The Montgomery advertiser., 1901-09-06
ELECTRICAL ENGINEERING
ay Arthur E. Watson, A. N.
 CHAPTER VIII.
Motors Adopted to Particular Uses

Meters Adopted to Particular uses.
 As explained in the preceding paper, . machine that generates electricity can pc used equally well as a motor. This rever- sibility of use has led to the retention of the word dynamo" in generic sense, to cover both ideas: that is. a dynamo machine e'th" that excnsnxes %schsSiesi and electrical energy either way Is dynamo: .c.
 Hereafter this nomenclature will DC
 in Assigning an electric motor all the calculations are Identical with those, for a similar generator, The efficiency" is first arbitrarily decided. the volts to be vested in the armaturs deter,nined. e,sr,rnno tive force is known; the armature is then calculated to generate this c. C. m. f. Field winding will ordinarily be series uniform speed is desired; 2 shunt field winding is then proper. For operating hoists, elevators or street cars, always controlled by an attendant; variable speed needed; but the series motor would be operated from the same sort of circuit, 1. e., constant potential ,as the shunt
 The case of a compound field winding needs g special inquiry. If shunt motor be used as generator 1t would be neces- sary to drive its armaturs in one direo- Generator were to be used without any change of connections. as motor. the field magretism would De due n to the, the aid, IT. the shunt winding the armature would tend to rotate in one direction and .ey the series winding the opposite direction load the series coil would be weak. hence the shunt would preponderate, ana tne armatuFe rotate in certain direction; in- creasing to heavy load, the current enable the series coil to everpower the shunt, whereby the motor would stop ana reverse It's direction of rotation. Al me
 moment of stopping the neld maSssesasm na crate no c. e. m. f. and such . large eur rent would flow as to ruin the motor
 Compound motors with rather weak were made years ago by the Edison com pany. In the previous article 1t was ex. plained that By weakening the field of 3 constant potential motor the sPeea o.,,s os used series coils just strong enough to accomplish this weakening of the field to compensate for an otherwise loss or tance, In present shunt motors these re. distances are so low as to make the speed at full only a few per cent less than as no load. and further refinement or speed
 A compound generator that Is to be used as a motor can have it's series coil permanently short circuited or cnnnsc- lions geverssd go thss sn l.F eTSct Se v;ndns T o is then called cumulative" and Is advan.. tageously applied to large motors that are compelled to start under heavy toads constant e the % seriss coli should be short circuited by closing a suitable switch Tn. Aividuai motors operating large pianers can well retain the use of the epmniaHve field; the continual starting and stopping makes heavy demands upon the motive power. In a given case the current con. sunptlon by shunt motor was reduced 9 per cent by. adding a cumulative series Some appiieations of electric motors re- auire reversal of direction of rotatieni principally Tn such 2 elass wnuia pc and street cars. This will also be reeog- niSed as the class that demands variable spede, hence series wound motors. simply sending the current ln the eppcas os,,S S'rsc net change the direction. of rotateni when ordinary motors are installed no selection is exercised In connection to either oi tns
 f wire from the, central station and yet the motors always turn the same way To change the direction of rotation eur rent direction should be changed In either motor Is shunt the field circuit should be kept unbroken. hence the armatuge must receive the change. With serlssSS
 wound motors eltHST dTnatuAC SA &'N can equally well be reversed. .,.
 For motors rotating in one direction only brushes may be empleyee wMcn touch the commutator somewhat tangens tialiy. Those In the former are compos- ed of a number of layers of very thin sheet copper, rolled hard and springy. 'sWoven wire" brushes are now the favor Ite fin eases where eOmmutat0ra are ton small or currents too large to allow use nse of carbon brushes: From Toy 70 svO be taken through copper nrusn, put only 2s to 70 anipeFss through eaFpont ing radially. The first railway Haetera were thus equipped with copper hrushesi they failed Of success. tor the exeeselye aparkiRg and rutting quickly ruined tne esmmutatoTt To avoid sparkling ut.,e sne brushes of generateF are set a lttie ahead of the neutral line, Of 3 motor a littiessb back of that position; since pre- ference cannot be gtven to etther dlree. tian of rotation, the reversing motor must have its brushes on the tneoIetlcSas. lSsa ployment of carbon for the brushes wss 2 brilliant thought and at once ramedled all the difficulties; carhon has such TesiSt. anes as almost entirely to. suppress the currents In the cpmmutated coils. Gon- siderable pressure is required to maintain good contact between carbon brushes fpio and some heatp8 results purely in consequence of friction. Several small brushes with independent tension springs are better than single larger brush. Electric motors are admirable TOT factories. instead of long lines of heavy