Method of Reducing the Energy of Magnetisation of Electrical Transformers when the Output is small.
Year: 1898

page_text: Date of Application, 22nd June, 1898-Accepted, 3rd Sept., 1898
COMPLETE SPECIFICATION.
Method of Reducing the Energy of Magnetisation of Electrical
Transformers when the Output is small.
We, SIEMENS BROTHERS & Co. Limited, of 12 Queen Anne's Gate, Westminster, S.W.,
Electrical Engineers, do hereby declare the nature of this invention, (as cominunicated
to us from abroad by Siemens & Halske Aktien Gesellschaft of Markgrafen Strasse 94,
Berlin, S.W.,), and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
In the specification to Patent No. 19821 of 1892 and No. 14533 of 1893, a method was
described of reducing the energy expended in magnetising transformers which was
mainly based upon the reduction of the pressure in one section of the winding the
work of magnetisation being reduced in consequence of the decreased induction of
the iron core of the transformer. This was effected in the arrangement described
by connecting the sections of the windings in parallel when the output of the trans-
former was considerable, whereby the windings were subject to considerable pressure,
while when the output was small, the sections were connected in series and conse-
quently they were subject to lower pressure.
When working with polyphase or rotary currents, the change of connection in the
several sections of the windings requires comparatively complicated appliances, as in
each of the limbs of the transformer both the primary and the secondary circuits
have to be connected in parallel or in series.
According to the present invention the number of the reversing contact switches
is reduced by the employment of mesh forin and star form connections in place of
the parallel and series connections, for the above named purpose.
In the previous arrangements, in order to be able to connect two or more trans-
formers in parallel, whether the primary and secondary circuits of each transformer
were respectively connected in parallel or in series, they complied with the necessary
condition that the ratio of transformation and the phase of the secondary potential
difference at the terininals must remain unchanged with both modes of connection.
It can be readily shewn that the same conditions will also be fulfilled if, in the one
case, the primary and secondary windings are connected in mesh form, and in the
other case, in star form.
The magnetisations in mesh form and star forin have the relative proportion
1
of 1:
✓ 3
..
Of course similar conditions apply equally to polyphase current-systems, the trans-
formers having their primary and secondary circuits connected in polygonal mesh.
form or in star form, according to the degree of magnetisation required.
Figures 1 and 2 shew diagrammatic drawings of transformers provided with the
above described circuit connections for rotary currents. Figure 1 shewing the con-
nections in mesh form, and Figure 2 those in star form.
a, b, c, represent the high pressure circuits, and A B C the low pressure circuits.
From the high pressure circuits a, b, c leads pass to the screw terminals a¹ a² a³ of
the high pressure windings, and the low pressure circuits A B C are similarly con-
nected by leads to the terminals A, A, A, of the low pressure windings.
CD
877

page_text: The ends of the corresponding windings are at e₁ е е, and E₁ E, E. From the
terminals of the beginnings and ends of all the winding-sections connecting leads pass
to the automatic change-over switch U. The corresponding terminals of the trans-
former and change-over switch that are connected with each other have the same
designations.
In the position of the switch, at Figure 1 there are connected in the low pressure
circuit, E-A¸, E₂-A₁, E₂-A₂; in the high pressure circuit: -αg, C₂-α,
-aq
The primary and secondary windings are therefore connected in nesh form.
In the position of the switch at Figure 2, E1 E2 E³ are connected together, as are
also el ees; the primary and secondary windings are therefore connected in star
form.
The change-over is shewn effected automatically by way of example.
The change-over levers are connected to a U shaped bar G. The contact positions
of the switches being effected in the one direction by the spring F and in the other
direction by the electromagnet S as described in the Specification to Patent No. 14533
of 1893.
When the output is large the electro-magnet S attracts the bar G and the switches
are brought into position for mesh connection of the transformer windings. The
transformer is in this case strongly magnetised, the current load on the windings
being less than with star form connections. With a light load the decreased
attraction of magnet S allows the bar G to bring the switches automatically into the
position for star form connection of the transformer, which then works with weaker
magnetisation.
The transformer will therefore always be so connected as to work in the most:
advantageous manner.
In place of the change-over apparatus U any other change-over switch may be
employed worked by hand or otherwise. The form of the electromagnetic device G S
can also be variously modified, thus, the electromagnet might have three limbs each
of which would be excited by one of the three rotary current branches.
The described improvement could of course also be combined with the arrangement
described in Patent No. 19821 of 1892.
The energy of magnetisation can then be reduced as follows.
By mesh and star form connection alone by
1
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
In polyphase current or rotary current transformers of the kind herein referred to
effecting the reduction of the energy of magnetisation by connecting the primary
and secondary circuits respectively by means of mesh form connections when the
load is considerable and by means of star form connections when the load is small
substantially as described.
4