The Montgomery advertiser., 1901-10-03
The ADVERTISERS
 & HOME STUDY CIRCLE

Enciency of transmission was about 75
 per cent. In thiB country both types of
 machinery are manufactured by Nesting
 sot Soase sns and esnssa, Electric Companies rather speciality of the two-phase vari-
 ety. exhibiting their first machines in Chicago in 1895. and the General Els Nic
 Considerable discussion has appeared in
 the technical magazines upon the relative
 merits of the two systems, but the agree
 ment seems to lie In regarding the two
 eral purposes of distribution, and the
 three-phase more economical for. long,
 distance transmission.
 As regards the field magnet. no differ
 ence of construction from that designed
 for single phase alternator is necessary.
 but for the armature the two-phase wind-
 ing requires twice as many coils and the
 three-phase three times as many as are employed for single-phase currents. Wind
 ing can be ''open coll" as is largely the
 scheme Of arc generators, or "closed. as
 for direct currents. Indeed, two and
 three phase experimental models can be
 obtained respectively from Brush and
 Thomson-H Houston arc machines by sub
 tator segments. Similarly. closed coil
 windings can be obtained Tom ordinary
 drum and ring armatures by slipping re-
 ccmmutators and providing electrical con
 tacts with set screws at four or three
 equidistant points. Each of the four
 wires would terminate in a collector ring.
 l. and N the other. Ordinary four line wires would be used, but L. and M could
 be united to single wire of twice the
 size of K or N. Leads are brought at
 four equal distant points and terminate
 in four collector rings. In each of the two circuits thus formed Is inserted the primary of a series transformer mounted inside the armature, and revolving with if- Secondary HtlrrantQ of nr0nOrttOnatA values are thereby induced in the other winding are rectified by the commutator and serve. auxiliary to that of the sep. strength co-incidently with increase of
 load. Mathematically, 1t could be proved that If the potential between two oppo- 2.ooo volts. the potential between two ad- tacent points, as l and ?. would at the same moment be about 1,40o volts. The derivation can be illustrated from simple gcometrical principles. If diameters be
 drawn through the armature from to 8
 this special case. soOo volts. From any
 one point to the center would be 1000: | points. draw a diagonal, representing the hypotenuse of a right angIed triangle If each of the equal sides is 100 the hypo-
 tenuse Is easily found to be 1, 400. A view figure "A.
 A diagramatic representation of three
 phase open circuit winding is given in l figure 75; only three terminals are brought
 out instead of six. for the three internal ends are conn ssteG together. rhis wind | ing will be recognized as identical with | article 8. but three rings in place of | three segments are connected to the ter minals A, and c. In consequence of
 the common connection of three ends | the left-hand portion of figure 75 shows | the scheme still clearer. and from It's rep- | resentation In this manrer Is denoted as the "" winding. If the field magnet is | to be excited as composite or compound | the three internal ends instead of being | directly connected together are attached | to three commutator segmerts and their brushes connected to the series portion | of the field winding. Thus the field wind ing represents the common connection be- | tween the three phases When a closed l circuit armature Is desired on the same
 scheme as that for two phases. three in-
 stead of four equidistant points are taped | and connected to three rings. If three | such points are geometrically joined by
 straight lines an equilateral triangle will | be formed like the Greek letter delta, | and this Is technically known as the If in addition to the collector rings. the | two or three phase closed circuit wind
 tator segments fin the ordinary direct cur | rent manner there will result the ability | to draw of either direct or alternating
 currents from ea. the same armaturTs To6ls As | current machines. Some of 200 K. w. l capacity have just been installed In Chi cago. and one of 1.50o K. W. is being set | up in Providence. The direct current is | led at once to the street mains for oper-
 ating lamps or motors:the alternating cur | rents traverse the primaries of | stop-up transformers; the second | aries generate 5000 to 5000 volts | and send the current to the
 required distance of five to ten miles. At | proper sub-stations or distributing points | step-down transformers ars put in circuit | from the secondaries of which the cur
 rent Is led to the collector rings of slmi- l lar but smaller double current machines | the armatures rotate and exchange the 1 alternating for direct currents which lat | ter are distributed. Used as a motor and | rectifier, the double current machine is | called a rotary converter" Its use is
 of increasing importance. as will be noted | in succeeding articles.
 | Copyright, 190o)