792 APPENDIX III 



In computing the turbine output in the turbine test, this is to be taken 

 as the kilowatt output of generator divided by the generator efficiency as 

 computed above, the result being converted from kilowatts to horse-power. 



If an exciter generator is also mounted on the unit shaft and is used to 

 excite the unit under test, then to the output of the main generator com- 

 puted as above without reference to excitation there is to be added the 

 kilowatt output of exciter divided by the exciter efficiency, this converted 

 to horse-power. It is recommended, however, for simplicity that when pos- 

 sible the exciter shall be run without load and the unit separately excited. 



It is recommended to avoid retests and to provide a reliable check, that 

 the electrical instruments used in all tests be installed in duplicate. These 

 instruments, together with the instrument transformers, shall be calibrated 

 both before and after the tests in the same condition as used in the tests. 

 When tests are made under slightly fluctuating loads, the output shall be 

 determined both by indicating wattmeters, read at short intervals, and by 

 recording watt-hour meters. During the turbine test the speed of the unit 

 shall be observed by accurately calibrated tachometer or by revolution 

 counter. 



(6) By Absorption Dynamometer. When a dynamometer, either of 

 the Prony brake, friction disc, or other type, is used, the dynamometer is 

 to be so arranged as to avoid imposing either end thrust or side thrust on 

 the turbine shaft and bearings, or to avoid adding any friction load which 

 is not measured. 



The brake must be capable of operating with the weighing beam floating 

 free of the stops during the entire duration of a run. A dash pot or equiv- 

 alent device may be used to assist this action if so arranged that the accuracy 

 of measuring the actual torque acting on the turbine shaft is not impaired. 



The dynamometer must be so constructed that the lengths of all lever 

 arms used for transmitting and reducing the loads can be accurately measured. 

 The zero load of the dynamometer must be capable of accurate measurement 

 and should not be large in comparison with the net load to be measured. 



When power is determined by dynamometer, particular care is to be 

 used in obtaining accurate measurement of the speed of the shaft. If ta- 

 chometers are used these are to be frequently calibrated by counting the revo- 

 lutions over an ample length of time. Under usual conditions it is recom- 

 mended that the speed be directly measured by revolution counter, a 

 tachometer being also used as a check and to indicate variations in speed 

 during a run. 



MEASUREMENT OF POWER INPUT OR WATER HORSE-POWER 



8. Measurement of Head. The intent of the provisions contained herein 

 for the measurement of head is the true determination of the difference 

 between the total energy contained in the water immediately before its 

 entrance into the turbine, and its total energy immediately after its dis- 

 charge from the draft tube. 



The turbine shall be tested if possible under the effective head stated in 

 the contract, and at the speed specified in the contract. If during the test, 

 however, the effective head shall differ from the specified head by an amount 



