Super (especially) High-voltage Transmission Line Protection Principles And Techniques Of Research

EHV and UHV transmission lines act as an important role in the security, stabilization and the economic profit of the whole power system operation. The importance of EHV and UHV transmission lines elevates the requirement of the performance of protective relaying. The micro-computer based protection equipments are now widely used in EHV and UHV transmission lines, the effects are good as a whole, but some limitations are also found through long-term filed operations. In order to solve these problems, systematic researches of principle problems of EHV and UHV transmission line protection is discussed in this thesis.The traits of impedance locus under different system conditions based on theoretical analysis are shown in this thesis. Its influence on regular distance relays is also discussed in the thesis from the aspects of the capabilities of anti over-reaching, internal resistance tolerance and fault direction distinguishability.The existence of fault resistance may add an additional reactive or capacitive component to the impedance seen by the relay. This may cause conventional quadrangular distance protection to over-reach or under-reach at different system conditions. A novel adaptive algorithm for digital distance relay based on real-time impedance locus estimation is put forward. Theoretical analysis and digital simulation show that the new protection with enhanced resistive tolerance can overcome steady-state over-reach.Fault on a transmission line connected to the bus behind the protection is equal to fault on the bus through a reactive 'fault impedances'. This problem has never been noticed. The study of impedance locus seen by the protection shows the possibility for directional distance protection with quadrangular characteristic to mal-operate upon this condition. A novel directional distance relay that can prevent the regular distance relay from mal-operating based on the study mentioned above is put forward in the thesis.The distributed capacitance current of UHV transmission line produces operational current of differential current protection on non-fault states and external faults. The operational current is also affected by digital filter algorithms and capacitance current compensation methods. In this thesis, the influences of digital filter algorithms and capacitance current compensation methods are studied by mass digital simulation based on the system model of 1000kV transmission line demonstration project of China.Regular transient capacitive current compensation methods can diminish the effect of capacitive current and increase the sensitivity of current differential protection. The compensation methods rely on voltages and parameters of the transmission line, and also require extra computation and communication costs. A novel adaptive current differential relay without any capacitive current compensation is put forward in the thesis. The relay adaptively alters the current threshold based on the estimation of noise level of the differential current signal. Theoretical analysis and digital simulation show that the new adaptive relay has very high sensitivity against high-resistance ground faults.The application of optical fiber communication network causes new problems to transmission line differential protection. In the fiber network, the routes of sending and receiving can be different, that means, the time latency of sending and receiving data can be different. This can cause an additional error to the protection which assumes the sending and receiving routes are equal. In this thesis, a new method based on DCE (device clock error) is put forward. The new method based on the fact that the channel latency of sending and receiving can be different. Providing accurate channel latency of both sending and receiving, the new method makes the protection more reliable.