Improvements in, or connected with, the Distribution of Electricity from a Common Generating Plant for Supplying Simultaneously Current both for Traction and for Lighting or Lighting and Power.
Year: 1896

page_text: Date of Application, 22nd Dec., 1896
Complete Specification Left, 22nd Sept., 1897-Accepted, 4th Dec., 1897
PROVISIONAL SPECIFICATION.
Improvements in, or connected with, the Distribution of Electricity
from a Common Generating Plant for Supplying Simultaneously
Current both for Traction and for Lighting or Lighting and
Power.
We, ALEXANDER BEWICKE BLACKBURN, Manager of the Electric Construction
Company Limited of Wolverhampton and ERNEST SHERWOOD WOOLLARD MOORE
of Waterloo Road North, Wolverhampton, Civil Engineer, do hereby declare the
nature of this Invention to be as follows:-
The object of this invention is to effect the economic distribution of electricity
from a common generating plant for the purpose of supplying current for traction
and for lighting or lighting and power simultaneously and to provide adequato
means for the regulation and variation of the pressure upon either of these systems
without interference with the other. We will refer to the portions as the traction
and lighting portions respectively. This invention applies particularly to com-
bined lighting and traction plant, in which it is desirable to use the three wire
method of distribution for lighting purposes, in combination with the ordinary
two wire trolley arrangement for traction purposes. In such a combined system
it is generally desirable that the middle or neutral lead (rather than the positive
or negative lead) of the lighting portion, and either the negative or the positive
lead of the traction portion should be at earth potential.
In such a system the potential of the line on the traction portion will be en-
tirely above or entirely below the earth potential, but upon the lighting portion,
as regards the positive lead, it will be above, and as regards the negative lead,
below the earth potential.
It is also generally desirable to maintain a constant potential (variable at will,
say 5 to 10 per cent) at the switchboard of the generating station, and when the
lighting load is the lesser portion of the system, the switchboard pressure is deter-
mined by the total demand upon the traction portion and the total pressure
between the outer positive and negative leads of the three wire lighting portion
by the distribution of load upon the supply network.
It has been usual to meet these general conditions, incidental to such a system,
by transforming the whole energy required for the purpose of lighting (assuming
the lighting load to be the lesser portion of the system) by means of variable
ratio transformers and by balancing the two halves of the three wire system in
the usual way, that is either by rotary balancers or by batteries.
This invention consists in improvements in the method of distribution of
electric energy from a constant potential circuit on a traction portion having one
pole (usually the negative) at the earth potential, to a three wire lighting and
power portion, having its middle or neutral lead at the earth potential, or vice
versa, by employing rotary weducing motor-generators in contradistinction to
rotary transformers, whereby the efficiency of the system is largely increased and
the cost of the apparatus reduced.
The reducing motor generators in this new method of distribution would be
working to the greatest advantage both in regard to economy and first cost when
the potential difference between the outer leads of the three wire lighting portion

page_text: is approximately equal to the potential difference between the positive and nega
tive leads of the traction portion. When these approximately equal differences of
potential are employed, and when the pressure of supply and the energy demanded
upon each half of the three wire lighting portion are maintained in proper balance,
either by batteries or by balancing transformers in the usual way, and when the
one pole of the traction portion and the middle or neutral lead of the lighting
portion are at the earth potential, then the two armature windings on the reducing
motor generators will be practically of equal current capacity. The one armature
winding will operate as a motor and be in series with the load upon its own side
of the lighting portion. The negative pole of this armaturo will be connected to
the positive lead of the lighting portion and its positive pole to the positive lead
of the traction portion at the constant potential point determined (generally the
switchboard). At the same time, and under the same conditions, the other
armature winding would be acting as a generator and supplying the energy
required upon that side of the lighting portion electrically remote from the
traction portion. i.e. its positive pole would be connected to the middle or neutral
wire at the earth potential and its negative pole connected to the negative lead of
the lighting portion.
It is generally advisable to use a rotary reducing motor-generator of a variable
ratio type, similar to the rotary transformer described in the Specification of
Letters Patent Nos. 24296, of 1895 and 11153 of 1895, in order that the varying
potential required independently in the traction and lighting portions may be
conveniently provided in the one set of apparatus.
Further, it is, sometimes desirable, when a balancing transformer is employed
in connection with this system, that it should be combined with the reducing
motor-generator hereinbefore described to form part of one and the same machine,
requiring only three, instead of four separate armature windings. These three
armature windings may he operated either. in a single field magnet system or in
two separate field magnet systems, as found most convenient. The capacities of
the several armatures referred to will be indicated by referring to the first as a
reducing motor armature, the second as a balancing armature, and the third as a
combined reducing generator and balancing armature. Under the conditions here-
inbefore indicated, and when the negative lead of the traction portion is earthed,
the connections for this combined reducer and balancer will be as follows:-
The nositive pole of the first armature will be connected to the positive.lead of
the lighting portion, and at the same time to the positive pole of the second or
balancing armature. The, negative pole of this second armature would then he
connected to the negative lead of the traction portion, and the middle lead of the,
lighting portion, hoth at the earth potential and also to the positive lead of the
third armature., the negative pole of which would be connected with the negative.
lead of the lighting portion.
Another method of using a reducing motor generator with this system is to
arrange the generator-half of the reducing motor generator, to give its output at
an electro-motive-force corresponding to the potential difference between the outer
positive and negative leads of the lighting. portion. Under these circumstances.
it is desirable that the load upon the two halves of the lighting portion he unequal
to such an extent that the work thrown upon the motor balancer will be, as, far
ns possible, a minimum.
In the foregoing description, the three wire system has alone heen referred to,
hut it will be obvious that by modifying the construction of, the balancers, the
invention is applicable to a five wire lighting system.
It has hereinbefore been assumed that the requirements of the traction portion
of the system will be the greater but should the lighting portion he in excess,
the converse arrangements can be applied..
Having described the nature of this invention generally, we proceed to illus
trate the same by a concrete example, in which, it is supposed that the traction
load will be the greater and that it is desirable to maintain a constant potential

page_text: at the generating station switchboard of 500 to 550 volts, according to the require-
ments of the system, and that, at the saine time it is necessary to maintain on
the three wire lighting portion a potential of 460 to 500 volts between the outer
leads. It is further supposed that the negative lead of the traction portion and
the middle or neutral lead of the lighting portion are earthed and that 100 Kilo-
Watts is required upon the lighting portion. There will then be a surplus voltage
between the positive lead of the lighting portion and the positive
lead of the traction system varying between 320 volts (550-230) and
250 volts (500 - 250), The motor portion of
of the reducer will be
employed to transfer the energy corresponding to the surplus voltage to the
negative side of the lighting portion at a suitable potential. Then each half of
the reducer must be designed to supply its energy at the same voltage (230 to 250
volts) and the variable ratio supplementary in series with the motor armature
should be equal to supplying the full variable electro-motive-force between 460
and 550 volts, (90 volts).
The supplementary to the motor armature (giving the variable ratio) in these
reducing motor generators is sometimes designed for supplying this full variation
of 90 volts electro-motive-force by adding or subtracting 45 volts from the voltage
of the motor armature. This motor armature would then be wound suitably for
the increased electro-motive-force, and equal to about 275 volts. The variation
in potential is produced by diminishing the supplementary field strength to zero
and by increasing it again to its normal strength in the reverse direction, in the
one case assisting the motor portion of the reducer, and in the other the generator
portion.
In estimating the currents flowing in the various circuits connected with a
combined system, such as that hereinbefore described, it will be seen that the
relation of the electro-motive-force of supply on the traction portion to the electro-
motive-force across the outer leads of the lighting portion will determine whether
it is most desirable to maintain the even balance upon the positive and negativo
sides of the three wire system, or whether they should be slightly unequal with an
excess of current on the positive or the negative side.
It will be seen from the foregoing example (1) that for 100 Kilo-Watts lighting
demand the reducing motor generator, with a ratio on the principal armature
windings of approximately "one to one," will have a capacity of only about 50
Kilo-Watts on each winding. (2) That with this system it is commercially
possible to obtain upon the lighting portion (with a reducer having a commercial
efficiency of 93 per cent) 96 per cent. of the energy delivered from the traction
portion, whilst the size and cost of the apparatus employed is reduced.
This invention does not include the use of a separate balancing transformer
upon a three wire system, the use of which is well-known and thoroughly under-
stood.
JOHNSONS & WILLCOX
47 Lincolns Inn Fields London W.C. Agents.
COMPLETE SPECIFICATION.
Improvements in, or connected, with, the Distribution of Electricity
from a Common Generating Plant for Supplying Simultaneously
Current both for Traction and for Lighting or Lighting and
Power.
We, ALEXANDER BEWICKE BLACKBURN, Manager of the Electric Construction
Company Limited of Wolverhampton and ERNEST SHERWOOD WOOLLARD MOORE

page_text: of Waterloo Road North, Wolverhampton, Civil Engineer, 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:-
The object of this invention is to effect the economic distribution of electricity
from a common generating plant for the purpose of supplying current for traction
and for lighting or lighting and power simultaneously and to provide adequate
means for the regulation and variation of the pressure upon either of these
system without interference with the other. We will refer to the portions as
the traction and lighting portions respectively. This invention applies particularly
to combined lighting and traction plant, in which it is desirable to use the three-
wire method of distribution for lighting purposes, in combination with the
ordinary two-wire arrangement for traction purposes. In such a combined system
it is generally desirable that the middle, or neutral, lead, (rather than the positive,
or negative, lead), of the lighting portion, and either the negative, or the positive,
lead of the traction portion should be at earth potential.
Tu such a system the potential of the line on the traction portion will be entirely
above, or entirely below the earth potential, but upon the lighting portion, as
regards the positive lead, it will be above, and as regards the negative lead, below,
the earth potential.
It is also generally desirable to maintain a constant potential (variable at will,
say 5 to 10 per cent.) at the switchboard of the generating station, and when the
lighting lead is the lesser portion of the system, the switchboard pressure is deter-
mined by the total demand upon the traction portion, and the total pressure
between the outer positive and negative leads of the three-wire lighting portion by
the distribution of load upon the supply network.
It has been usual to meet these general conditions, incidental to such a system,
by transforming the whole energy required for the purpose of lighting (assuming
the lighting load to be the lesser tion of the system) by means of variable
ratio transformers and by balancing the two halves of the three-wire system in
the usual way; that is either by rotary balancers, or by batteries.
This invention consists in improvements in the method of distribution of
electric energy from a constant potential circuit on a traction portion having one
pole (usually the negative) at the earth potential, to a three-wire lighting and
power portion, having its middle, or neutral, lead at the earth potential, or vice
cersu, by employing rotary reducing motor-generators in contra-distinction to
rotary transformers, whereby the efficiency of the system is largely increased and
the cost of the apparatus reduced.
The reducing motor generators in this new method of distribution would be
working to the greatest advantage both in regard to economy and first cost when
the potential difference between the outer leads of the three-wire lighting portion
is approximately equal to the potential difference between the positive and
negative leads of the traction portion. When these approximately equal differ-
ences of potential are employed, and when the pressure of supply, and the energy
demanded upon each half of the three-wire lighting portion, are maintained in
proper balance, either by batteries, or by balancing transformers, in the usual way,
and when the one pole of the traction portion, and the middle, or neutral, lead
of the lighting portion, are at the earth potential, then the two armature wind-
ings on the reducing motor generators will be practically of equal current capacity.
The one armature winding will operate as a motor, and be in series with the load
upon its own side of the lighting portion. The negative pole of this armature
will be connected to the positive lead of the lighting portion and its positive pole
to the positive lead of the traction portion at the constant potential point deter-
mined (generally the switchboard). At the same time, and under the same con-
ditions, the other armature winding would be acting as a generator and supplying
the energy required upon that side of the lighting portion, electrically remote
from the traction portion; that is its positive pole would be connected to the

page_text: middle, or neutral, wire at the earth potential and its negative pole connected to
the negative lead of the lighting. portion.
It is generally advisable to use a rotary reducing motor-generator of a variable
ratio type, similar to the rotary transformers described in the Specifications of
Letters Patent Nos. 24296, of 1895, and 11153, of 1895, in order that the varying
potentials is required, independently in the traction and lighting portions, may be
conveniently provided in the one set of apparatus.
Further, it is sometimes desirable, when a balancing transformer is employed
in connection with this system, that it should be combined with the reducing
motor-generator, herein before described to form part of one and the same machine,
requiring only three, instead of four, separate armature windings. These three
armature windings may be operated either in a single field-magnet system, or in
two separate field-magnet systems, as found most convenient. The capacities of
the several armature windings referred to will be indicated by referring to the
first as
a reducing motor armature, the second as a balancing armature, and
the third as a combined reducing generator and balancing armature. Under the
conditions herein before indicated and when the negative lead of the traction
portion is earthed, the connections for this combined reducer and balancer will
be as follows:-
The positive pole of the first armature will be connected to the positive lead of
the lighting portion and at the same time to the positive pole of the second, or
balancing armature. The negative pole of this second armature would then be
connected to the negative lead of the traction portion, and the middle lead of the
lighting portion, both at the earth potential and also to the positive lead of the
third armature, the negative pole of which would be connected with the negative
lead of the lighting portion.
Another method of using a reducing motor generator with this system is to
arrange the generator-half of the reducing motor-generator to give its output at
an electro-motive-force corresponding to the potential difference between the outer
positive and negative leads of the lighting portion. Under these circumstances,
it is desirable that the load upon the two halves of the lighting portion be unequal
to such an extent that the work thrown upon the motor balancer will be, as far as
possible, a minimum.
In the foregoing description, the three-wire system has alone been referred
to, but it will be obvious that by modifying the construction of the balancers,
the invention is applicable to a five-wire lighting system.
It has hereinbefore been assumed that the requirements of the traction portion
of the system will be the greater but should the requirements of the lighting
portion be in excess, the converse arrangements can be applied.
Having described the nature of this invention generally, we proceed to
illustrate the same by a concrete example, in which it is supposed that the traction
load will be the greater, and that it is desirable to maintan a constant potential
at the generatug station switchboard of 500 to 550 volts, according to the require-
ments of the system, and that, at the same time, it is necessary to maintain on
the three-wire lighting portion a potential of 460 to 500 volts between the outer
leads. It is further supposed that the negative lead of the traction portion, and
the middle, or neutral, lead of the lighting portion, are earthed and that 100 Kilo-
Watts is required upon the lighting portion. There will then be a surplus
voltage between the positive lead of the lighting portion and the positive lead of
the traction system varying between 320 volts (550-230) and 250 volts
(500-250). The motor portion of the reducer will be employed to transfer the
energy corresponding to the surplus voltage to the negative side of the lighting
portion at a suitable potential. Then each half of the reducer must be designed
to supply its energy at the same voltage (230 to 250 volts) and the variable ratio,
supplementary in series with the motor armature, should be equal to supplying
the full variable electro-motive-force between 460 and 550 volts. (90 volts).
The supplementary to the motor armature, (giving the variable ratio), in these

page_text: reducing motor-generators is sometimes designed for supplying this full variation
of 90 volts electro-motive-force by adding, or subtracting, 45 volts from the
voltage of the motor armature. This motor armature would then be wound suit-
ably for the increased electro-motive-force, and equal to about 275 volts. The
variation in potential is produced by diminishing the supplementary field strength
to zero, and by increasing it again to its normal strength in the reverse direction,
in the one case assisting the motor portion of the reducer, and in the other the
generator portion. In estimating the currents flowing in the various circuits
connected with a combined system, such as that herein before described, it will be
seen that the relation of the electro-motive force of supply on the traction portion
of the electro-motive-force across the outer leads of the lighting portion will
determine whether it is most desirable to maintain the even balance upon the
positive and negative sides of the three-wire system, or whether they should be
slightly unequal with an excess of current on the positive, or the negative, side.
It will be seen from the foregoing example, firstly, that for 100 Kilo-Watts
lighting demand the reducing motor generator, with a ratio on the principal
armature windings of approximately one to one will have a capacity of only about
50 Kilo-Watts on each winding; and secondly, that with this system it is com-
mercially possible to obtain upon the lighting portion (with a reducer having a
commercial efficiency of 93 per cent.) 96 per cent. of the energy delivered from the
traction portion, whilst the size and cost of the apparatus employed is reduced.
This invention does not cover the use of a balancing transformer upon a three-
wire or analogous system. Such Ikdancers may be considered as reducing trans-
formers but so used they are quite outside the scope of our present invention.
In order that the invention may be still more clearly understood, we will
doscribe it further with reference to the accompanying diagrams.
Figure 1 illustrates, in diagram, the method we usually prefer to adopt, employ-
ing separate reducing motor generator and balancer.
Figure 2 illustrates in, diagram an alternative method which we may use:
wherein the reducing motor generator and balancer are combined.
Figure 3 illustrates in diagram the method we may employ as an alternative
to Figure 1, with separate reducing motor generator having its generating arma-
ture across the outer leads of the lighting system.
In Figure 1, D1 D2 are dynamos, furnishing the main supply of energy, and con-
nected to the main bus bars of the switchboards at the points S1 S2 which are
usually kept at a constant potential of 500 to 550 volts. To these bus bars are
connected at $1 the trolley wire (T) of the traction system and at $2 the rail
return (R) and the middle lead of the lighting system (M L.) It is preferred to
make M L and R at the earth potential. The reducing motor generator contains
an armature winding (M), acting as a motor armature in series with the load, or
part of the load, upon the lighting circuit connected between the main leads, PL
and M L. The motor armature winding (G) is retated with and by the armature
winding M acting as motor and supplies energy to the load, or part of the load,
upon the lighting network between the leads ML and NL. These two arm-
atures (M and G) are under the magnetic influence of the shunt field (S F), and
one of them is under the variable ratio field (VRF). The general construction
of this part of the apparatus is similar to that described in the Specifications of
Letters Patent Nos. 24,29 of 1895, and 11,153 of 1895. It is preferred to balance
the loads between PL, ML and NL in the usual way by the employment of a
rotary balancer (B). A and A, are storage cells connected across the three-wire
network. These are very often advantageous in this system of distribution.
In Figure 2, the diagram is more elementary, but similar lettering refers to
similar parts. In this case the reducing motor generator and rotary balancer
are combinel and the three armature portions; the portion M acting as a motor,
the portion B acting as a balancer and the portion BG acting as a balancer and
generator, are mounted upon a common shaft, or upon connected shafts.
L1 L2, L3, and L4 represent loads upon the lighting system. In considering the

page_text: diagram it will be noted that in the event of L1 and L2 being greater in capacity
than are L3 and L4 the armature (1), actuated by the motor armature (M), acts
as a generator, carrying such portions of the load as will maintain the system in
equilibrium, and the difference of potential between PL and ML equal to that
between ML and NL. Conversely, if the load L3 and L4 be greater than the
load L1 and L2 the armature B acts as a motor and enables the portion BG to
supply the extra current required.
In Figure 3 is shewn the alternative arangement to Figure 1. In this case the
generating armature (G) of the reducing motor generator is shewn across the
outside leaves (PL NL). It is generally advisable that the load upon the two
halves of the three-wire system should be unequal, that between PL and ML
being the greater. The difference is represented by L1 and L2, which, for the
greatest economy, should be approximately equal to the energy delivered by the
generating armature (G) when the difference of potential between PL and NL
is equal to the difference of potential between T and ML and R.
.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, wo declare that what
claim is:-
we
1. In a system of electrical distribution from a common generating plant, the
hereinbefore described method of supplying a balanced, or equalised, three-wire
or five-wire distributing network for lighting, or analogous, purposes, having the
neutral, or middle, wire at earth potential with electric energy derived from a
constant potential two-wire carthed traction circuit, by means of a rotary reducing
motor generator; substantially as, and for the purposes, hereinbefore described.
2. In a system of electrical distribution from a common generating plant, the
hereinbefore described method of supplying an earthed two-wire traction circuit
with electric energy derived from a constant potential three-wire or five-wire
balanced, or equalised, system, having its neutral, or middle; wire at earth
potential by means of a rotary reducing motor generator; substantially as, and for
the purposes, herein before described.
"
3. In a system of electrical distribution from a common generating plant to
a traction and lighting system, as hereinbefore described and claimed, the com-
bination of a "reducing" with a "balancing motor generator, so constructed
that they form, together, part of one and the same machine, with three armaturo
windings connected as explained, and operated in a single field magnet system,
or in separate field magnet systems; substantially as, and for the purposes,
hereinbefore described.
4. In a system of electrical distribution from a common generating plant for
lighting and traction purposes, the use of a rotary reducing motor-generator as
a means of interconnection and transference of energy between the two systems,
in combination with a balancing transformer, or equivalent means of equalisa-
tion, on the lighting network.
5. The arrangements hereinhefore described and illustrated in the respective
diagrams, Figures 1, 2 and 3 of the accompanying drawings.
Dated this 22nd day of September 1897.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.