Improvements in Alternate Current Transformers for Variable Loads.
Year: 1892

page_text: Date of Application, 3rd Nov., 1892
Complete Specification Left, 28th July, 1893-Accepted, 2nd Sept., 1893
PROVISIONAL SPECIFICATION.
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of 94, Markgrafen
Strasse, Berlin, in the German Empire, Electrical Engineers.]
Improvements in Alternate Current Transformers for Variable
Loads.
We, SIEMENS BROTHERS & Co., LIMITED of 12 Queen Anne's Gate,
Westminster in the County of Middlesex, Electrical Engineers do hereby
declare the nature of this invention to be as follows:-
In alternate current transformers there occur two sources of loss of useful effect,.
namely first that due to the reduction of tension resulting from the heat given off
in the windings, and secondly the loss due to the energy expended in magnetising
the core.
The first named loss varies with the load on the transformer, while the
second is constant, no matter what the load may be.
With transformers that are subject to a very variable load there is consequently
a proportionately much greater loss of useful effect when the apparatus is working
with a small load than when it is working with its full load.
The present invention has for its object to remedy this defect by so arranging the
transformer that the nature of its windings can be varied according to the amount
of the load, so that when the latter is reduced, the energy required for effecting the
magnetisation shall be correspondingly reduced.
The invention is based on the fact that the relation existing between the primary
tension in the transformer and the secondary tension depends exclusively upon the
proportion between the primary and secondary windings, so that if both windings
be simultaneously varied in such manner as to maintain the same proportion the
ratio of conversion of the apparatus will remain the same.
According to this invention the windings of the transformer are varied in such
manner that when working with a reduced load, the windings of both the primary
and the secondary coil available for effecting magnetisation are simultaneously
increased so as to maintain the same ratio, by which means the amount of energy
expended in the magnetisation is correspondingly reduced.
The simplest way of effecting this is by the following construction. The primary
and secondary coils are each made to consist of two or more separate windings,
and these windings are in each case connected in parallel when the transformer is
working with about full load. The coils then have the greatest possible sectional
area, suited for the maximum current. The dimensions are so proportioned that
the loss of tension and the loss due to magnetisation shall be of the usual
percentages.
On the other hand when the load is considerably reduced, the separate sections
of the windings of the primary and secondary circuits respectively are coupled
together in series, thus increasing the number of effective windings for magnetisation
to a corresponding extent. The number of magnetic lines of force will then also
be proportionately reduced from the number occurring with the full load, and the
energy expanded for magnetising will sink still further, in proportion to the
1-6th power of the magnetic intensity.
A transformer constructed in the above described manner is shewn diagram-
matically on the accompanying drawing, in which D is the current generator,
w¹ and w² the two sections of the primary winding, while W' and W' are the two
sections of the secondary winding on the core K, S is the switch apparatus for
changing the connections. In the position of the switches h¹³ and H₁ H' shewn
on the drawing, the sections w¹ and w³ are connected in parallel, as
W' and W'.
are also
If these switches be moved into the dotted position by shifting the bar G to

page_text: which they are all connected, the sections 10' and was also those W₁ W' will be
coupled up in series.
In practical working, hardly any sparking will occur at the switches.
With such an arrangement the loss of tension with the reduced load will of course
be four times that occurring during the full load, as there is then ouly half the
section of the coils and these are of double the length.
Also, the working capacity of the transformer will only be half that with the full
load, as the section of the coils is reduced to half, the tension being maintained
constant. But as according to the practical results obtained at the central
installations the average supply during the time of reduced consumption is only
from 10 to 15 per cent. of the full load, the increased loss owing to decrease of
teusion is practically of no account, and secondly the working capacity of the
transformer will be amply sufficient, as it can supply up to 50 per cent. of the
full load.
Instead of dividing the primary and secondary coils into two or more sections
as described, the invention can also be carried out by making the coils in the usual
manner, and by providing an extra winding to each, which is out of circuit during.
the time of full load, but is put in series in the circuit so as to increase the length
of winding at the time of reduced load.
As by the connecting in series an increased loss of tension occurs, as stated, the
sections may be so proportioned that when coupled in series a small increase of
tension shall take place at the terminals of the secondary coil, in order to com-
pensate for the said decrease, such slight alteration being without practical effect
upon the above stated condition that the ratio of conversion must remain constant.
The above described invention is applicable not only to transformers working
with ordinary alternating currents, but also to those working with two phase or
polyphase alternating currents.
Dated this 3rd day of November 1892.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in Alternate Current Transformers for Variable
Loads.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Annes Gate,
Westminster, in the County of Middlesex, 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 :-
In alternate current transformers there occur two sources of loss of useful effect,
namely first that due to the reduction of tension resulting from the heat given off in
the windings, and secondly the loss due to the energy expended in magnetising the
core. The first named loss varies with the load on the transformer, while the
second is constant, no matter what the load may be.
With transformers that are subject to a very variable load there is consequently
a proportionately much greater loss of useful effect when the apparatus is working
with a small load than when it is working with its full load.
The present invention has for its object to remedy this defect by so arranging
the transformer that the nature of its windings can be varied according to the
amount of the load, so that when the latter is reduced, the energy required for
effecting the magnetisation shall be correspondingly reduced.
The invention is based on the fact that the relation existing between the primary
tension in the transformer and the secondary tension depends exclusively upon the
proportion between the primary and secondary windings, so that if both windings
be simultaneously varied in such manner as to maintain the same proportion, the
ratio of conversion of the apparatus will remain the same.

page_text: According to this invention the windings of the transformer are varied in such
manner that when working with a reduced load the windings of both the primary
and the secondary coil available for effecting magnetisation are simultaneously
increased so as to maintain the same ratio, by which means the amount of energy
expended in the magnetisation is correspondingly reduced. The simplest way of
effecting this is by the following construction. The primary and secondary coils
are each made to consist of two or more separate windings, and these windings are
in each case connected in parallel when the transformer is working with about full
load. The coils then have the greatest possible sectional area, suited for the
maximum current. The dimensions are so proportioned that the loss of tension and
the loss due to magnetisation shall be of the usual percentages.
On the other hand when the load is considerably reduced, the separate sections
of the windings of the primary and secondary circuits respectively are coupled
together in series, thus increasing the number of effective windings for magnetisation
to a corresponding extent. The number of magnetic lines of force will then also
be proportionately reduced from the number occuring with the full load, and the
energy expended for magnetising will sink still further, in proportion to the power
of 16 of the magnetic intensity.
A transformer constructed in the above described manner is shewn diagram-
matically on the drawing accompanying our Provisional Specification in which
D is the current generator, wol and to the two sections of the primary winding,
while W and W are the two sections of the secondary winding on the core K.
S is the switch apparatus for changing the connections. In the position of the
switches and H' H' shewn on the drawing, the sections w' and are connected
in parallel, as are also W¹ and W'. If these switches be moved into the dotted
position by shifting the bar G to which they are all connected, the sections w¹ and w³
as also those W W will be coupled up in series.
In practical working, hardly any sparking will occur at the switches.
With such an arrangement the loss due to decrease of tension with the reduced
load will of course be four times that occurring during the full load, as there is then
only half the section of the coils and these are of double the length.
Also, the working capacity of the transformer will only be half that with the
full load, as the section of the coils is reduced to half, the tension being maintained
constant. But as according to the practical results obtained at the central
installations, the average supply during the time of reduced consumption is only
from 10 to 15 per cent. of the full load the increased loss owing to decrease of tension
is practically of no account, and secondly the working capacity of the transformer
will be amply sufficient, as it can supply up to 50 per cent. of the full load.
Instead of dividing the primary and secondary coils into two or more sections as
described the invention can also be carried out by making the coils in the usual
manner, and by providing an extra winding to each, which is out of circuit during
the time of full load, but is put in series in the circuit so as to increase the length
of winding at the time of reduced load.
As by the connecting in series an increased loss of tension occurs, as stated, the
sections may be so proportioned that when coupled in series a small increase of
tension shall take place at the terminals of the secondary coil, in order to compensate
for the said decrease, such slight alteration being without practical effect upon the
above stated condition that the ratio of conversion must remain constant.
The above described invention is applicable not only to transformers working with
ordinary alternating currents, but also to those working with two-phase or polyphase
alternating currents.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
+
1. An alternate current transformer operating with single or polyphase alternating

page_text: capable of having their action varied in such manner while maintaining the ratio of
conversion constant that the energy expended in magnetising the core when working
with a full load shall be reduced when working with a reduced load, substantially
as described.
2. An alternate current transformer operating with single or polyphase alternating
currents wherein the primary and secondary windings are increased, while
maintaining the ratio of conversion. constant, when the transformer is working with
a reduced load, whereby the energy expended in magnetising the core will be
reduced during such time, substantially as described.
3. In an alternate current transformer operating as set forth in the preceding
claim, producing the increase in the primary and secondary windings during the
time of working with reduced load by dividing the said windings into sections
which are coupled in parallel when working with a full load, and in series when
working with a reduced load, substantially as described.
Dated this 28th day of July 1893.
ABEL & IMRAY,
Agents for the Applicants.