The Measurement of Electrical Output of Large A-C. Turbo Generators During Water-Rate Tests

The water-rate of large a-c. turbo-generators is determined in place with the generator supplying power to the existing commercial load. Such procedure requires that the electrical output be accurately measured under conditions where the load is practically always varying slightly, and where it may be varying considerably. Portable test meters are frequently used for such measurement. The use of portable indicating wattmeters is absolutely feasible for such measurement even where the load variations are extreme, with the resultant accruing advantage that the superior operating characteristics of the portable indicating wattmeters, particularly as regards their permanency, are utilized. Either the two-wattmeter or three-wattmeter method for-measuring the power of a three-phase circuit may be employed. Great care should be used in selecting instruments, particular reference being made to their past history. Comparisons against secondary standards should be made under conditions simulating those of the test. Observations are made at frequent intervals depending upon the accuracy desired in the final result. The accuracy of the final values of water-rate obtainable in practise is such that the per cent average deviation from the mean will be within ± 0.25 per cent. This means that practically all individual test results will fall in a belt 1 per cent wide, while the probably true value of water-rate will be located within a belt which will vary in width from 0.5 per cent to 0.25 per cent depending upon the conditions.