Technique on Flow Measurement and Its Application in Low Head and Large Discharge Pump Stations

Abstract

The accurate discharge measurement of single pump in low head and large discharge pump stations has been considered as a difficult problem for a long time. Recently, with the completion of some pump stations of South-to-North Water Transfer Project in China, many low head and large discharge pump stations completed with gradually contracted inlet conduit need high accuracy of discharge measurement which is necessary to optimize the operation of pump units, sum up the total discharge and get the efficiency of the pump stations. In this literature, problems came across from traditional measurement methods of discharge are given. These methods are including five-hole probe discharge measurement, discharge measurement using current meter and differential pressure transmitter measurement. Among all these methods, the measurement principle, performance, installation and application of 7510P portable ultrasonic flow-meter with multi-path ultrasonic are specially introduced. Generally speaking, the low head pump stations usually have the characteristic of irregular multi-culvert construction with short straight conduit and gradually contracted cross-sections along the flow direction, so the accurate discharge measurement is very difficult to process. By installing multi paths in conduit, adopting technique on installation elevation of international regulations on Gauss integration method which is also employed in calculating flow, the flow can be got. The number of acoustic paths is determined by conduit construction and hydraulic conditions. The arrangements of acoustic paths are placed in the mode cross-link. Then the discharge can be calculated through integrating the obtained velocity in corresponding cross-section. The installation of 7510P portable ultrasonic flow-meter mainly comprises three processes, including the installation of transducers, the arrangement of cables and its connection with flow-meter. Combining the measured discharge in Jiangdu No.2 Pump Station of the South-to-North Water Transfer Project in China, following conclusions are presented: it has well stability, good repeatability of measurement results, high measurement accuracy with the error around ±0.30%, high reliability and the flow-meter fits a wide range of discharge well. The successful application of 7510P ultrasonic flow-meter accumulates useful experience for discharge measurement of single unit of low head and large discharge pump stations and add a new method of accurate field discharge measurement of low head pump stations, meanwhile, it will play a constructive role in the design, construction and management of pump stations.