Improvements in the Cores of Dynamo-electric Machines and other Electrical Apparatus.
Year: 1896

page_text: Date of Application, 22nd Aug., 1896-Accepted, 17th Oct., 1896
COMPLETE
SPECIFICATION.
Improvements in the Cores of Dynamo-electric Machines and other
Electrical Apparatus.
I, JOUN FORREST KELLY, Electrician, a citizen of the United States, residing
in the City of Pittsfield, County of Berkshire and State of Massachusetts, U.S.A.,
do hereby declare the nature of this invention and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement :--
My invention relates to electrical apparatus which has a magnetic circuit
composed wholly or in part of iron, which is wholly or in part traversed by a
varying magnetic flux, when the apparatus is in operation. This invention is
applicable to parts of almost all dynamo electric machinery, and particularly to
what are known as secondary generators, transformers or converters.
In all such apparatus there is in those parts of the iron core where the magnetic
flux is varying even where Foucault currents are suppressed by laminating it-
a loss of energy due to hysteresis which appears as heat in the iron and is called
"core-loss." It has been known for some years that this core-loss in annealed iron
cores which become heated while the apparatus is in use, increases after such use
has continued for some time, the increase being due to an increase in hysteresis.
This increase in hysterosis accompanies long-continued heating such as that
produced by the reversal of the lines of force in uncooled transformers as now
ordinarily constructed. If the heating of the iron could be prevented, the incrense
of the hysteresis aud resulting increase of core-loss could also be prevented, but
the cost of prevention of heating is such as to make it commercially impossible;
hence the increase of core-loss has up to the present time been submitted to as a
necessary evil.
This evil is marked in alternating current dynamos and motors, but is probably
greater in transformers than in other kinds of electrical apparatus. Its magnitude
in transformers will be plain from the following figures: The average size of
transformers at present is fifty lights, being such a transformer as would be used
to light a large sized dwelling house of fifteon or twenty rooms. The average all
day load is quarter load, making its average output about 700 watts. The core-
loss in such a transformer, when new, will at a frequency of one hundred and
thirty-three alternations per second be about fifty-five (55) watts. After the
transformer has been in use under ordinary conditions for some time, there is, ae
above stated, an increase in the core-loss due to hysteresis. This increased core-loss
in a comparatively short time amounts to at least forty per cent. (40%), and later
frequently rises to 100 per cent. (100%) of the original core-loss. Taking it at only
forty-five per cent. (45%) it will in this case amount to about twenty-five (25) watts,
or over three and one-half per cent. (3%) of the average output; that is to say,
the average efficiency of the transformer will be reduced about three and one-half
per cent. (3%), or, to put it another way, the steady losses in a ten thousand
(10,000) light central plant installation would be increased by some five kilowatts,
which at the low rate of one cent per kilowatt hour would cost the producer one
dollar and twenty cents ($1.20) a day or four hundred and thirty-eight dollars
($438.) a year.
The object of my invention is to prevent the core-loss increase above referred to.

page_text: Heretofore, although the increased core-loss has been recognized, all attempts to
prevent it by changing the composition or character of the iron have been attempts
to make a purer iron, to exclude as far as possible all foreign substances. I, however,
have discovered that the hysteresis growth which gives rise to the increase of the
core-loss can be prevented by intentionally having the iron of the core contain one
foreign substance, silicon, in suitable proportions. One proportion suitable for
attaining the object of my invention is two hundred and thirty-five ten thousandths
per cent. (0-0235%) of silicon, the other parts being pure iron so far as it can be
conveniently made for commercial purposes. Such purity is, however, required
rather for convenience and assistance in manufacturing than for the purposes of my
invention. In that proportion the silicon alloy is a hysteresis-growth-preventing
alloy under any ordinary conditions to which a coro may be subjected. The iron
of the particular core to which I now have reference upon analysis was found to
have the following composition : Iron, 99-5215%; silicon, 0.0235%;
sulphur, 0-0316%; manganese, 0.1680% phosphorus, 0-0830% graphite
'carbon, 0.0076%; combined carbon, 0.1138%; copper, 0-0510 %. It is the
Bilicon which is the active agent in preventing the molecular change which results
in an increase in core-loss, and when the proportion of silicon is as that above
specified, such increase is prevented. The proportion of silicon admits of considerable
variation; I have, however, given one which I have found to be satisfactory.
The iron heretofore used in laminated coros as now mado, is as free from all
substances other than pure iron as is commercially practicable, the whole tendency
being to attempt to prevent hysteresis growth by making the iron purer. Such
purer iron has contained about one-hundredth of one per cent. (0-0100%) of silicon,
such an amount being usually present in iron as an incident of its manufacture.
Such an alloy is not a bysteresis-growth-preventing alloy. The amount of silicon
in the iron used by me, it will be noticed, is considerably larger than that present
in the ordinary iron used for laminated cores. The abnormal amount of silicon in
the iron does not increase the original core-losses in perfectly annealed iron, but
prevents the hysteresis growth at the temperatures to which the transformers are
subjected when in use. The iron with the hysteresis-growth-preventing silicon
alloy is, I have observed, more springy than iron ordinarily used in cores, in
addition to being more difficult to anneal. The alloy appears to resist molecular
change of any sort.
Methods of making iron containing approximately any particular proportion of
silicon or similar metals that may be desired, are known to those skilled in the art
of manufacturing irou, and form no part of my invention; no more do the methods
of annealing or of rolling, where rolling is desired, since these methods need be
only the ordinary ones. The annealing requires, however, more care and attention
than that of ordinary iron in order that it be perfectly doue, as tho increase of
silicon makes the metal more difficult to anneal. I have found that such iron can
bersufficiently annealed by subjecting it twice to the ordinary annealing process.
In making up the cores for the magnetic circuits in transformers and other
dynamo electrio.machines, any usual methods of construction and lamination now
used can be adopted.
Having now particularly described and ascertained the nature of my said inven
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. In an electrical apparatus having when in operation a varying magnetic flux,
a laminated iron core traversed by said varying flux having in its composition an
alloy preventing hysteresis growth, substantially as described.
2. uan electrical apparatus having when in operation a varying magnetic flux,
a laminated iron core traversed by said varying flux having in its composition an
abnormal proportion of silicon, substantially as described.
3. In electrical apparatus having when in operation a varying magnetic flux, an

page_text: annealed laminated irou core traversed by said varying flux having in its composition
sufficient silicon to prevent hysteresis growth at temperatures to which transformers
are subjected when in use, substantially as described.
Deted the 14th dex of August 1896
D. YOUNG & Co.,
11 & 12 Southampton Buildings, London, W.C.,
Agents for the Applicant.