Influence of hydraulic characteristics on transient behavior of ultra-high head pump turbine

Abstract

Pump turbines with ultra-high head or low specific speed have typically pronounced "S" characteristics in generation mode, which usually leads to a very challenging situation regarding the transient behavior, especially when it is not adequately considered in the power plant layout. Though some countermeasures, e.g. asynchronous guide vane closing or fast MIV closing, can be taken in the late stage to mitigate the problem, nowadays the customers are more in favour of a solution on root, i.e. improving the "S" characteristics by optimizing the hydraulic design of pump turbine during design stage. Recently Dongfang has successfully developed several pump turbines with a head range from 580m up to 750m. An important consideration during the development is to find out a compromise between hydraulic performance and transient behavior. This paper presents how the hydraulic design influences the "S" characteristics and subsequently the transient behavior, based on the investigations performed and improvements obtained through these pumped-storage projects.