冲击式水轮机两段折线关闭的临界折点与最大水锤

冲击式水轮机喷针两段折线关闭规律的折点以往只通过优化额定工况的水锤确定,未考虑冲击式水轮机在甩部分负荷时发生最大水锤的问题。针对该问题,应用冲击式水轮机喷针直线关闭规律下的最大水锤规律,分析得到适用于喷针关闭规律为一般情形时的两个推论:其一,喷针关闭规律图上某一大于等于一个相长直线段的区域性最大水锤总发生在该直线段末端时刻;其二,如果任意工况下喷嘴完全关闭前,喷嘴末端均无负水锤出现,喷针全工作范围全关闭时间范围内最大水锤压力等于所有工况下最大的第一相末水锤压力。基于两个推论,推导了冲击式水轮机两段折线关闭时临界折点公式,得出当三个判别公式成立时,临界折点公式推导所依据的两个区域性最大水锤也是全工作区域时间区域上最大水锤的结论。

Critical turning point and maximum water hammer in impulse turbine under two-segment linear valve closure

The turning point of two-segment linear closure law is commonly determined by using only the rated working condition of a impulse turbine, which neglects the fact that the maximum water hammer (MWH) happens at partial load rejection. This paper analyzes the MWH behaviors at linear valve closure and derives two inferences for the case of general needle-valve closure. First, for each linear closure region, the local MWH always happens at the end time of its line segment if its time duration is no less than that of one phase; second, the MWH pressure in the whole needle-closure region equals the greatest value of all the first-phase water hammers in all working conditions if in any working conditions no negative water hammer occurs at the nozzle until its total shutdown. Using these two inferences, we further derive a critical turning point formula and come to the conclusion that if the three discrimination formulas are true, then the two regional MWHs used as the basis of this derivation are also the MWH pressures in the whole region of needle valve closure.