Research On Back Up Protection Method As High Voltage Station-service Power Failure Happening

On the basis of the nearby short circuit such as station-service system bus short circuit, high voltage rotation mechanical fault etc. often occurs in power plant, and considering the importance of the station-service and the damage accumulation effect to high voltage transformer caused by short circuit, branch bus quick-break is required. Generally, low voltage branch bus of high voltage spare transformer and high voltage station-service transformer only has complex-voltage overcurrent protection, its delay time setting is2.0～3.0s. When the bus short circuit seriously happened, large short circuit current will lead to high voltage spare transformer, high voltage station-service transformer thermal deformation and insulation damage due to complex-voltage overcurrent action time is longer and can’t rapidly switch off the fault, transformer’s dynamic thermal stability is between1and1.5s. Furthermore, it will affect the normal production of the power plant. To resolve above problems reasonably, this paper compared the feasibility among the plans of improving tolerance of transformer short circuit, installing branch bus protection, installing branch time quick-break equipment, installing arc protection through consulting a large number of information and statistic data. As the back up protection of high voltage station-service fault, branch time quick-break protection needs a large number of setting calculation. When its sensitivity can meet the requirements, the only thing we need to do is adding this function in the original protection equipments of the start-up standby transformer and high voltage station-service transformer. Because the Analog quantity used by branch time quick-break protection has been introduced into the protection device, and TA loop need no reformation, so the whole reformation work is small, the cost is low and the popularization is easy. According to the load state of adjacent motor and low voltage station-service, the delay time of the branch time quick-break protection can be set in a range of0.3～0.6s. It can greatly shorten action time of the complex-voltage overcurrent protection, improve the efficiency requirements of the branch bus protection, and do not affect coordination with adjacent protection in time delay. Because the branch time quick-break protection is easily installed and its protection range is wide, so it is the one of the best methods to solve high voltage station-service fault.The boundary conditions of installing the branch time quick-break protection can be found out through formula deduction. Then, the conditions can be reached by adjusting the parameters of relevant motors and low voltage station-service load, or by adjusting the parameters of high voltage station-service transformers and start-up standby transformer. Furthermore, it can facilitate the selection of high\low voltage station-service transformers, start-up standby transformers and motors by founding the boundary parameters of these devices in a new project.In the same time, field experiment has been done in Hohhot Jinqiao thermal power plant. Under the conditions of several typical faults, the experiment results were analyzed in detail. The results show that the branch time quick-break can meet the requirements of operation of high voltage station-service and start-up standby transformer.