| With the rapid development of China’s economy, the power transmission capacity of the existing AC transmission lines cannot meet the rapidly growing load demand, and the uneven distribution of energy load distribution determines that the HVDC still has broad application prospects. HVDC has become the preferred transmission solution because of its fast and efficient power control, operation and maintenance experience and mature equipment manufacturing technology. Tri-pole HVDC transmission technology using current modulation control mode can take the advantages of HVDC and use the three-phase conductors to the transmit power, it can upgrade the DC transmission capacity fifty percent more than the capacity of the original AC line. Therefore, the tri-pole HVDC transmission technology is one potential solution to increase power transmission capacity.Converter is the most critical and complex part in tri-pole HVDC transmission system, and the theories and methods of its fault analysis, protection configuration and principles are different from traditional AC system. At present, the traditional HVDC protection system analysis, design and research need to be further deepened. Therefore, it is necessary to study the mechanism of converter fault and analyze its protection principle.This paper introduces the working principle and control strategy of tri-pole HVDC transmission system, and the protection configuration of converter and its function are analyzed. Based on tri-pole HVDC transmission system’s one pole12-pulse converter, a variety of converter protection zone fault were analyzed. This paper have studied of the converter’s main protection (including valve short circuit protection and commutation failure protection) and protection principles. Based on the calculation results fault current, the reaction of valve short circuit protection and commutation failure protection were studied.Using PSCAD/EMTDC simulation software, based on a tri-pole HVDC transmission test system, all the short-circuit fault in converters area simulated. The results show that the theory and methods of converter fault analysis is correct and reasonable. A tri-pole HVDC transmission system control and protection strategies was proposed. When a pole has failure, the control system will change the control mode to make the system work as a bi-polar HVDC to keep power transmission.Finally, some improvement measures of converter valve short circuit protection are proposed by analyzing changes in the electrical characteristics of each fault. A method to determine the fault location was developed in converter protection zone. |
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