| ALTERNATING CURRENT MOTORS | [1,267] to 1,376 |
|---|---|
| Classification—synchronous motors—essential parts—synchronous motor principles: condition for starting; effective pressure; dead centers; speed; limit of lag; effect of load changes—effect of altering the field strength—disadvantages of synchronous motors; advantages—the "V" curve—adaptation—efficiency—hunting of synchronous motors; mechanical analogy—use as condenser—surging—characteristics of synchronous motors: starting; running; stopping; effect upon circuit; power factor; auxiliary apparatus; adaptation—induction (asynchronous) motors—essential parts—types—oscillating magnetic field—rotating magnetic field—operation of single phase motor; why not self starting; provision for starting—operation of polyphase induction motor; why called asynchronous—speed; classification according to speed—the terms primary and secondary—why polyphase induction motors are explained before single phase—polyphase induction motors—features—essential parts—principles—production of rotating field—Tesla's rotating field—method of obtaining resultant flux of Tesla's field—Arago's rotations; explanation—Faraday's experiment—production of two phase rotating field; resultant poles—six and eight pole two phase rotating fields—physical conception of two phase rotating field—production of three phase rotating field; with ring winding—physical conception of three phase rotating field—three phase six pole winding—slip—copper cylinder illustrating principle of operation of induction motor—calculation of slip—table of synchronous speeds—variation of slip; why so small; variation with load; table of variation—sector method of measuring slip—evolution of the squirrel cage armature; construction—the field magnets; parts; construction—field windings for induction motors—calculation for revolutions of rotating field; objection to high speed of field—difficulty with low frequency currents—general character of field winding—formation of poles—grouping of coils—starting of induction motors: external resistance, auto-transformer, internal resistance methods—internal resistance induction motors; adaptation—how resistance is cut out—why not desirable for large sizes—external resistance or slip ring motors—operation—armature connections—single phase induction motors—service suitable for—disadvantage—parts—why not self-starting—how started—phase splitting; production of rotating field from oscillating field—methods—starting coils—shading coils—character of the starting torque—modification of armature for starting with heavy load—clutch type of single phase induction motor; its action in starting—commutator motors—classification—action of closed coil rotating in alternating field—the transformer pressure—generated pressure—self-induction pressure—local armature currents; reason for sparking; how reduced—high resistance connectors—effect of low power factor—effect of frequency—series motor—features—adaptation—neutralized series motor—conductive method—inductive method—shunt motors—repulsion motors—difficulty with early motors—means employed to stop sparking—essentials of single repulsion motors—the term repulsion induction motor—compensated repulsion motor—power factor of induction motors—its importance—false ideas in regard to power factor—speed and torque of motors. | |
| TRANSFORMERS | [1,377] to 1,456 |
| Their use—essential parts—basic principles—the primary winding—the secondary winding—magnetic leakage—the induced voltage—no load current—magnetizing current—action of transformer with load—classification—step up transformers—use—construction—copper economy—step down transformers—use—construction—core transformers—construction—advantages—shell transformers—comparison of core and shell types—choice—combined core and shell transformers—economy of construction—single and polyphase transformers—features of each type—choice of types for polyphase currents—operation of three phase transformer with one phase damaged—transformer losses—hysteresis—what governs the loss—how reduced—eddy currents—lamination—thickness of laminæ—importance of iron losses—how to reduce iron losses—copper losses—how caused—effect on power factor—effect of resistance—cooling of transformers—cooling mediums employed—heating of transformers—objection to heating—dry transformers—air cooled transformers—natural draught type—forced draught or air blast type—construction of coils for air cooling—requirements with respect to air supply—quantity of air used—oil cooled transformers—circulation of the oil—action of the oil—objection to oil—kind of oil used—oil requirements—moisture in oil—water cooled transformers—internal coil type—external coil type—thermo-circulation—quantity of circulating water required—transformer insulation—the "major" and "minor" insulation—mica—outdoor transformers for irrigation service—oil insulated transformers—efficiency of transformers—efficiency curve—all day efficiency of transformers—transformer fuse blocks—auto-transformers—constant current transformers for series arc lighting; elementary diagram illustrating principles—regulation—transformer connections—single phase connections—combining transformers—precautions—operating secondaries in parallel—connections for different voltages—precautions—two phase connections—three phase connections: delta, star, delta star, star-delta—comparison of star and delta connections—three phase transformers—comparison of air blast, water cooled, and oil cooled transformers—standard transformer connections—how to test transformers—transformer operation with grounded secondary—transformer capacity for motors—transformer connections for motors—arc lamp transformer—transformer installed on pole—static booster or regulating transformer. | |
| CONVERTERS | [1,457] to 1,494 |
| Where used—kinds of converter—A.I.E.E. classification—rotary converters—operation—speed—principles—relation between input and output pressures—single and polyphase types—advantage of polyphase converters—armature connections of polyphase converter—pressure relation—voltage variation—advantage of unity power factor—effect of field too strong—compounding of rotary converters—ratio of conversion—voltage regulation—split pole method—regulating pole method—best location of regulating poles—reactance method—multi-tap transformer method—synchronous booster method—winding connections—field connections—adaptation—motor generator sets—classification—standard practice—behavior of rotary when hunting; comparison with motor generator sets—racing—frequency changing sets—parallel operation of frequency changers—cascade converter—speed—action in motor armature winding—advantages—how started—comparison of cascade converter with synchronous converter. | |
| RECTIFIERS | [1,495] to 1,530 |
| Classification—mechanical rectifiers—essential features—construction—application—electrolytic rectifiers—principles of operation—Mohawk rectifier—the term "valve"—metals for electrodes—electrolyte—Nodon valve—Audion valve—Buttner valve—Churcher valve—De Faria valve—Fleming oscillation valve—Grisson valve—Pawlowski valve—Giles electric valve—Buttner valve—mercury vapor rectifiers—principles—the terms "arc" and "vapor"—three phase mercury vapor rectifier—construction—auxiliary apparatus—series mercury arc rectifier—dissipation of heat from bulb—replacement of bulb—advantages of rectifier—precautions in installing—electromagnetic rectifiers—construction and operation. | |
CHAPTER LI
ALTERNATING CURRENT MOTORS
The almost universal adoption of the alternating current system of distribution of electrical energy for light and power, and the many inherent advantages of the alternating current motor, have created the wide field of application now covered by this type of apparatus.
As many central stations furnish only alternating current, it has become necessary for motor manufacturers to perfect types of alternating current motor suitable for all classes of industrial drive and which are adapted for use on the kinds of alternating circuit employed. This has naturally resulted in a multiplicity of types and a classification, to be comprehensive, must, as in the case of alternators, divide the motors into groups as regarded from several points of view. Accordingly, alternating current motors may be classified:
1. With respect to their principle of operation, as
a. SYNCHRONOUS MOTORS;
b. ASYNCHRONOUS MOTORS:
1. Induction motors;
{series;
2. Commutator motors {compensated;
{shunt;
{repulsion.
2. With respect to the current as
- a. Single phase;
- b. Polyphase;
