Control And Protection Configuration Scheme Research And Harmonic Analysis Of Hvdc Converter Station

HVDC transmiassion has vantages of large capacity, small loss, controllable, long distance and so on. It has developed rapidly in China and worldwide. Two multi-infeed HVDC systems has been formed in Guangdong and East China. The proportion of DC transmission capacity in some areas of China has been already very considerable. There are more or less some defects in the design or operation of control and protection in existing projects. The further study and improve is urgent and necessary. In addition, as a typical system, due to short electrical distance of each DC project, their interaction phenomena is prominent in the multi-infeed HVDC system, especially in harmonic interaction and the protection at AC side. As huge power capacity delivered by each HVDC line, it is significant to analyze these interactions to ensure safe and reliable operation of the converter stations. Take several HVDC transmission projects that have been put into operation as the research object, some key achievements specialised in HVDC control and protection configration,power converse in AC lines, harmonic analysis are as follows:(1)The new redundancy configuration scheme of HVDC control and protection. The dual and triple modular redundancy concept and implementation principle in HVDC control and protection system are presented in detail. The protections whose single component fault may lead to HVDC blocked are listed. For the circumstances that the protection is dual modular redundancy, but the sensor is singly or doubly configured, two solutions in order to prevent failures caused by single component fault are compared and recommended. The disposal advice is given to the existing deficiencies about dual modular redundancy in current HVDC projects. When a system is in maintenance, abnormalities of the other system may lead to HVDC outage. A recommended fundamental solution is the signal contacts, control and protection are all triple modular redundancy.(2)The configuration scheme research and analysis of UHVDC control and protection. The configuration scheme of UHVDC control and protection is proposed. The differences with the conventional HVDC control and protection are discussed, such as control framework, LAN safety, main computer stability and so on. Some optimizations have made in UHVDC control algorithm, such as the power compensation, valve control, the online input and withdrawal strategy of converters, de-icing operation mode and so on. Triple protection configuration requirement is proposed. The implementation scheme for valve protection, dc line protection, ac filter protection are described. The improvement solutions of last circuit breaker protection, converter transformer saturation protection are proposed on the basis of the conventional HVDC operation experience.(3) The new scheme of control and protection of converter valve cooling system. Take the valve cooling system of Nanqiao converter station as an example, the valve cooling system protection theory and its settings are introduced in this paper. The hidden dangers of single or dual poles blocking include single sensors, power lost, water leakage, wrong settings, etc. A new scheme of control and protection and the corresponding countermeasures for hidden dangers are also presented. The forced outage rate of HVDC system is greatly reduced by eliminating these hidden dangers.(4) The new scheme of pilot line protection at AC side of converter station. Based on the multi-infeed HVDC system simulation mode, the happen mechanism of power converse during commutation failure is studied and presented. The main reason of power converse is that the demand of reactive power will be increased rapidly during the recovery period. A new scheme of pilot line protection at AC side of converter station is put forward. The misoperation of pilot protection is solved be revising power converse logic.(5) Harmonic interaction analysis at AC side of several converter stations and countermeasure research. The harmonics characteristics and problems at DC side and AC side are analyzed. The relationship between the harmonic content and operation mode are investigated. The simulation model of the multi-infeed HVDC system is established with EMTDC. The harmonic interaction phenomena and its mechanism are verified through simulations of switching on or switching off AC filters. The harmonic impedance scanning analysis on the AC side of the converter stations shows that, the necessary conditions of harmonic absorption and amplification are greater difference values of equivalent harmonic self-impedance amplitudes or angles at the AC side of the converter stations. Measures are proposed to reduce the harmonics interaction effects at AC side of converter stations and reduce the harmonic impact on relay protections.