Advanced Materials Research Vols. 805-806

Abstract: This paper investigates the state of insulation characteristic of single-core underground cable. The distributed model of single-core cable was built, which involved the insulation resistance and the leakage current. Based on the distributed model, sheath voltage and ground current on metallic sheath was examined under several kinds of insulation ageing such as various degree of insulation ageing occur in the main insulation, or in the sheath insulation, or partial insulation ageing. The results show that the voltage and current on metallic sheath indicate the degree and position of the ageing. Also the trend of the voltage and current on sheath indicates the part the ageing occurs - the sheath insulation or the main insulation.

Abstract: In this paper, the shock wave characteristics of pulsed discharge in liquid which occurred in the pipe with rod-rod electrodes were studied. The effects of shock wave peak pressure in the discharge were studied with changed the discharge voltage and electrode gap. The results show that the peak pressure of shock wave increased with the increasing of voltage. When the discharge voltage 22kV, the peak pressure of shock wave increased first and then decreased with the electrode gap increased. However, the discharge voltages 26kV and 28kV, the peak pressure of shock waves increased with electrode gap increased. The pressure of the shock wave (Pr) decays exponentially with the distance (r) from the discharging center. Under this experimental condition, the shock wave intensity is calculated by averaging many values of the experiment, and the experience formula is Pr = 2.56E·e^-0.4831r.

Abstract: With the HVDC transmission projects developing rapidly, the relevent electromagnetic environment problems are widely concerned, of which the transient electric caused by the conductor electrification in ionized field may seriously influences the feelings of people. To invesigate the tansient electric shock procedure, the transient current is measured in the experiment. The simulation results agrees well with the measured values and the validity of the simulation model is verified. The simulation results show that the resistance in the discharging circuit can reduce the current evidently. It is also found that the metal objects under the HVDC lines should be grouded to avoid discharging when touched by the people.

Abstract: Radio interference is an important issue that must be considered in designing HV transmission lines. It is caused by corona current which is due to the complex movement of charged particles around the conductors. Corona current has the characteristics of wide spectrum and strenuous diversification, so it is difficult to measure. In this paper, a corona current measurement system is developed for the investigation of HV test line. The measurement principle and system configuration is described. Problems such as high-voltage insulation, high-frequency signal sampling, interference suppression, signal record and transmission etc. are considered. The system has high measuring accuracy and the characteristic of small size, light weight and easy operating. The signal would not be interrupted and transferring data and the safety of person is ensured. The feasibility of the developed measurement system is validated by the experiments carried out in laboratory.

Abstract: Torsional interaction exists between HVDC converters and turbine-generators, and negative electrical damping provided by HVDC may cause subsynchronous oscillation (SSO) that can lead to turbine-generator shaft failure and electrical instability at oscillation frequencies lower than the fundamental system frequency. This paper makes a preliminary inquiry about the subsynchronous oscillation mechanism caused by the HVDC system, and puts forward Subsynchronous Damping Controller, and eventually makes a damping synchronous oscillation of the electrical Damping torque increment out of the generator electromagnetic torque to suppressing SSO.

Abstract: Because of time urgent before putting into operation and different place line protection equipment located, joint debugging for extra high voltage (EHV) transmission line is often not perfect although EHV transmission line is very important for modern grid. In joint debugging process, we tend to adopt static method to do fault simulation, that apply analogue to the device. To overcome the shortages of static fault simulation commonly used, which cannot accurately simulate fault characteristics in runtime, a synchronous joint debugging device is designed based on based on the analysis of the joint debugging process for line longitudinal protection. The device is a lightweight and low cost embedded system with the functions of communication and phase shift, and can offer analog signals to protection devices on both ends of the line. Based on the functions and characteristics of the synchronous joint debugging device, the joint debugging process with this device of optical fiber differential protection is analyzed. The functions of this synchronize testing device can meet the requirements, turning static to dynamic joint debugging.

Abstract: The defect types of 10kV VS1 circuit breaker were surveyed in order to reduce the defective ratio. Then, the main reason of these defects was found that the opening time of circuit breaker was too long. The reasons that cause circuit breaker opening time exceed were studied, and the effective reconstruction measures were developed though test verification and analysis. To compare with the statistics before reconstruction, the result shows that the reconstruction methods using in this paper were simple and easy to perform, which can reduce the opening time of circuit breaker, improve the reliability of the devices, and play a positive role in the security and stabilization of power system. It provides a basis for improving the efficiency of characteristics test at other voltage levels.

Abstract: three kinds of digital programs used in power system simulation are summarized in this paper. The electromagnetic and electromechanical transient simulation software ADPSS is introduced. Electromagnetic transient simulation, electromechanical transient simulation and electromagnetic-electromechanical transient hybrid simulation are performed respectively on Deyang-Baoji ±500KV HVDC system. The simulation result shows that the electromagnetic-electromechanical transient hybrid simulation has the advantage of electromagnetic transient simulation and electromechanical transient simulation. It can effectively analyze the process of the local electromagnetic transient in large-scale grid. The simulation speed is fast and the result is accurate and reliable.

Abstract: With the three-dimensional field analysis software Ansoft Maxwell 3D, the three-dimensional finite element model of the contacts pair is established. They belong to a kind of miniature circuit breaker. The simulation is carried out in the transient magnetic field. Under the condition with or without eddy current effect, we get the position and numerical solution of the contact mechanism heat loss under different short-circuit current.

Abstract: GaN high electronic mobility transistor (HEMT) was fabricated on silicon substrate. A breakdown voltage of 800V was obtained without using field plate technology. The fabrication processes were compatible with the conventional GaN HEMTs fabrication processes. The length between drain and gate (L_gd) has a greater impact on breakdown voltage of the device. A breakdown voltage of 800V with maximum current density of 536 mA/mm was obtained while L_gd was 15μm and the W_g was 100μm. The specific on-state resistance of this devices was 1.75 mΩ·cm², which was 85 times lower than that of silicon MOSFET with same breakdown voltage. The results establish the foundation of low cost GaN HEMT power electronic devices.