Improvements in or connected with the Distribution of Electricity on the Three-wire Direct Current System.
Year: 1898

page_text: Date of Application, 15th Sept., 1898
Complete Specification Left, 7th June, 1899-Accepted, 15th Sept., 1899
PROVISIONAL SPECIFICATION.
Improvements in or connected with the Distribution of Electricity on
the Three-wire Direct Current System.
We, ALEXANDER BEWICKE BLACKBURN, Manager of The Electric Construction
Company Limited, and WILFRID L. SPENCE, Civil Engineer, of Dunluce,
Tettenhall Road, both of Wolverhampton, do hereby declare the nature of this
invention to be as follows:
This invention relates to improved means of, and apparatus for, balancing
the circuits of a three-wire direct current system of distribution of electricity.
Several methods have been practised for equalising the potential in three-
wire systems. These have been, the use of two generators coupled in series or
the employment of separate balancing transformers with two armatures con-
nected in series: the transformers preferably being placed at, or near, the
It has been
centres of consumption, rather than at the point of generation.
proposed to use a choking coil connected by slip rings to two diametrically
opposite points of the generator winding; the middle point of the choking coil
being connected to the neutral conductor of the distributing system.
The present invention relates to a method based upon a principle similar to
that of the last described arrangement but giving increased efficiency, improved
regulation, and decrease in cost.
Instead of a single phase choking coil we use a two, or three, phase star coupled
coil, or transformer, connected by means of slip rings, to a correspondingly
increased number of symmetrically situated points in the generator winding,
or in the winding of a motor, or auxiliary generator, connected to the circuit.
Choking coils of more than three phases may be used, but usually two, or
three, phase coils will be found convenient.
The neutral point, (the common centre in a star coupling), is connected to the
middle conductor of the direct current distributing system.
By the present invention the cost of auxiliary balancing apparatus is con-
siderably reduced as any single-commutator motor installed on a consumer's
premises and fitted with slip rings may be utilised for balancing purposes, and
further, independent balancers may be of a multipolar single commutator type,
running at comparatively high speed, and having a sufficiently high frequency
to minimise the cost of the polyphase choking coils.
The improvements according to this invention may be applied to the so-called
* Oxford system of distribution and to the numerous modifications thereof.
We may apply it, for example, to a reducer system of transformers in the
following way:- -Generating at about four times the pressure of individual
translating devices (that is, at about double the extreme pressure on the three-
wire low tension distributing network), variable ratio reducing transformers of
the general type described in the Specification of Letters Patent No. 11153 of
A.D. 1895, will be used in sub-stations. These will have three windings, two
of which, for motoring, will be alike, and the third will be for generating.

page_text: The commutators of the two first named windings are at one end and the com-
mutator for the other winding, together with three slip rings, connected thereto,
are at the other end of the armature. This commutator will carry the full
voltage across the outers of the three-wiré distributing network to which it is
connected, while the two motoring commutators will each carry about one half
this voltage, and they are connected, respectively, to the positive and negative
sides of the higher tension transmission system, the whole three windings being
in series. One set of windings only, either the two half voltage, or the one
full three-wire voltage, winding, is carried through the auxiliary regulating
field so as to secure adequate capacity for regulation. The three slip rings are
connected to the free ends of a three phase star-coupled transformer, or choking
coil, to the common neutral point of which the middle wire of the low tension
distributing network is connected. This point may be earthed if desired, and
so also, by similar means, may the electrical middle point of the direct current
generators be connected to earth.
By this invention we are enabled to obtain permanent access, so to speak, to
the middle (electrically) of a rotating armature winding, that is to the point of
mean potential between the brushes. If therefore two machines, so fitted, be
connected in series, there are five points at which direct current connection can
be made, namely, two on the extreme outer brushes, which may be called
positive outer and negative outer; one the common series connection between
the two commutators which may be called the neutral; and two more, one the
mean point in the positive side armature (positive mean); and one the mean
point in the negative side armature (negative mean). If the extreme outers be
supplied with current at, say, 1,000 volts a three wire low tension system with
250 volts on either side can be tapped, by means of the polyphase choking coils,
off the positive mean, and off the negative mean, for the positive and negative
respectively of the low tension distributing system and directly off the neutral
for the middle wire of the same low tension system.
Dated this 15th day of September 1898
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.
Improvements in or connected with the Distribution of Electricity on
the Three-wire Direct Current System.
We, ALEXANDER BEWICKE BLACKBURN, Manager of The Electric Construction
Company Limited, and WILFRID L. SPENCE, Civil Engineer, of Dunluce,
Tettenhall Road, both of Wolverhampton, 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 improved means of, and apparatus for, balancing
the circuits of a three-wire direct current system of distribution of electricity.
Several methods have been practised for equalising the potential in three-
wire systems. These have been, the use of two generators coupled in series, or
the employment of separate balancing transformers with two armatures con-
nected in series; the transformers preferably being placed at, or near, the
centres of consumption, rather than at the point of generation. It has also been
proposed to use a choking coil connected by slip rings to two diametrically
opposite points of the generator winding, the middle point of the choking coil
being connected to the neutral conductor of the distributing system.

page_text: The present invention relates to a method based upon a principle similar to
that of the last described arrangement but giving increased efficiency, improved
regulation, and decrease in cost.
Instead of a single phase choking coil we use a two or three phase star coupled
coil, or transformer, connected, by means of slip rings, to a correspondingly
increased number of symmetrically situated points in the generator winding,
or in the winding of a motor, or auxiliary generator connected to the circuit.
Choking coils of more than three phases may be used, but usually two
three phase coils will be found convenient.
or
It will be understood that the neutral point (the common centre in a star
coupling), is connected to the middle conductor of the direct current distributing
system.
By the present invention the cost of auxiliary balancing apparatus is con-
siderably reduced as any single-commutator motor installed ou al consumer's
premises and fitted with slip rings may be utilised for balancing purposes, and
further, independent balancers may be of a multipolar single commutator type,
running at comparatively high speed, and having a sufficiently high frequency
to minimise the cost of the polyphase choking coils.
The improvements according to this invention may be applied to the so-called
"Oxford system of distribution and to the numerous modifications thereof.
We may apply it, for example, to a reducer system of transformers in the
following way:-Generating at about four times the pressure of individual
translating devices (that is, at about double the extreme pressure on the three-
wire low tension distributing network), variable ratio reducing transformers of
the general type described in the Specification of Letters Patent No. 11153 of
A.D. 1895, will be used in sub-stations. These will have three windings, two
of which, for motoring, will be alike, and the third will be for generating.
The commutators of the two first named windings are at one end and the com-
mutator for the other winding, together with three slip rings connected thereto,
are at the other end of the armature. This commutator will carry the full
voltage across the outers of the three-wire distributing network to which it is
connected, while the two motoring commutators will each carry about one half
this voltage, and they are connected, respectively to the positive and negative
sides of the higher tension transmission system, the whole three windings being
in series. One set of windings only, either the two half voltage, or the one
full three-wire voltage, winding, is carried through the auxiliary regulating
field so as to secure adequate capacity for regulation. The three slip rings are
connected to the free ends of a three phase star-coupled transformer, or choking
coil, to the common neutral point of which the middle wire of the low tension
distributing network is connected. This point may be earthed if desired, and
so also, by similar means, may the electrical middle point of the direct current
generators be connected to earth.
By this invention we are enabled to obtain permanent access, so to speak, to
the middle (electrically) of a rotating armature winding, that is to the point of
mean potential between the brushes. If therefore two machines, so fitted, be
connected in series, there are five points at which direct current connection can
be made, namely, two on the extreme outer brushes, which may be called
positive outer and negative outer; one the common series connection between
the two commutators; which may be called the neutral; and two more, one the
mean point in the positive side armature (positive mean), and one the mean
point of the negative side armature (negative mean). If the extreme outers be
supplied with current at, say, 1,000 volts a three wire low tension system with
250 volts on either side can be tapped, by means of the polyphase choking coils,
off the positive mean, and off the negative mean, for the positive and negative
respectively of the low tension distributing system and directly off the neutral
for the middle wire of the same low tension system.
We will now describe this invention more particularly with reference to the

page_text: accompanying drawings whereon Figure 1 shews diagrammatically a bipolar
dynamo armature tapped at three points and connected to a like number of con-
tact rings. Figure represents the same armature in side elevation with the
free ends of a three phase star connected choking coil or reducing trans-
former R, T, connected to the slip rings. The common middle point of this
reducing transformer, which is at a mean potential between the brushes, +
and
is connected to the middle wire + of the distributing system and it
serves to take up any unbalanced current flowing in the network. The applica-
tion of this invention to a modified "Oxford" system of distribution is shewn
diagrammatically in Figure 3. Here the generator G, gives say, 1000 volts
pressure and it may be earthed at its neutral point by the three phase
reducer R, T, as hereinbefore described, so that the difference of potential
between any point and earth cannot rise above 500 volts. The sub-station
transformer armature carries two motoring windings M and M each of about
250 volts electromotive force and one generating winding G₁ of about 500 volts
pressure (resistance drop being neglected). This latter winding is tapped in
accordance with this invention by polyphase rings and reducing trans-
former R, T, for the middle wire connection which may be earthed if desired.
Obviously where a relatively high feeding pressure is used the generating
winding G may be split up into two separate windings G G each provided
with the tapping connection and with its own reducing transformer R¹, T¹, as
shewn in Figure 4. The arrangements Figures 3 and 4 afford facilities for
building the transformers as variable ratio machines.
A simpler arrangement is available where variable ratio machines are not
essential. This (see Figure 5) consists of a single reducing transformer with two
windings M¹ G', M G" each tapped and provided with its own reducing
transformer R T the two armature windings being connected in series. The
supply is fed in at the extreme outer brushes 1 and 5, and the third or neutral,
distributing wire is connected to the inner brush lead 3, the outer distributing
wires being connected to the mean points 2 and 4 of the two armature windings
as shewn.
In the constructions, Figures 3 to 5, it is obvious that what have been referred
to as transformers may equally well be generators.
This invention is also particularly applicable to battery charge and discharge
boosters on a three wire system. Hitherto such batteries have commonly been
charged by two separate and independent boosters one for the positive and one for
the negative side.
By means of the improved construction according to this invention we are
able with a single booster, to control the charge, or discharge and maintain a
balance in the same manner as now practised with two machines.
The improved booster is placed in the middle between the positive and negative
batteries, the third wire connection with the distributing system being pre-
served by means of the polyphase auxiliary, so that the battery can still fulfil
the function of an equalizer on the system when being charged, and to this
extent it is available for steadying purposes. The two batteries can thus be
charged equally, or unequally if desired as either half of the booster circuit can
be opened without interfering with the other half. The diagrams, Figures 6
and 7, clearly indicate the system.
In both figures G represents the generator with middle wire connection at R, T.
The batteries are indicated at B and B and the booster by B M and G¹, motor
and generator ends respectively, R T is the middle wire reducing transformer
for the latter. In Figure 6 the two batteries are indicated as being equally
charged or discharged while in Figure 7 the battery B¹ is cut out leaving the
battery B still in circuit for such further charge as may be necessary.
We regard it as an essential part of our invention that the polyphase star-
connected reducing transformer be wound with a single set only of electrical
circuits for the purpose herein specified that is as a means of affording access to

page_text: the electrical middle point of the armature. We make no claim to the analogous
use of the common middle point in a star connected polyphase transformer
feeding energy into an alternating-direct current rotary converter.
Having now particularly described and ascertained the nature of our invention
and in what manner the same is to be performed, we declare that what we
claim is:-
1. In a direct current dynamo motor or transformer the means substantially
as hereinbefore described for obtaining a terminal of mean potential between
the brushes.
2. A direct current armature provided with contact rings tapped into the
winding as a means of affording a polyphase supply, together with a corresponding
polyphase reducing transformer, or balancing coil, having a single set of electrical
circuits, substantially as hereinbefore described.
3. The application of a direct current armature, with auxiliary apparatus as
claimed by the preceding claiming clause, to a three-wire system, or to similar
systems, for equalizing purposes, substantially as hereinbefore described.
4. The application of our improved apparatus as set forth in Claim 2, to reducer
systems of distribution substantially as hereinbefore described.
5. The application of our improved apparatus as set forth in Claim 2, for
charging, or discharging, two blocks of batteries one on either side of a three
wire system; substantially as hereinbefore described and illustrated.
Dated this 7th day of June 1899.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.