Yu Zhanqing

Research on the upward leader emerging from transmission line by simulation experiments

This paper presents some simulated experimental results and characteristics of upward leader emerging from transmission line, which carried out at the Ultra High Voltage Engineering Technology (Kunming) National Engineering Laboratory. Different measurements were conducted in a 6 m plane-conductor gap under positive and negative polarities impulses of 1 to 3 MV with waveform of 200/2000 μs. The process of discharge was observed by using the high speed camera and the current was measured with the current shunt with frequency response of at least DC-6.5MHz. Upward leader from the conductors were captured during the process of discharge. The velocities of upward leader have been estimated to be 1–3 cm/μs, which is in accordance with the velocities of leader that observed in the process of discharge in rod-plane gap under positive pulse with waveform of 200/2000 μs. The experimental results were compared with those in the natural lightning and some parameters of the equality were discussed. Obviously, the upward leader will occur during natural lightning.

Research on impulse discharge characteristics of parallel gap

With parallel gap, by controlling the motion path of the electric arc, effectively avoid burning and damaging the insulator during lightning strike so that its importance in measures of lightning protection for transmitting line is continually improved. Initial discharge position is key consideration during design of parallel gap and depends on discharge characteristics of parallel gap under the action of lightning surge when the lightning strikes the tower or line. This paper gives three types of parallel gap used to protect the composite insulator, sets up the impulse discharge test and observation platform including high-speed camera, studies the impulse discharge characteristics of parallel gap and analyzes the influence of structural parameters on the discharge characteristics. This study showed that there is randomness for discharge path of parallel gap; three types of parallel gap given in this paper can achieve 100% discharge rate of parallel gap; the determinant of discharge rate in the presupposition discharge area (PDA) is the distance that the presupposition discharge area stands out of the whole electrode plane. When this distance exceeds 20mm or more, it can ensure that most of the discharge occurs in the PDA; the parallel gap can reduce the insulation distance of 4000mm insulator about 40mm, U50 about 1%, which may approximately consider that the parallel gap has no influence on the insulating property of the insulator.

Research on characteristics of conductor surface electric field considering downward lightning leader

Shielding failures of lightning is a key problem for the reliable operation of transmission lines. The Leader Progression Method (LPM), based on the theory of long air gap discharge, is an advanced method to evaluate the shielding failure probability of transmission line nowadays. The calculation of surface electric field on phase conductors and ground wires is the key factor that influences the upward leader inception. In this paper, the operation voltage of transmission line, the distance between adjacent check points set on the surface of transmission lines and some other factors that influence the surface electric field were analyzed. The influence of these factors on surface electric field was presented in this paper.

Prediction method on corona inception field intensity for HVDC fittings in high altitude area

Corona inception field strength was one of important parameters for designing fittings in ±800kV DC transmission line. So far Peek formula was based on calculating corona inception field strength of the DC lines fittings with large size in high altitude area. Peek formula was obtained by a large of experimental results for electrode with curvature radius less than 50mm at standard atmospheric pressure. Because of different discharge mechanism, Peek formula was inaccurate for predicting corona inception field strength for the electrode with large curvature radius and non-cylinder structure. For predicting accurately corona inception field strength for the fittings with larger curvature and non-cylinder structure, test platform for HVDC fittings was setup in ultra-high voltage(UHV) Nation Engineer laboratory (Kunming) with 2100 meters altitude. Corona inception voltage was measured for test tubes and rings with kinds of size in the Kunming lab. Prediction method to Peek formula was proposed firstly for the electrode with larger curvature radius and non-cylinder structure in high altitude. The method would become one of theory evidence for design to HVDC fittings.

1 Year report & results on 10kV multi-chamber arresters field test in Guangdong Province, China

This paper represents describes method and results of field test on 10kV Multi Chamber Arresters (MCA) in high lightning density area. Application of these devices allows to protect durably and efficiently overhead power lines rated at 10 kV from induced overvoltage.

Research on surface electric field of parallel gap

With parallel gap, by controlling the motion path of the electric arc, effectively avoid burning and damaging the insulator during lightning strike so that the effect to reduce the accident rate of line is obvious. Because of simple structure, convenient installation and good economical efficiency, its importance in measures of lightning protection for transmitting line is continually improved. Electric field characteristics on the surface of parallel gap electrode have obvious influence on corona generation and the gap breakdown position and are the key parameters that must be considered in the design. Based on the finite element method, this paper sets up the analysis model of electric field of parallel gap including the tower, the conductor and the insulator, uses ANSOFT software for simulation, studies the surface electric field characteristics of parallel gap electrode, compares the electric field of four types of parallel gap put forward in the paper and analyzes the law of influence of parallel gap electrode parameters on the electric field characteristics. The results show that, when the short circuit distance is increased, the maximum values of electric field of ball end and snap ring body are obviously increased; the opening angle of snap ring is larger and the maximum value of electric field of ball end is higher; when the pipe diameter is increased, the maximum value of electric field of snap ring body is reduced considerably; the ball end is bigger and the maximum value of electric field of ball end is less; the ring pipe diameter is the structure parameter having the largest influence on the surface electric field; for the ball end at the end of ring electrode, the structure parameter having the largest influence on the electric field is the diameter of ball end. Reducing the distance that the ball end stands out of the ring plane can decrease the maximum value of electric field of ball end.