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Full text of "Determination of current and candle power curves of the alternating current arc under impressed voltage of various wave forms"

Dstermination of Current and 

Candle Power Curves of the 

Alternating Current Arc 

Under Impressed Voltage 

Of Various Wave Forms 



H. E. Brashares 
J. R. Armstrong 



905 



537.831 
B73 



ARMOUR 

INST.OFTECH.Ua 

CHICAGO. 




Illinois InsUtute 
•f Tcduwltfly 



AT 3 

Brashares, H. E, 
Determination of current and 
candle power curves of the 



■--#■ 

■i 



Try 



DETEEIvIIKATIOH OF CUiSEliTT AITD CixKDLE POWER CimVES 

OF 
THE ^LTEEHATIl^G CURSEnT ^C 
IffiDER ILIPKESSi;!) VOLTAGE 0? V^P.IOUS 7/aVE F0K.1S. 

ii THESIS PEESEITED 



to tll« 
PRESIDEITT AITD F^iCULTY 
Of 
^HvIOim IHSTITUTE OF TECmiOLOGY 
For the degree 
•of 
BACHELOR OF SGIEUCE II? 3:iECTRICAL EFr^HTESRIITG 
Having completed the prescribed course of study in 

SLEGTSIC^L ZKGIIJESRIISIG. 

ILLINOIS INSTITUTE OF TECHNOLOGY 
PAUL V. GALVIN LIBRARY 

^ ^ y '"'^-so, .u.e 16. 1905. SforsoeT" 



'P^>^y 







J^^Of^^ (^ (3ul£^t^tA.^ Z^^'., 




ns 



Table of cohtmts. 

Subject. Page, 

Preface, containing statement of Thesis subject 2 

A Brief History of the Electric ixrc 4 

The Apparatus: 

The Rotation of the Arc 10 

The Photometer 13 

The Llagnetic Coupling and Contact llaker 17 

The Llotive Power E3 

The Curve Tracing Table Z5 

The Enown Resistance 28 

The Regulation of the Current E8 

Calibration of the Standard Lamp 29 

The Arc from a Peaked Wave 32 

The -arc from a Flat Top V/ave 37 

Comparison of the Results Obtained from the Flat 

Top and Peaked E. LI. F. Y/aves 42 

-tinnotations 43 



LIST OF ILLUSTRATIONS, 

Machine for Rotating Arc 

Photometer Bench Complete 

Photometer Bench without Discs 

The Disc 

The Llagnetic Coupling 

The Contact Maker 

The SjoiohronouB Ivlotor 
4. The Curve Tracing Table 



f Print 1) 


11 


(Print 2) 


15 


(Print 3) 


15a 


(Print 4) 


16 


(Print 5) 


19 


(Print 6) 


20 


(Print 7) 


24 


(Print 8) 


26 



1T979 



PREFACE. 

The oTDJcot of this thesis is to point out the 
relation of the useful light emitted by the alternating 
current arc to the wave form of the voltage impressed 
upon it. 

The existence of different wave forms of voltage 
in alternating current practice is a well knovna and use- 
ful fact. ^11 forms varying from the peaked to the 
flat or rectangular are found, both in regular and ir- 
regular ways. For a given effective value, the flat top 
wave gives more nearly a constant val'ae to the current 
through a half cycle, while the peaked form gives a rap- 
idly varying current which rerches c. high maxirauja. It 
is desired that the light given out by the alternating 
current arc be as uniform as possible in order that it 
may be applicable to commercial problems of lighting. 
Since the current producing the arc pa.sses through a 
zero value twice per cycle, the wave form which best 
adapts itself to the arc light is that one which will 
store the greatest amount of energy in the arc to main- 
tain its brightness through these periods. 

The plan adopted for the study of the effects as 



pointed out above is that of the photometric determina- 
tion of the light given out by the arc for the instanta- 
neous values of the current and the voltage producing it, 
This plan necessitates a combination of the well known 
contact maker and the flicker photometer. This appara- 
tus is described in detail in the following pages, as it 
was constructed and operated in this work. In these 
descriptions, numerous references are made to lettered 
prints of the different parts, by which it is hoped that 
they may be more clearly understood. 



A BRIEF HISTORY OF THE ELECTRIC -tiRC. 

The Electric ^rc v/as probably first discovered 
by Volta in 1802 or 1803 v/hile experiment iiig with the 
heating power of a current, especially with the sparks 
produced on the breaking of a live circuit. It v/as 
first brought to general notice by Davy in 1808, during 
his experiments with the great battery of the Royal In- 
stitution, 

The arc is the most intense artificial illuninant 
and the chief comuercial source of very powerful light. 
The slow breaking of an electric circuit, carrying con- 
siderable current at a medium voltage, does not inter- 
rupt the flow of the current even after the conductor is 
parted. The current jumps across the break however Vi/ith 
the evolution of great heat and a vivid light. If this 
separation is at the ends of two carbon rods, the light 
is enormously brilliant, and by proper mechanism can be 
maintained fairly constant. This passage of current 
from one carbon tip to the other is accompanied by the 
production of great heat, and the tips of the carbon 
rods will grow white hot, thus serving as a so\u-ce of 
light. In the ordinary direct current arc lamp, the 
upper carbon is the positive pole of the circuit and is 



fed slowly downwurd, bo as to keep the arc wiiform as the 
cartoB. is consulted. 

The main consximption of energy appears to be at 
the tip of this positive carbon which is by far the most 
brilliant part of the arc. Tlie carbon fairly boils away 
into vapor, producing a slight hollow in the center of 
the carbon, commonly Icnown as the crater. The carbon 
of this pole is consujued about twice as fast as that of 
the negative pole. The positive carbon resembles in 
shape a blxmt pointed pencil, while the negative carbon 
becomes more nearly like a sharp pointed pencil. 

With the introduction of the alternator into the 
commercial world, the alternating current was at once 
applied to arc lighting. QQie alternating current arc 
has grown in the lighting field until it is most v/idely 
used in the United States as well as on the Continent. 
In this country, it is used on both the constant poten- 
tial and constant current systems. 

It is very evident that there is neither a posi- 
tive nor a negative carbon, each one being positive and 
negative alternately and changing from one to the other 
between 3,000 and 14,000 times per minute, according to 
the frequency of the current in the circuit. Under these 
conditions, no marked crater is formed on either carbon 
and the two are consumed at about an equal rate. ^s a 
natural result of this intermittent coi:dition, the heat 



whioh is stored up in the carbons is depended upon to 
produce sufficient ligiit while the current is passing 
through the zero value, to maintain the effect constant. 
This intermittent supply and the lack of a localized 
crater causes a lower average temperature in this arc 
than in the similar direct current arc. The tempera- 
ture of the alternating arc varies hetween 2,800 and 
4,000 degrees 0. 

Careful tests have been made with the alternat- 
ing arc with regard to the freq.uency and it has been 
found that it operates best at from 40 to 50 cycles 
per second. whien operated belov; 40 cycles, the light 
flickers to a troublesome extent, v/hile above 60 cycles 
it becomes very noisy. Enclosed arcs, or very soft 
carbons, e.nd heavy currents in open arcs, decrease these 
above defects to some extent. 

Exhaustive tests have been carried on in the 
various engineering laboratories of the electric compan- 
ies to determine the best carbon for use in the alternat- 
ing arc. It is found that a specially fine soft carbon 
is the best adapted for open arc work. These carbons 
not only muffle the vibration to a remarkable degree but 
also when used at high current densities give off a large 
quantity of vapor in the arc, which adds stability to it. 
The result of using soft volatile carbons is a q.uiet 
steady brilliant arc of the most excellent illuminating 
powers. V/here this class of ce.rbon is either too costly 



or impossible to obtain, the harder carbons must be used 
and especially with enclosed arcs. 

The alternating current arc produces a singing 
sound \fhich is partially due to the vibrations produced 
in the mechanism and partially to the pulsations im- 
pressed directly on the air by the oscillatory action 
in the arc itself. The former can be luodified to a 
considerable degree by proper design of the mechanism 
and care in the manufacture of it. The latter however 
is hard to suppress. With all of the precautions possi- 
ble and V7ith the best carbons possible, the arc still 
sings ii: a tone pitched about a semi-tone below bass G 
with very ujipleasant harmonics. 

Tests to determine the difference of efficiency 
between direct and alternating current arcs have given 
a collection of varied results which are hard go formu- 
late into a definite rule. Ki'. Louis Bell drav/s the 
conclusion that for xmit energy actually applied to the 
arc, the direct current arc v/ill give about 25^o more 
light than the alternating current arc. "Tien operated 
on a constant potential lighting system (comparing en- 
closed i,-rcs!, the suarplus voltage is taken up in a re- 
active coil which wastes very little energy, while a 
direct current arc light has a dead resistance which 
wastes considerable, so that the two arcs are on about 
even terms. The following table will c-ive some idea of 



the relative efficiencies of the different arcs. 

Kind of ^rc. 7/atts per S.C.P. 

Direct current open 1»0 

Direct current shaded 1«3 

i-:.lternating current open 1»7 

Alternating current shaded 2«a 

Direct current enclosed 2»4 

Direct current enclosed 2*9 

Direct current enclosed 3»0 

Alternating current enclosed 2»6 

Alternating current enclosed 3.3 

Alternating current enclosed 3.6 

The sizes of carbons which are on the market vary 
from 5/l6 to 3/4 inch in diameter. The current em- 
ployed varies from 6 to 10 amperes according to condi- 
tions of locality and the size of carbon used. The volt- 
age also varies under different conditions. 

l^s. -.yrfcon, I,Ir. Stein and other prominent photo- 
metricians have carried out extensive tests with differ- 
ent carbons varying sizes, current densities and voltages 
under similar conditions to determine the best adapted 
and the most economical combinations for these conditions. 
The mean spherical candle power, the horizontal candle 
power and the distribution of alternating arcs have been 
carefully tested on both constant potential and constant 
current circuits by Prof. Schaler Katthews of Purdue 
University, under the direction of the national Electric 
Light AsBOCiation. Extensive experiments have been made 
to determine the time resistance of the arc iinder differ- 
ent conditions of current and voltage. This, and the 



determination whether there exists a "back E. M, F. in the 
aro are two prohlems which have never heen satisfactorily 
solved. The effect of the different wave forms on the 
light giving (jualities of the aro has received, seemingly, 
little attention hy the experimenters. Since this 
subject of wave form has "been given positions of consider- 
able weight in other commercial lines of electricity, it 
should receive soirie consideration. 

In the above discussion, it has only been desired 
to give a brief history of the electric arc and the treat- 
ment it has received in fche hands of experimenters whose 
conclusions have decided the practice at the present time. 
For a detailed and extensive history of the arc, the reader 
is referred to specially prepared works on the subject, 
chief of which is that of Ivlrs. Ayrton, "The Electric ^rc." 



10 



THE APPARATUS. 
The Rotation of th.e Arc. 

One of the peculiar actions of the alternating 
current arc, v*hich has not been most satisfactorily under- 
stood, is that it wanders continually around the tips of 
the carbons maintaining it. To counteract this action 
and obtain a condition which more accurately represents 
aoi average effect of the arc, a special machine is used. 
Vhit nit chine, es shov.r ir Print 1, was designed by Prof. 
Snow of the Armour Institute of Technologj;^, and built in 
the Institute shops under the direction of Mr. Sommers. 
At the beginning of this work, it was altered in some re- 
spects, chief of which was the support of the lower car- 
bon. This alteration was m6.de to eliminate the shadows 
produced by the supports as much as possible. The main 
purpose of the machine is to rotate the arc a.^ a high 
speed and thus eliminate the effects of its wandering. 

The machine consists of a suitable v/rought iron 
frame, a, v/hich supports the cast iron ?/heel, b, at its 
central point, c. This ?;heel is graduated on its back 
side in degrees from zero to ninety in each direction 
from d, which represents the zero or vertical position 
of the arc. The wheel, b, carries the white metal frame, 
e, which is secured rigidly to it. The frame, e, supports 




PRIET 1. 



12 

the meohanism for adjusting and rotating the carbone. 
The upper- carhon is supported on the I'od-, f',' wjiich 
passes through the sleeve, g, through6ut its entire 
length and is -secured to it by a feather. key which permits 
of easy movement up or down, by the thumb .screw, k, v/hile 
the key insures rotation with the sleeve. Upon sleeve, 
g, and insulated from it is the second sleeve, i, which 
Bupi'Orts the lower carbon. The brush, j, serves to con- 
nect the lower carbon with the binding post, o, which 
is connected to the line. The other terminal of the 
line is connected to the binding post, n, v/hich makes 
connections with the upper carbon through the frame, e, 
and the sleeve, g. Keyed to sleeve, g, is the pulley, 
m,' which is driven by a belt running over two small idler 
pulleys in the back of the frame to the shaft of the smc:.ll 
Crocker-lVheeler motor, q.. The shaft of this motor is 
in line with the horizontal axis of the wheel, b, v/hich 
permits of three movements of b about its axis without 
disturbing the rotation of the motor armature. The en- 
tire part supported uy the sleeve, g, may be moved through 
a Blight distance along its axis by the thiimb screw, 1, 
which allows of close adjustment. The r;lobe, h, is 
supported by the cover plate, s, by means of the copper 
springs which permit it to be easily removed. ^ white 
metal frame, t, is also supported by the frame, e. 



13 



for the purpose of holding an outer globe. It may be 
raised or lowered by the thumb screw, v, and adjusted as 
desired. The motor is connected to the mains through a 
starting box uud rheostat by which its speed can be gov- 
erned as desired. Thus the arc is rotated and at the same 
time easily adjusted as to length and position. 

The Photometer. 

In order to measure the light given out by the 
arc as operated by the machine described above, it must 
be compared with the light of a stuiidarcl lamp, the candle 
power of which is known under certain conditions of im- 
pressed voltage. To do this, use is made of the physical 
principle that the intersity of a light at any point varies 
inversely as the square of the distance from the source. 
The comparison is made between the standard light and the.t 
of the one to be measured, by placing a screen between them 
which is illuminated by both. The screen is then moved in 
the line connecting the two lights Ujitil the ill--aninations 
on both sides are eq.ual. The distance from the screen 
to each light is noted, and thus the candle power of the 
unknown light can be calculated from the relation that the 
candle powers of the two lights are to each other as the 
squares of their distances from the screen. 

In common incandescent light photometry, the con- 
stancy of the light and the accuracy of reproduction are 
the primary considerations, but in arc light photometry 
the color of the light is of first importance. The criter- 



14 

ion for the accurate arc liglit phot one try is that compar- 
isona be made only between equally lighted and similarly 
colored fields. The impossibility of obtaining any 
standard giving the same colored liglit or any where near 
the same intensity as the arc compels the adoption of other 
methods, to be used in connection with the ordinary photom- 
etric scherae. The incandescent lamp is the one standard 
v/hose quality of light may be made to approach closely to 
that of the arc and that can be easily and accurately 
standardized. This necessitates the balancing of a yellow 
light against that of the arc which varies in color from 
a yellowish V7hite through a white to a bluish white. To 
accomplish this comparison and also obtain instantaneous 
values, if possible, of the light emitted by the arc as 
the current passes through a complete cycle, a form of 
flicker photometer is used in this work. 

The flicker photometer as here used is shown com- 
plete in Print 2. The steel frame, d, rests upon the table, 
c. This fra,me serves as a runway for the two carriages, e 
and i, the former carrying a Lummer-Brodhun screen, f, and 
the latter carrying the standard lamp, b. The arc light 
is placed at the opposite end of the bench, at a. This is 
the machine as described above. The discs, g and h, are 
secured to the shaft, 1, which runs in the bearings, m, n 
and 0. These discs are better shov/n by Print 4. They 
are made of aluminum, and are 20 inches in diameter by 3/52 
of an inch thick. Two of these discs are mounted on the 



eo3lb 38 



15 




PRIHT 2 



_.*'^^-- 



15a 




?RI1. 



16 





Print 4. 



17 

oast iron hub, d, and secured "by the screws, e. TJae slits, 
a, "b and c, are spaced 120 degrees apart and may be adjust- 
ed in size by moving the two disos I'elative to each other. 
The maximuia opening is as shown. 

Referring again to Print 2, these discs are so 
placed that when one of the three slits of h is directly 
between the screen, f, and the standard light, b, one 
slit of disc, g, is 60 degrees from this position. That 
is, at this position of h, the line joining the arc and 
the screen would cut disc, g, midway between tvo slits. 
Thus, as the shaft, 1, is rotated, light is admitted to 
the screen, f , alternately by the standard light and the 
arc. The purpose of this is, as suggested above, to 
illuminate the effects of the two different colors of 
light, and thus to obtain a balance on the screen. Since 
these slits are small, the light passing through them and 
being measured repx'esents practically the instantaneous 
values, as the current of the arc passed through a cycle. 
Thus, one position of the discs gives one point on the 
instantaneous candle power curve. Therefore, it requires 
only to alter the position of the discs relative to the 
armature of the machine ftirnishing the power to the arc, 
to obtain the candle power curve for a complete cycle. 
The Llagnetic Coupling and Contact l.tlcer. 

i*s a means of altering the relative positions 
of the machine armature and the shaft carrying the flicker 



18 

disos, the magnetic coupling shown in Prints 5 and 5 was 
designed and constructed by the authora. This instrument 
not only serves as a coupling "but also as a contact maker. 
Print 5 shows the coupling mechanism while Print 6 shows 
the arrangement of the contact maker. Referring to Print 
5, a is an annular "brass gear having 144 teeth. The driver, 
h, is of "brass and carries the two electro-magnets, d and 
f, (f and d are symmetrical with respect to the axis of 
rotation of b). These two magnets are identical in con- 
struction, and are of the horseshoe type with the coil 
wound on one leg. The coil was wound on a wrought iron 
core 3/8 of an inch in diameter and fitted into the outer 
casing of iron pipe of V/s inch inside diameter and 1 inch 
outside diameter. A cap was riveted to the bottom of the 
core and also to the bottom of the casing, thus completing 
the horseshoe. The armatures of the magnets are of 
wrought iron, and are hinged at g to the clip h, support- 
ing the magnet. An arm projects from the armature through 
the slot, m, in the driver, b, and again is pivoted to a 
bar sliding the full length of b, in a slot l/4 inch deep 
and 9/I6 inch wide. The ends of this bar are constructed 
to fit into the spaces between the teeth of the gear, a, 
and are so £ rranged that when the finger on one end occu- 
pies the space between two teeth, that on the opposite 
end is directly over the point of a tooth. The length 
of this sliding bar is such that in moving from one 
position to the other, the two fingers are never dis- 



, i.(&ia>'. 




k 



.','y^^''^^ 



phi::! 5. 




PRIHT 6. 



ai 



engaged from a tooth of gear, a, at tlie same time, but the 
finger on one end enters the space before that on the other 
end disengages the tooth. When the current is passed 
through the coil of one magnet, the armature is dravm to- 
ward it, thus causing the sliding bar to engage a tooth 
of the gear. It is held in this position as long as the 
current remains in the coil. How if the current be changed 
to the other magnet coil, its armature drav/s the sliding 
bar in the opposite direction, and since the finger on 
this end is directly over a tooth, the friction of the 
parts driven and attached to gear, a, is depended upon to 
cause it to drop back slightly and the finger engages a 
tooth which has moved the gear, a, backward relative to 
the driver, b, through a distance equal to one-half the 
distance between two teeth, i.e., one-half the circumfer- 
ential pitch of the gear teeth. Since there are 144 teeth, 
this distance corresponds to 1-J- mechanical degrees. Thus, 
by shifting the current from one coil to the other of the 
magnets, the space represented by any number of teeth may 
be moved through as desired. 

One terminal of each magnet coil is connected to 
a slip ring carried on the hub of the driver, "b, and in- 
sulated from it. The copper brush, n, slips on this ring 
and thus serves as the common connection to the outside 
circuit. The remaining terminal of each magnet is connect- 
ed to a separate slip ring, one to o and the other to p. 



zz 

Copper brushes again supply a comieotion to the outside 
circuit . A two point switoli serves to control the oper- 
ation of the magnets, and a current of Z^ amperes is suf- 
ficient for successful operation. 

The gear, a, carries on its circumference the 
hai'd ruhber ring, f, (Prints 5 and 6) which is secured to 
it by screws as shown in Print 6. Lt the point, q, in this 
hard rubber ring, a narrow brass strip is inserted, which 
is connected by hidden connections to slip ring, r, on the 
hub of the gear, a, A copper brush, the terminal of 
which is shown at s, makes sliding contact with this ring, 
while a second brush, t, slips upon the circumference of 
the hard rubber ring. At the instant the brush, t, comes 
in contact with point, q., the circuit is closed between 
the binding posts, u and v, if no break exists in the out- 
side circuit connected to these points. The brush, t, 
remains stationary, but the point, q., changes its posi- 
tion relatively when the magnetic coupling is operated. 
Thus, instantaneous values of the current and voltage can 
be obtained as with an ordinary contact maker. 

Print 2 shows the connection of the coupling to 
the disc shaft of the photometer. The gear, a, (Print 6) 
is connected to the shaft, 1, by the universal joint, p. 
For operation, the relative positions of the contact point 
and the disc slits are so adjusted that at the instant of 
contact, the slit on the disc, g, is in the line of the 
arc and screen. This is done by placing the brush, t. 



..:03'x: 



23 



(Print 6) in the correct position where it remains fixed. 

Tlie coupling is mounted upon the wooden pedestal, 
y. Print 7 shows its connection to the rotary converter 
used to drive the apparatus. This connection is made by 
the steel coupling, a, which is fixed to the shaft of 
the driver of the coupling, while on the generator end it 
has a pin which fits into the keyway of the armature shaft, 
and is free to move along the axis of this shaft. This 
does not interfere with the end play of the rotary arma- 
ture. 

The Motive Pov/er. 

The power required to rotate the flicker photom- 
eter discs as described above, is furnished by a 5 E.^. 
wood rotary converter, shown in Print 7 at b. This ro- 
tary has a capacity of 36 amperes at 140 volts at the 
direct current end, and 85 volts at the alternating current 
end. It is a six pole machine and its armature is wound 
for one, two, three or six phases. In this work, the 
rotary is operated as a single phase synchronous motor by 
the machine furnishing the power to the arc. The synchro- 
nizing is arranged for by the lamps, c, in series with one 
side of the line controlled by switch, d. The direct 
current side of the rotary is connected through the start- 
ing box, e, and has an auxiliary rheostat, and single pole 
switch, h, in the armature circuit, jx rheostat, f, is also 
used in the rotary field circuit. By using a rotary in 
this position, a convenient method for synchronizing is 




PRiifr 



afforded, "by getting synohronous speed as a direct current 
motor. 

The Curve Tracing Tatle. 

To obtain the instantaneous values of the voltage 
impressed upon the arc, the method used consists of balanc- 
ing these instantaneous values by the direct current volt- 
age of the storage batteries. To obtain the instantaneous 
values of the current through the arc, a known resistance 
is inserted in series with it and the drop over this re- 
sistance balanced, as in obtaining the instantaneous 
values of the voltage against the voltage of the storage 
batteries. Since this kiiovm resistance is non-inductive, 
the current is then easily calculated by Ohn's law, for 
each value of the drop obtained. 

The connections of the curve tracing table are 
shown on Print 8. The leads from the storage batteries 
are brought to the binding posts, a, which are connected 
to one side of the potential rheostat, c, through the 
double pole switch, b. The remaining side of the rheostat 
is connected to the middle points of the double throw 
switch, t. Across these same points, the terminals of the 
voltmeter, d, through the contact switch, e, which pei-mits 
the use of either scale of the voltmeter. In series with 
the switch, t, are connected the galvanometer, f, the con- 
tact key, h, and the contact maker, which is connected 
between the binding posts, i. The voltage to be measured 
is brought to the binding posts, s, v/hich serve as the 




PRINT 8. 



27 



terminals of IE sixteen candle power incandescent lamps 
in series. The drop over two of these lamps is used in 
balancing. The leads across these lamps are shown at the 
"binding posts, k, which are connected to the switch, m. 
The connections to the switch, n, and to the galvanometer 
circuit are shov/n and are such that with switches, m and n, 
as shown, the instantaneous values of the alternating 
voltage mfy he balanced against the storage battery volt- 
age by means of adjusting the rheostat, o. The balance 
is shown by no deflection of galvanometer, f, when the 
key, h, is closed. The voltmeter, d, then reads the in- 
stantaneous values of the voltage, which multiplied by 
ratio of the number of lamps used, gives the total volt- 
age at that instant. The binding posts, j, are connect- 
ed across the terminals of the known resistance mentioned 
above. V/ith switch, 1, in position shown, the drop over 
this resistance may be thrown across the galvanometer cir- 
cuit by throwing switch, n, to the right, v/hich at the 
same time opens the pressure circuit. The balance and 
reading are obtained as before. 

The voltmeter, q., is used in synchronizing, and 
is BO connected that it may be thrown across the genera- 
tor or motor terminals by means of the single pole double 
throw switch, p. The switch in the position shown places 
trie voltmeter across the motor terminals. The voltmeter, 
0, is connected to the terminals of electric tachometer 
by which the speed at any instant is determined. The 



28 



The small two point key, g, controls the magnets of tlie 
magnetic coupling. Point 1 is counected tlirough three 
storage cells to the common ring of the coupling described 
ahove, while points 2 and 3 are connected respectively 
to rings 1 and S. The coupling is reversed hy moving 
the key from 2 and 2 and vice versa. 

The Known Resistance. 

The resistance used for measuring the instant- 
aneous values of current consists of tv/o twelve inch 
carbon rods, one-half inch iu dianeter, connected in series, 
This is inserted in series with the arc, and tv/o pressure 
leads run from its terminals to the curve tracing table. 
The Regulation of the Current. 

Ill series \iith tlie arc, there is a carbon rheo- 
stat and a low inductive coil. This coil is suspended 
by a steel v^ire over a laminated iron core, about which 
it may be moved up or down by means of a count erv?eight 
to vary its impedence. In this way, the current through 
the arc is kept constf-rt. 

Tne above described apparatus was carefully test- 
ed, each part by itself, and under operating conditions, 
before any tests v/ere made on the actions of the arc it- 
self. 



. 1)0^. 



E9 



GALIBKATIOII OF THE ST^TDaRD LAllP. 

The light used as a standard is thtit of a 110 
volt 50 candle power incandescent lamp. It is designed 
for electric headlight and has a spherical globe, while 
the filament is wound in the shape of a spiral cone. 
This lamp was calibrated on the photometer bench by means 
of a 16 candle pov/er standard incandescent lamp, which 
was standardized to give 16 candle pov/er at 102 volts. 

It vas proposed that instead of varying the posi- 
tion of the photometer sci-een to obtain a balance, the 
candle pov/er of the standard lamp be changed by varying 
the voltage impressed upon it. ^ curve plotted betv/een 
Candle power and voltage could then be used and the 
light given off by the lamp be read off of this curve 
directly. To calibrate the lamp in this v/ay, five 
different tests were made at different times, between 
which was a sufficient period to rest the eyes of the 
observer. Sach bench reading recorded is the average 
of two different settings of the photometer screen. 
Tlie average of the five recorded values was used to 
calculate the candle power for that corresponding 
voltage. The following curve shows the relation of 
the candle power of the lamp and the voltage impressed 



20 



upon it. 

From this curve and the data from v/hioh it is 
constructed, the ujiifomiity and consistency of the var- 
iations are very evident. That is, for a given im- 
pressed voltage, the 0c.ndle pov/er of the li.up is con- 
stant under normal conditions. 



31 



G-o.LIBr;i.TIOII OF THE STxJDaPvD L^^iP. 

Standard lamp used #E30, 16 c.p., at 102 volts, position 1. 

£ Standard to Screen Centimeters. 

12 3 4 5 Average C.P. 

75 171.5 170.8 171.1 170.4 171. i3 171.06 S.42 

80 150.4 160.2 160.3 160.6 159.5 160.02 5.05 

85 142.2 14S.2 142.2 142.0 142.5 142.06 8.80 

90 135.1 125.1 125.8 125.8 125.1 125.28 11.50 

95 122.1 122.0 122.4 122.7 122.9 122.22 16.90 

100 111.7 111.2 110.6 110.8 110.4 110.94 25.25 

105 100.8 100.8 1G0.6. 100.4 ICO. 4 100.60 201.80 

110 91.5 91.2 81.9 92.2 91.7 91.54 47.90 

115 82.2 82.4 82.5 82.2 82.5 82.28 6G.50 

Distance from screen to lamp laeing calibrated 

equals 250 Centimeters - Distance standard to screen. 



32 



THE ARC FROM A PEAEED WixVE. 

A peaked pressure wave, because of its applica- 
bility to systems in v/hicli transformers must be used, 
should be very suitable to arc lighting systems on uhioh 
the distance of transmission is comparatively short. 
However, it would be expected that on account of the 
great variation in the instantaneous values of the volt- 
age, the variation of the light given out by an arc oper- 
ated on such a wave v/ould be more noticeable than on a 
flat top wave. 

It was found by operating the arc under test in 
this Work from a generator giving a wave form which was 
very peaked, that the most satisfactory results were ob- 
tained with regard to regulation and steadiness of the 
arc. The instantaneous values of the candle power of 
the arc at different positions on the wave seem to be 
governed to a great extent by the action of the carbons. 
ITo distinct v/ave form of candle power was obtained which 
followed very closely that of the current producing it. 
On the other hand, a candle power curve was obtained 
which seemed to be independent of the current curve. 

In some instances, the maximum candle pov/er was given 
out at the aero values of the cxirrent. This result may 



33 



be attributed to some extent to the difficulty in "bal- 
anoing two different colors of light on the photometer 
screen. This however was reduced greatly by the use 
of the rotating discs which have been fully described 
above. 

The generator used to give this wave form is 
a Westinghouse single phase machine with a normal volt- 
age of 1000 at 1000 revolutions per minute. For this 
work, it was operated at 600 revolutions per minute so 
as to obtain the frequency desired and generated a volt- 
age of 800. This was stepped down through a 77esting- 
house transformer of 18f II.W. to 80 volts, which was 
applied directly across the arc and its regulating ap- 
paratus. This pressure gave an arc operating under 
the normal open arc current of 9.6 amperes and consuming 
450 watts which is the nominal rating of a 2000 candle 
power arc light. The voltage req.uired to maintain these 
conditions was 49. The arc was rotated at about EGO 
revolutions per minute throughout the period of taking 
the bench readings and the instantaneous values of the 
current and voltage. The instantaneous values of the 
voltage v/ere taken directly over the arc. 

The follov/ing curves show the relation between 
the candle powei; current and voltage over the arc. On 
the same sheet is given the curve showing the wave form 
of the voltage used. 



34 



Arc operated at 9.6 amperes, 49 volts, 450 watts, 40 p.p.s. 
by Weatingiiouse alternator #2441. normal 1000 volts, 45 
amperes, 1000 R.P.K. , 66 p.p.s. 
Candle power of standard - 48 at 110 volts. 



Magnetic 


Instantaneous 


Bench Re 


lading cm. 


Instantaneous 


Degrees 


Yoltage 


Current 


To ^rc 


To Std. 


candle pov/er 











272.4 


52.2 


1310. 


7.5 


20.3 


5.5 


278.5 


46.1 


1750. 


15.0 


36.3 


7.7 


280.4 


44.2 


1940. 


22.5 


55.0 


11.7 


289.0 


35.6 


3180. 


30.0 


63.8 


12.6 


291.4 


33.2 


3680. 


37.5 


63.8 


19.4 


290.6 


34.0 


3525. 


45.0 


58.0 


29.5 


291.9 


32.7 


3830. 


52.5 


58.0 


28.9 


288.2 


36.4 


3030. 


50.0 


55.1 


11.1 


294.4 


30.2 


4575. 


67.5 


39.7 


14.5 


294.1 


30.5 


4600. 


75.0 


42.5 


8.0 


286.4 


38.2 


2720. 


82.5 


33.1 


9.2 


258.9 


65.7 


750. 


90.0 


33.3 


21.2 


276.8 


47.8 


1610. 


97.5 


31.9 


22.6 


290.4 


34.2 


3475. 


105.0 


39.2 


23.2 


285.9 


38.7 


2625. 


112.6 


33.1 


31.7 


282.1 


42.5 


2120. 


120.0 


31.3 


24.6 


282.3 


42.3 


2150. 


127.5 


20.8 


17.9 


283.8 


40.8 


2325. 


135.0 


37.7 


4.9 


294.3 


30.3 


4540. 


142.5 


45.8 


.2 


296.5 


28.1 


5350. 


150.0 


34.8 


.1 


294.6 


30.0 


4625. 


157.5 


76.5 


.1 


297.3 


27.3 


57C0. 


165.0 


63.8 


.1 


295.8 


28.8 


5050. 


172.5 


58.0 


0. 


293.8 


30.8 


4375. 


180.0 


0. 


0. 


291.4 


33.2 


37C0. 


Hesistanc 


e over which current drop 


was taken 


- .325 ohms. 



35 



THE E. M. P. lUYK OF THE WESTIKGHOUSE ALTERNATOR #2441 

DATA. 
Magnetic Degrees Instantaneous Voltage 









4 


6 


6 


12 


12 


15 


16 


19 


ao 


24 


24 


30 


28 


35 


32 


44 


36 


52 


40 


58 


44 


64 


48 


74 


5E 


8S 


56 


99 


60 


118 


64 


135 


68 


154 


72 


171 


76 


186 


80 


195 


84 


201 


88 


203 


9£ 


202 


96 


198 


100 


193 


104 


184 


108 


166 


112 


150 


116 


132 


120 


114 


124 


100 


128 


85 


1S2 


70 


156 


63 


140 


57 


144 


46 


148 


35 


162 


32 


156 


26 


160 


EO 


164 


13 


168 


11 


172 


7 


176 


3 


180 


-2 



d 



37 



THE .iRC FROL: ^ FLLT TOP '.7^VE. 

IThe flat top v/ave of E. LI. F. is in modern praooioe 
prolDa'bly the one wtLich is most desired for lighting sys- 
tems. This results from the faot that it may be easily 
adapted to all classes of woi-k and especially for long 
distance transmission. ^s compared to the peaked wave, 
the light given out from an arc operated on a flat wave 
would "be expected to "be steadier and of a more desirable 
quality. 

A generator giving a flat top wave was used l;o 
supply the arc under test and the results obtained follow 
to some extent in a general way those obtained from the 
peaked wave previously discussed. Some difficulty v/as 
encountered in obtaining a candle power curve from which 
any conclusions could be drawn. 

The generaoor used to r-ive the flat top v/ave is 
a General Electric three phase machine v;ith a normal volt- 
age of 1S6 at ISOO revolutions per minute. For this v;ork, 
it was operated at 800 revolutions per minute and a single 
phase used. The machine is of the revolving field type 
and has six poles. Thus, under the above conditions, the 
frequency of 40 cycles per second was obtained. The arc 



38 



was operated ae before at the nornal open arc current 
of 9.6 amperes and a pressure of 49 volts \ms required to 
maintain tlie 2000 candle power rating of 450 watts. The 
carbons v/ere rotated at about 200 revolutions per minute 
during the period of obtaining the bench readings and in- 
stantaneous values of current and voltage. 

The following curves show the relation Letv/een the 
candle power, current and voltage over the arc. On the 
Scixie sheet is given the curve shov/ing the wave form of the 
voltacre used. 



39 

EEE ARC FROM ^ FI^T TOP WAVE. 

Aro operated nt 9.6 amperes, 49 volta, 450 watts, 40 p.p.s. 
by General Electric alternator #65447. lomal 1£0 volts, 

72 amperes, 1200 revolutions per minute, 60 p.p.s. 
Candle power of standard - 48 at 110 volts. 



Kagnetic 


Instantaneous 


Bench Reading cm. 


Instantaneous 


Degrees 


Yoltage 


Current 


To iirc 


To Std. 


candle pov/er 











274.7 


49.9 


1457. 


7.5 


6.2 


1.5 


276.3 


48.3 


1580. 


16.0 


15.8 


3.8 


282.0 


42.6 


£110. 


22.5 


18.5 


4.9 


286.8 


37.8 


2760. 


30.0 


36.1 


8.0 


291.6 


33.0 


3750. 


37.5 


58.8 


8.4 


293.1 


31.5 


4160. 


45.0 


65.8 


10.6 


294.9 


29.7 


4740. 


52.5 


69.6 


11.0 


£94.0 


30.6 


4440. 


60.0 


68.7 


13.6 


395.8 


27.8 


5470. 


67.5 


58.2 


15.6 


259.1 


65.5 


750. 


75.0 


62.5 


16.7 


259.0 


65.6 


748. 


82.5 


62.6 


16.7 


259.0 


65.6 


748. 


90.0 


55.4 


14.8 


263.4 


61.2 


892. 


97.5 


58.8 


16.4 


270.6 


54.0 


1252. 


105.0 


61.5 


17.1 


276.4 


48.2 


1580. 


112.5 


71.2 


16.4 


277.5 


47.1 


1667. 


120.0 


61.6 


15.6 


269.3 


55.3 


1140. 


127.5 


60.7 


14.4 


263.7 


70.9 


618. 


125.0 


59.8 


12.6 


244.0 


80.6 


441. 


142.5 


58.2 


1C.6 


254.4 


70.2 


632. 


150.0 


55.4 


8.0 


261.9 


62.7 


840. 


157.5 


60.0 


4.9 


267.8 


66.8 


1066. 


165.0 


33.5 


3.0 


271.3 


53.3 


1250. 


172.5 


11.4 


1.1 


272.5 


52.1 


1315. 


180.0 


0. 


0. 


274.7 


49.9 


1454. 



Resistance over whicli current drop was taken - .326 ohms. 



40 



Ihe E. M. F. Wave op THE GEI^ERaI. ELECTRIC aITERUaTOR #G5447 

li^Tix. 
Magnetic Degrees Instantaneous Voltage 









6 


8 


12 


16 


18 


21 


24 


24 


SO 


34 


26 


44 


42 


46 


48 


50 


54 


53 


60 


65 


66 


76 


72 


74 


78 


76 


84 


68 


90 


76 


96 


78 


102 


74 


108 


74 


114 


68 


120 


74 


126 


66 


132 


66 


138 


52 


144 


44 


150 


42 


156 


32 


162 


28 


168 


22 


174 


16 


180 


6 


186 


-12 



^1.^ 



&■.: j'x, -A 



42 



COtilPAKISOII OF THE RESULTS OBT^.IHED FEOIJ THE FLaT TOP -uBD 
PEiJaSD E. K. F. iLLYEZ, 

The action of the arc liiider tlie flat top and peaked 
E. M. F. waves may "be compared "by observing the curves 
given on pages 36 and 41. Under both forms, tlie effects 
of the arc upon the current curves are very similar. The 
single peak anticipated in both oases has been replaced 
lay two separate peaks. This is especially noticeable in 
the current curve of the peaked S. M. F. , given on page 
36. It is only slightly shown on the current curve of 
the flat top B. M. F. wave given on page 41. The same 
result is observed in the arc voltage curve. It will be 
noted that the candle pov/er of the aro tinder the peaked 
wave lags behind the current while under the flat top v/ave 
the first peak obtained leads the current to a slight ex- 
tent. 

The sudden drop iu the candle pov/er curve on page 
41 can not be satisfactorily explained. It is the opinion 
however that it is due to the effect of the carbon alone. 
Solid carbons were used in both cases, and were practically 
of the same hardness. 



43 



AMOTATIOTIS. 

It is a disappointment to the authors that do little 
has "been accompli shed along the escperimental determinations 
pertaining to this suhject. It v^as the desire to make 
more extensive tests but owing to the fact that almost all 
the time given to this work was consumed hy the designing 
and making of the greater part of the apparatus, very- 
little remained to he given to the experimental wox'k. The 
apparatus as it now stands completed requires hut few al- 
terations in the mechanical features to insure satisfactory 
operation in every respect, ^e recommend that the magnet- 
ic coupler he replaced hy one larger, hoth mechanically 
and magnetically, as its duty is heavier that was pre- 
supposed. 

We desire to thank Prof. G. E. Freeman, Prof. Snow, 
Prof. E. H. Freeman, and llr. Somiaers for their many val- 
uable suggestions. We also wish to eagoress our appre- 
ciation to Kr. Tyler, a class.nate, for his assistance in 
our experimental efforts. 

H. E. Brashares. 
J. R. io-mstron?.