The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. I35. DIAGRAM OF ARRANGEMENT OF ARMATURE COILS AND
COLLECTING RINGS IN AN ALTERNATING CURRENT DYNAMO.
Dynamo, Alternating Current, Regulation of.
Transformers, converters, or induction coils are used to regulate
alternating current dynamos, somewhat as compound winding is applied in
the case of direct-current dynamos. The arrangement consists in
connecting the primary of an induction coil or transformer into the
external circuit with its secondary connected to the field circuit. Thus
the transformer conveys current to the field picked up from the main
circuit, and represents to some extent the shunt of a direct-current
machine.
Dynamo, Commercial Efficiency of.
The coefficient, q. v., obtained by dividing the mechanically useful or
available work of a dynamo by the mechanical energy absorbed by it. This
only includes the energy available in the outer circuit, for doing
useful work.
196 STANDARD ELECTRICAL DICTIONARY.

Fig. 136. COMPOUND WOUND DYNAMO.
Dynamo. Compound.
A compound wound dynamo; one which has two coils on its field magnet;
one winding is in series with the external circuit and armature; the
other winding is in parallel with the armature winding, or else with the
armature winding and field winding, both in series. (See Winding, Long
Shunt--Winding, Short Shunt.)
Such a dynamo is, to a certain extent, self-regulating, the two coils
counteracting each other, and bringing about a more regular action for
varying currents than that of the ordinary shunt or series dynamo.
The extent of the regulation of such a machine depends on the
proportions given its different parts. However good the self-regulating
may be in a compound wound machine, it can only be perfect at one
particular speed.
To illustrate the principle on which the approximate regulation is
obtained the characteristic curve diagram may be consulted.

Fig. 137. CURVES OF SERIES AND SHUNT WINDINGS SUPERIMPOSED.
One curve is the curve of a series winding, the other that of a shunt
winding, and shows the variation of voltage in each with resistance in
the external or working circuit. The variation is opposite in each case.
It is evident that the two windings could be so proportioned on a
compound machine that the resultant of the two curves would be a
straight line. This regulation would then be perfect and automatic, but
only for the one speed.
197 STANDARD ELECTRICAL DICTIONARY.
Dynamo, Direct Current.
A dynamo giving a current of unvarying direction, as distinguished from
an alternator or alternating current dynamo.
Dynamo, Disc.
A dynamo with a disc armature, such as Pacinotti's disc, q. v. (See also
Disc, Armature.) The field magnets are disposed so that the disc rotates
close to their poles, and the poles face or are opposite to the side or
sides of the disc. The active leads of wire are those situated on the
face or faces of the disc.

Fig. 138. POLECHKO'S DISC DYNAMO.
Dynamo-electric Machine.
A machine driven by power, generally steam power, and converting the
mechanical energy expended on driving it into electrical energy of the
current form. The parts of the ordinary dynamo may be summarized as
follows: First, A circuit as complete as possible of iron. Such circuit
is composed partly of the cores of an electro-magnet or of several
electro-magnets, and partly of the cylindrical or ring-shaped core of an
armature which fits as closely as practicable between the magnet ends or
poles which are shaped so as to partly embrace it. Second, of coils of
insulated wire wound upon the field-magnet cores. When these coils are
excited the field-magnets develop polarity and the circuit just spoken
of becomes a magnetic circuit, interrupted only by the air gaps between
the poles and armatures. Thirdly, of coils of insulated wire upon the
armature core. These coils when rotated in the magnetic field cut
magnetic lines of force and develop electro-motive force.
198 STANDARD ELECTRICAL DICTIONARY.
Fourthly, of collecting mechanism, the commutator in direct current
dynamos, attached to the armature shaft and rotating with it. This
consists of insulated rings, or segments of rings to which the wire
coils of the armature are connected, and on which two springs of copper
or plates of carbon or some other conductor presses. The electro-motive
force developed by the cutting of lines of force, by the wires of the
armature, shows itself as potential difference between the two springs.
If the ends of a conductor are attached, one to each of these brushes,
the potential difference will establish a current through the wire. By
using properly divided and connected segments on the commutator the
potential difference and consequent direction of the current may be kept
always in the same sense or direction. It is now clear that the external
wire may be connected with the windings of the field-magnet. In such
case the excitement of the field-magnets is derived from the armature
and the machine is self-excited and entirely self-contained.
The above is a general description of a dynamo. Sometimes the coils of
the field-magnets are not connected with the armature, but derive their
current from an outside source. Such are termed separately excited
dynamos.
Some general features of dynamo generators may be seen in the
definitions under this head and elsewhere. The general conception is to
cut lines of force with a conductor and thus generate electromotive
force, or in some way to change the number of lines of force within a
loop or circuit with the same effect.
Dynamo, Electroplating.
A dynamo designed for low potential and high current intensity. They are
wound for low resistance, frequently several wires being used in
parallel, or ribbon, bar or rectangular conductors being employed. They
are of the direct current type. They should be shunt wound or they are
liable to reverse. They are sometimes provided with resistance in the
shunt, which is changed as desired to alter the electro-motive force.
Dynamo, Equalizing.
A combination for three and five-wire systems. A number of armatures or
of windings on the same shaft are connected across the leads. If the
potential drops at any pair of mains, the armature will begin to be
driven by the other mains, acting to an extent as an element of a motor,
and will raise the potential in the first pair.
Dynamo, Far Leading.
A motor dynamo, used to compensate the drop of potential in long mains.
Into the mains at a distant point a series motor is connected, driving a
dynamo placed in shunt across the mains. The dynamo thus driven raises
the potential difference between the two mains.
199 STANDARD ELECTRICAL DICTIONARY.
Dynamograph.
A printing telegraph in which the message is printed at both
transmitting and receiving ends.
Dynamo, Inductor.
A generator in which the armature or current-generating windings are all
comprised upon the poles of the field magnets. Masses of iron, which
should be laminated and are the inductors, are carried past the field
magnet poles concentrating in their passage the lines of force, thus
inducing currents in the coils. In one construction shown in the cut the
field magnets a, a .. are U shaped and are arranged in a circle, their
poles pointing inwards. A single exciting coil c, c ... is wound around
the circle in the bend of the V-shaped segments. The poles carry the
armature coils e, e ... The laminated inductors i, i ... are mounted on
a shaft S, by spiders h, to be rotated inside the circle of magnets,
thus generating an alternating current.
Synonym--Inductor Generator.

Fig. 139. INDUCTOR DYNAMO.
Dynamo, Interior Pole.
A dynamo with a ring armature, with field magnet pole pieces which
extend within the ring.
200 STANDARD ELECTRICAL DICTIONARY.
Dynamo, Iron Clad.
A dynamo in which the iron of the field magnet is of such shape as to
enclose the field magnet coils as well as the armature.
Dynamometer.
A device or apparatus for measuring force applied, or rate of
expenditure of energy by, or work done in a given time by a machine. A
common spring balance can be used as a force dynamometer, viz: to
determine how hard a man is pulling and the like. The steam engine
indicator represents an energy-dynamometer of the graphic type, the
instrument marking an area whence, with the aid of the fixed factors of
the engine, the work done may be determined. Prony's Brake, q. v., is a
type of the friction dynamometer, also of the energy type. In the latter
type during the experiment the whole power must be turned on or be
expended on the dynamometer.
Dynamo, Motor.
A motor dynamo is a machine for (a) converting a continuous current at
any voltage to a continuous current of different strength at a different
voltage or for (b) transforming a continuous current into an alternating
one, and vice versa.
For the first type see Transformer, Continuous Current; for the second
type see Transformer, Alternating Current.
Dynamo, Multipolar.
A dynamo having a number of field magnet poles, not merely a single
north and a single south pole. The field magnet is sometimes of a
generally circular shape with the poles arranged radially within it, the
armature revolving between the ends.
Dynamo, Non-polar.
A name given by Prof. George Forbes to a dynamo invented by him. In it a
cylinder of iron rotates within a perfectly self-contained iron-clad
field magnet. The current is taken off by brushes bearing near the
periphery, at two extremities of a diameter. A machine with a disc 18
inches in diameter was said to give 3,117 amperes, with 5.8 volts E. M.
F. running at 1,500 revolutions per second. The E. M. F. of such
machines varies with the square of the diameter of the disc or cylinder.
Dynamo, Open Coil.
A dynamo the windings of whose armatures may be grouped in coils, which
are not connected in series, but which have independent terminals. These
terminals are separate divisions of the commutator and so spaced that
the collecting brushes touch each pair belonging to the same coil
simultaneously. As the brushes come in contact with the sections forming
the terminals they take current from the coil in question. This coil is
next succeeded by another one, and so on according to the number of
coils employed.
Dynamo, Ring.
A dynamo the base of whose field magnets is a ring in general shape, or
perhaps an octagon, and with poles projecting inwardly therefrom.
201 STANDARD ELECTRICAL DICTIONARY.
Dynamo, Coupling of.
Dynamos can be coupled exactly like batteries and with about the same
general results. An instance of series coupling would be given by the
dynamos in the three wire system when no current is passing through the
neutral wire, and when the lamps on each side of it are lighted in equal
number.
Dynamo, Self-exciting.
A dynamo which excites its own field. The majority of dynamos are of
this construction. Others, especially alternating current machines, are
separately excited, the field magnets being supplied with current from a
separate dynamo or current generator.
Dynamo, Separate Circuit.
A dynamo in which the field magnet coils are entirely disconnected from
the main circuit, and in which current for the field is supplied by
special coils carried for the purpose by the same armature, or by a
special one, in either case a special commutator being provided to
collect the current.
Dynamo, Separately Excited.
A dynamo whose field magnets are excited by a separate current
generator, such as a dynamo or even a battery. Alternating current
dynamos are often of this construction. Direct current dynamos are not
generally so. The term is the opposite of self-exciting.