Title: Hawkins Electrical Guide v. 01 (of 10)
Author: N. Hawkins
Release date: December 22, 2011 [eBook #38384]
Most recently updated: December 14, 2023
Language: English
Credits: Produced by Juliet Sutherland, Henry Gardiner and the
Online Distributed Proofreading Team at https://www.pgdp.net
The word “guide” is defined as:
One who leads another in any path or direction; a person who shows or points out the way, especially by accompanying or going before; more particularly, one who shows strangers or tourists about; a conductor; leader, as “let us follow our guide.”
This book, or “Guide,” is so called because it leads or points out the way to the acquirement of a theoretical and practical knowledge of Electricity.
There are several guides, each covering in detail a certain phase of the broad subject of Electricity and leading the reader progressively, and in such a way, that he easily grasps, not only the simple fundamental facts, but the more complex problems, encountered in the study of Electricity. This is accomplished by the aid of a very large number of illustrations, together with specific explanations, worded in concise and simple language.
The Guides are written partly in the question and answer form, as this style of presentation has met with hearty approval, not only from those of limited education, but also from the better informed.
Where recourse is had to the question and answer form, the special aim of the author has been to give short and direct answers, in such plain language as to preclude a misconception of the meaning. With this in view, the answer gives simply the information sought by the question.
The answer is limited to one paragraph so that the reader may concentrate upon the fact or facts demanded by the question.
Any enlargement of the answer or specific explanations of items contained therein, are presented in separate paragraphs printed, in smaller type.
With this plan of separating the answer, as it were, from items of secondary importance, and making it short and simple, its content is more forcibly impressed upon the mind of the reader.
In a text book, it is necessary to illustrate and explain the various species of commercial apparatus met with in practice, and in this connection the Publishers desire to call attention to the manner in which the author has treated what may be classed as the “descriptive matter.” Contrary to the usual custom of giving descriptions of commercial machines in the main text, where they would occupy considerable space, to the exclusion of the more important matter, all such descriptions are placed in small type directly under the illustrations, leaving space for an adequate presentation of the underlying principles, theories, and for the large amount of practical information that is essential to obtain a general knowledge of Electricity and its numerous applications.
Credit is largely due to Frank D. Graham, B.S., M.S. (Princeton University), and M.E. (Stevens Institute), practical engineer, for the authorship of the Guides, and for original sketches illustrating electrical principles and construction.
| INTRODUCTORY CHAPTER | |
| SIGNS AND SYMBOLS | |
| ELECTRICITY | 1 to 4 |
| Nature and source—kinds of electricity: static, current, dynamic, radiated, positive, negative, atmospheric, frictional, resinous, vitreous. | |
| STATIC ELECTRICITY | 5 to 26 |
| Electrical attraction and repulsion—the charge—distribution of the charge—free and bound electricity—conductors and insulators—electroscopes—gold leaf electroscope—electric screens—electrification by induction—nature of the induced charge—the electrophorus—condensers; Leyden jar—electric machines—action of Toepler-Holtz machine—Wimshurst machines. | |
| THE ELECTRIC CURRENT | 27 to 34 |
| Volt—ampere—ohm—Ohm’s law—production of the electric current—current strength—voltage drop in an electric current. | |
| PRIMARY CELLS | 35 to 67 |
| The word “battery”—action of cell—chemical changes; polarization—effects of polarization—methods of depolarization—depolarizers—depolarizer bag—Volta’s contact law—contact series of metals—laws of chemical action in cell—requirements of a good cell—single and two fluid cells—the Leclanche cell—Fuller bichromate cell—the Edison cell—Grenet bichromate cell—Daniell cell—directions for making a Daniell cell—gravity cells—Daniell gravity cell—so-called “dry” cells—points relating to dry cells—care of cells—cleanliness—separating the elements—creeping—amalgamated zinc—battery connections. | |
| CONDUCTORS AND INSULATORS | 68 to 74 |
| The so-called “non-conductors”—table of conductors and insulators—mode of transmission—effect of heat—heating effect of the current—insulators—impregnating compounds—water as a conductor. | |
| RESISTANCE AND CONDUCTIVITY | 75 to 82 |
| Standard of resistance—conductivity of metals and liquids—effect of heat—laws of electrical resistance—conductivity—specific conductivity—divided circuits. | |
| ELECTRICAL AND MECHANICAL ENERGY | 83 to 92 |
| Definitions: energy, matter, molecule, work, foot-pound, volt-coulomb, ampere-hour, power, horse power, watt, kilowatt, watt-hour—mechanical equivalent of heat—British thermal unit—electrical horse power—the farad. | |
| EFFECTS OF THE CURRENT | 93 to 104 |
| Thermal effect—use of heat from the current—magnetic effect—chemical effect—electrolysis—electro-chemical series—electric osmose—electric distillation—muscular contractions—electroplating—electrotyping. | |
| MAGNETISM | 105 to 124 |
| Two kinds of magnetism—nature of each—poles—magnetic field—magnetic force—magnetic circuit—magnetic flux—the Maxwell—the Gauss—magnetic effect of the current—corkscrew rule—solenoids—permeability—magnetic saturation—magnetomotive force—reluctance—analogy between electric and magnetic circuits—hystereses—residual magnetism. | |
| ELECTROMAGNETIC INDUCTION | 125 to 136 |
| Faraday’s discovery—Faraday’s machine—Faraday’s principle—line of force—induction of current—laws of electromagnetic induction—rules for direction of induced current—Fleming’s rule—Ampere’s rule—the palm rule—self-induction. | |
| INDUCTION COILS | 137 to 154 |
| Self-induction—mutual induction—primary induction coils—secondary induction coils—plain secondary induction coils—secondary induction coils with vibrator and condenser; cycle of action—magnetic vibrators—vibrator adjustment—table of induction coil dimensions—table of sparking distances in air—points relating to induction coils—wiring diagram. | |
| THE DYNAMO | 155 to 160 |
| Operation—essential parts—field magnets—armature—construction of dynamos—parts; bed plate, field magnets, armature, commutator, brushes. | |
| THE DYNAMO: BASIC PRINCIPLES | 161 to 170 |
| Definitions—essential parts—elementary alternator—operation—direction of induced current—application of Fleming’s rule—cycle of operation—the sine curve; its construction and application. | |
| THE DYNAMO: CURRENT COMMUTATION | 171 to 180 |
| How the current is produced—how direct current is obtained—the commutator—inductors—“continuous current”—action of four coil elementary dynamo—conditions for steadiness of the current. | |
| CLASSES OF DYNAMO | 181 to 198 |
| Classification—bipolar and multi-polar dynamos—difference between dynamo and magneto—self-exciting dynamo—the series dynamo—regulation of series dynamo; difficulties experienced—the shunt dynamo—adaptation—operation—characteristic—regulation—the compound dynamo—service intended for—regulation—over compounding—usual degree of over compounding—short shunt—long shunt—voltage of short and long shunt machines—separately excited dynamos—Dobrowolski three wire dynamo. | |
| FIELD MAGNETS | 199 to 220 |
| Object—essential parts—classes of field magnet—multi-polar field magnets—construction—choice of materials—design—pole pieces—eddy current—laminated fields—construction to reduce reluctance of the magnetic circuit—magnetizing coils—methods of winding—coil ends—insulation—attachment of coils—coil connections—heating—ventilation. |
The subject matter of this work relates to one of the secrets of creation which appears to have been intended at the very beginning to be “sought out.” This idea is expressed in a certain saying copied three or four thousand years ago by the men of Hezekiah, King of Judah: from Solomon’s proverbs: “It is the glory of God to conceal a thing: But the glory of Kings (i.e., wise men), to search out a matter.”
In all that may be said hereafter through the work, it is admitted that the results recorded are the determinations of experiments performed by an incredible number of searchers extending through many ages. These inquiries have been pursued with a generous rivalry which has permitted discovery to be added to discovery, until the sum total has been wrought into such exactness that it has been thoughtlessly stated that there is nothing more, save its application.
It may be well, however, to state a few fundamental facts relating to electricity: 1, Electricity and magnetism are one and the same thing; 2, what is really known about it has come as a discovery and not as an invention. Thus, we say the intrepid explorer discovered the pole, not that he invented it. So with electricity it has been a subject of discovery while its many applications to useful purposes have been veritable inventions; 3, the earth itself is a magnet.
This last is shown by the fact that the earth affects a magnet just as one magnet affects another. Magnets are bodies, either natural or artificial, which have the property of attracting iron, and the power, when freely suspended, of taking a direction toward the poles of the earth. The natural magnet is sometimes called the loadstone. This word is said to be derived from loedan, a Saxon word which signifies to guide. It is an oxide of iron of a peculiar character, found occasionally in beds of iron ore. Though commonly met with in irregular masses only a few inches in diameter, however, loadstones of larger sizes are sometimes found.
By means of simple experiments it may be ascertained that the magnet has the following general properties, viz: 1, power of attraction; 2, power of repulsion; 3, power of communicating magnetism to iron or steel; 4, polarity, or the power of taking a direction toward the poles of the earth; 5, power of inclining itself toward a point below the horizon.
Speaking generally we may say, that magnetism is a department of electrical science which treats of the properties and effects of the magnet. The same terms are also used to denote the unknown cause of magnetic phenomena, as when we speak of magnetism as excited, imparted, and so on.
Lightning and the Northern Lights are displays of electricity on a grand scale. Electricity is a term derived from the Greek word for amber, that being the substance in which a property of the agent now denominated electricity was first observed.
The ancient Greek philosophers were acquainted with the fact that amber, when rubbed, acquired the property of attracting light bodies; hence the effect was denominated electrical and in later times, the term electricity has been used to denote the unknown cause of electrical phenomena, and broadly the science which treats of electrical phenomena and their causes.
Electricity, whatever it may prove to be, is not matter nor is it energy; it is however a means or medium of transmitting energy.
If electricity is to transmit or convey energy along a wire, this energy must be imparted to the electricity from some external source, that is to say, before electricity can perform any work it must be set in motion, against more or less resistance. This involves that pressure must be applied, and to obtain this pressure, energy must be expended from some external source.
Accordingly, in electrical engineering, the first principle to be grasped is that of energy. Without the expenditure of energy no useful work can be accomplished.
Energy may be defined as the capacity for performing work.
Although electricity is not energy, electricity under pressure is a form of energy spoken of as electrical energy.
In an expenditure of energy in this form, the electricity acts simply as a transmission agent or medium to transmit the energy imparted to it in causing it to flow.
In a similar manner, steam acts as a transmission agent or medium to transmit the heat energy of the coal to the steam engine, where it is converted into mechanical energy.
As just stated, electricity under pressure is a form of energy, and its generation is simply a transformation of energy from one form into another. Usually, mechanical energy is converted into electrical energy, and a dynamo is employed for effecting the transformation.
In transforming the mechanical energy of waterfalls into electric energy, this natural power of water due to its weight and motion is first converted into rotary motion by a turbine or water wheel, and then converted into electric energy by a dynamo, or an alternator.
All dynamos are but machines for converting into electric energy the energy which is given to them by some prime mover, as a steam engine, a gas engine, by hydraulic or even by wind power.
All electric motors are merely machines for reconverting the electric energy which they receive by means of the conducting wires or mains, into mechanical energy.
All electric lamps are contrivances for converting into luminous energy a percentage of the electric energy that is supplied through the mains.
Potential and Kinetic Energy.—Potential energy is the capacity for performing work which a body possesses by virtue of its position. Kinetic energy is the capacity for performing work which a body possesses by virtue of its motion.
It must be evident that position or motion given to a body enables it to perform work. In the first instance, for example, a heavy weight at the top of a high tower possesses potential energy. A ten pound weight supported one foot above a plane has ten foot pounds of potential energy.
The flywheel of a steam engine in motion is an example of a body possessing kinetic energy. Some of this kinetic energy which was stored up in the fly wheel during the working stroke is expended in moving the engine over the “dead center,” and any other point where no torque is produced by the pressure on the piston.
Chemical Energy can be converted into electric energy to a limited extent by means of the electric battery, but the cost of this energy is so high that it is commercially feasible only where small quantities are required, and the cost of production is secondary to the convenience of generation, as for signalling purposes, the operation of bells and annunciators, etc.
The chemical energy of coal and other fuels cannot be directly converted into electric energy. For power producing purposes, the chemical energy of a fuel is first converted into heat by combustion, and the heat thus obtained converted into mechanical energy by some form of heat engine, and the mechanical energy subsequently transformed into electric energy in an electric generator.
Energy cannot be created or destroyed. This is the law known as the conservation of energy which has been built up by Helmholtz, Thomson, Joule and others. It teaches further, that energy can be transmitted from one body to another or transformed in its manifestations.
Energy may be dissipated, that is, converted into a form from which it cannot be recovered, as is the case with the great percentage of heat escaping from the exhaust nozzle of a locomotive or in the circulating water of a steamship, but the total amount of energy in the universe, it is argued, remains constant and invariable.
Following this law comes the doctrine of the conservation of electricity as announced by Lippman, being undoubtedly the outcome of the ideas of Maxwell and of Faraday as to the nature of electricity. According to their doctrine, electricity cannot be created or destroyed, although its distribution may be altered.
Lippman states that every charge of electricity has an opposite and equal charge somewhere in the universe more or less distributed; that is, the sum of positive charges is always equal to the sum of negative charges.
In altering the distribution of electricity, we may cause more to appear at one place and less at another, or may change it from the condition of rest to that of motion, or may cause it to spin round in whirlpools or vortices, which themselves can attract or repel other vortices. According to this view all our electrical machines and batteries are merely instruments for altering the distribution of electricity by moving some of it from one place to another, or for causing electricity, when accumulated or heaped, together in one place, to do work in returning to its former distribution.
Electrical engineering has developed largely and widely within a very short time and its many applications has created so great a demand for various kinds of electrical apparatus, that their manufacture forms one of the leading industries.
Electricity is very valuable as a medium for the transmission of energy, especially to long distances; it is also used to great advantage in lighting, being free from the disagreeable properties of gas or oil.
Again, electricity finds various applications, in extracting gold from the ore, pumping and ventilation of mines, traction, telephone, telegraph, electroplating, therapeutics, etc.
These few, of its many applications will perhaps serve to indicate the far reaching interest and importance of electricity, and possibly help to kindle in the student something of the eagerness in his work and enthusiasm without which he will fail to do justice either to his calling or to himself.
The following signs, symbols and abbreviations are almost universally employed in descriptive and technical works on electrical subjects.
Although, in the arrangement of the Guides, the direct current and alternating current matter has been kept separate, it is perhaps advisable in the case of signs and symbols, to combine those relating to the alternating current with the direct current and other symbols, making a single table, rather than have them scattered throughout the work.
| 1. Fundamental. | |
| l, | Length. cm. = centimeter; in., or ″ = inch, ft. or ′ = foot. |
| M, | Mass. gr. = mass of 1 gramme kg. = 1 kilogramme. |
| T, t, | Time, s = second. |
| 2. Derived Geometric. | |
| S, s, | Surface. |
| E, | Volume. |
| α, β, | Angle. |
| 3. Derived Mechanical. | |
| v, | Velocity. |
| ω, | Angular velocity. |
| r, | Momentum. |
| a, | Acceleration. |
| g, | Acceleration due to gravity = 32.2 feet per second. |
| F, f, | Force. |
| W, | Work. |
| P, | Power. |
| δ, | Dyne. |
| ε, | Ergs, |
| ft. lb., | Foot pound. |
| H.P., h.p. | Horse power. |
| I.H.P., | Indicated horse power. |
| B.H.P., | Brake horse power. |
| E.H.P., | Electrical horse power. |
| J, | Joule’s equivalent. |
| p, | Pressure. |
| K, | Moment of inertia. |
| 4. Derived Electrostatic. | |
| e, | Pressure difference. |
| i, | Current. |
| r, | Resistance. |
| q, | Quantity. |
| c, | Capacity. |
| sc, | Specific inductive capacity. |
| 5. Derived Magnetic. | |
| m, | Strength of pole. |
| , | Intensity of magnetization. |
| , | Magnetic moment. |
| , | Horizontal intensity of earth’s magnetism. |
| , | Field intensity. |
| φ, | Magnetic flux. |
| , | Magnetic flux density or magnetic induction. |
| , | Magnetizing force. |
| , | Magnetomotive force. |
| , | Reluctance, magnetic resistance. |
| μ, | Magnetic permeability. |
| κ, | Magnetic susceptibility. |
| ν, | Reluctivity (specific magnetic resistance). |
| 6. Derived Electromagnetic. | |
| R, | Resistance, ohm. |
| O, | do, megohm. |
| E, | Volt, pressure. |
| Eim | Impressed pressure. |
| Ea, Eo | Active pressure; ohmic drop. |
| Ev | Virtual pressure. |
| Emax | Maximum pressure. |
| Eav | Average pressure. |
| Eef | Effective pressure. |
| Ei | Inductance pressure. |
| Ec | Capacity pressure. |
| U, | Difference of pressure, volt. |
| I, | Intensity of current, ampere. |
| Iim | Impressed current. |
| Ia | Active current. |
| Iv | Virtual current. |
| Imax | Maximum current. |
| Iav | Average current. |
| Ief | Effective current. |
| Q, | Quantity of electricity, ampere-hour; coulomb. |
| C, | Capacity, farad. |
| W, | Electric energy, watt-hour; Joule. |
| P, | Electric power, watt; kilowatt. |
| p, | Resistivity (specific resistance) ohm centimeter. |
| G, | Conductance, mho. |
| γ, | Conductivity (specific conductivity). |
| Y, | Admittance, mho. |
| Z, | Impedance, ohm. |
| X, | Reactance, ohm. |
| Xi | Inductance reactance. |
| Xc | Capacity reactance. |
| B, | Susceptance, mho. |
| L, | Inductance (coefficient of Induction), henry. |
| v, | Ratio of electromagnetic to electrostatic unit of quantity = 3×1010 centimeters per second approximately. |
| 7. Symbols in general use. | |
| D, | Diameter. |
| r, | Radius. |
| t, | Temperature. |
| θ, | Deflection of galvanometer needle. |
| N, n, | Number of anything. |
| π, | Circumference ÷ diameter = 3.141592. |
| ω, | 2πf = 6.2831 × frequency, in alternating current. |
| ~, f, | Frequency, periodicity, cycles per second. |
| φ, | Phase angle. |
| G, | Galvanometer. |
| S, | Shunt. |
| N, n, | North pole of a magnet. |
| S, s, | South pole of a magnet. |
| A.C. | Alternating current. |
| D.C. | Direct current. |
| P.D. | Pressure difference. |
| P.F. | Power factor. |
| C.G.S. | Centimeter, Gramme, Second system. |
| B.&S. | Brown & Sharpe wire gauge. |
| B.W.G. | Birmingham wire gauge. |
| R.p.m. | Revolutions per minute. |
| C.P. | Candle power. |
| , | Incandescent lamp. |
| , | Arc lamp. |
| , OR , | Condenser. |
| , | Battery of cells. |
| , | Dynamo, or direct current motor. |
| , | Alternator, or alternating current motor. |
| , | Converter. |
| , | Static transformer. |
| , | Inductive resistance. |
| , | Non-inductive resistance. |
Nature and Source of Electricity.—What is electricity? This is a question that is frequently asked, but has not yet been satisfactorily answered. It is a force, subject to control under well known laws.
While the nature and source of electricity still remain a mystery, many things about it have become known, thus, it is positively assured that electricity never manifests itself except when there is some mechanical disturbance in ordinary matter.
The true nature of electricity has not yet been discovered. Many think it a quality inherent in nearly all the substances, and accompanied by a peculiar movement or arrangement of the molecules. Some assume that the phenomena of electricity are due to a peculiar state of strain or tension in the ether which is present everywhere, even in and between the atoms of the most solid bodies. If the latter theory be the true one, and if the atmosphere of the earth be surrounded by the same ether, it may be possible to establish these assumptions as facts.
The most modern supposition regarding this matter, by Maxwell, is that light itself is founded on electricity, and that light waves are merely electromagnetic waves. The theory “that electricity is related to, or identical with, the luminiferous ether,” has been accepted by the most prominent scientists.
But while electricity is still a mystery, much is known about the laws governing its phenomena. Man has mastered this mighty force and made it his powerful servant; he can produce it and use it.
Electricity, it is also conceded, is without weight, and, while it is without doubt, one and the same, it is for convenience sometimes classified according to its motion, as:
Other useful divisions are:
Static Electricity.—This is a term employed to define electricity produced by friction. It is properly employed in the sense of a static charge which shows itself by the attraction or repulsion between charged bodies.
When static electricity is discharged, it causes more or less of a current, which shows itself by the passage of sparks or a brush discharge; by a peculiar prickling sensation; by a peculiar smell due to its chemical effects; by heating the air or other substances in its path; and sometimes in other ways.[1]
Current Electricity.—This may be defined as the quantity of electricity which passes through a conductor in a given time—or, electricity in the act of being discharged, or electricity in motion.
An electric current manifests itself by heating the wire or conductor; by causing a magnetic field around the conductor and by causing chemical changes in a liquid through which it may pass.
Dynamic Electricity.—This term is used to define current electricity to distinguish it from static electricity.
Radiated Electricity.—Electricity in vibration. Where the current oscillates or vibrates back and forth with extreme rapidity, it takes the form of waves which are similar to waves of light.
Positive electricity.—This term expresses the condition of the point of an electrified body having the higher energy from which it flows to a lower level. The sign which denotes this phase of electric excitement is +; all electricity is either positive or negative.
Negative Electricity.—This is the reverse condition to the above and is expressed by the sign or symbol -. These two terms are used in the same sense as hot and cold.
Atmospheric Electricity is the free electricity of the air which is almost always present in the atmosphere. Its exact cause is unknown.
The phenomena of atmospheric electricity are of two kinds; there are the well known manifestations of thunderstorms; and there are the phenomena of continual slight electrification in the air, best observed when the weather is fine; the Aurora constitutes a third branch of the subject.
Frictional Electricity is that produced by the friction of one substance against another.
Resinous Electricity.—The kind of electricity produced upon a resinous substances such as sealing wax, resin, shellac, rubber or amber when rubbed with wool or fur. Resinous electricity is negative electricity.
Vitreous Electricity.—A term applied to the positive electricity developed in a glass rod by rubbing it with silk. This electric charge will attract to itself bits of pith or paper which have been repelled from a rod of sealing wax or other resinous substance which had been rubbed with wool or fur.
Static electricity may be defined simply as electricity at rest; the term properly applies to an isolated charge of electricity produced by friction. The presence of static electricity manifests itself by attraction or repulsion.
Electrical Attraction and Repulsion.—When a glass rod, or a stick of sealing wax or shellac is held in the hand and rubbed with a piece of flannel or cat skin, the parts will be found to have the property of attracting bodies, such as pieces of silk, wool, feathers, gold leaf, etc.; they are then said to be electrified. In order to ascertain whether bodies are electrified or not, instruments called electroscopes are used.
There are two opposite kinds of electrification:
Franklin called the electricity excited upon glass by rubbing it with silk positive electricity, and that produced on resinous bodies by friction with wool or fur, negative electricity.
The electricity developed on a body by friction depends on the rubber as well as the body rubbed. Thus glass becomes negatively electrified when rubbed with catskin, but positively electrified when rubbed with silk.