Improvements in the Construction of Electrical Transformers for use in Three-wire Systems."
Year: 1897

page_text: Date of Application, 9th Nov., 1897-Accepted, 18th Dec., 1897
66 Improvements in the Construction of Electrical Transformers for
use in Three-wire Systems."
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, and HENRY METCALF
HOBART, all of 83, Cannon Street, in the City of London, Electrical Engineers,
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:-
This invention relates to electrical transformers for use in three-wire systems,
and has for its object to provide for better automatic regulation of a transformer
in order to prevent unbalancing of the voltage when used on a three-wire secondary
system.
Assuming a transformer of the single magnetic circuit type of usual construc-
tion to be connected to a three-wire system of which one side is fully loaded and
the other unloaded, it is evident that the reactance voltage across the primary
wound over the unloaded secondary will be much greater than across the primary
wound over the loaded secondary. In extreme cases this might result in a rise
of about 25% in the voltage on the unloaded side and a drop of about 25% in
the voltage on the loaded side, and even with small variations of load in the two
sides of the system, the unbalancing may be unduly large. The aim of the pre-
sent invention is to avoid this unbalancing and to so construct a transformer with
due regard to cost and efficiency and the relative proportions of iron and copper,
and according to our improved construction and for the particular purpose de-
scribed we use in combination with a primary interposed between two secondaries
on each side of the magnetic circuit a novel method of interconnecting the
secondaries as hereinafter appears. Our improved construction of transformer and
its connections are diagrammatically shown in Figs. 1 and 2 of the drawing
attached hereto. On each side leg CC of the iron core, Fig. 2, are wound re-
spectively the secondaries S¹ S³ then a primary P, then secondaries S2 S. The
secondaries S¹ and S4 are connected in series on one side of the three-wire system,
and the secondaries S2 S3 are connected in series on the other side thereof as
shown plainly in the diagram Fig. 1, and the line connections are arranged as
shown in Fig. 2; and by such an arangement the unbalancing above referred to
is effectually avoided.
Having now particularly described and ascertained the nature of our said in-
vention, and in what manner the same is to be performed, we declare that what
we claim is:
In electrical transformers for use in three-wire systems the combination with a
primary coil interposed between two secondary coils on each leg of the transformer
core, of the novel method of interconnecting the respective coils consisting in con-

page_text: necting two of the secondaries S¹ S4 in series on one side of the three-wire system,
and two 0° 02 in series on the other side of the three-wire system, as described
for the purpose specified.
for the purpose specified.
the other side of the three-wire system, as describe
Dated the 9th day of November, 1897.
For the Applicants.
J. C. CHAPMAN.
Chartered Patent Agent, 70 Chancery Lane, London, W.C.