Evaluation of Measurement Uncertainties in Performance Testing of Hydraulic Turbines and Pump/Turbines

Abstract

ASME Performance Test Code Committee No. 18 on Hydraulic Prime Movers is currently engaged in writing the first edition of a performance test code for the pumping cycle of reversible pump/turbines, after which it will undoubtedly update the 1949 performance test code for hydraulic turbines to be used also for the turbine cycle of pump/turbines. As members of the Canadian and United States national advisory groups, most of the ASME PTC-18 committee are also involved in the work of Technical Committee No. 4 on Hydraulic Turbines of the International Electrotechnical Commission for which the United States maintains the Secretariat with ASME as sponsor. The international codes for field acceptance tests of hydraulic turbines (IEC Publication 41-1963) and storage pumps (IEC Publication 198-1966) are currently in the process of being reworked and updated for combination into a single publication (or a coordinated set). Consequently, the subject material of this paper is now under world-wide discussion. The paper outlines the need for a universally-accepted method of determining field test inaccuracies or uncertainties. It suggests new testing procedures, suitable for statistical analysis, plus laboratory research on, and painstaking technical analysis of, each method of flow measurement. Until more accurate procedures are developed for the measurement of large water flow rates, the “best possible” test cannot justify the use of the best available instruments and techniques for measurement of hydraulic head and electrical power. Since the current state-of-the-art of field testing large hydraulic machines results in a sizable uncertainty in efficiency, this fact must be recognized by both parties to an equipment contract, and the commercial method of dealing with it should be carefully delineated in the purchase specifications.