Protection of ultra long HVDC transmission lines.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.HVDC transmission is today widely used in modem Power Systems as an alternative to HVAC. Current trends indicate that many future conventional HVDC systems will be systems of increasing power ratings, delivered over larger distances as well as multi-terminal systems. In order to ensure the security and dependability of such systems, the current protection schemes need to be evaluated to assess their ability to provide adequate protection for the envisaged HVDC systems. This research work firstly reviews the present HVDC transmission line protection systems, and highlights their advantages and disadvantages, including factors that adversely influence their performance. The author critically evaluates the current protection schemes and reveals the drawbacks and other factors that render them unsuitable for the protection oflong dc transmission lines. The author then goes on to propose and develop an HVDC line protection system that will be able to provide adequate protection for proposed long HVDC transmission lines. The proposed protection system is able to make decisions based solely on local detection increasing its overall reliability. The author then recommends that the proposed protection system be used in conjunction with the existing main protection system in order to optimise the protection response times for both close in and distant faults. The author also proposes and develops a method of further enhancing the reliability of the protection system by the use of the telecommunication infrastructure when available. Finally the performance and feasibility of the proposed protection system is evaluated using the results obtained from the extensive fault simulations performed in EMTDC and Matlab. The simulations are performed using a bipole model of an HVDC System on which the required line and protection systems are modelled. The simulation results obtained are very favourable and promote the use of this proposed protection system, for the protection of long HVDC transmission lines