The Study Of High Temperature Superconducting Power Cable Protection

With the development of economy in China, the increasing power demand puts forward a great requisition on power transmission, especially on urban area. The current power transmission capacity can not satisfy the increasing load demand, and the loss of transmission difficult to reduce, big area of transmission passage, all of these have engendered a bottle-neck of power transmission of large quantities. The High Temperature Superconducting (HTS) cable with Zero-Resistance, which is the combination of superconducting technology and electrical technology, has some distinct advantages including huge power transmission capacity, little power loss, good flexibility, compact dimensions and no-pollution, so it is a good choice to resolve the bottle-neck of power transmission. The protective relay and online-state monitoring are the important means to ensure the HTS cable's safe operation, also are the key technology problem which must be solved on the process of HTS cable's application, so that the study of HTS cable protection has great significance of theory and application.At first, the summary of development of superconducting technology and high temperature superconducting wire is presented here. And, the features of HTS cable and its application on power grid are introduced. Also, The history, nowadays and future of quench protection, protective relay and monitoring device for HTS cable is given. The dissertation is based on these surveys.The temperature of HTS cable may change a lot because of over-current, cooling system failure and HTS cable's self failure, so that it can destroy the safe operation of HTS cable. According to the structure of HTS cable, the dissertation establishes a model of temperature distribution for HTS cable, and analyses the stable and transient process of HTS cable's temperature with different boundary condition for farther study of HTS cable's quench protection.Quench protection for HTS cable is one of the important problems which must be solved on the application process of HTS cable. The quench is very complicated on theory, and it involves many other problems. The quench made by short-circuit is a big threat against safe operation of HTS cable, and it is a difficult work on the research of quench protection. Based on normal method of quench detection and protection for superconductor, the dissertation analyses the relationship of over-current with temperature of HTS cable, and a three-layer protection strategy based on different current level for HTS cable is given. And it offers a base on engineering application of quench protection.Different from normal power cable, the HTS cable may be cut-off because of transient quench which is caused by extern short-circuit current. HTS cable has a huge power transmission capacity, so the auto-reclosure device must be installed in the transmission line of HTS cable to improve the reliability and stability of power grid. The dissertation analyses the temperature change of the HTS cable during reclosing, and an appropriate strategy of auto-reclosure for HTS cable is presented.The electrical characteristic of HTS cable is very important, which is the base on study of power flow, operation state and relay scheme for power grid including HTS cable, also it is significant for the mathematic model of HTS cable. Taking an instance as the HTS cable in the PUJI power station, the dissertation calculates and analyses the electrical characteristic including inductance and capacitance, and compares the calculation result with the measurement result, finally a deep research of transient process of HTS cable's short-circuit is carried out.Comparing with overhead line and normal power cable, the HTS cable has little resistance and big distributed capacitance, which will affect the protective relay, so it is necessary to consider the difference in the relay scheme for HTS cable. The dissertation establishes a transmission line model of HTS cable based on distributed parameter, and a differential current protection for HTS cable is given, at the same time, the feasibility of capacitance current compensation on overhead line applying to HTS cable is discussed, also simulation of some different differential current protections is carried out, including no capacitance current compensation, half capacitance current compensation and differential current based on Bergeron model.According to the engineering application of HTS cable system in PUJI power station, a practical monitoring and protection system for HTS cable was developed for the first time in China. The monitoring and protection system has operated well in the power grid more than one year up to the present. The dissertation illustrates the monitoring and protection system, including design principle, hardware structure, protection strategy. At last, the dissertation gives the systematical summarize and points out the further work.