. Electrical world. ) Auxiliary Armature Windings.—Between the main armaturewinding and the commutator a commutation winding is arrangedwhich is either shifted towards the pole tips (Sayers) or induced bya special small field frame by the main current (Seidener) ;in each case the induced must act against the reactance voltage. (/) Spark-extinguishing btozv-out devices, acting either by com-pressed air (Thury) or by condensers switched between the com-mutator segments (Thury, German patent, No. 142,562). (g) Replacement of the commutator type by the unipolar orhomopolar machine,
. Electrical world. ) Auxiliary Armature Windings.—Between the main armaturewinding and the commutator a commutation winding is arrangedwhich is either shifted towards the pole tips (Sayers) or induced bya special small field frame by the main current (Seidener) ;in each case the induced must act against the reactance voltage. (/) Spark-extinguishing btozv-out devices, acting either by com-pressed air (Thury) or by condensers switched between the com-mutator segments (Thury, German patent, No. 142,562). (g) Replacement of the commutator type by the unipolar orhomopolar machine, in which direct current is produced without anycommutation. The main trouble is the fact that all existing unipolartypes generate only very low voltages (50 volts and less) and thatlarge eddy currents often occur. By using the most recent materialsiif exceptionally high mechanical resistivity, like nickel-steel, more-atisfactory results may be expected. (2) The temperature rise. T. in degrees Centigrade of a body. FIG. 4.—DIRECT-CURRENT TURBO-DYNAMO. rotating at v meters per second and in which JV watts are trans-formed into heat is approximately either T — k 3 (i + v) W T — k 5- (I -f Vi.) where 5 := radiating surface in square centimeters andconstant. If the speed of a given type is increased from v to m v. the voltage and k are rises from e to e volts. If the main current, /, remains the samefor both speeds, the copper losses, IV do not vary for both cases,but the iron losses, H/i -\- IVe (hysteresis 4- eddy currents) growto the value m W/, -{- m-Wg-The ratio of the temperature rise Tm (with mv) to T (with v)is, therefore, using the Vi; formula, the best for wide variationsof speed : ;;: -h w ii/, -f w-ife iVc + iv/, + iv^ T,„ : T = I 4- 0-3 ^ ^i I + Vz This equation proves that with increasing values of w, that is withincreasing speed or circumferential velocity, the temperature risegrows more and more and for a fixed maximum value of T,,, thereexists
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
