The Standard Electrical Dictionary Part 70

Faraday's Transformer.

The first transformer. It was made by Michael Faraday. It was a ring of soft iron 7/8 inch thick, and 6 inches in external diameter. It was wound with bare wire, calico being used to prevent contact of the wire with the ring and of the layers of wire with each other, while twine was wound between the convolutions to prevent the wires from touching.

Seventy-two feet of copper wire, 1/20 inch diameter, were wound in three superimposed coils, covering about one-half of the ring. On the other half sixty feet of copper wire were wound in two superimposed coils.

Faraday connected his coils in different ways and used a galvanometer to measure the current produced by making and breaking one of the circuits used as a primary.

The coil is of historic interest.

Faraday's Voltameter.

A voltameter, in which the coulombs of current are measured by the volume of the gas evolved from acidulated water. (See Voltameter, Gas.)

Faradic. adj.

Referring to induced currents, produced from induction coils. As Faraday was the original investigator of the phenomena of electro-magnetic induction, the secondary or induced electro-magnetic currents and their phenomena and apparatus are often qualified by the adjective Faradic, especially in electro-therapeutics. A series of alternating electrostatic discharges, as from an influence machine (Holtz), are sometimes called Franklinic currents. They are virtually Faradic, except as regards their production.

251 STANDARD ELECTRICAL DICTIONARY.

Faradic Brush.

A brush for application of electricity to the person. It is connected as one of the electrodes of an induction coil or magneto generator. For bristles wire of nickel plated copper is generally employed.

Faradization.

In medical electricity the a.n.a.logue of galvanization; the effects due to secondary or induced currents; galvanization referring to currents from a galvanic battery; also the process of application of such currents.

Faults.

Sources of loss of current or of increased resistance or other troubles in electric circuits.

Feeder.

A lead in an electric central station distribution system, which lead runs from the station to some point in the district to supply current.

It is not used for any side connections, but runs direct to the point where current is required, thus "feeding" the district directly. In the two wire system a feeder may be positive or negative; in the three wire system there is also a neutral feeder. Often the term feeder includes the group of two or of three parallel lines.

Feeder Equalizer.

An adjustable resistance connected in circuit with a feeder at the central station. The object of the feeder being to maintain a definite potential difference at its termination, the resistance has to be varied according to the current it is called on to carry.

Feeder, Main or Standard.

The main feeder of a district. The standard regulation of pressure (potential difference between leads) in the district is often determined by the pressure at the end of the feeder.

Feeder, Negative.

The lead or wire in a set of feeders, which is connected to the negative terminal of the generator.

Feeder, Neutral.

In the three wire system the neutral wire in a set of feeders. It is often made of less diameter than the positive and negative leads.

Feeder, Positive.

The lead or wire in a set of feeders, which wire is connected to the positive terminal of the generator.

Ferranti Effect.

An effect as yet not definitely explained, observed in the mains of the Deptford, Eng., alternating current plant. It is observed that the potential difference between the members of a pair of mains rises or increases with the distance the place of trial is from the station.

[Transcriber's note: This effect is due to the voltage drop across the line inductance (due to charging current) being in phase with the sending end voltages. Both capacitance and inductance are responsible for producing this phenomenon. The effect is more p.r.o.nounced in underground cables and with very light loads.]

252 STANDARD ELECTRICAL DICTIONARY.

Ferro-magnetic. adj.

Paramagnetic; possessing the magnetic polarity of iron.

Fibre and Spring Suspension.

A suspension of the galvanometer needle used in marine galvanometers.

The needle is supported at its centre of gravity by a vertically stretched fibre attached at both its ends, but with a spring intercalated between the needle and one section of the fibre.

Fibre Suspension.

Suspension, as of a galvanometer needle, by a vertical or hanging fibre of silk or coc.o.o.n fibre, or a quartz fibre. (See Quartz.)

This suspension, while the most delicate and reliable known, is very subject to disturbance and exacts accurate levelling of the instrument.

Fibre suspension is always characterized by a rest.i.tutive force. Pivot suspension, q. v., on the other hand, has no such force.

Field, Air.

A field the lines of force of which pa.s.s through air; the position of a field comprised within a volume of air.

Field, Alternating.

Polarity or direction being attributed to lines of force, if such polarity is rapidly reversed, an alternating field results. Such field may be of any kind, electro-magnetic or electrostatic. In one instance the latter is of interest. It is supposed to be produced by high frequency discharges of the secondary of an induction coil, existing in the vicinity of the discharging terminals.

Field Density.

Field density or density of field is expressed in lines of force per unit area of cross-section perpendicular to the lines of force.

Field, Distortion of.

The lines of force reaching from pole to pole of an excited field magnet of a dynamo are normally symmetrical with respect to some axis and often with respect to several. They go across from pole to pole, sometimes bent out of their course by the armature core, but still symmetrical.

The presence of a ma.s.s of iron in the s.p.a.ce between the pole pieces concentrates the lines of force, but does not destroy the symmetry of the field.

When the armature of the dynamo is rotated the field becomes distorted, and the lines of force are bent out of their natural shape. The new directions of the lines of force are a resultant of the lines of force of the armature proper and of the field magnet. For when the dynamo is started the armature itself becomes a magnet, and plays its part in forming the field. Owing to the lead of the brushes the polarity of the armature is not symmetrical with that of the field magnets. Hence the compound field shows distortion. In the cut is shown diagrammatically the distortion of field in a dynamo with a ring armature. The arrow denotes the direction of rotation, and n n * * * and s s * * * indicate points of north and south polarity respectively.