Time-Domain Characteristics Of Corona Current Pulses On DC Conductors

HVDC power transmission is playing an increasingly important role in energy resources distribution of China, nowadays. However, radio inteference due to coronas on the HVDC power lines is one of the most important factors which determine the choice of conductor type, conductor height, corridor width, etc. Fundamental aspects of corona current pulses, i.e. the origin of radio interference (RI), are the main subjects of the present investigation. The work of the present investigation includes, establishing the time-domain measurement method of corona current pulses from HVDC conductors, based on which, obtaining the time-domain characteristics and their variations with exterior factors of corona current pulses on HVDC conductors. Furthurmore, based on the time-domian characteristics of corona current pulses, the stochastic time-domain prediction model for radio interference from HVDC conductors is established, the validity of which is preliminarily verified by the empirical formula. The work of the dissertation is of academic and engineering value, providing a reference for the prediction study of radio interference from HVDC power lines.Firstly, a corona cage test method to accurately measure the corona current pulses is proposed. The difference between the proposed method and the conventional method is that in the proposed method, the high voltage is applied to the corona cage which is insulated to the ground, whereas the test conductors is near ground-potential and is connected to the ground in series with the matching resistor at both ends, and the free-reflection test circuit for corona current pulses is therefore established, and consequently the pulse shape distortion of the corona current pulses produced by reflection in conventional corona cage test method is overcome. Experimental measurements as well as theoretic calculations confirm that the proposed method is capable of accurately measuring the the corona current pulses on test conductors. In addition, the equivalence of the corona current pulses produced by high-potential corona conductor and that produced by nearly-ground-potential corona conductor is experimently testified, which provide a solid support for the application of the method.Secondly, detailed investigations on time-domain characteristics of corona current pulses on HVDC conductors are carried out. Contents of the present investigation include not only the characteristic parameters of corona current pulses of both polarities, such as amplitudes, repetition rate, rise time, half-wave time, duration, and 0.5MHz spectral density, but also the detailed characteristics of positive intermittent corona current pulses which are in the form of "burst" in time-domain, such as the number of pulses per burst, burst repetition rate, amplitude ratio of the primary pulse to the secondary pulse, and the amplitude of the secondary pulses. The comparison between the positive and negative corona current pulses evidenced the predominant effect of positive corona current pulses on radio interference. Meanwhile, by establishing a positive ion-cloud model, the physical mechanism of formation of the burst-type corona current pulses is revealed.Thirdly, the influence of the conductor surface electric field, conductor radius, conductor height, discharge point dimension, discharge point spacing, humidity, and wind velocity on positive corona current pulses is explored, and the influence of these factors on radio interference is further discussed.At last, a stochastic time-domain prediction model of radio interferences from HVDC conductors is proposed. By applying the model, the lateral and longitudinal spatial attenuation property of radio interference produced by a single corona source on HVDC conductors is analyzed, and the contributions between the convection current in the ionized region and the conductor current is quantitatively compared. Furthermore, combining the model with the time-domain characteristics of the corona current pulses obtained in the laboratory, the prediction of RI caused by bipolar 5.55mm-diameter steel reinforced aluminium conductors is performed. The comparison between the RI predictions determined by the proposed model and that determined by the empirical formula preliminarily evidences the validity of the proposed stochastic time-domain RI prediction model.