Research Of HVDC Protection Value Setting Method

High voltage direct current transmission has the advantages of low cost and low power consumption. Compared with AC transmission, it has significant economic advantages in long distance and large power transmission, and has been widely used in China in recent years. HVDC protection is an important part of the operation, which can be operated on different kinds of faults, component damage, incorrect switching and other abnormal operation mode, and the rationality of value setting a is the guarantee of correct action of the protection system.Existing HVDC protections are generally classified according to the position of the protected equipment, which is not beneficial to the fixed value setting. In this paper, based on the principle and nature of the protection, device characteristics and failure characteristics, all present protections were reclassified, and then the setting process for each classification of protection was put forward. Transmission line protection and differential protection aim at reflecting the faults. Their operating characteristics are closely related to fault feature. The setting process based on fault feature is proposed for these two protections.The traveling wave protection is the main protection of HVDC transmission line. Effect of different factors on the protection criterion operating characteristics, and the immunity of protection logic when traveling wave dramatic changes was studied. The results indicated that the traveling wave amplitude would decrease due to the fault location far away from measuring point, large fault resistance increase, low-voltage operating mode and converters out of service. Combined with the protection logic cooperation, judging method of criterion and protection configuration scheme, the value was set, and its rationality was verified with simulation method. Double-circuit HVDC effectively conserves land resources. In this paper, the effect of electromagnetic coupling relationship and circuit arrangement on the operation of the system and the fault characteristics were analyzed. The characteristics of the double-circuit HVDC traveling wave protection are studied with simulation method.Differential under-voltage protection is one of the main protection of HVDC transmission line, which is complementary to the traveling wave protection. The influence of different factors on the criterion was analyzed, especially the relation of all kinds of faults and criterion, such as voltage differential, current differential and voltage amplitude. According to their characteristics and functions, each value of the criterions was set, the reliability of which was verified.Due to the characteristics of strong nonlinearity of DC power transmission system, the value setting of HVDC protection is dependent on the software simulation, and tedious, time-consuming and laborious. In this paper, a value setting software was written, which is able to call the PSCAD/EMTDC to simulate automatically, save and screen the effective test data, save and effective screening test data. Combined with the corresponding HVDC engineering and protection model, it automatically set the value of line protection and differential protection, which greatly improves the efficiency. In addition, it achieves fault simulation, waveform display and other functions, and can filter and view the existing HVDC projects and protection information. The rationality of the value in this paper was verified with RTDS simulation method.