. The Street railway journal . shes, which,with dynamos with brushes at fixed lead for variable load,plays a most important part. Since the reversing field isonly of proper value for one current output, this resistance October 13, 1900.] STREET RAILWAY JOURNAL. 943 acts (1) to prevent abnormal current when the coils areshort-circuited in strength of field not corresponding tothe current output, (2) to increase the rate at which thecurrent falls ofif in the coils when short-circuited, and (3), -— / 100 200 300 400 500 Ampere turns per inch of length. FIG. 3.—CURVE FOR GOOD QUALITY OF WROUGHT IR
. The Street railway journal . shes, which,with dynamos with brushes at fixed lead for variable load,plays a most important part. Since the reversing field isonly of proper value for one current output, this resistance October 13, 1900.] STREET RAILWAY JOURNAL. 943 acts (1) to prevent abnormal current when the coils areshort-circuited in strength of field not corresponding tothe current output, (2) to increase the rate at which thecurrent falls ofif in the coils when short-circuited, and (3), -— / 100 200 300 400 500 Ampere turns per inch of length. FIG. 3.—CURVE FOR GOOD QUALITY OF WROUGHT IRON ANDSHEET STEEL to shunt into a short-circuited .coil a portion of the reversecurrent, so that on leaving a brush the current is in phasewith the current in the main circuit. The contact resist-ance may be varied according to the quality of carbonused, which varies from 590 x iO; ohms per cubic inch to3900 x io6 ohms per cubic inch, but in ordinary practice itis found advisable to limit the contact resistance so that the. 20 10 GO 80 100 120 140 160 180 200 220 240 260Ampere turns per ineh of length. street FIG. FOR GOOD QUALITY OF CAST IRON drop in the brushes at full load amounts to not more than\ per cent, otherwise the commutator becomes excessivelylarge and costly and efficient collection difficult. Thirdly, the self induction of the individual armaturecoils, which is a measure of the maximum field strengthrequired for current reversal, as also the amount of distor-tion produced locally in the line of commutation, this dis- tortion being backward for diminishing current, and for-ward for increasing current. This inductance voltage,which may be calculated from the laws of the magneticcircuit or on the basis of 20 c. g. s. to 25 c. g. s. lines perampere per inch length of armature iron, has been limitedin value in terms of the volt drop in the brushes, with fullload current density, and in terms of the average strengthof magnetic field as expressed b
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Keywords: ., bookcentury1800, bookdecade1880, bookidstreetrailwa, bookyear1884
