The Standard Electrical Dictionary Part 42

Core-discs, Segmental.

Core-discs made in segments, which are bolted together to form a complete disc or section of the core. The plan is adopted princ.i.p.ally on large cores. The discs thus made up are placed together to form the core exactly as in the case of ordinary one piece discs.

Fig. 114. PIERCED OR PERFORATED CORE-DISC.

Core-discs, Toothed.

Core-discs of an armature of a dynamo or motor, which discs are cut into notches on the periphery. These are put together to form the armature core, with the notches corresponding so as to form a series of grooves in which the wire winding is laid. This construction reduces the actual air-gaps, and keeps the wires evenly s.p.a.ced. Distance-pieces of box-wood, m, m, are sometimes used to lead the wires at the ends of the armature.

Fig. 115. TOOTHED CORE-DISC.

Core, Laminated.

A core of an armature, induction coil or converter or other similar construction, which is made up of plates insulated more or less perfectly from each other. The object of lamination is to prevent the formation of Foucault currents. (See Currents, Foucault.) As insulation, thin sh.e.l.lacked paper may be used, or sometimes the superficial oxidation of the plates alone is relied on. The plates, in general, are laid perpendicular to the princ.i.p.al convolutions of the wire, or parallel to the lines of force. The object is to break up currents, and such currents are induced by the variation in intensity of the field of force, and their direction is perpendicular to the lines of force, or parallel to the inducing conductors.

A core built up of core discs is sometimes termed a tangentially laminated core. Made up of ribbon or wire wound coil fas.h.i.+on, it is termed a radially laminated core.

155 STANDARD ELECTRICAL DICTIONARY.

Core Ratio.

In a telegraph cable the ratio existing between the diameter of the conducting core and the insulator. To get a ratio approximately accurate in practical calculations, the diameter of the core is taken at 5 per cent. less than its actual diameter. The calculations are those referring to the electric constants of the cable, such as its static capacity and insulation resistance.

Core, Ribbon.

For discoidal ring-shaped cores of armatures, iron ribbon is often used to secure lamination and prevent Foucault currents.

Synonym--Tangentially Laminated Core.

Core, Ring.

A core for a dynamo or motor armature, which core forms a complete ring.

Core, Stranded.

In an electric light cable, a conducting core made up of a group of wires laid or twisted together.

Core, Tubular.

Tubes used as cores for electro-magnets. For very small magnetizing power, tubular cores are nearly as efficient as solid ones in straight magnets, because the princ.i.p.al reluctance is due to the air-path. On increasing the magnetization the tubular core becomes less efficient than the solid core, as the reluctance of the air-path becomes proportionately of less importance in the circuit.

Corpusants.

The sailors' name for St. Elmo's Fire, q. v.

Coulomb.

The practical unit of quant.i.ty of electricity. It is the quant.i.ty pa.s.sed by a current of one ampere intensity in one second. It is equal to 1/10 the C. G. S. electro-magnetic unit of quant.i.ty, and to 3,000,000,000 C.

G. S. electrostatic units of quant.i.ty. It corresponds to the decomposition of .0935 milligrams of water, or to the deposition of 1.11815 milligrams of silver.

[Transcriber's note: A coulomb is approximately 6.241E18 electrons. Two point charges of one coulomb each, one meter apart, exerts a force of 900,000 metric tons.]

Coulomb's Laws of Electrostatic Attraction and Repulsion.

1. The repulsions or attractions between two electrified bodies are in the inverse ratio of the squares of their distance.

2. The distance remaining the same, the force of attraction or repulsion between two electrified bodies is directly as the product of the quant.i.ties of electricity with which they are charged.

156 STANDARD ELECTRICAL DICTIONARY.

Counter, Electric.

A device for registering electrically, or by electro-magnetic machinery, the revolutions of shafts, or any other data or factors.

Counter-electro-motive Force.

A potential difference in a circuit opposed to the main potential difference, and hence, resisting the operation of the latter, and diminis.h.i.+ng the current which would be produced without it. It appears in electric motors, which, to a certain extent, operate as dynamos and reduce the effective electro-motive force that operates them. It appears in the primary coils of induction coils, and when the secondary circuit is open, is almost equal to the main electro-motive force, so that hardly any current can go through them under such conditions. It appears in galvanic batteries, when hydrogen acc.u.mulates on the copper plate, and in other chemical reactions. A secondary battery is charged by a current in the reverse direction to that which it would normally produce. Its own potential difference then appears as a counter-electro-motive force.

Synonym--Back Electro-motive Force.

Counter-electro-motive Force of Polarization.

To decompose a solution by electrolysis, enough electro-motive force is required to overcome the energy of composition of the molecule decomposed. A part of this takes the form of a counter-electromotive force, one which, for a greater or less time would maintain a current in the opposite direction if the original source of current were removed.

Thus in the decomposition of water, the electrodes become covered, one with bubbles of oxygen, the others with bubbles of hydrogen; this creates a counter E. M. F. of polarization. In a secondary battery, the working current may be defined as due to this cause.

Synonym--Back Electro-motive Force of Polarization.

Couple.

Two forces applied to different points of a straight line, when opposed in direction or unequal in amount, tend to cause rotation about a point intermediate between their points of application and lying on the straight line. Such a pair const.i.tute a couple.

Couple, Voltaic or Galvanic.

The combination of two electrodes, and a liquid or liquids, the electrodes being immersed therein, and being acted on differentially by the liquid or liquids. The combination const.i.tutes a source of electro-motive force and consequently of current. It is the galvanic or voltaic cell or battery. (See Battery, Voltaic--Contact Theory--Electro-motive Force--Electro-motive Series.)

Coupling.

The joining of cells of a galvanic battery, of dynamos or of other devices, so as to produce different effects as desired.

157 STANDARD ELECTRICAL DICTIONARY

Couple, Astatic.