Research On Dynamic Characteristic And Protection Setting Of HVDC Converter And Line Protection

HVDC is today being widely used to connect regional power grids and transmit bulkpower to distant locations since they have more advantages in the aspects of transmissionability and economic benefit compared to HVAC. Converter and dc line are the two corecomponents of HVDC systems. They characterize the HVDC system well in fault analysisand protection principle, and their performance determines the reliability and efficiency of thewhole HVDC system. Therefore, we focus on the two components in this paper. Of thespecial importance are: the uncertain behavior of HVDC protective relaying and the lack ofefficient method for setting determination and performance evaluation.This paper proposes a fault analysis model for the research of protective relaying. Thebehavior of the converter protective relay is uncertain when faults occur on the link betweenthe converter and transformer. To solve the problem, we analyze the relaying quantitycharacteristics and protection criterion function of the converter protective relaying, in whichthe effect of fault location, fault type and operation condition of HVDC system are fullyconsidered. The study results clarify the response of the protective relay to the faults on thelink between the converter and transformer, which in turn gives a basis for the optimization ofconverter protective relaying.This paper proposes a method for the behavior analysis of HVDC protective relayingbased on the relaying quantity studies. The method is used to study the behavior of dc lineprotective relays. The dynamic characteristics of the relaying quantities are firstly studiedconsidering the effect of fault condition, system operation condition, and control systembehavior. The fault condition contains faults on the concerned pole and on the other pole,faults on the converter side of the smoothing reactor, and faults on the commutation bus. Theoperation condition contains bipolar operation, monopolar metallic return operation, andmonopolar ground return operation. The study results clarify the boundary, constraintcondition, and function of the protection criterions, which in turn gives a basis for the settingdetermination and optimization of dc line protective relaying.This paper also proposes a unified method for the setting determination of various dc line protections. The principle of selecting protection thresholds is proposed and the protectionsensitivity is fully analyzed considering various factors. A special attention is given to theproblem that the sampling frequency will affect the threshold settings of dc line protections.By doing so, we effectively solve the problem of lacking efficient method for the settingdetermination and performance evaluation of dc line protections, and incorporate the probleminto the framework of conventional power system protection.Based on the proposed theories, this paper finally develops a setting determinationprogram for dc line protections. The program can be applied to threshold selection, thresholdevaluation and electrical quantity analysis, etc. The program has been used in several actualHVDC projects. The performance verifies the correctness and validation of the theoriesproposed in this paper.This work is supported by the National High Technology Research and DevelopmentProgram (“863” Program) of China (No.2012AA050209). Some of the research results havebeen applied to the operation of actual HVDC systems, obtaining great economic and socialbenefit.