The Standard Electrical Dictionary Part 55

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 ill.u.s.trate 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. Ma.s.ses of iron, which should be laminated and are the inductors, are carried past the field magnet poles concentrating in their pa.s.sage 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.