Improvements in or connected with the Distribution of Electricity on the Three-wire System with the Neutral Wire at Earth Potential.
Year: 1898

page_text: Date of Application, 17th Feb., 1898
Complete Specification Left, 12th Nov., 1898-Accepted, 7th Jan.,
1899
Improvements in or connected with the Distribution of Electricity on
the Three-wire System with the Neutral Wire at Earth Potential.
We, ALEX NDER BEWICKE BLACKBURN, Manager of The Electric Construction
Company Limited, WILFRID L SPENCE, Civil Engineer, of Dunluce, Tettenhall
Road, and ERNEST SHERWOOD WOOLLARD MOORE, Civil Engineer, of Fermain,
Tettenhall Road, all of Wolverhampton, do hereby declare the nature of this inven-
tion to be as follows:-
Our invention consists in improvements in electric distribution more especially
intended for traction purposes, but applicable also for other purposes.
Hitherto it has been usual to operate electric vehicles on the two-wire system at
or about 500 volts pressure on the line, and, in the case of long distance feeders
to augment (technically termed boosting up) the pressure, in certain instances,
as much as 300 or 400 volts, which represents the loss in transmission. In a few
cases vehicles have been operated on the three-wire system, but without any signal
success, owing to the want of proper methods of balancing the load on each side
of the network. With either method the limits of economic distribution are soon
reached and only at great cost can vehicles be operated at, say, more than four or
five, miles away from the generating station. The objects of our invention are to
greatly extend the limits within which large numbers of vehicles can be
economically operated, with sufficient constant potential to secure satisfactory light-
ing of the vehicles and to provide means by which the three-wire system can be
efficiently balanced without any considerable middle wire current reaching the
station and to simplify the power house switchboard equipment by doing away with
independent bus bars for separate pressures, and further, to reduce the number of
power house units by running all in parallel, and enabling any one to deal with the
full load of which it is capable independently of voltage regulation, which becomes
automatic on each circuit.
Our invention consists in the combination with a three-wire system, with earthed
neutral, for distribution on the power consumption circuits, of a two or three wire
generating and feeding system at considerably more than the extreme pressure
across the outers of the aforesaid power consumption circuits, together with four
circuit reducing transformers to connect the feeders with the distributors. The
four circuits of the reducing transformers are connected in series with the feeders
on the extreme outer brushes, numbers 1 and 5; and the distributors on the inter-
mediate, and neutral, sets of brushes, numbers 2, 3 and 4.
Our invention is applicable with the greatest advantage when the pressure of
main supply by the feeders is double, or about double, that between the outers of
the distributing network.
For example, supposing that trolleys in a direct current traction system to be
run at about 500 volts above and below earth potential, then each reducing and
balancing transformer will have four armature circuits wound with a normal

page_text: (no load) ratio of about one-to-one and carrying, say, 500 volts on each com-
mutator. These armatures being connected in series, the potential across the
extreme outer brushes will be 2000 volts plus the amount due to resistance drop
in the machine, say 15 to 20 volts.
This combination gives the full advantages of a 2000 volt supply with small
transformers, and an extremely high efficiency of conversion. Thus for
the supply of 200 kilowatts of energy two coupled transformers of 50 kilowatts
each are necessary. As converters transforming the whole of the energy, their
efficiency would be about 92'5 per cent.; but as reducing transformers their
efficiency is fully 96 per cent.
Obviously the method can be used with either higher, or lower, primary pressures,
but, in the former case, while the line loss is reduced, the transformers are larger,
and more expensive, and they have a correspondingly reduced efficiency of conver-
sion. In the latter case the line drop becomes serious and is not compensated by
the reduced loss in conversion.
sure.
Although we prefer a two-wire generating system this is not essential, as it is
possible to combine any number of generators in series to give the requisite pres-
It will be seen- that if the neutral wire of generators, so connected, be earthed
by connection to the rail circuit the feeding system at once becomes a three-wire
arrangement also. The same effect is obtainable by the use in the power house
of a reducing balancer for supplying the local trolley circuits.
Where both long and short feeders are in use it is desirable to provide means
for automatically compensating for the drop thereon. This can be done by means
of variable ratio transformers constructed as described in the Specifications of
Letters Patent No. 11153 of 1895, and No. 24296 of 1895 used as reducing machines,
the auxiliary field being either compounded (series wound) or controlled by an
electrical governor for example, as described in the Specification of Letters Patent
No. 19871 of 1896.
By means of this present invention great distances can be economically covered
and good regulation be secured. The reducing transformers may, or may not, act
as balancers; we generally prefer that they should so act. If constructed as two
separate machines, one with both positive circuits and the other with both negative
circuits, then, by coupling the shafts, they will act as balancers. This is the
preferable arrangement as it ensures the least differences of potential in contiguous
windings. Or we may couple the extreme positive circuit with the inner negative
on one machine and the extreme negative with the inner positive on the other, but
generally this is not desirable.
By earthing the neutral in the power house it will be seen that, in the case of
a 2000 volt system the greatest electro-motive-force does not differ from that of
earth by more than about 1000 volts, and in the sub-stations no commutator is
working at more than about 500 volts.
Dated this 17th day of Februam 1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London W.C., Agents.
Improvements in or connected with the Distribution of Electricity on
the Three-wire System with the Neutral Wire at Earth Potential.
We, ALEXANDER BEWICKE BLACKBURN, Manager of The Electric Construction
Company Limited, WILFRID L. SPENCE, Civil Engineer, of Dunluce, Tettenhall
Road, and ERNEST SHERWOOD WOOLLARD MOORE, Civil Engineer, of Fermain,

page_text: Tettenhall Road, all of Wolverhampton, do hereby declare the nature of this inven
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement:-
-
Our invention relates to an improved method of electric distribution primarily
adapted for traction purposes but applicable also for other uses.
Hitherto it has been usual to operate electric railways on the two wire system at
or about 500 volts pressure on the line, and in the case of long distance feeders
to boost up (augment) the pressure in certain instances as much as 300 to 400 volts
which represents the loss in transmission. In a few cases railways have been
operated on the three wire system, but without any signal success owing to the want
of proper methods of balancing the load on each side of the net work. With either
method the limits of economic distribution are soon reached, and only at great
cost can cars or locomotives be operated at, say more than 4 or 5 miles away from
the generating station. Our invention has for its object 1st. to greatly extend the
limits within which large numbers of cars can be economically operated with
sufficiently constant potential to secure satisfactory lighting inside the cars.
2ndly to provide means by which the three wire system can be efficiently balanced
without any considerable middle wire current reaching the station. 3rdly to
simplify the power house switchboard equipment, by doing away with independent
bus bars for separate pressures, and 4thly to reduce the number of power house
units by running all in parallel and enabling any one to deal with the full load, of
which it is capable, independently of voltage regulation, which becomes automatic
on each circuit. Our invention consists in combining a three wire system with
earthed neutral, for distribution on the power consumption circuits, with a two or
three wire generating and feeding system at considerably more than the extreme
pressure across the outers of the aforesaid power consumption circuits, together
with four-circuit reducing transformers to connect the feeders with the distributors.
It will be understood that the four circuits of the reducing transformers are con-
nected in series with the feeders on the extreme outer brushes Nos. 1 and 5 and the
distributors on the intermediate and neutral sets of brushes Nos. 2, 3 and 4. Our
invention is applicable with the greatest advantage when the pressure of main
supply by the feeders is double or about double that between the outers of the
distributing network. For example supposing the trolleys in a three wire direct
current traction system to be run at about 500 volts above and below earth
potential, then each reducing and balancing transformer will have four armature
circuits wound with a normal (no load) ratio of about one-to-one and carrying,
say, 500 volts on each commutator. These armatures being connected in series,
the working potential across the extreme outer brushes will be 2000 volts plus the
amount due to resistance drop in the machine, say, 15 to 20 volts.
This combination gives the full advantages of a 2000 volt supply with small
transformers and an extremely high efficiency of conversion. Thus for
the supply of 200 kilowatts of energy two coupled transformers of 50 kilowatts
cach are necessary. As converters transforming the whole of the energy their
efficiency would be about 92'5 per cent.; but as reducing transformers their
efficiency is fully 96 per cent.
Obviously the method can be used with either higher or lower primary pressures,
but in the former case, while the line loss is reduced, the transformers are larger
and more expensive and they have a correspondingly reduced efficiency of con-
version. In the latter case the line drop becomes serious and may not be compen-.
sated by the reduced loss in conversion.
Although a two wire generating system may be used this is not essential, as it
is possible to combine any number of generators in series to give the requisite
pressure. It will be seen that if the neutral wire of generators so connected be
earthed by connection to the rail circuit, the feeding system at once becomes a
three wire arrangement also. The same effect is obtainable by the use in the
power house of a reducing balancer for supplying the local trolley circuits.
Where both long and short feeders are in use some means of automatic compen-

page_text: ,
sation for the drop thereon is desirable. This we may arrange by using variable
ratio transformers, constructed in accordance with our earlier Patents, No. 11153,
1895 or No. 24296, 1895, as the reducing machines, the auxiliary field being either
compounded, i.e. series wound, or controlled by an electrical governor as described
in the Specification of Letters Patent No. 19871-1896.
By means of our present invention we are enabled to cover economically great
distances while securing good regulation. The reducing transformers may or may
not be solely relied upon to act as balancers, although we prefer that they should.
If constructed as two separate machines, one with both positive circuits and the
other with both negative circuits, then by coupling the shafts they will act as
balancers. This is the preferable arrangement as it ensures the least differences
of potential in contiguous windings. Another plan is to couple the extreme positive
circuit with the inner negative on one machine and the extreme negative with the
inner positive on the other but in some instances this is not desirable.
By earthing the neutral in the power house it will be seen that in the case of a
2,000 volt system the greatest E. M. F. does not differ from that of the earth by
more than about 1,000 volts, and in the substations no commutator is working at
more than about 500 volts.
We will further describe our invention with reference to the accompanying
drawings of which-
Figure 1 shows diagrammatically the system; a single generator or group of
generators G having the electrical middle point earthed, either directly, or in any
other suitable way, as for instance by the balancing and reducing transformer T,
supplies current by high tension feeders F to the outlying sub-station transformer T
the neutral of which is also earthed by connection to the rail circuits R R¹. The
trolley wires W+ and W- are supplied from the intermediate brushes of the trans-
formers T and T¹. Obviously the generator G and the power house transformer. T
may be replaced by a series of generators collectively or independently driven.
Figure 2 shews also diagrammatically a modification which may be used but
which is not generally so advantageous, as it involves a very special and somewhat
complicated design of machine with three commutators.
The generator end G of the system may be arranged in any desired way. The
transformer T has three commutators, two, C₁ and C, being connected respectively
to the positive and negative feeders, and the third, C being intermediate between
the others and carrying the full three wire distributing network voltage across its
brushes, that is, double the voltage across either C₁ or C. This arrangement
necessitates an additional balancing transformer which is indicated at B. The
earthed point is shewn in both figures by the arrow head marked E.
We would have it understood that we make no claim to any system of distribution
in which the pressure of supply on the feeder ends is equal to or approximately
the same as the maximum pressure across the distributors, nor do we claim any
system of transmission or distribution, however supplied, in which the greatest
difference of potential between any part, and earth materially exceeds the maximum
pressure across the distributors, but what we claim is :-
1. The combination with a three wire system of distribution for traction pur-
poses having the neutral at earth potential, of a two or three wire system of feed-
ing at a terminal pressure approximating to double that across the outers of the
said distribution system, together with four-circuit reducing transformers or their
equivalent for connecting the feeder and distribution systems, and in such a manner
that the greatest difference of potential between any part of the system and earth
cannot materially exceed the difference of potential between the outers of the dis-
tributing network, substantially as and for the purposes hereinbefore described.
2. A three wire system of distribution having the neutral at earth potential
supplied through four-circuit reducing transformers, or their equivalent, by means
of a two wire feeding system at a difference of potential approximating to double
that across the outers of the said distributing system, and in such manner that the

page_text: greatest difference of potential between any part of the system and earth cannot
materially exceed the voltage across the outers of the distributing network, sub-
stantially as and for the purposes herein before described.
3. A three wire system of distribution having earthed neutral supplied through
four-circuit reducing transformers, or their equivalent, of the variable ratio type
compounded or controlled to compensate for line drop and fed by means of a two
wire system at about double the extreme pressure across the outers of the said three
wire distributing system, substantially as and for the purpose herein before described.
Dated this 12th day of November 1898.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London W.C., Agents.