circuits to iron, to withstand for one minute at 20 deg. Cent, the
application of the following R.M.S. voltages :
Rated Voltage. Test Voltage.
Incidentally the assertion is made that low reactance voltage
greatly outweighs in importance low armature strength so far as
relates to excellence in commutation, and high commutator
peripheral speeds are advocated on account of the very great im-
provement in commutating constants thereby rendered practicable.
Careful attention to all these different considerations still permits
of a fair degree of interchangeability and uniformity in the designs
for different voltages of the same kilowatts output.
The paper treats in considerable detail of the author's (*) method
of estimating the reactance voltage. The following principles
underlie this method : Experiments on various arrangements of
armature slots of a wide range of shapes and sizes, with variously
proportioned coils arranged in many ways with respect to these
slots, have shown that the number of c.g.s. lines of magnetic flux
* This method of estimating the reactance voltage is based upon substanti-
ally the same principles as the method published two years ago by Mr.
H. F. Parshall and the present writer. The novelty in the method, as
then described by them, consisted chiefly in starting from the basis of
representative values for the inductance, as expressed in terms of the
lines set up per ampere turn per unit of length of laminations, and it led
to substantially the same results as one obtains by the method in its
present form. As now set forth, it allocates the components of the in-
ductance in the " free " and " embedded " lengths respectively, giving
guiding values for estimating these components, and supporting them by
fairly thorough tests and by experience gained in applying the method to
a great variety of machines, so that now, it is believed, the method may
be employed still more effectively.
336 MODERN COMMUTATING DYNAMO MACHINERY.
set up per ampere-turn of these coils may, as an average, be
4.0 lines per centimetre of " embedded " length.
0.8 " free "
The tests made showed a very much smaller range of variation
in these values for different proportions than has generally been
considered to be the case ; hence, while in abnormal cases modified
values should be taken, one may, nevertheless, in the great majority
of designs, make an amply sufficient approximation to the reactance
voltage by the use of these average values. In the course of the
description of this method, the following rather interesting con-
clusion is pointed out :
The inductance of a coil laid upon the surface of the armature
i.e., on the lines formerly so frequently employed, and sometimes
nowadays termed " smooth core " construction is, with customary
proportions, rarely much less than one-third, and often one-half
or more as great as in the case of the same coil laid in slots.
This conclusion follows from the experimental result that with
ordinary open slots, with parallel sides, of the proportions generally
found in modern continuous-current generators, the inductance per
centimetre of " embedded " length is generally only some 4 to 6
times greater than the inductance per centimetre of " free " length,
and with the dimensions of face conductors and end connections
nowadays generally used, the inductance of the " free " length is
a very considerable percentage, say 25 to 40 per cent., of the total
inductance of a coil.
After illustrating these methods and principles by data of a
number of designs of machines of all sizes, the paper takes up the
consideration of the case of large high-speed commutating machines,
and it is stated that, by the employment of high armature reaction
(as expressed in armature ampere-turns per pole piece), and high
commutator peripheral speeds, even 600 volt machines of large
capacity may be designed with excellent commutating properties
for high speeds.
The paper closes with mention of the large number of ratings
required to meet all the present commercial requirements for a
line of small motors, and expresses the opinion that it is false
economy not to admit at the outset the magnitude of the under-
taking of manufacturing such a complete line.
The Discussion on this paper was combined with that on the
paper by Mr. H. A. Mavor (see p. 340).
The author replied at the meeting and by correspondence, and
a vote of thanks was accorded to him.
" DESIGN OF CONTINUOUS-CURRENT DYNAMOS."
Paper by HENRY A. MAYOR.
THE present methods of designing dynamos and recording results
do not readily lend themselves to comparison of machines of
different outputs. It would, therefore, be of advantage if a
suitable unit of comparison could be devised, and it is suggested
that a consideration of the continuous-current dynamo, leaving out
of account all the non-essential elements of design and construction,
and concentrating attention upon the vital portion of the machine
which alone is concerned in the direct generation of energy, would
lead to a suitable basis of comparison.
It is therefore proposed to consider as a whole the region
occupied by the armature conductors in the magnetic field. This
region may be named the " active belt " of the armature. It is
bounded by the peripheral surface of the armature, the surface of
the core at the bottom of the slots and the ends of the core. An
examination of the machine in the terms ot- the energy generated
in this " active belt " leads to the interesting result that machines
of very widely varying size, output, and speed, give a remarkably
constant value in watts generated per cubic centimetre at unit
velocity in unit field. This constant may be expressed in symbols
/-i \ -rr
" vdls x Trdn x F
The value of the constant K must be a compromise between
economy in first cost and efficiency of radiation of lost watts. The
maximum value gives zero electrical efficiency; the maximum
possible output of the machine is at half this value.
A reduction of value of the constant leads to increased quantity
of material, increased cost of construction, and increased electrical
efficiency. A consideration of the dynamo from this point of view
suggests increase in the depth of the " active belt/' reduction in the
watts generated per cubic centimetre, and reduction in the depth
of the core so as to minimise hysteresis and eddy current losses in
the core, with consequent increase in diameter and multiplication
of the number of poles. A comparison between the results obtained
by different designers of the proper value of this constant should
338 DESIGN OF CONTINUOUS-CURRENT DYNAMOS.
be of immediate interest. It will be noted that this consideration
includes the radiation of all lost energy from the surface of the
armature, the value being the total watts generated by the machine.
The total electromotive force of the machine in volts is given by
(%} E = % ir( 'WFG mn
~~p x 10 8
The reactance voltage of any machine considered on the lines
of Messrs, Parshall & Hobart's book on " Electric Generators ; '
may be ascertained by a very simple calculation. Assuming a
sine wave form for the fluctuations in the current under com-
mutation, the value of the reactance voltage is given by the
(3)r = h
p x 10 8
and from 2 and 3
The value of the field / due to the current under commutation
is probably not so constant as indicated in the work above referred
to, but any desired correction may be made on this factor by
introducing the relation between the depth and width of the slot
or any elements which the designer may consider it necessary to
introduce. The value of F, the average field, per unit surface of
the core being practically constant, the reactance voltage of any
machine can be ascertained practically by inspection. This formula
(4) indicates that the reactance voltage is not subject to much
modification for any given output.
The average emf generated in m turns of the winding
In lap wound armatures e equals difference of potential between
adjacent sections of the commutator.
In wave wound armatures the difference of potential between
adjacent sections of the commutator equals
From these formulae are derived
/cx GmC K x irds x 10 8 A
(o) - = - - - = Ampere turns in the armature.
(From 1 and 2.)
DESIGN OF CONTINUOUS-CURRENT DYNAMOS. 339
< 7 > f = ~jS^- (^-3 and 5.)
(8) 1 K ^ Q8 . (Prom 1, 4, and 5.)
Curves are plotted of 7, 8, and 9, showing the relation of ampere
turns on armature, slot depth and armature dimensions, to the
reactance voltage and e.m.f. between commutator segments.
Turning now to the consideration of cost, it is found that in the
case of many groups of machines there is no regular ratio between
the cost and the output. There ought to be such a regular
relation, and the following method is suggested for obtaining this
Plotting watts per revolution as abscissae and costs as ordinates,
the position of each machine is marked, and the points representing
cost and output for each carcase of a given diameter with varying
length are joined by a straight line which is produced to the origin.
The point where this line cuts the zero ordinate gives the limit of
cost to which this carcase approaches as the core length is reduced
to zero, and may be called the base cost of any given carcase;
the slope of the line drawn through the costs of the machine at
different lengths show the cost per inch length of " active belt "
on that carcase. Increase of diameter increases the base cost and
reduces the slope of the line passing through the costs of the actual
machines, so that, starting from the smallest diameter and passing
to the largest, will give a succession of straight lines, each touching
its next lower neighbour at one point, and producing a curve made
up of segments of the lines representing each machine, each
segment showing the economical range of length for the machine
which it represents.
Symbols used in this Paper.
A = Length of air space.
b = The maximum number of sections of commutator covered
by the brush.
C = Total armature current in amperes.
d = Diameter of core measured to the middle of the active
belt in centimetres.
e = Average e.m.f. generated in m turns of the winding
E = Total e.m.f. generated by armature in volts.
f = Induction Field in c.g.s. lines per centimetre length of
slot, due to one complete turn.
340 DESIGN OF CONTINUOUS-CURRENT DYNAMOS.
F Average Flux taken over the whole surface of the
armature, in c.g.s. lines per square centimetre.
G = Number of sections in the commutator.
K = Watts generated per cubic centimetre of active belt
at unit velocity in unit field, called energy factor.
I = Nett length of armature core in centimetres.
m = Armature turns per commutator section.
n = Eevolutions of armature per second.
P = Number of poles in magnets.
p = Number of paths through armature.
r = Eeactance voltage.
s = Depth of slot in centimetres.
E = 6Qn = revolutions per minute.
W = E C = Total watts generated by active belt.
The Discussion on this paper was combined with that on Mr.
Hobart's paper, and was taken part in by the following members :
Mr. H. A. Mavor, Mr. Gisbert Kapp, Professor Silvanus P.
Thompson, Mr. W. A. Chamen, Mr. W. B. Sayers, Col. R. E.
Crompton, and Mr. W. B. Esson (communicated).
The authors replied, and a vote of thanks was accorded to them.
The following votes, proposed by the President, were passed:
(first) that the thanks of the members of the Section be given to
Dr. Caird and the Committee of the Congress, and to the General
Secretary, for the admirable arrangements made both for the
comfort and convenience of the members, and (second) that the
best thanks of the Institution of Electrical Engineers be given to
the University of Glasgow and to Professor Gray for the use of
the Natural Philosophy Theatre for the meeting.
A vote of thanks was also accorded to the President on the
motion of Professor Jamieson.
This closed the business of the Section.
List of Societies and Institutions in Great Britain and
Ireland which took part in the Congress.
The Aberdeen Mechanical Society.
The Cleveland Institution of Engineers.
The Glasgow University Engineering Society.
The Glasgow and West of Scotland Technical College Scientific
The Hull and District Institute of Engineers and Naval
The Incorporated Association of Municipal and County
The Incorporated Gas Institute.
The Incorporated Institution of Gas Engineers.
The Incorporated Municipal Electrical Association.
The Institution of Civil Engineers.
The Institution of Civil Engineers of Ireland.
The Institution of Electrical Engineers.
The Institution of Engineers and Shipbuilders in Scotland.
The Institution of Junior Engineers.
The Institute of Marine Engineers.
The Institution of Mechanical Engineers.
The Institution of Mining Engineers.
The Institution of Naval Architects.
The Iron and Steel Institute.
The Liverpool Engineering Society.
The Manchester Association of Engineers.
The Mining Institute of Scotland.
The North British Association of Gas Managers.
The North-East Coast Institution of Engineers and Shipbuilders..
The Royal Engineers Institute.
The Society of Engineers.
The South Wales Institute of Engineers.
The West of Scotland Iron and Steel Institute.
List of Foreign and Colonial Delegates and
Australasian Institute of Mining Engineers, Melbourne.
James Stirling, 15 Victoria Street, Westminster, London, S.W.
Victorian Institute of Engineers.
George Higgins, 60 Martel Street, Melbourne, Victoria, Australia.
R. W. Richards, City Surveyor, Sydney, N.S.W.
J. M. Smail, Chief Engineer to the Metropolitan Board of Works,
Ministry for Education and Public Worship.
Professor Karl Hochenegg, Technical High School, Vienna.
Ministry for Railways.
Oesterreichischer Ingenieur-und Architekten Verein Vienna.
Professor Fritz Edler von Emperger, Technical High School,
Oskar Guttmann, 12 Mark Lane, London, E.G.
C. de Kierzkowski- Stewart, 17 Victoria Street, Westminster,
F. Krauss, Seilerstrasse 11, Vienna, I/I.
J. Spacil, 1 Zollamtstrasse, Vienna, HI/2.
Karl Jenny, Chief of Locomotive Shops, Austrian Southern Bail-
Emil Kolben, Vysocan-Prag, Austria.
M. Pichler, Chief of the Construction and Traffic Department,
Austrian State Railways, Vienna.
M. G. Rank, Fuhrmannsgasse, Vienna, VIII/2.
A. Smreck, Belcredi Strasse, 831, Prag, Austria.
344 FOREIGN AND COLONIAL DELEGATES
Minis tere des Finances et des Travaux Publics.
J. Troost, Inspecteur General des Fonts et Chaussees, Bruxelles.
J. Pierrot, Directeur des Fonts et Chaussees, Bruxelles.
L. Van Gansberghe, Directeur des Fonts et Chaussees, Ostend.
H. Vander Vin, Ing6nieur Principal des Fonts et Chaussees,
Ministere des Chemins de Per, Posies et Tdegraphes.
M. Gerard, Ingenieur en Chef,f.f. d'Inspecteur Gen6ral, Bruxelles.
M. Van Bogaert, Ingenieur Principal, Bruxelles.
Ministere de l'Indust?ie et du Travail, Bruxelles.
J. F. Demaret, Ingenieur Principal, Corps des Mines, Bruxelles.
M. Libert, Ingenieur en Chef, Corps des Mines, Bruxelles.
V. Watteyne, Ingenieur en Chef, Corps des Mines, Bruxelles.
Societe Geologique de Belgique, Liege.
Professor A.. Habets, 4 Eue Paul Devaux, Liege.
Societe Beige de Geologie, de Paleontologie et d'Hydrologie, Bruxelles,
Ernest Van den Broek, S6cretaire-General, 39 Place de 1'Industrie,
Association des Ingdnicurs Sortis de I'Ecole de Litge.
Adolphe Greiner, General Manager, Soci6t6 Anonyme John
Cockerill, Seraing, Belgium.
Association des Gaziers Beiges, Lidge.
M. Boscheron, 13 Eue Simon, Liege.
M. Busine, Boulevard Baudoire-le-Batisser, Mons.
M. Escoyez, Tertre-lez-Baudour, Belgium.
M. Salomons, 133 Chaussee d'lxelles, Bruxelles.
M. Tricot, Directeur de 1'Usine & Gaz de Mons, Mons.
M. Trifet, Administrateur, D6legu6 de la Societ6 des Usines a Gaz
M. Van Heede, Usine a Gaz de Koekelberg-Bruxelles, Belgium.
M. Verstraeten, 26 Eue Marie de Bourgogne, Bruxelles.
AND HONORARY MEMBERS. 345
Soctitt des Ingtnieurs Sortis de I' E cole Provincial* d' Industrie et des
Mines du Hainaut.
Professor Henry Van Laer, 83 Eue de Berckmons, Bruxelles.
E. Bouillon, Chef du Service des Voies et Travaux, Soci6t6
Nationale des Chemins de Fer, Vicinaux, Bruxelles.
Emile Harze, 213 Kue de la Chaussee, Bruxelles.
A. Heyland, 32 Eue du Marteau, Bruxelles.
John Kraft de la Saulx, Seraing, Belgium.
A. Lecointe, 38 Eue Albert, Ostende.
L. Petit, Ingenieur-en-Chef de la Traction et du Material, Soci6te
Nationale des Chemins de Fer, Vicinaux, Bruxelles.
E. Putzeys, Ingenieur-en-Chef, Directeur de la Ville, Bruxelles.
E. de Eudder, Ing6nieur-en-Chef des Voies et Travaux, Chemins
de Fer de 1'Etat, IJruxelles.
Jules Semol, 148, Eue Gollait Bruxelles.
Gustave Wolters, Universite de Gand, Gand.
BRITISH CENTRAL AFRICA.
Percy Cullen, Fort Johnston, British Central Africa.
Canadian Society of Civil Engineers, Montreal.
G. C. Cunningham, Tramway Office, Birmingham, England.
James Eoss, 877 Dorchester Street, Montreal.
E. O. Wynne-Eoberts, City Engineer, Cape Town.
Francis A. Cooper, Director of Public Works, Colombo.
Eobert Skelton, Municipal Engineer, Colombo.
Alejandro Bertrand, 41 Victoria Eoad, Kensington, London, W.
C. Mayne (Shanghai), c/o Mrs Bartlett, Church Street, Steyning
346 FOREIGN AND COLONIAL DELEGATES
J. O. V. Irminger, Gas Works, Copenhagen, Denmark.
C. Hummel, Engineer of Danish State Maritime Works, Copen-
H. A. E. Elben, Engineer-in-Chief, Way and Works Department,
Danish State Eailways, Copenhagen.
Captain A. Easmussen, E.D.N., Eoyal Dockyard, Copenhagen.
Professor C. Ph. Teller, Hellerup.
Dansk Ingenitor Forening, Copenhagen.
C. E. Oellgaard, 32 Oestersogade, Copenhagen K.
G. A. Hagemann, 51 Bredgade, Copenhagen K.
Christian Otterstrom, Helenevig 5, Copenhagen.
Captain J. C. Tuxen, E.D.N., Eoyal Dockyard, Copenhagen.
Tekniska Foreningen i Finland, Hetsingfors.
Baron K. E. Palmen, Forssa, Finland.
Minis tere de la Marine,, Paris.
M. Berrier-Fontaine, Directeur du Genie Maritime, Paris.
M. Bertin, Directeur du Genie Maritime, 8 Eue Garanciere, Paris.
M. Pollard, Directeur de 1'Ecole d'Application du Genie Maritime,
M. de Courville, Attach6 a la Section Technique des Construc-
tions Navales, Paris.
M. de Miniac, Directeur des Travaux Hydrauliques du Port de
Brest, Brest, France.
M. Callou, Ingenieur en Chef de la Marine, Portrieux (c6te du
Ministere des Travaux Publics.
Baron Quinette de Eochemont, Inspecteur - Gen6ral des Ponts
et Chaussees, 43 Avenue du Trocadero, Paris.
M. Eibi&re, Ingenieur en Chef des Ponts et Chaussees, Paris.
Sodtti des Ingenieurs Civils de France.
E. Cornuault, 10 Eue Cambaceres, Paris.
M. Jannettaz, 78 Eue Claude-Bernard, Paris.
M. Eegnard, 53 Eue Bayen, Paris.
AND HONORARY MEMBERS. 347
Societt de V Industrie Minerale, ^aint Etienne.
M. Le Neve Foster, Llandudno, North Wales, England.
M. Verney, Ingenieur Civil des Mines, St. Etienne.
Societt Geologique de France.
Professor J. Bergeron, 157 Boulevard Haussmann, Paris.
Association Technique Maritime.
A. Normand, 67 Eue du Perrey, Havre.
E. Bertin, 8 Eue Garanciere, Paris.
Socittt d' Encoviragement pour I' Industrie Nationale.
M. Eoze, 62 Eue du Cardinal, Paris.
Societt Technique de V Industrie du Gaz en France.
E. Cornuault, 10 Eue Cambaceres, Paris.
Fernand Bruyere, 65 Eue de Provence, Paris.
C. H. Baudry, Eue Blanche 19, Paris.
Georges Bechmann, 9 Place de l'Hotel-de-Ville, Paris.
Voisin Bey, Eue Scribe 3, Paris.
M. Briere, Ingenieur-en-Chef de la Voie et des Travaux, Chemin
de Fer d' Orleans, Paris.
C. J. Canet, 42 Eue d'Anjou, Paris.
M. Chevalier, Ingenieur-en-Chef des Travaux, Compagnie des
Chemins de Fer Departmentaux, Paris.
M. Comble, Ingenieur-en-Chef de la Traction Compagnie des
Chemins de Fer Departmentaux, Paris.
V. Daymard, 6 Eue Auber, Paris.
L. de Bussy, Eue de Jouy 7, Paris.
Haton de la Goupilliere, Boulevard St. Michel 60, Paris.
F. B. de Mas, Avenue Jules Janin 8, Paris.
M. Denis, Ingenieur-en-Chef de la Voie, Chemin de Fer Paris,
Lyon et de la Mediterranee, Paris.
A. de Montgolner, St. Chamond, Loire, France.
L. Fevre, Ingenieur au Corps des Mines, Arras. France.
X. Gosselin, Eue de St. Quentin 12, Paris.
M. Goupil, Ingenieur-en-Chef de la Voie, Chemin de Fer de
1' Quest, Paris.
Adolphe Guerrrd, Eue Picot 8, Paris.
P. Holts, Eue de Milan 24, Paris.
F. Hospitaller, Eue de Chautilly 12, Paris.
Maurice Levy, Avenue du Trocc*dero 15, Paris.
348 FOREIGN AND COLONIAL DELEGATES
C. Linder, Eue de Eennes 44, Paris.
Prof. E. Mascart, Eue de 1'Universite 176, Paris.
P. Mengin-Lecreulx, Eue de Eennes 148, Paris.
L. Eibourt, Eue Caumartin 64, Paris.
E. Schneider, Eue d'Anjou 42, Paris.
M. Vainet, Ingenieur-en-Chef des Travaux, Chemin de Fer du
Schiffba it tech nit che Gesellschaft .
H. Eudloff, Leipziger Platz 13, Berlin W.
H. Zimrnermann, Schiffswerft Vulcan, Bredow b/. Stettin.
Vereiti Deutscher Ingenieure.
O. von Miller, Ferdinand Miller Platz 3, Miinchen.
Professor M. Schroter, Miinchen.
E. Diesel, Maria Theresia Str. 32, Miinchen.
O. Lasche, c/o Verein Deutscher-Ingenleure, Berlin.
Deutscher Verein von Gas und Wasserfachmcennern.
Dr. Leybold, Gas Works, Hamburg.
Ernst Borsig, Heydtstrasse 6, Berlin.
Eichard Broja, Kaiser Wilhelmstrasse, Breslau.
C. E. L. Brown, Messrs Brown, Boveri & Co., Baden.
Prof. Carl Busley, Imperial German Navy, 2 Kronprinzen Ufer,
M. von Dolivo-Dobrowolski, Bruckenallee 23, Berlin, N.W.
W. Fischer, Chief Engineer, Bavarian State Eailways, Miincben.
Prof. Oswald Flamm, Goethestrasse 78, Charlottenburg, Berlin.
L. Franzius, Oberbaudirektor der freien Hansestadt, Bremen.
Otto von der Hagen, Kautstrasse 162, Charlottenburg, Berlin.
G. Kapp, 16 Ulmen Allee Westend, Charlottenburg, Berlin.
GT. Langner, Bayreutstr. 20, Berlin W.
M. Meyer, Mechanical Engineer, Eoyal Prussian State Eailways,
Ludwig Peschect. Oberster Baudirektor, Breslau.
H. Eathenau, Allgemeine Elektricitaets-Gesellschaft, Berlin.
H. Schroder, Director of the Construction Department, Eoyal
Prussian State Eailways, Berlin.
Alfred Schultze, Director of the Ministry of Public Works, Berlin.
A. von Siemens, Markgrafen Strasse 94, Berlin.
W. von Siemens, Markgrafen Strasse 94, Berlin.
H. Wedding, Genthinerstrasse 13, Villa C., Berlin W.
AND HONORARY MEMBERS. 349
M. Hoogenboom, Bois le Due, Holland.
H. Wortman, The Hague.
Koninklijh Insntuut van Ingcnieurs.
J. H. Beucker Andreae, Eetired Engineer-in-Chief, R.D.N., The
H. Enno van Gelder, Director Engineer of the " Maatschappij de
R. A. Van Sandick, General Secretary of the Royal Institute of
Dutch Engineers, The Hague.
Pereenigiitg van Gusfabri/canlen in Nederland.
J. van Rossum du Chattel, Gas Works, Linnaenstraat, Amsterdam.
N. W. van Does burgh, Gas Works, Ley den.
A. E. R. Collette, Heemskerkstraat 30, The Hague.
J. F H. Conrad, Van de Spieghel Staat 3, The Hague.
T. van Hasselt, 28 Weespergyde, Amsterdam.
Ritthem van Lambretchsen, Director of Public Works, Amsterdam.
C. L. Loder, Director of Naval Construction, R.D.N., The Hague.
W. Verweij, Chief Engineer. Dutch State Railways, Utrecht.
Hungarian Government and Association of Hungarian Engineers
and Architects, Budapest.
L. Letay, Nador-uteza 5 32, Budapest V., Ker.
B. Uhlarik, Krisztina-kbrut, 36, Budapest I.
Professor C. Zipernowsky, Polytechnicum, Oszloputeza, 7,
Budapest II., Ker.
O. T. Blathy, Messrs Ganz & Co., Budapest.
Johan Brockh, IX. Bez. Ulloer-Strasse N. 19, Budapest.
Alex. Robitsek, Director of Construction, Hungarian State Bail-
3.50 FOREIGN AND COLONIAL DELEGATES
Bombay- Earoda, and Central Indian Railway.
E. S. Luard, Locomotive and Carriage Superintendent,
T. C. Deverell, City Engineer, Calcutta.
C. L. Griesbach, C.I.E., Director, Geological Survey of India,
M. C. Murzban, " Gutestan," Murzban Eoad, Esplanade, Bombay.