The numerical simulation of the delayed load rejection of a pump-turbine powerplant

Abstract

This paper presents results of a numerical simulation of the transient behaviour of a 4×320MW pump-turbine powerplant, where all 4 units are connected on the same headrace tunnel, the same surge tank tail water side and the same tailrace tunnel. The minimum allowable pressure at draft tube entrance during the transient will be discussed at the beginning. The simulation reveals a severe pressure drop down to -30mwc in the draft tube of the last unit, if this is load rejected app. 5 seconds later than the other 3 units. Possible active countermeasures (asynchronous guide vane closing, stepped closing of spherical valve, or limiting the operation of the powerplant) as well as the structural (passive) countermeasure (hillchart modification through new PT hydraulic design) for mitigation of this problem will be discussed and investigated in detail. © Published under licence by IOP Publishing Ltd.