Method of controlling wicket gates of a pump-turbine

Claim 1

In a hydraulic system comprising an upper and a lower reservoirs, a plurality of turbine operation means, penstock means including a plurality of pipelines each extending from the upstream side of each of said turbine operation means and communicated with said upper reservoir, and tailrace means including a plurality of pipelines each extending from the downstream side of each of said turbine operation means and communicated with said lower reservoir, at least one of the upstream ends of the pipelines of said penstock means and the downstream ends of the pipelines of said tailrace means being connected through a multi-branched manifold to a common pipeline which in turn is connected to the corresponding reservoir, at least two of said turbine operation means including a pump-turbine with wicket gates closable and openable to control the flow of fluid through the turbine and which has S-section performance in the turbine operation area, said S-section performance being defined on an N 1 versus Q 1 performance curve drawn with a parameter of opening degree of wicket gates as that where dQ 1 /dN 1 >0 is satisfied along said performance curve, where Q 1 is the discharge through said pump-turbine per unit head and N 1 is the rotating speed of said pump-turbine per unit head, a method of controlling wicket gates of each of said pump-turbines to reduce abnormal pressure rises in the system upon sudden reduction or removal of load which comprises the steps of: detecting the sudden reduction or removal of load from the turbine; in response to said detecting, closing the wicket gates down to an opening degree where said S-section is smaller in length but still exists on the corresponding Q 1 versus N 1 performance curve, for the short period while the operation point of said pump-turbine on said N 1 versus Q 1 performance curve approaches to but still remains out of said S-section; and controlling the pattern of said closing so that the resultant pressure rise in said penstock means is larger than any pressure rises in said penstock means that arise thereafter during the subsequent transient state through said S-section.