| Pumped storage plants play a more and more important role in power system net. The reversible pump turbines applied in the pumped storage plants tend to have a bigger unit capacity and higher pumping head. It will induce a more serious safety problem in water conveyance systems in pumped storage plants if a turbine full-load rejection occurs under abnormal conditions. In order to guarantee the safety and eliminate the potential danger in the pumped storage plants, the following comprehensive analysis and research are illustrated: the theory of misaligned guide vanes, the simulation model of hydraulic transient in pumped storage, and the hydraulic characteristics of pressure at spiral case inlet (casing pressure for short) under turbine load rejection.Firstly, a new transformation method is developed to eliminate the multi-numerical values of unit discharge and unit moment and the nonuniform distances between the transformed curves. It transfers the complete characteristics curves of the unit into a series of continuity function. As a consequent, the numerical simulation on hydraulic transient in pumped storage plants can be computed at any opening of guide vanes, including small opening and zero-opening, without extra programs With regards to the surface fitting, the mesh free method, moving least square (MLS) approximation, is introduced to approximate the transformed curves. It fits the surface 'locally' instead of 'globally' with a higher fitting accuracy. The effects of different basis functions and weight functions, weight function parameters and scaling parameters on the error norms of MLS approximation are discussed one by one. The basis function, weight function and the ranges of other parameters suitable to simulate the characteristic curves are recommended.Secondly, misaligned guide vanes (MGV) have a great effect on S-shape effectzone of characteristics curves, which is analyzed comprehensively here. Based on the internal character analysis theory of hydraulic turbomachinery and the external characteristics curves of pump turbines, the mathematical expressions of the complete characteristic curves of pump turbine over all zones are established. Then the mathematical expressions with the effect of MGV in turbine zone and reverse pump zone are developed, as well as the empirical expressions of runaway special condition point and zero-flow special condition point. Consequently, a flow chart is illustrated to compute the new characteristic curves with the effect of MGV in the above three zones. Following that, the mechanisms of MGV to stabilize the turbine zero-load condition and reduce the turbine efficient are discussed.Thirdly, the numerical simulation on hydraulic transient in pumped turbine is one of the most important measures to ensure the safety of plants. Based on the method of characteristics and the theory of MGV, an application software of this numerical simulation with the effect of MGV is developed, which is being applied in the engineering practical.Fourthly, the following hydraulic characters of the casing pressure under turbine load rejection are analyzed based on above mentioned theories. While MGV are not on work, different closure law of guide vanes and different closure rates have much different effects on the phenomenon of two pressure peaks of casing pressure. While MGV is on work, the delayed time of MGV, the variation law of additional opening and the nominal head of pumped storage also exert influences on the two pressure peaks. Meanwhile, MGV can low the maximum casing pressure. According to the hydraulic characters of the casing pressure mentioned above, some measures to reduce the casing pressure are introduced in this paper.Finally, some examples and comparisons in Tianhuangping pumped storage and Tongbai pumped storage are presented based on the above theory. The results show that the computed results satisfied the requirements of the engineering application, which means that it can be applied in the engineering practice.
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