Showing papers in "Journal of the Institution of Electrical Engineers in 1919"

The determination of the efficiency of the turbo-alternator

Abstract: With the methods ordinarily employed of establishing the efficiency of the turbo-alternator, the stray loss that is present on load is either deduced by a substantially conventional method or is ignored altogether. As alternators for larger outputs are constructed, the stray loss becomes of greater importance and, indeed, may prove to be one of the factors that will limit the maximum size of unit that it is desirable to employ. A still more unsatisfactory feature of the existing methods is that it is becoming impracticable to apply them to the very large alternators now being constructed, on account of the difficulty of providing a driving motor of sufficient power. Further, with a driving motor, it is obviously impracticable to make any tests on site. It becomes increasingly important, therefore, to introduce a method of establishing the alternator efficiency which is based on the measurement of the actual losses on load.The object of this paper is to show that the actual losses on load can be deduced conveniently and accurately from measurements of the cooling air flowing through the alternator. It is further shown, however, that although such methods are sound in principle, misleading results may be obtained unless certain precautions are taken in applying them.

The sparking voltages between sperical electrodes

Abstract: (1) Simplified formulae are given by means of which the maximum electric stress between equal spherical elctrodes can be readily found. (2)Experimental results on sparkling voltages when the potentials of the equal spherical electrodes are equals and opposite are analysed. It is found that it a be the length of the radius of each electrodes in centimetres, the maximum potential gradient Rmax at the instant of discharge is given by the Rmax. = 27.4 + 14.1/α Kilovolts per cm. very approximately when the temperature of the air is 25° C. and the height of the barometer is 76 cm. (3) The sparking voltage E between two spherical electrodes, the radius of each being a, and x being the distance between them, is given by E = x/f (27.4 + 14.1/√a) Kilovolts at 25° C. and 76 cm. pressure, where f is a factor which can be easily calculated from the geometrical dimensions. It has to be remembered that these formulae do not apply to air-gaps less than 1 mm. or air-gaps so great that brush discharges take place. (4)It follows from the formulae given above that in general for a fixed spark-gap there are certain sized spherical electrodes which offer the maximum resistance to sparking. Increasing or diminishing the size of the electrodes from this value makes the spark take place more readilly. (5) The results when one electrode is earthed given in the "Standardization Rules" of the American Institute are analysed. From the results it appears that the potentials of the electrodes were not E and o, but were 0.57 E and - 0.43 E. These values of the potentials make the values of Rmax. deduced the same as the values found when the potentials are equals and opposite.