Tímarit Verkfræðingafélags Íslands - 01.06.1950, Síða 9

TlMARIT V.F.l. 1950
31
An arrangement that obviates the necessity for any
mechanical bracing of the copper is therefore highly
desirable, and this is achieved by the simple expedient
of arranging the copper as shown on the right hand
side of Fig. 6. By providing suitably shaped collars
which hold the copper at right-angles to a radius of
the machine, the sole effect of the centrifugal force R
is to compress the copper against the collar, and the
bursting force is entirely eliminated. In fact, by slightly
increasing the cant of the copper, a force causing the
copper to press in against the pole body can be pro-
duced.
With the arrangement shown on the right hand side
of Fig. 6, the copper experiences only the compressive
force R, but the top collar is, of course, subjected to
forces corresponding to P and M on the left hand side
of the drawing, the effect simply being to transfer these
resolved forces from the relatively weak copper to the
strong collar. In practice, however, no separate collar
■would be necessary as the inner surface of the pole
shoe would simply be made with the appropriate slope.
By comparing the two sides of Fig. 6, it will be seen
that, when a canted winding is used, the winding space
is less than that available for a normal winding. It may
therefore not be possible to use the canted strip arrange-
rnent on a machine if the poles are of short radial
depth.
When the peripheral velocity of the rotor can reach
a very high value, such as in certain waterwheel-driven
alternators when overspeeding, it is sometimes desir-
able to make the field winding of aluminium instead
°f copper, in order to reduce the stresses in the pole-
shoe overhangs, which act as cantilevers to hold the
ivinding on the pole, and in the pole dovetails. Alumini-
um is used in such cases solely because it is lighter
than copper, but experience has Siiown that it is also
more resistant to bulging (when non-canted coils have
to be used) than copper, which is an additional advantage.
TRANSPOSED CONDUCTOR.
When the current in a transformer or reactor is large,
it is necessary to divide the conductor from which the
coils are wound into several strands insulated from each
other, in order to reduce eddy-current losses; and it is
also necessary to transpose the strands at frequent inter-
vals, to reduce circulating-current losses caused by the
induction of unequal voltages in the individual strands.
If, as is usual, these transpositions are formed by
hand during the winding of the coil, the work is labori-
ous and costly, and the number of transpositions that
can be economically provided is limited. To overcome
this difficulty, a transposing machine has been devis-
ed, which automatically produces stranded conductor.
This not only saves time and expense in the winding of
the coil, since the transposed conductor can be wound
straight on to the insulating cylinder, but also reduces
the stray loss considerably, since the strands are continu-
ously transposed, thus giving a much greater number of
transpositions than it is practicable to make by hand.
While this type of conductor can be used with advan-
tage in large transformers, it is particularly suitable
for large reactors, in which the flux density is invari-
ably high, the strand loss being only about half as much
as with hand-transposed conductor.
The individual strands of the transposed conductor
consist of thermex-covered rectangular copper; and,
when the conductor is for use in a transformer or reac-
tor, the transposing machine covers the finished con-
ductor with the necessary layers of insulating paper.
By omitting the paper wrapping, the transposed conduc-
tor is suitable for use in the stators of low-voltage
heavy-current alternators, where it is equivalent to a
Roebel-bar winding.
ACKNOVVLEDGEMENT.
The author thanks the British Thomson-Houston Co.,
Ltd., for permission to publish the foregoing information.
ÝM5AR FRÉTTIR.
Nordisk IVIetodik-Komite for Levnedsmidler
hefur hafið útgáfu á standardblöðum um þau efni, er
starfsemi nefndarinnar varðar. Fyrsta blaðið er þegar
komið út og heitir „Ákvörðun á bórsýru (HsBO,)“, 3
síður í broti A4. Tekstinn er bæði á dönsku og ensku.
Næsta blað er væntanlegt í desember. Þeir, sem vilja
gerast áskrifendur að blöðunum eða kaupa einstök blöð,
eru beðnir að snúa sér til ritstjóra Tímarits VFl.
Ný
vegagerðarvél.
Blaw-Knox Co. hefur að undanförnu gert tilraunir
hieð vegasteypuvél af nýrri gerð. Hún er að því leyti
fl'ábrugðin eldri vélum, að steypumótin eru föst við vél-
lr>a, sem dregur þau með sér jafnóðum og hún steypir
veginn. Sparast þannig öll mótavinnan. Steypuhraðinn er
!80 m/klst. Vélin getur aðeins lagt ójárnbenta vegi, en
þensluraufir má setja í steypuna eins og venjulega. Til-
vaunavegur, sem lagður var með þessari vél í Iowa, kost-
aði $7900, en lægsta tilboð í byggingu hans með venju-
legum vélum var $15500. Tvær gerðir af þessari vél munu
væntanlega koma á markaðinn á næsta ári.
(McGraw-Hill Digest, júli 1950).
Steinsteypa varin frosti með infra-rauðum geislum.
1 Bandaríkjunum eru menn farnir að nota infra-rauða
geisla til að verja steypu gegn frosti. Við stíflugerð
nokkura voru notaðir 5 250w lampar. Var þeim fest á
6 m langa fjöl, sem komið var fyrir utan á vinnupöllunum.
(McGraw-Hill Digest, júlí 1950).
Syntetiskt A-vitamin.
Hoffmann—La Roche i Sviss hefur tekizt að framleiða
syntetiskt A-vitamin, sem er mjög sterkt og laust við
fiskbragðið, sem einkennir A-vitamín úr lýsi. Vinnslan
fer fram í 12 stigum, en hráefnið er citral. Með þessari
nýju vinnsluaðferð hefur verð á A-vitamíni lækkað um
30 cent pr. 1 millj. einingar. Má því búast við verðlækk-
un á þorska-, lúðu- og hákarlalýsi, en A-vitamln hefur
hingað til verið unnið úr því.
(McGraw-Hill Digest, maí 1950).