. The Street railway journal . gainst the wire by means of aspring, but is lowered and automatically locked down by theapplication of compressed air. Application of the air to an-other point will then unlock the trolley and allow it to rise. To reduce the trolley voltage for use at the motors anoil-insulated, self-cooling auto-transformer is used. As thisis ordinarily the heaviest single piece of apparatus on thecar, it is commonly mounted in the center in order to sim-plify the matter of balancing. As with direct-current motors, the speed of the single-phase motor varies with the voltage at i
. The Street railway journal . gainst the wire by means of aspring, but is lowered and automatically locked down by theapplication of compressed air. Application of the air to an-other point will then unlock the trolley and allow it to rise. To reduce the trolley voltage for use at the motors anoil-insulated, self-cooling auto-transformer is used. As thisis ordinarily the heaviest single piece of apparatus on thecar, it is commonly mounted in the center in order to sim-plify the matter of balancing. As with direct-current motors, the speed of the single-phase motor varies with the voltage at its terminals, andthe motor is controlled in this way. In order to get avariable voltage for this purpose, however, it is not neces-sary, as in direct-current practice, to change the groupmgof the motors or to introduce resistance into the circuit,but simply to connect the motors to different taps on theauto-transformer. The various connections between motors and transformermay be made either by drum type controllers or by unit. FIG. 11.—REVERSER WITH COVER REMOVED switches, as with direct-current equipments. On account ofthe absence of any necessity for making series-parallel con-nections, both drum type controllers and unit switch groupsfor single-phase equipments are simpler than those for di-rect-current operation. For instance, a switch group forhandling four loo-hp direct-current motors weighs approxi-mately 760 lbs., while one for handling four single-phasemotors of the same capacity weighs only 400 lbs. An en-tire equipment of single-phase motors, however, is consid-erably heavier than an equipment of direct-current motorsof the same capacity, so that a car equipped with the formerand carrying the same passenger load will ordinarily weighfrom 10 to 15 per cent more than one equipped with the lat-ter. Switch groups for single-phase operation are controlledby small storage batteries in the same way as those for usewith direct-current equipments, but in this case the batt
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
