Chuyan Zhang

Pollution flashover performance of full-scale ±800 kV converter station post insulators at high altitude area

On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ±800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U50%) was determined by the up-and-down method. The artificial contamination test results indicated that the shed configuration and the rod diameter had a significant influence on the flashover voltages. Shed parameters of one big and one small alternating shed composite post insulator which had superior dc pollution flashover performance had been recommended. The relationship between U50% and insulation height was approximately linear at actual high altitude area for post insulators. It was found that partial discharges occurred at the top section firstly and partial arcs easily appeared at the parts nearby the connecting fittings during the flashover process. And arc floating phenomenon was significantly serious in actual high altitude area. Furthermore, comparison was made between the U50% values of composite post insulators in fog and in rain. The U50% values in fog of composite post insulators were generally higher than that in rain. Thus, the outdoor insulation design of composite post insulators should primarily consider the U50% value in fog. This work thus provides useful reference for the design, operation and maintenance of UHV dc converter stations outdoor insulators in China.

Investigation of DC discharge behavior of polluted porcelain post insulator in artificial rain

The surface discharge of natural polluted post insulators in rain is an important factor which affects the external insulation of HVDC converter stations. With the artificial contamination flashover tests in rain for porcelain post insulators, this paper has obtained the flashover process and discharge characteristics of the test samples under artificial rain condition. It has been observed that the discharge of water droplet on the shed edge plays a very important role in the whole process of pollution flashover in rain. When a water droplet hangs on the shed edge, the maximum electric field strength appears in the vicinity of vertices, rather than the lateral area of the water droplet. Thus, the streamer propagates only in the direction of the air gap between sheds. Moreover, the influence of raining conditions including intensity and conductivity on the flashover voltage has been investigated. Test phenomena also indicate that due to the different damp and dry band conditions, surface discharge characteristics of post insulator in rain are different with that in fog, which lead to different flashover voltages. This study provides a new understanding for the HVDC insulator pollution flashover in wet environment.

Extreme bending of composite insulators on 750 kV compact transmission lines

In designing and constructing the first 750 kV double-circuit compact transmission line, much pioneering work is necessitated in the choice of tower, insulator strings and phase-to-phase spacers. In this paper the mechanical characteristics of three possible phase-to-phase composite spacers for such compact transmission lines are considered in respect of very large bending of the spacer. A large deflection theory is introduced to calculate the lateral deflections and longitudinal compressions caused by applied axial loads and these are compared with the results of tests on three spacers of different lengths and diameters. Agreement between calculation and test results was good and the necessity for the larger diameter demonstrated. No permanent damage due to the extreme bending was found and two of the spacer samples were found to be suitable for use in the compact transmission lines with a good safety margin in respect of such bending.

Time-domain performance of audible noise for positive dc corona: Numerical simulations and measurements

Corona-generated audible noise of HVDC transmission lines is a paramount parameter for design consideration. An acoustic source model and a computational technique are proposed to simulate the sound pressure pulse of positive dc corona discharge. A reduced-scale experimental platform with artificial defeat conductor is built up to verify this numerical method and used to study the time-domain characteristics of the audible noise of the single, three and five corona sources, respectively. The measured and computational results show that calculations of sound pressure are reasonable agreement with the measurements. The repetition frequency of the audible noise pulses increases more significantly than their amplitude, as the number of the corona discharge points increase. Furthermore, with the increase of the applied voltage, the repetition frequency and amplitude of the audible noise pulses increases.

Conductor Surface Conditions Effects on the Ion-Flow Field of Long-Term Operating Conductors of the HVDC Transmission Line

The influence of conductor surface conditions of new and aged conductors on ground-level resultant electric field and ion current density is analyzed in this paper. The surface roughness and morphology of conductors are measured and analyzed by 3-D phase shift Micro-Xam (MicroXAM-3D) and scanning electron microscopy. Calculations are made using the upstream finite-element-finite difference method for the corona cage model to obtain the influence of surface conditions on the ion-flow field, consequently, changing the resulting electric field and ion current density. An indoor corona cage platform is build up to check the impact of surface conditions on the ground-level resultant electric field and ion current density in the laboratory. Considering the aging characteristics of the conductor surface, a typical

Pollution flashover performance of 220 kV glass insulator strings covered with incomplete spraying PRTV coatings

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Positive dc corona inception on dielectric-coated stranded conductors in air

800 kV ultra-high voltage direct current transmission line is analyzed. The calculated results show that compared with the new conductor, the electric field and ion current density of the long-term operation conductors increase very significantly.

Experimental investigation on pollution flashover performance of multiple parallel suspension insulators

The PRTV coating materials had perfect performance in antipollution flashover for porcelain and glass insulators because of the surface hydrophobicity. Usually, the whole strings of insulators were coated with PRTV coatings in engineering application. In order to reduce the consumption of materials, a way of incomplete spraying PRTV coatings was mentioned in this paper. And the pollution flashover performance of 220kV glass insulator strings covered with incomplete spraying PRTV coatings were investigated by artificial contamination test under AC voltages. Conclusions were obtained that the flashover voltage can be enhanced greatly by covering PRTV coatings and the leakage current can be reduced. Compared with the whole string of insulators covered with PRTV coatings, the outdoor insulation performance showed little difference for 220kV glass insulator strings covered with incomplete spraying coatings. This work can provide theoretical support for external insulations maintenance and design of 220kV AC transmission lines.