Zizhao Zhu

Study on Traveling Wave Propagation Characteristics of ±800 UHVDC Transmission Lines

Traveling wave produced by a short-circuit fault or lightning will propagate along transmission lines with deformation and attenuation, which are due to energy loss and frequency-dependent line parameters. By the phase-modal transform method, the multi-conductor transmission lines could be decoupled into independent modal. Each modal is a single uniform line described as two-port networks. In this paper, the frequency-dependent parameters of uniform transmission lines are calculated in complex frequency domain. Based on the telegraph equation in complex frequency domain, the transfer functions between traveling wave signal source and observation point (relay location) are derived. The time domain waveforms of traveling wave at the observation point are calculated by Hosono numerical Laplace inverse transform method. Compared with PSCAD/EMTDC simulation results, the proposed method in this paper is proved effective.

Modeling and Simulation of Lightning Electromagnetic Transient and Identification of Shielding Failure and Back Striking in ±800kV UHVDC Transmission Lines - Part II: Identification of Shielding Failu

The identification of shielding failure and back striking in transmission lines has always been a difficult subject. This paper analyzed the process of back striking and shielding failure in ±800kV UHVDC transmission lines. Because the mechanisms of produced transient zero module voltage and its propagation paths is different between back striking and shielding failure, their wavelet energy of different frequency bands of transient voltages is different. Thereby, from the perspective of protective relaying, this paper proposed an identification method to shielding failure and back striking in ±800kV UHVDC transmission lines based on wavelet energy. The data can be acquired from high speed protection device. The EMTDC simulation shows that the proposed method can effectively identify shielding failure and back striking in the whole UHVDC transmission lines, and is not affected by various wave shapes of lightning current.

Modeling and Simulation of Lightning Electromagnetic Transient and Identification of Shielding Failure and Back Striking in ±800kV UHVDC Transmission Lines - Part I: Modeling and Simulation of Lightni

Lightning stroke to transmission lines was introduced in this paper. Modeling and implementation method of tower, corona and insulator for lightning electromagnetic transient research was discussed. Comprehensive model for study of UHVDC lightning electromagnetic transient was built, and lightning caused fault and lightning disturbance were simulated in PSCAD/EMTDC based on the model, which offered a research platform for identification of shielding failure and back striking in plusmn800 kV UHVDC transmission lines.

Dynamic characteristics of ±800kV DC transmission system under single phase breaker failure action

Severe impact will be brought to hybrid AC/DC system when three-phase faults occur and single-phase breaker refuse to act, especially when disturbances are near DC converter. To perform the dynamic characteristics study under such condition, electromagnetism transient model of Yun-Guang plusmn800 kV DC transmission system is established, and dynamic characteristics of DC system such as DC power, voltage of converter bus and commutation failure condition are calculated and analyzed, when faults respectively occur on head and end terminal of transmission line near inverter. DC dynamic characteristics under different control mode are also compared. DC power is higher when constant power control mode is used comparing with constant current control mode, while reactive power consumed by converters are higher after disturbance under constant power control. And it will provide reference to the operation of plusmn800 kV DC transmission system.

Comparison study on machine-electricity and electromagnetic transient model of UHVDC dynamic characteristic

A parallel AC/DC power system with long distance and heavy capacity will be formed till 2010 in southern China power grid. In simulation program BPA, machine-electric transient model of HVDC is used, which is not proper for unsymmetrical fault. To verify its distortion under unsymmetrical fault and its validity under symmetrical fault, quasi steady-state model and electromagnetic transient model of Yun-Guang UHVDC are respectively established, and dynamic characteristic such as DC power,DC current and voltage of converter bus are simulated and analyzed under unsymmetrical and symmetrical disturbance, which provides reference for the operation and simulation for Yun-Guang UHVDC-AC hybrid system.