COME LEAD DI MUITIVATION Method for Dividing an Alternating Current into twos, are Deed Angle.
Year: 1899

page_text: Date of Application, 19th Aug., 1899-Accepted, 11th Nov., 1899
COME LEAD DI MUITIVATION
Method for Dividing an Alternating Current into two Currents,
whose Phases are shifted Relatively to each other through a
Determined Angle.
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 com-
municated to us from abroad by Siemens and Halske Aktien Gesellschaft, of
Markgrafen Strasse 94, Berlin, S.W., Electrical Engineers) and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
In their Specification No. 2559 of 1897 our foreign correspondents gave the general
laws according to which it is possible to produce in a branch of a Wheatstone bridge
an alternating current whose phase has any desired shift relatively to the pressure in
the working circuit.
The present invention relates to an arrangement of bridge in which the generation
of the bridge current is effected with the least possible expenditure of energy.
In favourable cases there need be expended for the whole combination only so
much energy as is consumed in the bridge leads. This indeed is never quite achieved
as the branches of the bridge also consume energy. It is therefore necessary to
reduce this latter energy as far as possible without detracting from the working of
the arrangement.
For this purpose there are interposed in two opposite branches of the bridge suit.
able self inductors and in the other two opposite arms suitable condensers as shewn
in Fig. 1, in which s¹ and s² are two self induction coils in the branches ac and b dand
el and are two condensers in the branches b c and a d. For the latter may be used
a dry condenser or a liquid condenser consisting of a series of metal plates placed
side by side in a conducting liquid, the first and last being connected with the source
of current. m is the motor or the rotary field measuring instrument one of whose
fields is excited directly from the working circuit and the other field through
the bridge.
Fig. 2 is a diagram of the pressures and current strengths. A B is the working
circuit pressure, and A, B, C and D are the potentials of the points a, b, c and d in
Fig. 1; thus C D is the pressure in the bridge leads. The current strength in the
bridge leads may be represented by CE and has the phase shift f relatively to the
pressure CD. CF is the current strength in the condenser c¹ and has the lead x
with respect to the pressure C B. The current strength C G, the resultant of CE
and C F is the current strength present in the induction coils 8¹, and has a phase
shift Z of nearly 90° relatively to the pressure AC. According to the figure this
phase shift amounts to 90°-yo, KG being G C produced and the angle AKC
being a right angle. If 82-81 and c²=c¹ the current strength in c² is equal to that
011

page_text: ==
in cand the total current strength in the bridge is represented by CH, and by
geometrical addition C H = [CG + CF]=[CE+2CF] CG and CH become
smaller the larger is the angle a°. In practice, with a liquid condenser the value 0.6
may be reached for cos xo, which corresponds with the angle shewn in Fig. 2.
Noteworthy is the proportionately small phase-shift to between the current strength
CH and the working circuit pressure A B. In starting motors a small phase-
shift is very favourable, because for equal consumption of current the drop of
pressure in the generator and in the transformer is greater the greater the phase-
shift. The total energy passing through the bridge is
where is the proportionally small phase shift between the total current
strength C L and the working circuit pressure A B.
By using a solid condenser the phase-shift a° between the current strength CF in,
the condenser and the generated pressure C B may be made considerably greater and
thus still better values may be achieved. In this case an especially good proportion
is attained if the pressures A B and C D are taken of nearly equal value. The phase-
shift between the driving pressure and the total current passing directly to the motor
and to the bridge can be made nearly zero so that the energy consumed has
cos fo=1. In this case the arrangement serves not only to create a rotary field but
also to do away with the phase-shift. Just as it is possible to wind both induction
coils 8 and 82 on a common solid core, so only one condenser may be used if the
pressure C B and A D be transformed from a lower to a higher pressure by a common
transformer with three windings by which the condenser is fed. Such an arrange-
ment is shewn in Fig. 3, and is used particularly when the working circuit pressure
is disadvantageously high for the liquid condenser or when the circuit pressure is not
high enough for the use of a dry condenser.
As the apparent out-put of a condenser of constant capacity increases with the
square of the pressure for large charges dry condensers can only be used with effect
when very high pressures, for example 10,000 volts. are employed for them. Weight
and. increased cost of transformers and condensers are in large measure compensated
for by the facts that the motor itself as a two phase motor has an output nearly
double that of a single phase motor, that it can be more cheaply and easily worked
as such and that the load factor of the energy supplied may be made nearly unity
while the consumption of current is considerably reduced.
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 :-
1. The improvement in the method described in Specification No. 2559 of 1897.

page_text: consisting in interposing in two opposite branches of the bridge suitable self inductors
and in the other two opposite branches suitable condensers substantially as described
and for the purpose set forth.
2. In the arrangement referred to in Claim 1 substituting for the two condensers
a single condenser in the secondary circuit of a transformer which has two primary
windings, substantially as described.
ABEL & IMRAY,
Agents for the Applicants.