Studies Of Travelling Wave Current Integration Differential Protection Algorithm For EHV AC Transmission Lines

With the development of the strategy of the diversion of natural electricity from the western to the eastern regions, the EHV/UHV grid is building rapidly. Consequently, the speed of action of the relay protections must be higher than beforetime to meet the demands for the safe and stable operation of the EHV/UHV grid. The conventional current differential protection of transmission line acts sensitivity, and can protect the total track length of transmission line reliably. And it doesn’t be affected by the oscillation of power system and operation scheme changes. Therefore,it is widely used.But the conventional current differential protection acts more slowly because it works based on power frequency signals, and it may be affected easily by the saturation of the current transformer,transition resistor,distribution capacitance,and so on. Therefore it difficults to adapted to need of development of the EHV/UHV grid and long distance power transmission. Some scholars at home and abroad put forward several schemes of ultra high-speed relay protection based on fault transients, the travelling wave differential protection is an important research field.The travelling wave differential protection makes up the action criterion with the differentials of the direction current travelling wave both ends of transmission line. Its action speed is very rapidly, and it doesn’t be affected by the transition resistance, distribution capacitance, oscillation of power system, saturation of the current transformer,busbar structure and so on. Therefore it is very useful. This dissertation systematically researches the choose of the characteristic quantity of the travelling wave differential protection,the uses of,the filtering,the applicative range of the protection. The main contents and contributions of this dissertation are as follows:1. The travelling wave process on the EHV/UHV transmission line is systematically and completely researched in this dissertation. First of all the analytic solutions of the wave equations of the single phase distribution parameter lead wire at given the boundary conditions are investigated, and the travelling wave spreading law on the transmission line and the refraction and the reflection law of it at the point of the wave impedance discontinuousness are discussed.Afterward, the travelling wave process of single phase lead wire is deducted into the three-phase transmission line, the concept of phase-mode transformation is led out. After analyzing the problems of the frequently-used phase-mode transformation (Clarke and Karenbauer), this dissertation deduces a novel phase-mode transformer and its new transformation matrix. By using this new phase-mode transformation we can obtain any one of the line mode quantity (1mode or2mode) which can reflect all types of fauls. Any one of the line mode quantity of the Clarke phase-mode transformation and Karenbauer phase-mode transformation can not reflect all types of fauls, two line mode quantities have to be used as constructing the algorithm of the relay protection, for this reason, the calculated amount of the algorithm is huge. By new phase-mode transformation, only one line mode quantity is used for constructing the algorithm of the relay protection. Therfore, the calculation workload is decrease, the action speed of the protection is increase.A menthod of selecting bigger one both of the1mode and2mode quantity in constructing the algorithm of the protection is proposed too in this dissertation, which can improve the sensitivity of the travelling wave differential protection. The pratical methods are:while the phase selector exports the BG,BC,AB,we must choose1mode quantity,while the phase selector exports the AG,CG,CA,we must choose2mode quantity.If phase selector exports the BCG,ABG,CAG or ABC,we mast choose bigger one both of the1mode and2mode quantity.2. In order to filter out the noise in the travelling wave, this dissertation systematically researches the morphological filters and the morphological gradient. In this dissertation, we research the corrosion operation and expand operation from the standpoint of the set theory. For the sake of accurately measuring the time of the head wave arrived the busbar, the geometry center must be at coordinate origin. After discussing respectively the morphological open-close filter and close-open filter, the morphological alternation combination filter, the multiresolution morphological filter, and the morphological gradient, this dissertation presents a new multiresolution morphological alternation combination filter whose structure element’s length is growing linearly and a new noise cancelling morphological gradient whose input signal is the export of the multiresolution morphological alternation combination filter.By simulation computation, a multiresolution morphological alternation combination filter applicable to the travelling wave differential protection and a noise cancelling morphological gradient are selected.3. On the basis of the research achievements of our predecessors, the novel method that selects the integral quantity of the direction current travelling wave in between head wave and very short time after as the characteristic quantity of the travelling wave differential protection is proposed in this dissertation. The new action criterion of the travelling wave differential protection is the differentials of the characteristic quantities both ends of the protected transmission line.Take some500kV power grid for illustration, by large numbers of simulation computation, the correctness and the effectiveness of the new travelling wave differential protection are verified.4. In order to verify the proposed travelling wave differential protection is true of the transmission line with the shunt reactor or not, the. travelling wave transmition law when it across the point of a shunt reactor set up is studied whateyer the fault takes place inside of the transmission line with the shunt reactor or outside.By theory and practice of simulation, we full prove the proposed method is true of the transmission line with the shunt reactor.