| The experimental demonstration project was passed trial operation for 168 hours for China's first ultra-high-voltage grid, a power transmission network with 1000 kilovoltages AC , a demonstration project starting in the southeastern part of Shanxi, running through Nanyang and finishing at Jingmen. China has own R & D, design and construction, with independent intellectual property rights and then the project was put into commercial operation. With the implementation of development stratagem about "transmit electricity from west to east, north supports power supply to south and vice versa, connect power grids nationwide," The next 5 ~ 10 years, China's power grids will be developed into the world's most technologically complex, which is one of the largest power grid. It is foundational, crucial and urgent to improve the reliability of large-scale interconnected power system operation. Conventional backup protection relays generally take actions to protect a localized region of the network without considering the impact on the whole network. This is further aggravated as networks grow bigger and are stressed more heavily. Conventional backup protection is designed primarily to protect local equipment and to ensure reliable fault clearance, but it may mal-operate under heavy loading conditions causing cascading trips on the network which lead to a wide spread blackout. Wide area protection systems have wide view of the power grid based on their wide measured inputs. They can offer more accurate and dependable faults isolation, and at the same time, they considerate the influence on the system operation and prevent disturbances from protection actions.In this paper, the background and research situation of the wide area protection are introduced. The characteristics function making up and system structures are discussed, and a practical wide area transmission line backup protection scheme is proposed in this dissertation.The distance protection, differential current protection and directional protection, which are used extensively in high voltage transmission line protection, are analyzed detailedly in action characteristic and special problem. On the basis of the high voltage transmission line protection, this wide area protection systems can obtain wide area operation information of power system via power communication Network to imply different protection. The concept of aggregate protection and the method for determining limited wide-area of information and activated areas were discussed, a wide area relay protection criteria based on the relationship factor and the action factor of protection intelligent electronic device (IED) is proposed. Program study shows that the wide area relay protection criteria can locate faults exactly, and this criteria can overcome the drawbacks of long time relay and large fault-affected regions, so this program can greatly enhance the security and reliability of large-scale interconnected power grid.As wide area protection systems based on the use of Phasor Measurement Units (PMU), this paper has analyzed the changes in energy at both ends of a line. If the result is more than a pre-specified value, an internal or in-zone fault is indicated. The proposed technique is evaluated using a MATLAB simulator configured to model the effect of faults on 3-machines 6-buses. 500 kV transmission lines. Power differential protection of the simulation has a certain significance with the application of the principle of wide area protection. |
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