The Motor and the Dynamo (Paperback)


This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...the shaft into the bearings. The formula for power developed by the motor is then Lbs. X ft. circumference X r.p.m. Horse-power =. 33,000 This is the output. The input in watts may be obtained by an ammeter in the general circuit (field and armature) and a voltmeter across the terminals. Horse-power input is the watts divided by 746, and the per cent. efficiency is output input X 100. (b) Varieties of Field Excitation. Fig-59 shows the characteristic curves of a Bell Electric Company's shunt motor, rated at 3 horse-power, 115 volts, 25 amperes 1,200 revolutions per minute. Fig. 60 shows the characteristic of a General Electric Company's crane motor (series), rated at 5 horse-power, 220 volts, 25 amperes full load. From the formula E, = c. e. m. f.-f-I R it is evident, that. the smaller the resistance of the armature circuit, the more nearly constant will be the speed of a shunt motor under varying loads. For the smaller the changes in I R, the more nearly will c. e. m. f. y =--8 J approach a constant value. In the actual operation of nearly every motor, on the other hand, it must not be overlooked that the speed variation is considerably greater than appears from the manufacturer's curves. The reason is the IR drop is always present to a greater or less degree in the live wires leading to the machine from the source of supply. Unless the generator is compounded for this particu Fig. 59.--Curves of a shunt-motor. Bell Electric Motor Co. 3 H. P. lar circuit or unless some other equally efficient means is adopted to maintain constant load-voltage, this IR drop lowers the voltage at the motor as the load increases, and has to be reckoned with in considering motor speeds. Again, the speed of a motor, both shunt and series, is...

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...the shaft into the bearings. The formula for power developed by the motor is then Lbs. X ft. circumference X r.p.m. Horse-power =. 33,000 This is the output. The input in watts may be obtained by an ammeter in the general circuit (field and armature) and a voltmeter across the terminals. Horse-power input is the watts divided by 746, and the per cent. efficiency is output input X 100. (b) Varieties of Field Excitation. Fig-59 shows the characteristic curves of a Bell Electric Company's shunt motor, rated at 3 horse-power, 115 volts, 25 amperes 1,200 revolutions per minute. Fig. 60 shows the characteristic of a General Electric Company's crane motor (series), rated at 5 horse-power, 220 volts, 25 amperes full load. From the formula E, = c. e. m. f.-f-I R it is evident, that. the smaller the resistance of the armature circuit, the more nearly constant will be the speed of a shunt motor under varying loads. For the smaller the changes in I R, the more nearly will c. e. m. f. y =--8 J approach a constant value. In the actual operation of nearly every motor, on the other hand, it must not be overlooked that the speed variation is considerably greater than appears from the manufacturer's curves. The reason is the IR drop is always present to a greater or less degree in the live wires leading to the machine from the source of supply. Unless the generator is compounded for this particu Fig. 59.--Curves of a shunt-motor. Bell Electric Motor Co. 3 H. P. lar circuit or unless some other equally efficient means is adopted to maintain constant load-voltage, this IR drop lowers the voltage at the motor as the load increases, and has to be reckoned with in considering motor speeds. Again, the speed of a motor, both shunt and series, is...

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Product Details

General

Imprint

Rarebooksclub.com

Country of origin

United States

Release date

July 2012

Availability

Supplier out of stock. If you add this item to your wish list we will let you know when it becomes available.

First published

July 2012

Authors

Dimensions

246 x 189 x 2mm (L x W x T)

Format

Paperback - Trade

Pages

34

ISBN-13

978-1-151-74612-2

Barcode

9781151746122

Categories

LSN

1-151-74612-6



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