Study On Novel Protection Principle And Engineering Problems Of Large Generator Relaying Protection

Along with the fast erection of clean and effective energy system in China, the number of large turbogenerators and hydrogenerators in operation are increasing rapidly. For their stable and reliable power supply support being vital to the secure operation of the power grid, large generators are playing a more and more essential role in nowadays bulk power system, whereas their security is remarkably chanllenged on account of the complicated external operation environment and changeable operation requirements. In order to satisfy the coordination requirements of safety of the power grid and generators as well as improving generators' own safeguarding measures, and enhancing a better application of large generators' relaying protection in the meanwhile, the dissertation aims to investigate some large generator protection principles that have great influence on power grid operation, and several engineering problems in large generators relaying protection application.Current stator ground protection critetia do not respond to the ground fault degree, leading to poor sensitivity or overreaction in some cases, being unable to ensure the security of the generator and power grid at the same time. Based on the research of fault degree measurement method, an innovative stator ground protection scheme is presented, which has superior protection feature of adaptive tripping manner in accordance with fault degree. With further study on the supporting technology of the above scheme, a ground fault location algorithm is proposed, based on the distribution characteristic of the stator winding voltage to neutral point along the turns of stator winding coils, and a ground fault current calculation method is also proposed, considering fundamental current in addition with third harmonic component.Due to its protection character oriented to one single unit, conventional out-of-step protection scheme cannot function as expected in actual multi-generator system in the power plant. After analyzing large generators' typical out-of-step forms and apprarent impedance locus character measured at the generator terminal under different out-of-step circumstances, the convential out-of-step protection's deficiency in the aspects of the protection characterstic and tripping manner is indicated. The dissertation then presents a novel out-of-step protection scheme with its realization in the way of hierarchical relaying protection system. By means of information exchange and comprehensive decision achieved by the interaction of bay-level protection with substantion-level protection, the new scheme is capable of adjusting its operation characteristic, leading to appropriate reaction to different out-of-step scenario in all kinds of system and power plant operation condition, with the capability of optimized tripping.Several engineering problems in large generators relaying protection application are discussed. Construction mode of the relaying protection determines the safeguarding scope and information source of the large generator protection. Having probed into the funcition defect of the current large generator protection system structure considering current power system operation feature and its demand, a hierarchical relaying protection system scheme is proposed, which is adapted to the requirements of smart gird. Appropriate relaying protection setting calculation scheme with a smart and automatic calculation tool will ensure and reinforce large generator protection's secure operation. On the basis of summarizing the procedure and essentials of large generator protection setting calculation, the paper proposes a general scheme of large generator protection setting calculation software. At last, several specific issures related to protection setting calculation is studied via an engineering practice in a large power plant.