TRANSFORMERS  . An See also:

• ELECTRICAL
• ELECTRICAL (or ELECTROSTATIC) MACHINE

electrical transformer is the name given to any See also:

• DEVICE

device for producing by means of one electric current another of a different See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character . The working of such an appliance is, of course, subject to the See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

law of conservation of See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy . The resulting current represents less See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power than the applied current, the difference being represented by the power dissipated in the translating See also:

• PROCESS

process . Hence an electrical transformer corresponds to a See also:

• SIMPLE

simple See also:

• MACHINE
• MACHINE (through Fr. from Lat. form machina of Gr. µnxavil)

machine in See also:

• MECHANICS

mechanics, both transforming power from one See also:

• FORM (Lat. forma)

form into another with a certain energy-dissipation depending upon frictional losses, or something See also:

• EQUIVALENT

equivalent to them . Electrical transformers may be divided into several classes, according to the nature of the transformation effected . The first See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

division comprises those which See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change the form of the power, but keep the type of the current the same; the second those that change the type of the current as well as the form of power . The power given up electrically to any See also:

• CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit is measured by the product of the effective value of the current, the effective value of the difference of potential between the ends of the circuit and a See also:

• FACTOR (from Lat. facere, to make or do)

factor called the power factor . In dealing with periodic currents, the effective value is that called the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root-mean-square value (R.M.S.), that is to say, the square root of the mean of the squares of the See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time equidistant instantaneous values during one See also:

• COMPLETE

complete See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period (see See also:

• ELECTROKINETICS

ELECTROKINETICS) . In the See also:

• CASE
• CASE, JOHN (d. 1600)

case of continuous current, the power factor is unity, and the effective value of the current or voltage is the true mean value . As the electrical measure of a power is always a product involving current and voltage, we may transform the character of the power by increasing or diminishing the current with a corresponding decrease or increase of the voltage . A transformer which raises voltage is generally called a step-up transformer, and one which lowers voltage a step-down transformer .

Again, electric currents may be of various types, such as continuous, single-phase alternating, polyphase alternating, undirectional but pulsating, &c . Accordingly, transformers may be distinguished in another way, in accordance with the type of transformation they effect . (I) An alternating current trans-former is an appliance for creating an alternating current of any required magnitude and electromotive force from another of different value and electromotive force, but of the same frequency . An alternating current transformer may be constructed to transform either single-phase or polyphase currents . (2) A continuous current transformer is an appliance which effects a similar transformation for continuous currents, with the difference that some See also:

• PART

part of the machine must revolve, whereas in the alternating current transformer all parts of the machine are stationary; hence the former is generally called a rotatory transformer, and the latter a static transformer . (3) A rotatory or rotary transformer may consist of one machine, or of two See also:

• SEPARATE

separate See also:

• MACHINES

machines, adapted for converting a single-phase alternating current into a polyphase current, or a polyphase current into a continuous current, or a continuous current into an alternating current . If the portions receiving and putting out power are separate machines, the See also:

• COMBINATION (Lat. combinare, to combine)

combination is called a motor-generator . (4) A transformer adapted for converting a single-phase alternating current into a unidirectional but pulsatory current is called a rectifier, and is much used in connexion with arc See also:

• LIGHTING

lighting in alternating current See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply stations . (5) A phase trans-former is an arrangement of static transformers for producing a polyphase alternating current from a single-phase alternating current . Alternating current transformers may be furthermoredivided into (a) single-phase, (b) polyphase . Transformers of the first class change an alternating current of single-phase to one of single-phase identical frequency, but different power; and transformers of the second class operate in a similar manner on polyphase currents . (6) The See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary See also:

• INDUCTION (from Lat. inducere, to lead into; cf. Gr. ilrayu yli)

induction or spark coil may be called an intermittent current transformer, since it transforms an intermittent See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

low-tension See also:

• PRIMARY

primary current into an intermittent or alternating high-tension current .

Alternating Current Transformer.—The typical alternating current transformer consists essentially of two insulated electric circuits See also:

• WOUND (O. Eng. wund,connected with a Teutonic verb, meaning to strive, fight, suffer, seen in O. Eng. winnan, whence Eng. " win ")

wound on an See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron core constituting the magnetic circuit . They may be divided into (r) open magnetic circuit static transformers, and (2) closed magnetic circuit static trans-formers, according as the iron core takes the form of a terminated See also:

• BAR
• BAR (0. Fr. barre, Late Lat. barra, origin unknown)
• BAR, CONFEDERATION OF
• BAR, FRANCOIS DE (1538-1606)
• BAR, THE

bar or a closed See also:

• RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring . A closed circuit alternating current trans-former consists of an iron core built up of thin sheets of iron or See also:

• STEEL, FLORA ANNIE (1847– )

steel, insulated from one another, and wound over with two insulated conducting circuits, called the primary and secondary circuits . The core must be laminated or built up of thin sheets of iron to prevent See also:

• LOCAL

local electric currents, called eddy currents, from being established in it, which would See also:

• WASTE (O. Fr. wast, guast, gast, gaste; Lat. vastus, vast, desolate)

waste energy . In See also:

• PRACTICAL

practical construction, the core is either a simple ring, See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round or rectangular, or a See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double rectangular ring, that is, a core whose See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section is like the figure 8 . To prepare the core, thin sheets of iron or very mild steel, not thicker than •014 of an See also:

• INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch, are stamped out of See also:

• SPECIAL

special iron (see See also:

• ELECTROMAGNETISM

ELECTROMAGNETISM) and care-fully annealed . The preparation of the particular See also:

• SHEET

sheet steel or iron used for this purpose is now a speciality . It must possess extremely small See also:

• HYSTERESIS (Gr. IQTEprIo-es, from vvrkp€iv, to lag behind)

hysteresis loss (see See also:

• MAGNETISM
• MAGNETISM, TERRESTRIAL

MAGNETISM), and various See also:

• TRADE (O. Eng. trod, footstep, from tredan, to tread; in M. Eng. the forms teed, trod and trade appear, the last in the sense of a beaten track)
• TRADE, BOARD OF

trade names, such as " stalloy," " lohys," are in use to describe certain brands . See also:

• BARRETT, LAWRENCE (1838-1891)
• BARRETT, LUCAS (1837-1862)

Barrett, See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

Brown and Hadfield have shown (Journ . Inst . Elec . Eng .

Lond., 1902, 31, p . 713) that a See also:

• SILICON [symbol Si, atomic weight 28.3 (0= 16)]

silicon iron containing 2.87 % of silicon has a hysteresis loss far less than that of the best See also:

• SWEDISH

Swedish soft iron . In any case the hysteresis loss should not exceed 3•0 See also:

• WATTS, ALARIC ALEXANDER (1797-1864)
• WATTS, GEORGE FREDERICK (1817-1904)
• WATTS, ISAAC (1674-1748)

watts per kilo-See also:

• GRAM

gram of iron measured at a frequency of 5o — and a See also:

• FLUX (Lat. fluxus, a flowing; this being also the meaning of the English term in medicine, &c.)

flux-See also:

• DENSITY (Lat. densus, thick)

density of 10,000 lines per square centimetre . This is now called the " figure of merit " of the iron . Examples of the shapes in which these stampings are supplied are shown in fig . 1 . The plates when annealed are varnished or covered with thin See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

paper on one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side, and then piled up so as to make an iron core, being kept together by bolts and nuts or by pressure plates . The designer of a transformer y in core has view, eco i. j eeonom in See also:

• METAL
• METAL (through Fr. from Lat. metallum, mine, quarry, adapted from Gr. µATaXAov, in the same sense, probably connected with ,ueraAAdv, to search after, explore, µeTa, after, aAAos, other)

metal, so that there may ma be no waste fragments, and second, a mode of construction that facili- tates V ' \~O the winding of the See also:

• WIRE (A.S. wir, a wire; cf. Swed. vire, to twist, M.H.G. wiere, a gold ornament, Lat. viriae, armlets, ultimately from the root wi, to twist, bind)

wire circuits . These consist of coils of See also:

• COTTON
• COTTON (Fr. coton; from Arab. qutun)
• COTTON, CHARLES (163o–1687)
• COTTON, GEORGE EDWARD LYNCH (1813–1866)
• COTTON, JOHN (1585–1652)
• COTTON, SIR ROBERT BRUCE

cotton- covered See also:

• COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper wire which are wound on formers and baked after being well ~, . saturated with shellac See also:

• VARNISH

varnish . The primary and secondary circuits are j~~'I' ~~I I I ! I See also:

• ILL

ill sometimes formed of separate bobbins !i l which are sandwiched in between each other; in other cases they are wound one over the other (fig .

2) . In any case the primary and secondary coils must be symmetrically distributed . If they were placed on opposite sides of the iron circuit the result would be considerable magnetic leakage . It is usual to insert sheets or cylinders of micanite between the primary and secondary windings . The transformer is then well baked and placed in a See also:

• CAST (from the verb meaning " to throw "; the word is Scand. in origin, cf. Dan. kaste, and Swed. kasta; " cast " in Middle Eng. took the place of the A.S. weor pan, cf. Ger. werf en)

cast-iron case sometimes filled in with heavy insulating oil, the ends of the primary and secondary circuits being brought out through See also:

• WATER

water-tight glands . The most ordinary type of alternating current transformer is one intended to transform a small electric current produced by a large electromotive force (2000 to 10,000 volts) into a larger current of low electromotive force (100 to 200 volts) . Such a step- down transformer may be obvi- ously employed in the See also:

• REVERSE

reverse direction for raising pressure and !~~ !! Primary reducing current, in which case it circuit is a step-up transformer . A trans- former when manufactured has to $econdary be carefully tested to ascertain, ` Circuit first, its power of resisting break- down, and, second, its energy- dissipating qualities . With the first See also:

• OBJECT

object, the transformer is subjected to a See also:

• SERIES (a Latin word from serere, to join)

series of pressure tests . If it is intended that the primary shall carry a current II ,, Trams produced by an electromotive force of 2000 volts, an insulation test must be applied with double this voltage between the primary and the secondary, the primary and the case, and the primary and the core, to ascertain whether the insulation is sufficient . To prevent electric discharges from breaking down the machine in ordinary See also:

• WORK

work, this extra pressure ought to be applied for at least a See also:

• QUARTER (through Fr. from Lat. quartarius, fourth part)

quarter of an See also:

• HOUR

hour .

In some cases three or four times the working pressure is applied for one See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute between the primary and secondary circuits . When such an alternating current transformer has an alternating current passed through its primary circuit, an alternating magnetization is produced in the core, and this again induces an alternating secondary current . The secondary current has a greater or less electromotive force than the primary current according as the number of windings or turns on the secondary circuit is greater or less than those on the primary' . Of the power thus imparted to the primary circuit one portion is dissipated by the See also:

• HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat generated in the primary and secondary circuits by the currents, and another portion by the iron core losses due to the energy wasted in the cyclical magnetization of the core; the latter are partly eddy current losses and partly hysteresis losses . In open magnetic circuit transformers the core takes the form of a laminated iron bar or a bundle of iron wire . An ordinary induction coil is an inst:ument of this description . It has been shown, however, by careful experiments, that for alternating current trans-formation there are very few cases in which the closed magnetic circuit transformer has not an See also:

• ADVANTAGE

advantage . An immense number of designs of closed circuit transformers have been elaborated since the See also:

• YEAR

year 1885 . The See also:

• PRINCIPAL

principal See also:

• MODERN

modern types are the Ferranti, Kapp, Mordey, See also:

• BRUSH (from Fr. brosse, which, like the English word, means both the undergrowth of a wood and the instrument; if the word in both these meanings is ultimately the same, then the origin is from a bundle of brushwood used as a brush or broom, but this is h
• BRUSH, GEORGE DE FOREST (1855– )

Brush, Westinghouse, See also:

• BERRY, CHARLES ALBERT (1852-1899)
• BERRY, CHARLES FERDINAND
• BERRY, JOHN, DUKE OF (1340-1416)
• BERRY, or BERRI

Berry, See also:

• THOMSON, JAMES (1822-1892)
• THOMSON, JAMES (1834-1882)
• THOMSON, JAMES (r700-1748)
• THOMSON, JOHN (1778-184o)
• THOMSON, JOSEPH (1858-1895)
• THOMSON, SIR CHARLES WYVILLE (1830-1882)
• THOMSON, THOMAS (1773-1852)
• THOMSON, WILLIAM (1819-189o)

Thomson-See also:

• HOUSTON
• HOUSTON, SAM, or SAMUEL (1793-1863)

Houston and Ganz . Diagrammatic representations of the arrangements of the core and circuits in some of these transformers are given in fig . 3 . A B C (C) Ganz Transformers .

r, i Primary circuit; 2, 2 Secondary circuit . Alternating current transformers are classified into (i.) Core and (ii.) See also:

• SHELL
• SHELL (O. Eng. scell, scyll, cf. Du. sceel, shell, Goth. skalja, tile; the word means originally a thin flake,. cf. Swed. skalja, to peel off; it is allied to " scale " and " skill," from a root meaning to cleave, divide, separate)

Shell transformers, depending upon the arrangements of the iron and copper circuits . If the copper circuits are wound on the outside of what is virtually an iron ring, the transformer is a core transformer if`the iron encloses the copper circuits, it is a shell transformer . Shell transformers have the disadvantage generally of poor ventilaton for the copper circuits . Berry, however, has overcome this difficulty by making the iron circuit in the' form of a number of bunches of rectangular frames which are set in radial See also:

• FASHION (adapted from Fr. facon, agon, Lat. factio, making, facere, to do or make)

fashion and the adjacent legs all embraced by the two copper circuits in the form of a pair of concentric cylinders . In this manner he secures See also:

• GOOD, JOHN MASON (1764-1827)

good See also:

• VENTILATION (Lat. ventilare, from ventus, wind)

ventilation and a minimum See also:

• EXPENDITURE

expenditure in copper and iron, as well as the possibility of insulating the two copper circuits well from each other and from the core . An important See also:

• MATTER

matter is the cooling of the core . This may be effected either by ordinary See also:

• RADIATION, THEORY OF

radiation, or by a forced See also:

• DRAUGHT (from the common Teutonic word " to draw "; cf. Ger. 7'racht, load; the pronunciation led to the variant form " draft," now confined to certain specific meanings)

draught of See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air made by a See also:

• FAN (Lat. vannus; Fr. eventail)

fan or else by immersing the transformer in oil, the oil being kept cool by pipes through which See also:

• COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold water circulates immersed in it . This last method is adopted for large high-tension transformers . The ratio between the power given out by a transformer and the power taken up by it is called its efficiency, and is best Efficiency . represented by a See also:

• CURVE (Lat. curvus, bent)

curve, of which the See also:

• ORDINATE

ordinate is the efficiency expressed as a percentage, and the corresponding abscissae represent the fractions of the full load as decimal fractions . The output of the transformer is generally reckoned in kilowatts, and the load is conveniently expressed in decimal fractions of the full load taken as unity .

The efficiency on one-tenth of full load is generally a fairly good criterion of the See also:

• ECONOMY

economy of the transformer as a transforming agency . "In large transformers the one-tenth load efficiency will reach go% or more, and in small transformers 75 to 80% . copper circuits increase about 0•4% per degree C. with rise of temperature . The current taken in at the primary side of the transformer, when the secondary circuit is unclosed, is called the magnetizing current, and the power then absorbed by the transformer is called the open circuit loss or magnetizing watts . The ratio of the terminal potential difference at the primary and secondary terminals is called the trans-formation ratio of the transformer . Every transformer is designed to give a certain transformation ratio, corresponding to some particular primary voltage . In some cases trans-formers are designed to transform, not potential 'difference, but current in a See also:

• CONSTANT, BENJAMIN (1845-1902)

constant ratio . The product of the root-meansquare (R.M.S.), effective or virtual, values of the primary current, and the primary terminal potential difference, is called the apparent power or apparent watts given to the transformer . The true electrical power may be numerically equal to this product, but it is never greater, and is sometimes less . The ratio of the true power to the apparent power is called the power factor of the transformer . The power factor approaches unity in the case of a closed circuit transformer, which is loaded non-inductively on the secondary circuit to any considerable fraction of its full load, but in the case of an open circuit transformer the power factor is always much less than unity at all loads . Power factor curves show the variation of power factor with load .

Examples of these curves were first given by J . A . See also:

• FLEMING, PAUL (1609-1640)
• FLEMING, RICHARD (d. 1431)
• FLEMING, SIR SANDFORD (1827- )
• FLEMING, SIR THOMAS (1S44-1613)

Fleming, who suggested the See also:

• TERM

term itself (see Jour . Inst . Elec . Eng . Lond., 1892, 21, p . 6o6) . A low power factor always implies a magnetic circuit of large reluctance . The operation of the alternating current is then as follows: the periodic magnetizing force of the primary circuit creates a periodic magnetic flux in the core, and this being linked with the primary circuit creates by its variation what is called the back electromotive force in the primary circuit . The variation of the particular portion The See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general form of the efficiency curve for a closed circuit trans-former is shown in fig . 4 .

The See also:

• HORIZONTAL

horizontal distances represent fractions of full secondary load (represented by unity), and the See also:

• VERTICAL (from Lat. vertex, highest point)

vertical distances efficiency in percentages . The efficiency curve has a maximum value corresponding to that degree of load at which the copper losses in the transformer are equal to the iron losses . In the case of modern closed magnetic circuit transformers the copper losses are proportional to the square of the secondary cur-See also:

• RENT

rent (I2) or to 022, where q=Ria2+See also:

• R2(rt-s2)

R2; RI being the resistance of the primary and . R2 that of the secondary circuit, while a is the ratio of the number of secondary and primary windings of the transformer . Let C stand, for the core loss, and V2 for the secondary terminal potential difference (R.M.S. value) . We can then write as an expression for the efficiency (n) of the transformer (n=I2V2/ (C + 4122+I2Vz)• It is easy to show that if Ci, V2 and q are constants, but I2 is variable, the above expression fore has a maximum value when C-gI22=O, that is, when the iron core loss C =the See also:

• TOTAL

total copper losses 022 . The iron core energy-waste, due to the hysteresis and eddy currents, may be stated in watts, or expressed as a fraction of the full load secondary output . In small trans- iron and formers of r to 3 kilowatts output it may amount copper to 2 or 3%, and in large transformers of ro to 5o Losses. kilowatts and upwards it should be r or less than 1% . Thus the core loss of a 3o-kilowatt transformer (one having a secondary output of 30,000 watts) should not exceed 250 watts . It has been shown that for the constant potential transformer the iron core loss is constant at all loads, but diminishes slightly as the core temperature rises . On the other See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, the copper losses due to the resistance of the UIN x U 100 90 80 70 .60 80 40 30 20 10 0 2 3 •4 5 •6 7 8 •9 •10 Fraction of Full Load . Closed Circuit Transformer .

of this periodic flux, linked with the secondary circuit, originates in this last a periodic electromotive force . The whole of the flux linked with the primary circuit is not interlinked with the secondary circuit . The difference is called the magnetic leakage of the trans-former . This leakage is increased with the secondary output of the transformer and with any disposition of the primary and secondary coils which tends to separate them . The leakage exhibits itself by. increasing the secondary drop . If a transformer is worked at a constant primary potential difference, the secondary terminal potential difference at no load or on open secondary circuit is greater than it is when the secondary is closed and the transformer giving its full output . The difference between these last two See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences of potential is called the secondary drop . This secondary drop should not exceed 2 °o of the open secondary circuit potential difference . The facts required to be known about an alternating current transformer to appraise its value are (t) its full load secondary output or the numerical value of the power it is See also:

• HOURS, CANONICAL

hours, and at full load for three hours . The matters of most practical importance in connexion with an alternating current transformer are (i) the iron core loss, which affects the efficiency chiefly, and must be considered (a) as to its initial value, and (b) as affected by " ageing " or use; (2) the secondary drop or difference of secondary voltage between full and no load, primary voltage being constant, since this affects the service and power of the transformer to work in parallel with others; and (3) the temperature rise when in normal use, which affects the insulation and See also:

• LIFE

life of the transformer . The shellacked cotton, oil and other materials with which the transformer circuits are insulated suffer a deterioration in insulating power if continuously maintained at any temperature much above 8o° C. to too° C . In taking the tests for core loss and drop, the temperature of the transformer should therefore be stated .

The iron losses are reduced in value as temperature rises and the copper losses are increased . The former may be to to 15% less and the latter 20% greater than when the trans-former is cold . For the purpose of calculations we require to know the number of turns on the primary and secondary circuits, represented by N, and N2; the resistances of the primary and secondary circuits, represented by Rr and R2; the See also:

• VOLUME

volume (V) and See also:

• WEIGHT

weight (W) of the iron core; and the mean length (L) and section (S) of the magnetic section . The hysteresis loss of the iron reckoned in watts per lb per too cycles of magnetization per second and at a maximum flux density of 2500 C.G.S. See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units should also be determined . The experimental examination of a transformer involves the measurement of the efficiency, the iron core 'loss, and the Testing. secondary drop; also certain tests as to insulation and See also:

• HEATING

heating, and finally an examination of the relative phase position and graphic form of the various periodic quantities, currents and electromotive forces taking See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place in the trans-former . The efficiency is best determined by the employment of a properly constructed See also:

• WATTMETER

wattmeter (see See also:

• WATT, JAMES (1736-1819)

WATT-See also:

• METER, ELECTRIC

METER) . The trans-former T (fig . 5) should be so arranged that, if a constant potential trans-former, it is supplied with its normal working pressure at the primary side and with a load which can be varied, and which is obtained either by incandescent lamps, L, or resistances in the secondary circuit . A wattmeter, W, should be placed with its series coil, Se, in the primary circuit of the transformer, and its175 shunt coil, Sh, either across the primary mains in series, with a suitable non-inductive resistance, or connected to the secondary circuit of another transformer, Ti, called an See also:

• AUXILIARY (from Lat. auxilium, help)

auxiliary transformer, having its primary terminals connected to those of the transformer under test . In the, latter case one or more incandescent lamps, L, may be connected in series with the shunt coil of the wattmeter so as to regulate the current passing through it . The current through the series coil of the wattmeter is then the same as the current through the primary circuit of the transformer under test, and the current through the shunt coil of the wattmeter is in step with, and proportional to, the primary voltage of the transformer . Hence, the wattmeter See also:

• READING

reading is proportional to the mean power given up to the transformer .

The wattmeter can be standardized and its See also:

• SCALE
• SCALE (1) A

scale reading interpreted by replacing the transformer under test by a non-inductive resistance or series of lamps, the power absorption of which is measured by the product of the amperes and volts supplied to it . In the secondary circuit of the trans-former is placed another wattmeter of a similar See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind, or, if the load on the secondary circuit is non-inductive, the secondary voltage and the secondary current can be measured with a proper alternating current ammeter, See also:

• A2(z)

A2, and See also:

• VOLTMETER

voltmeter, V2, and the product of these readings taken as a measure of the power given out by the transformer . The ratio of the See also:

• POWERS, HIRAM (1805-1873)

powers, namely, that given out in the See also:

• EXTERNAL

external secondary circuit and that taken in by the primary circuit, is the efficiency of the transformer . In testing large transformers, when it is inconvenient to load up the secondary circuit to the full load, a See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close approximation to the power taken up at any assumed secondary load can be obtained by adding to the value of this secondary load, measured in watts, the iron core loss of the transformer, measured at no load, and the copper losses calculated from the measured copper resistances when the transformer is hot . Thus, if C is the iron core loss in watts, measured on open secondary circuit, that is to say, is the power given to the transformer at normal frequency and primary voltage, and if RI and R2 are the primary and secondary circuit resistances when the transformer has the temperature it would have after See also:

• RUNNING

running at full load for two or three hours, then the efficiency can be calculated as follows: Let 0 be the nominal value of the full secondary output of the transformer in watts, Vi and V2 the terminal voltages on the primary and secondary, side, NI and N2 the number of turns, and Al and A2 the currents for the two circuits; then O/V2 is the full load secondary current measured in amperes, and N2N1 multiplied by O/V2 is to a sufficient approximation the value of the corresponding primary current . Hence O2R2/V22 is the watts lost in the secondary circuit due to copper resistance, and O2R1N22/V22Ni2 is the corresponding loss in the primary circuit . Hence the total power loss in the transformer (=L) is such that Appraise- designed to transform, on the See also:

• ASSUMPTION, FEAST OF

assumption that it See also:

• MEAT

meat . will not rise in temperature more than about 6o° C. above the See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere when in normal use; (2) the primary and secondary terminal voltages and currents, accompanied by a statement whether the transformer is intended for producing a constant secondary voltage or a constant secondary current; (3) the efficiency at various fractions on secondary load from one-tenth to full load taken at a stated frequency; (a) the power factor at one-tenth of full load and at full load; (5) the secondary drop between full load and no load; (6) the iron core loss, also the magnetizing current, at the normal frequency; (q) the total copper losses at full load and at one-tenth of full load; (8) the final temperature of the transformer after being See also:

• LEFT

left on open secondary circuit but normal primary potential for twenty-four Transformers . L = C + V22 R2 -h \N~/ ? 2zRi = C -}- (R2 -{- Ria2)O2/V22 . Therefore the power given up to the transformer is 0+L, and the efficiency is the fraction O/(O+L) expressed as 'a percentage . In this manner the efficiency can be determined with a considerable degree of accuracy in the case of large transformers without actually loading up the secondary circuit .

The secondary drop, however, can only be measured by loading the transformer up to full load, and, while the primary voltage is kept constant, measuring the potential difference of the secondary terminals, and comparing it with the same difference when the transformer is not loaded . Another method of testing large transformers at full load without supplying the actual power is by W . E . Sumpner's See also:

• DIFFERENTIAL

differential method, which can be done when two equal transformers are available (see Fleming, Handbook for the Electrical Laboratory and Testing See also:

• ROOM

Room, ii . 6o2) . No test of a transformer is complete which does not comprise some investigation of the " ageing " of the core . The slow changes which take place in the hysteretic quality wing of iron when heated, in the case of certain brands, give rise to a time-increase in iron core loss . Hence a trans-former which has a core loss, say, of 300 watts when new, may, unless the iron is well chosen, have its core loss increased from 50 to 300% by a few months' use . In some cases specifications for transformers include fines and deductions from See also:

• PRICE
• PRICE, BARTHOLOMEW (1818–1898)
• PRICE, BONAMY (1807-1888)
• PRICE, RICHARD (1723-1791)

price for any such increase; but there has in this respect been See also:

• GREAT

great improvement in the manufacture of iron for magnetic purposes, and makers are now able to obtain supplies of, good magnetic iron or steel with non-ageing qualities . It is always desirable, how-ever, that in the case of large sub-station transformers tests should be made at intervals to discover whether the core loss has increased by ageing . If so, it may mean a very considerable increase in the cost of magnetizing power . Consider the case of a 3o-kilowatt transformer connected to the mains all the year round; the normal core loss of such a transformer should be about 300 watts, and therefore, since there are 876o hours in the year, the total See also:

• ANNUAL

annual energy dissipated in the core should be 2628 kilowatt hours .

Reckoning the value of this electric energy at only one See also:

• PENNY (Mid. Eng. peni or peny, from O. Eng. form penig, earlier penning and pending; the word appears in Ger. Pfennig and Du. penning; it has been connected with Du. pand, Ger. Pfand, and Eng. " pawn,". the word meaning a little pledge or token, or with G
• PENNY, GIANFRANCESCO (1488–1528)

penny per unit, the core loss See also:

• COSTS

costs £Io, 19s. per annum . If the core loss becomes doubled, it means an additional annual expenditure of nearly iii . Since the cost of such a transformer would not exceed roo, it follows that it would be economical to replace it by a new one rather than continue to work it at its enhanced core loss . In Great See also:

• BRITAIN (Gr. Hperavuml vi7vot, Bperravia; Lat. Britannia, rarely Britannia)

Britain the sheet steel or iron alloy used for the trans-former cores is usually furnished to specifications which See also:

• STATE
• STATE, GREAT OFFICERS OF

state the maximum hysteresis loss to be allowed in it in watts per lb (See also:

• AVOIRDUPOIS

avoirdupois) at a frequency of 50, and at a maximum flux-density during the See also:

• CYCLE
• CYCLE (Gr. KUK)^os, a circle)

cycle of 4000 C.G.S. units . When plates having a thickness t mils are made up into a transformer core, the total energy loss in the core due to hysteresis and eddy current loss when worked at a frequency is and a maximum flux-density during the cycle B is given by the empirical formulae T = •oo32nB1.55IO-l+(tnB)'I0-'' T' =o•88nBII.55Io 5+1.4(t1nBI)2io 10, where T stands for the loss per cubic centimetre, and TI for the same in watts per See also:

• POUND
• POUND (2)—(a)

pound of iron core, B for the maximum flux-density in lines per square centimetre, and BI for the same in lines per square inch, t for the thickness of the plates in thousandths of an inch (mils), and ti for the same in inches . The hysteresis loss varies as some power near to 1.6 of the maximum flux-density during the cycle as shown by See also:

• STEINMETZ, KARL FRIEDRICH VON (1796-1877)

Steinmetz (see ELECTROMAGNETISM) . Since the hysteresis loss varies as the 1.6th power of the maximum flux-density during the cycle (B max.), the advantages of a low flux-density are evident . An excessively low flux-density increases, however, the cost of the core and the copper by increasing the See also:

• SIZE

size of the transformer . If the form factor (f) of the primary voltage curve is known, then the maximum value of the flux-density in the core can always be calculated from the See also:

• FORMULA
• FORMULA (Lat. diminutive of forma, shape, pattern, &c., especially used of rules of judicial procedure)

formula B=EI/4fnSNI, where E is the R.M.S. value of the primary voltage, NI the primary turns, S the section of the core, and is the frequency . The study of the processes taking place in the core and circuits of a transformer have been greatly facilitated in See also:

• RECENT

recent years by Curve the improvements made in methods of observing and Tracing. recording the variation of periodic currents and electromotive forces . The See also:

• ORIGINAL

original method, due to See also:

• JOUBERT, BARTHELEMY CATHERINE (1769–1799)
• JOUBERT, JOSEPH (1754–1824)
• JOUBERT, PETRUS JACOBUS (1834–1900)

Joubert, was greatly improved and employed by See also:

• RYAN, LACY (c. 1694-176o)

Ryan, See also:

• BELL
• BELL, ALEXANDER MELVILLE (1819—1905)
• BELL, ANDREW (1753—1832)
• BELL, GEORGE JOSEPH (1770-1843)
• BELL, HENRY (1767-1830)
• BELL, HENRY GLASSFORD (1803-1874)
• BELL, JACOB (1810-1859)
• BELL, JOHN (1691-178o)
• BELL, JOHN (1763-1820)
• BELL, JOHN (1797-1869)
• BELL, ROBERT (1800-1867)
• BELL, SIR CHARLES (1774—1842)

Bell, See also:

• DUNCAN
• DUNCAN, ADAM DUNCAN, 1ST VISCOUNT (1731-1804)
• DUNCAN, PETER MARTIN (1824-1891)
• DUNCAN, THOMAS (1807—1845)

Duncan and See also:

• HUTCHINSON
• HUTCHINSON, ANNE (c. 1600-1643)
• HUTCHINSON, JOHN (1615-1664)
• HUTCHINSON, JOHN (1674-1737)
• HUTCHINSON, SIR JONATHAN (1828– )
• HUTCHINSON, THOMAS (1711-1780)

Hutchinson, Fleming, See also:

• HOPKINSON, FRANCIS (1737–1791)
• HOPKINSON, JOHN (1849-1898)

Hopkinson and See also:

• ROSA, CARL AUGUST NICHOLAS (1843-1889)
• ROSA, MONTE
• ROSA, SALVATOR (1615-1673)

Rosa, Callendar and Lyle; but the most important improvement was the introduction and invention of the See also:

• OSCILLOGRAPH

oscillograph by See also:

• BLONDEL, DAVID (1591-1655)
• BLONDEL, JACQUES FRANCOIS (1705-1774)

Blondel, subsequently improved by Duddell, and also of the ondograph of Hospitalier (see OSCILLOGRAPH) . This See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument enables us, as it were, to look inside a transformer, for which it, in fact, performs the same See also:

• FUNCTION

function that a See also:

• STEAM
• STEAM (0. Eng. steam, vapour, smoke, cf. Du. steam; the origin is unknown)

steam See also:

• ENGINE
• ENGINE (Lat. ingenium)

engine See also:

• INDICATOR (from Lat. indicare, to point out)

indicator does for the steam See also:

• CYLINDER (Gr. KvAwSpos, from KvXivaety, to roll)

cylinder.' Delineating in this way the curves of primary and secondary current and primary and secondary electromotive forces, we get the following result: Whatever may be the form of the curve of primary terminal potential difference, or primary voltage, that of the secondary voltage or terminal potential difference is an almost exact copy, but displaced 18o° in phase .

Hence the alternating current trans-former reproduces on its secondary terminals all the See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

variations of potential on the primary, but changed in scale . The curve of primary current when the transformer is an open secondary circuit is different in form and phase, lagging behind the primary voltage curve (fig . 6) ; but if the transformer is loaded up on its or ' For a useful See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list of references to published papers on alternating current curve tracing, see a paper by W . D . B . Duddell, read before the See also:

• BRITISH

British Association, See also:

• TORONTO

Toronto, 1897; also Electrician (1897), xxxix . 636; also Handbook for the Electrical Laboratory and Testing Room (J . A . Fleming), i . 407.secondary side, then the primary current curve comes more into step with the primary voltage curve . The secondary current curve, if the secondary load is non-inductive, is in step with the secondary voltage curve (fig . 7) .

These transformer diagrams yield much See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information as to the nature of the operations proceeding in the transformer . The form of the curve of primary current at no secondary load is a consequence of the hysteresis of the iron, combined with the fact that the form of the core flux-density curves of the transformer is always not far removed from a simple sine curve . If el is at any moment the electromotive force, iI the current 'on the primary circuit, and bI is the flux-density in the core, then we have the fundamental relation el=Rlii+SNI dbI/dt, where RI is the resistance of the primary, and NI the number of turns, and S is the See also:

• CROSS

cross-section of the core . In all modern closed'circuit trans-formers the quantity RIi, is very small compared with the quantity SNdb/dt except at one instant during the phase, and in taking the integral of the above See also:

• EQUATION (from Lat. aequatio, aequare, to equalize)

equation, viz. in finding the value of feldt, the integral of the first term on the right-hand side may be neglected in comparison with the second . Hence we have approximately bI = (SNI)—;feldt . In other words, the value of the flux-density in the core is obtained by integrating the See also:

• AREA

area of the primary voltage curve . In so doing the integration must be started from the time point through which passes the ordinate bisecting the area of the primary voltage curve . When any curve is formed such that its ordinate y is the integral of the area of another curve, viz. y = fy'dx, the first curve is always smoother and more See also:

• REGULAR

regular in form than the second . Hence the process above described when applied to a complex periodic curve, which can by See also:

• FOURIER, F
• FOURIER, FRANCOIS CHARLES MARIE (1772-1837)
• FOURIER, JEAN BAPTISTE JOSEPH (1768-1830)

Fourier's theorem be resolved into a series of simple periodic curves, results in a relative reduction of the magnitude of the higher harmonics compared with the funda- See also:

• MENTAL

mental term, and hence a wiping out of the See also:

• MINOR
• MINOR (Lat. for smaller, lesser)
• MINOR, ROBERT CRANNELL (1839-1904)

minor irregularities of the curve . In actual practice the curve of electromotive force of alternators can be quite sufficiently reproduced by employing three terms of the expansion, viz. the first three See also:

• ODD (in middle English odde, from old Norwegian oddi, an angle of a triangle; the old Norwegian oddamann is used of the third man who gives a casting vote in a dispute)

odd harmonics, and the resulting flux-density curve is always very nearly a simple sine curve . We have then the following rules for predetermining the form of the current curve of the transformer at no load, assuming that the hysteresis curve of the iron is given, set out in terms of flux-density and See also:

• AMPERE, ANDRE MARIE (1775–1836)
• AMPERE, JEAN JACQUES (1800-1864)

ampere-turns per centimetre, and also the form of the curve of primary electromotive force . Let the time See also:

• BASE

base See also:

• LINE

line be divided up into equal small elements .

Through any selected point draw a line perpendicular to the base line . Bisect the area enclosed by the curve representing the See also:

• HALF

half See also:

• WAVE

wave of primary electromotive force and the base line by another perpendicular . Integrate the area enclosed between the electromotive force curve and these two perpendicular lines and the base . Lastly, set up a length on the last perpendicular equal to the value of this area divided by the product of the cross-section of the core and the number of primary turns . The resulting value will be the core flux-density b at the phase instant corresponding . Look out on the hysteresis See also:

• LOOP

loop the same flux-density value, and corresponding to it will be found two values of the magnetizing force in ampere-turns per centimetre, one the value for increasing flux-density and one for decreasing . An inspection .of the position of the point of time selected on the time line will at once show which of these to select . See also:

• DIVIDE

Divide that value of the ampere-turns per centimetre by the product of the values of the primary turns and the mean length of the magnetic circuit of the core of the transformer, and the result gives the value of the primary current of the transformer . This can be set up to scale on the perpendicular through the time instant selected . Hence, given the form of the primary electromotive force curve and that of the hysteresis loop of the iron, we can draw the curves representing the changes of flux-density in the core and that of the corresponding primary current, and thus predict the rootmean-square value of the magnetizing current of the transformer . It is therefore possible, when given the primary electromotive force curve and the hysteresis curve of the iron, to predetermine the curves depicting all the other variables of the transformer, provided that the magnetic leakage is negligible . The elementary theory of the closed iron circuit transformer may be stated as follows: Let NI, N2 be the turns on the primary and secondary circuits, RI and R2 the resistances, S the Elementary section of the core, and bI and b2 the co-instantaneous Theory .

values of the flux-density just inside the primary and secondary windings . Then, if iI and i2 and el and e2 are the primary el, Primary voltage curve; iI, Primary current curve; e2, Secondary voltage curve . Curves 7.–Transformer load . el, Primary voltage curve; Primary current curve; e2, Secondary voltage curve; i2, Secondary current curve . Curves–at full eiii =e2i2 + (Riii2 +R2i 2) +Sat (Niii — N2i2) 1 %is equation merely expresses the fact that the power put into tl e transformer at any instant is equal to the power given out on tl e secondary side together with the power dissipated by the cc pper losses and the constant iron core loss . The efficiency of a transformer at any load is the ratio of the re an value, during the period, of the product to that of the product e2i2 . The efficiency of an alternating current transformer is a function of the form of the primary electromotive force curve . Eeperiment has shown' that if a transformer is tested for efficiency o. i various alternators having electromotive force curves of different fi rms, the efficiency values found at the same secondary load are r. of identical, those being highest which belong to the alternator crith the most peaked curve of electromotive force, that is, the curve having the largest form factor . This is a consequence of the tact that the hysteresis loss in the iron depends upon the manner in which the magnetization (or what here comes to the same thing, the flux-density in the core) is allowed to change . If the primary electromotive force curve has the form of a high See also:

• PEAK, THE

peak, or runs up suddenly to a large maximum value, the flux-density curve will be more square-shouldered than when the voltage curve has a See also:

• LOWER

lower form factor . The hysteresis loss in the iron is less when the magnetization changes its sign somewhat suddenly than when it does so more gradually . In other words, a diminution in the form factor of the core flux-density curve implies a diminished hysteresis loss .

The variation in core loss in transformers when tested on various forms of commercial alternator may amount to as much as 10% . Hence, in recording the results of efficiency tests of alternating current transformers, it is always necessary to specify the form of the curve of primary electromotive force . The power factor of the transformer or ratio of the true power absorption at no load, to the product of the R.M.S. values of the primary current and voltage, and also the secondary drop of the transformer, vary with the form factor of the primary voltage curve, being also both in-creased by increasing the form factor . Hence there is a slight advantage in working alternating current transformers off an alternator giving a rather peaked or high maximum value electromotive force curve . This, however is disadvantageous in other ways, as it puts a greater See also:

• STRAIN (through O. Fr. straindre, estraindre, mod. i treindre, from Lat. stringere, to draw tight, related to stress, stretch, string, &c.)

strain upon the insulation of the trans-former and cables . At one time a controversy arose as to the relative merits of closed and open magnetic circuit transformers . It was, however, shown by tests made by Fleming and by See also:

• AYRTON, WILLIAM EDWARD (1847-1908)

Ayrton on See also:

• SWINBURNE, ALGERNON CHARLES (1837–1909)

Swinburne's " See also:

• HEDGEHOG, or URCHIN

Hedgehog " transformers, having a straight core of iron wires bristling out at each end, that for equal secondary outputs, as regards efficiency, open as compared with closed magnetic circuit transformers had no advantage, whilst, owing to the smaller power factor and consequent large R.M.S. value of the magnetizing current, the former type had many disadvantages (see Fleming, " Experimental Researches on Alternate Current Transformers," Journ . Inst . Elec . Eng., 1892) . The discussion of the theory of the transformer is not quite so simple when magnetic leakage is taken into See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account . In all cases Magnetk a certain proportion of the magnetic flux linked with Leakage. the -primary circuit is not linked with the secondary .m1-cult, and the difference is called the magnetic leakage .

This magnetic leakage constitutes a wasted flux which is non- effective in producing secondary electromotive force . It increases with the secondary current, and can be delineated by a curve on the transformer See also:

• DIAGRAM

diagram in the following manner . The curves of primary and secondary electromotive force, or terminal potential difference and current, are determined experimentally, and then two curves are plotted on the same diagram which represent the variation of (ei—Riii)/Ni and (e2+R2i2)/N2; these will represent the time differentials of the total magnetic fluxes Sbi and Sb2 linked respectively with the primary and secondary circuits . . The above curves are then progressively integrated, starting from the time i See Dr G . Roessler, Electrician (1895), See also:

• XXXVI

xxxvi . 150; Beeton, See also:

• TAYLOR
• TAYLOR, ANN (1782-1866)
• TAYLOR, BAYARD (1825–1878)
• TAYLOR, BROOK (1685–1731)
• TAYLOR, ISAAC (1787-1865)
• TAYLOR, ISAAC (1829-1901)
• TAYLOR, JEREMY (1613-1667)
• TAYLOR, JOHN (158o-1653)
• TAYLOR, JOHN (1704-1766)
• TAYLOR, JOSEPH (c. 1586-c. 1653)
• TAYLOR, MICHAEL ANGELO (1757–1834)
• TAYLOR, NATHANIEL WILLIAM (1786-1858)
• TAYLOR, PHILIP MEADOWS (1808–1876)
• TAYLOR, ROWLAND (d. 1555)
• TAYLOR, SIR HENRY (1800-1886)
• TAYLOR, THOMAS (1758-1835)
• TAYLOR, TOM (1817-1880)
• TAYLOR, WILLIAM (1765-1836)
• TAYLOR, ZACHARY (1784-1850)

Taylor and See also:

• BARR

Barr, Journ . Inst . Elec . Eng. See also:

• XXV

xxv . 494; also J . A . Fleming, Electrician (1894), =ill .

580.point through which passes the ordinate bisecting the area of each half wave, and the resulting curves plotted to See also:

• EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express by their ordinates Sbi and Sb2 . A curve is then plotted whose ordinates are the differences Sb,—Sb2, and this is the curve of magnetic leakage . The existence of magnetic leakage can be proved experimentally by a method due to Mordey, by placing a pair of thermometers, one of See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

mercury and the other of See also:

• ALCOHOL

alcohol, in the centre of the core See also:

• APERTURE (from Lat. aperire, to open)

aperture . If there is a magnetic leakage, the mercury bulb is heated not only by radiant heat, but by eddy currents set up in the mercury, and its rise is therefore greater than that of the alcohol thermometer . The leakage is also determined by observing the secondary voltage drop between full load and no load, and de-ducting from it the part due to copper resistance; the See also:

• REMAINDER, REVERSION

remainder is the drop due to leakage., Thus if V2 is the secondary voltage on open circuit, and V2' that when a current A2 is taken out of the transformer, the leakage drop v is given by the equation v = (V2 —V2') — l R2A2 +R1A2 (N2/Nl)2} . The term in the large See also:

• BRACKET

bracket expresses the drop in secondary voltage due to the copper resistance of the primary and secondary circuits . In See also:

• DRAWING

drawing up a See also:

• SPECIFICATION (from Med. Lat. specificatio, specificare, to enumerate or mention in detail)

specification for an alternating current trans-former, it is necessary to specify that the maximum secondary drop between full and no load to be allowed shall not exceed a certain value, say 2 % of the no-load secondary voltage; also that the iron core loss as a percentage of the full secondary output shall not exceed a value, say, of i %, after six months' normal work . In the See also:

• DESIGN (Fr. desiin, drawing; Lat. designare, to mark out)

design of large transformers one of the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief points for See also:

• ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention is the arrangement for dissipating the heat gene-rated in their See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass by the copper and iron losses . For every watt expended in the core and circuit, Uesig a Transfonrmer . See also:

• SURFACE

surface of 3 to 4 sq. in. must be allowed, so that the heat may be dissipated . In large transformers it is usual to employ some means of producing a current of air through the core to ventilate it . In these, called air-blast transformers, apertures are left in the core by means of which the cooling air can reach the interior portions .

This air is driven through the core by a fan actuated by an alternating current motor, which does not, however, take up power to a greater extent than about 4 or 10-% of the full output of the transformer, and well repays the outlay . In some cases transformers are oil-insulated, that is to say, included in a cast-iron See also:

• BOX
• BOX (Gr. irl or, Lat. buxus, box-wood; cf. 2r6Eir, a pyx)

box which is filled in with a heavy insulating oil . For this purpose an oil must be selected See also:

• FREE

free from See also:

• MINERAL

mineral acids and water: it should be heated to a high temperature before use, and tested for See also:

• DIELECTRIC

dielectric strength by observing the voltage required to create a spark between metal balls immersed Material . Dielectric Material . Dielectric strength in strength in kilowatts per kilowatts per centimetre . centimetre . See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

Glass 285 Lubricating oil . . 83 Ebonite . 538 See also:

• LINSEED

Linseed oil 67 Indiarubber 492 Cotton-See also:

• SEED (from the root seen in Lat. serere, to sow)

seed oil . 57 See also:

• MICA

Mica 2000 Air film •02 cm . 27 Micanite . . .

. 4000 thick . . 48 See also:

• AMERICAN

American See also:

• LINEN

linen paper 540 Air film I.6 cm . L paraffined . thick . . . . in it at a distance of 1 millimetre apart . See also:

• OILS (adopted from the Fr. oile, mod. huile, Lat. oleum, olive oil)

Oils, however, are inferior in dielectric strength or spark-resisting power to solid dielectrics, such as micanite, ebonite, &c., as shown by the above table of dielectric strengths (see T . See also:

• GRAY
• GRAY (or GREY), WALTER DE (d. 1255)
• GRAY, ASA (1810-1888)
• GRAY, DAVID (1838-1861)
• GRAY, ELISHA (1835-1901)
• GRAY, HENRY PETERS (1819-18/7)
• GRAY, HORACE (1828–1902)
• GRAY, JOHN DE (d. 1214)
• GRAY, JOHN EDWARD (1800–1875)
• GRAY, PATRICK GRAY, 6TH BARON (d. 1612)
• GRAY, ROBERT (1809-1872)
• GRAY, SIR THOMAS (d. c. 1369)
• GRAY, THOMAS (1716-1771)

Gray, Plays . Rev., 1898, P . 199)• Polyphase Transformers are appliances of similar construction to the single-phase trans-formers already described, but modified so as to enable them to transform two or more phase-related primary alternating cur-rents into similar secondary currents . Thus, a three-phase transformer may be constructed with a core, as shown in fig . 8 .

Each core See also:

• LEG
• LEG (a word of Scandinavian origin, from the Old Norwegian leggr, cf. Swed. lagg, Dan. laeg; the O. Eng. word was sceanca, shank)

leg is surrounded with a primary coil, and these are joined up either in See also:

• STAR

star or See also:

• DELTA (from the shape of the Gr. letter A, delta, originally used of the mouth of the Nile)

delta fashion, and connected to the three or four line wires . The secondary circuits are then connected in a similar fashion to three or s, s2 s four secondary lines . In the case of two- phase transmission with two separate pairs FIG . 8.—Brush Three-of leads, single-phase transformers may be phase Transformer . and secondary currents and potential differences at the same instant, these quantities are connected by the equations er=R+SNidbi e2=SN2 dt2—R2i2. at, Hence, if 61 = b2, and if See also:

• RAIL

Rail is negligible in comparison with SNidb/dt, and i=o, that is, if the secondary circuit is open, then ei/e2=N1/N2, or the transformation ratio is simply the ratio of the windings . This, however, is not the case if br and b2 have not the same value; in other words, if there is magnetic leakage . If the magnetic leakage can be neglected, then the resultant magnetizing force, and therefore the iron core loss, is constant at all loads . Accordingly, the relation between the primary current (Si), the secondary current (i2), and the magnetizing current (i); or primary current at no load, is given by the equation Nlii—N2i2=Nit . Then, See also:

• WRITING
• WRITING (the verbal noun of " to write," O. Eng. writan, to inscribe)

writing b for the instantaneous value of the flux-density in the core, everywhere supposed to be the same, we arrive at the identity nected with opposite ends of th sulated rings on its See also:

• SHAFT
• SHAFT (O. Eng., sceaft, from scafan, to shave; the word is common to Teutonic languages)

shaft See also:

• CONE (Gr. Kwvos)

cone arma-Phase Transformers are arrangements of static or rotary trans- See also:

• TURE

ture winding (fig. to) . If such a ring is placed in a bipole See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field formers intended to transform single-phase alternating currents into magnet, and if a pair of brushes make contact with the commutator polyphase currents . An important See also:

• SYSTEM

system of phase transformation C and another pair with the two rings called slip rings, Si S2, and if continuous current at a constant voltage is supplied to the com- mutator side, then the See also:

• ARMATURE (from Lat. armatura, armour)

armature will begin to revolve in the field, the resulting electromotive force will in general differ in phase and and from the brushes in contact with the slip rings we can draw off value from either of the components . Thus, if two alternating an alternating current .

This reaches its maximum value when the points of contact of the rings with the armature circuit pass the See also:

• AXIS (Lat. for " axle ")

axis of See also:

• COMMUTATION (from Lat. commutare, to change)

commutation, or line at right angles to the direction of the magnetic field, for it has at this moment a value which is three can be represented by the sides of a triangle which is half double the steady value of the continuous current being poured an equilateral triangle . If then a two-phase alternator, D (fig . 9), into the armature . The maximum value of the electromotive provides two-phase cur- force creating this alternating current is nearly equal to the electro- rents, and if the two circuits See also:

• MOTIVE (from Lat. movere, to move)

motive force on the continuous current side . Hence if A is the are connected, as shown, to maximum value of the continuous current put into the armature a pair of single-phase trans- I and V is the value of the brush potential difference on the See also:

• CON

con- formers, Ti and T2, we can tinuous current side, then 2A is the maximum value of the out- obtain three-phase alter- coming alternating current and V is the maximum value of its nating currents from the ar- voltage . Hence 2AV/2 =AV is the maximum value of the out- rangement . The primaries coming alternating current of both transformers are C B the same . The secondary O circuit of one transformer, T2, has, say, too turns, and A a connexion is made to its See also:

• MIDDLE

middle point 0, and this is connected to the secondary of the other transformer T which has 87 (=5o 43) turns . From the points A, B, C we can then tap off three-phase alternating cur- !-- - O rents . The advantages of the See also:

• SCOTT, ALEXANDER (fl. 1550)
• SCOTT, DAVID (18o6-1849)
• SCOTT, MICHAEL (1789-1835)
• SCOTT, ROBERT (1811-1887)
• SCOTT, SIR GEORGE GILBERT (1811-1878)
• SCOTT, SIR WALTER, BART
• SCOTT, WILLIAM BELL (1811-1890)
• SCOTT, WINFIELD (1786-1866)<