. Electrical world. s and balances of the other two quarters, and to circulate an alternatingcurrent through the armature from an external source of the samefrequency as the machine under test, and whose phase with rela-tion to this machine may be readily adjusted. This external sourcemay consist of a small alternator with the same number of polesas the machine under test, and coupled to the same shaft; or it maybe a machine of a different number of poles, driven from the shaftthrough chain or spur gearing. This machine, of course, mav be in circuit with the large one, either direct
. Electrical world. s and balances of the other two quarters, and to circulate an alternatingcurrent through the armature from an external source of the samefrequency as the machine under test, and whose phase with rela-tion to this machine may be readily adjusted. This external sourcemay consist of a small alternator with the same number of polesas the machine under test, and coupled to the same shaft; or it maybe a machine of a different number of poles, driven from the shaftthrough chain or spur gearing. This machine, of course, mav be in circuit with the large one, either direct or through a transformer,and need only be of a size capable of supplying the electrical lossesin the large generator and connections. By this arrangement prac-tically all the effects of full load can be simulated, in a manner toget practically reliable results. The auxiliary alternator can hiso driven with relation to the machine under test as to circulate acurrent of leading, lagging or any desired power factor. O^. FIG. 3.—\GRAM OF TESTING .\PPAR.\TUS. The heating can, therefore, be determined for any of these condi-tions, and the regulation likewise. The efficiency can be determinedfrom the balance of power required to drive the machine at itsworking speed with full load current circulating through the arma-ture (at any desired power factor), after subtracting the power lostin the outside connections, the auxiliary alternator and the gearingdriving it, all of which can be easily determined with an accuracynear enough to give materially correct results for the machine undertest. Fig. 3 shows the manner of testing the regulation of the machine,the voltmeter and power factor indicator being in connection withthe half of the machine in which the current flows in the directionof the ; the frequency meter being connected any convenientplace, say in parallel with the voltmeter. A reading is first taken with no current passing through the arma-ture; afterwards a reading
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
