Sigre 2015. — 6 с.
NR Electric Co., Ltd., ChinaStator winding inter-turn short circuit protection is essential for large generator. Phase-segregated transverse differential protection is an ideal scheme against that fault. Unfortunately, for most of steam turbine generators and some of hydro turbine generators, there is no room at neutral point for installing conventional electromagnetic current transformer (CT) on each group of winding branches of each phase to facilitate phase-segregated transverse differential protection. To a steam turbine generator, only a dedicated voltage transformer (VT) for inter-turn short circuit protection can be installed and longitudinal zero sequence voltage protection can be applied against the fault. As to a hydro turbine generator, only one dedicated CT for unit transverse differential protection can be installed at connecting point between the neutral points of two groups of three phase winding branches. In some inter-turn fault cases, The sensitivity and operating time of unit transverse differential protection and longitudinal zero sequence voltage protection may not be satisfactory for clearing the fault quickly and preventing the generator from damage. As an example, a generator of a hydropower plant in China Zhejiang province has been badly damaged after experiencing long-lasting stator winding inter-turn short circuit fault twice, although the unit transverse differential protection operated correctly.
New solution has to be explored. One solution is to find smaller CT appropriate for this application, such as fibre optical current transformer (FOCT).
