In general, parameter pressure × gap distance (p × d) in dielectric barrier discharge is used to control the electrical breakdown and plasma characteristics. In this paper, we investigate the critical pd value for air discharge transition from filamentary to homogeneous mode by controlling the pressure. Dynamics of the air discharge show that the discharge transits from filamentary to homogeneous mode when the operating pressure decreases from 9 to 4 kPa. With 1-mm thickness alumina applied pulsed power, the critical pd value obtaining homogeneous air plasma is 40 kPamm.

The dielectric constants and the high temperature resistant performance of solid insulation used in oil-immersed transformer would limit the capacity and size of an oil-immersed transformer. In this paper, 3 polymers(polyester film, polycarbonate and phenylene sulfide) are aged under 130℃ up to 1 200 hours. The dielectric spectroscopy(here refers to the change tendency of relative permittivity and tanδalong with the change of temperature) and the AC electric breakdown strength of 3 polymers are investigated at different aging stages. According to the test results, the dielectric constants of three polymers is always less than the dielectric constant of insulating paper/board and more close to that of transformer oil, and their tanδare also less than that of insulating paper/board. Before aging test, the dielectric constants and tanδof polyester film and phenylene sulfide would be increased obviously at about 90℃, but not the polycarbonate. There shows the same change tendency of the dielectric constants and tanδfor 3 polymers at different aging stages as without aging test. It is also found that the AC breakdown voltage of 3 polymers at different aging stages have almost kept the same as the value of non-aged state. Considering the dielectric properties of these 3 polymers, comparing the properties of insulating paper/board, in terms of the lower dielectric constant and the higher ac breakdown voltage, polycarbonate may be used as one of suitable replacement materials for insulating paper/board used in oil-immersed transformer.

The insulation of the multi-loop AC-DC transmission lines with the same tower has been more concerned as the erect of which meets the needs of resource- saving society. The paper analyzed the contamination characteristics and polluted external insulation design of the multi-loop AC-DC transmission lines based on dirt retention data, which obtained from natural pollution deposit contamination tests, and dirt retention characteristics calculated by simulation of electric field calculation. The result shows that there exists differences of the dirt retention characteristic between DC insulator and AC insulator, and the former`s pollution grade is more serious. The surface accumulated pollution of surrounded insulators are greatly affected when they are close to HVDC field. The degree of the dirt retention is determined by the distance between the AC insulator and the DC field in certain ranges.

Among the detection methods of partial discharge in high voltage electrical equipment, optical method is new and competitive. This paper presents a diaphragm type optical fiber EFPI (External Fabry-Perot Interfering) sensor, which is developed by external Fabry-Perot interfering method and used for detection of partial discharge. We made a needle-plane electrode in oil, detected it with joint detection of optical fiber sensor and VHF (Very High Frequency) sensor. The study finds: optical fiber sensor can pick up signals effectively on PD (partial discharge) detection in early stage, have high sensitivity. The signal picked up by optical fiber sensor and VHF sensor not only has well correspondence, which can identify partial discharge signals effectively, but also has broad application, such as the on-line detection of transformer or other high voltage electrical equipment.

Water drop on conductor line surface caused by rain or fog would distort the voltage gradient around the conductor line and change the corona performance of conductor line.The first UHV DC transmission project,Yun-Guang transmission line would be in rain fed areas,corona performance of conductor line should consider the effect of water drop.To research the effect of water drop on corona performance of UHV DC transmission line,water drop level was defined,a conductor corona performance test system was set up,corona onset voltage was defined,and the corona inception voltage and audible noise level of DC conductor were measured in different water drop level in corona cage.Moreover,the effect of water drop on DC conductor corona performance was observed,and a reference for engineering design of UHV DC transmission line was suggested.Test results show that corona onset voltage rapidly decreases as the water drop level increases;Conductor would sloshing acutely and water drop will be vaporized or throw off from conductor after corona onset;Audible noise level of conductor increases as the water drop level increases at the same voltage;however,Audible noise level of conductor decreases with the water drop level increases at its onset voltage.

To study the corona performance of full scale UHV DC transmission line, a 4 m long, 2 m times 2 m corona cage has been constructed. At the same time, a corona performance measuring system consists of audible noise level meter, EMI receiver and ultraviolet imaging telescope has been set up too. Audible noise level, radio interference level and total of ultraviolet photon of a 4 times 500 mm2 transmission line have been measured at different voltages. According to the test results, a method to determine the inception corona voltage of the full scale transmission line has been presented.

To research the effect of temperature and humidity on radio interference generated from UHV DC transmission lines, a mini corona cage has been constructed and put in a manual environment room, which temperature and humidity can be controlled. At the same time, a radio interference performance measuring system by using loop method has been set up too. The radio interference generated from a copper line have been measured in a mini corona cage not only at different humidity from 30% to 99% at 20 but also at different temperature from 0 to 30. The relationship between radio interference level and temperature and humidity have been achieved.

To research the effect of temperature and humidity on corona performance of UHV DC transmission line, a mini corona cage has been constructed and put in a manual environment room, which temperature and humidity can be controlled. At the same time, a corona performance measuring system by using vary methods such as current impule method, acoustic method have been set up too. The corona inception corona voltage gradient of a copper line have been measured in a mini corona cage not only at different absolute humidity from 3 g/m3 to 12 g/m3 but also at different temperature from 0degC to 35degC . The relationship between inception corona voltage gradient and temperature and humidity have been achieved.

A new partial discharge(PD)location method in power transformer is presented based on time delay measurement of electromagnetic(EM)wave signals using antenna array.Firstly,the relationship between location resolution of EM wave method and the detecting frequency is discussed,and a new frequency band of 1~5GHz is proposed for accurate PD location;Then,the effect of iron core model and transformer winding to the propagating time delay of EM wave is studied experimentally;At last,a 4-element antenna array and time difference algorithm for PD location are developed,the practical effect is tested through experiment.The results indicate that the method effectively avoid the adverse effect of the iron core to the time delay and realize accurate location to single PD source successfully,with the minimum error of only several centimeters.

The application of the BP neural network to the partial discharge patterns recognition of generator stator windings is discussed.Five types of simulation models for the insulation PD in the large generator stator windings are presented.The PD simulation models include the surface discharge at end windings,the discharge between two slots and the interior discharge in three different positions of the insulation.The recognition ability of the ANN is studied.A higher recognition rate for the partial discharge types of the large generator stator insulation is gained.