasonic array sensor and genetic MUSIC algorithm in partial discharge DOA estimation. The genetic MUSIC algorithm constructed fitness function by spatial spectrum estimation formula, searched the spectral peak of azimuth based on the idea of genetic iterative searching in order to obtain the global optimal solution. This paper carried out a large number of simulation experiments through the establishment of signal model and array model, then used three indicators of searching precision, searching success rate and searching time as the basis, to compare the direction finding results of classical MUSIC and genetic MUSIC. The results show that the optimization precision and searching success rate based on the genetic MUSIC algorithm is improved greatly, can obtain higher accuracy of partial discharge DOA angle.

Abstract: Trees which are growing beneath high-voltage transmission lines have to be cut down if the distance to the conductor rope gets too close. It is very hard to find those if only single trees are affected. Chopping simply all trees under a transmission line, which was done in former times, is not a desirable solution for environmental and economic reasons. In this paper a solution is shown which uses an unmanned aerial vehicle and a laser scanner to generate a 3d point-cloud representing the trees and the conductor ropes. Using this point-cloud the decision for cutting down a specific tree can easily be made.

Abstract: Ultra high frequency (UHF) partial discharge (PD) detection technique is drawing attention to transformer insulation accident prevention. However, the configuration of a large oil-immersed transformer is very complicated, so the reflection, refraction and absorption phenomena between PD sources and UHF sensors need to be considered. The phenomena make it difficult to calibrate the magnitude and locate the source of a PD activity. Therefore, detailed investigation of EM wave propagation inside the tank is carried out to enhance the performance of UHF method. Numerical simulations are performed on the 3D models using finite difference time domain (FDTD) method. From the results, the effects of transformer oil, cores and the tanks are clarified.

Abstract: An on-line monitoring system based on ultra high frequency (UHF) partial discharge (PD) measurements was developed for power transformers. The UHF PD signals were coupled by a UHF sensor and preprocessed by peak envelope detection technique. The system has high sensitivity, strong ability of interference suppression and well real-time capability according to the simulated experiment in lab and field test of a power transformer. Experimental results showed that the forepart PD faults could be discovered by the analysis of UHF PD signals. The on-line monitoring system has already been applied on a power transformer for years.

Abstract: Concentration detection of gases dissolved in transformer insulation oil is an effective method to diagnose incipient fault in electrical equipment. The permeation process of gases dissolved in transformer oil through extraction membrane is studied. Temperature dependence with accuracy of on-line DGA results through gases extraction with polymer membrane is analysed. An algorithm which includes temperature coefficient which can improve the accuracy of DGA results is proposed. An on-line DGA system with Teflon membrane and electrochemical gas sensors is constructed; while the results are adjust by temperature coefficient. Compared with GC results in the laboratory, the accuracy of the on-line DGA results has been improved.

Abstract: Serious icing on overhead ground wires threatens the safe running of power system. Common overhead ground wires are difficult to realize ice-melting. A novel overhead ground wire structure for ice-melting is proposed. Some conductors coated with insulation layer are winded around the galvanized steel wires in a special way. Ice-melting experiments are performed on the novel overhead ground wire. Experimental results show that 30 W per meter of the wire is an economic power while 40 W per meter of the wire is an effective power for ice-melting. Engineering application of the novel overhead ground wire with insulated conductors is carried out. With the light moveable de-icer, onsite experiment is performed. Under the power of 40 W per meter of the wire, a temperature rise of 10 °C is achieved in 30 minutes. The result shows that the novel overhead ground wire can meet the demands of engineering application.

Abstract: Aeolian vibration of overhead groundwires is intense in transmission lines located in flat and windy areas; which easily leads to line failure caused by material fatigue. To suppress the aeolian vibration of lines located in Hexi corridor, new dampers for groundwires were developed and configured, based upon analysis of the characteristics of aeolian vibration. Simulation tests were conducted according to the energy balance principle (EBP), and field vibration tests were also performed. The test results show that the dampers meet the requirements of the prescribed standard and the efficiency is verified. The dampers have been applied to 750kV transmission lines, and they offer easy installation, slip resistance and a satisfactory vibration suppression effect.

Abstract: Structural optimization for the highly sensitive mechanical sensor elements was studied. Using Molecular Beam Epitaxy (MBE) technology, three different RTD structures were fabricated on the GaAs substrates. From the I-V characterizations, it can be concluded that, the PVCR of the best design is up to 6, VP is reduced to 0.41V, and then we analyzed the relationship between the device material structure and I-V characteristics, providing a reference for the better performance of RTD structure design.