IMPROVEMENTS IN DISTRIBUTING ELECTRICITY AND APPARATUS THEREFOR
Year: 1885

page_text: therefor.
I WILLIAM PHILLIPS THOMPSON Fel. Inst. P.A. of the Agency for Foreign
Patent Solicitors Lord Street Liverpool in the County of Lancaster and
323 High Holborn in the County of Middlesex Civil Engineer do hereby declare
the nature of the said invention for IMPROVEMENTS IN DISTRIBUTING ELECTRICITY
AND APPARATUS THEREFOR (a communication from abroad by Carl Zipernowsky
and Max Déri both of Budapest in the Empire of Austria Engineers) to be as
follows:-
This invention relates to improvements in means for distributing electricity.
The induction bobbins consisting of two insulated wire coils and a common core
of iron wire, like the Ruhmkorff apparatus, have already been used since a certain
time in combination with alternating currents, to. transform electricity.
By means of this transformation the electricity may be transmitted in a cheap
way in large distances, and employed in several local circuits for lighting and other
purposes.
It has not been possible hitherto to effectuate the distribution of electrical
currents by these means in such a manner as is necessary for practical application,
that is to say, that the number of the places of consumption may be optionally
increased or diminished without altering the functions of the other places. Further-
more it has not been possible hitherto, to obtain a satisfactory result of the
mechanical effect of the transformation in proportion to the power applied, when
the consumption of current in the different places, as lamps etcetera is at one time
a large one, and at another time a small one.
In order to obtain this important result, that is to say, to make the different
places independent of each other and to make the mechanical effect of the trans-
formation as favorable and as constant as possible, even when the working is
variable, the following proceeding for the application of induction-bobbins has been
devised.
The induction bobbins are grouped in secondary distributing stations, and the
primary bobbins of such a station of second order are intercalated either successively
in series or parallelly. In the first case the secondary or induced bobbins of all

page_text: the stations must foran only one local circuit, the induced bobbins may be grouped
in quantity or in series. In the other case, when the primary bobbins are arranged
parallelly, each induced bobbin may form a special secondary circuit, or, as in the
first case all the induced bobbins of such a station may be united to one common
local circuit. The places of consumption are intercalated in the local current, in
all cases, in a parallel manner. The main rule is, that the several groups of
induction bobbins or the different stations of second order form, in reference to the
main distributing line of the primary current, always only branch circuits. A dis-
tributing net consisting of an optional number of parallelly arranged branch
stations and of an optional number of local circuits separated from one another is
thus obtained.
The stations of second order are made independent from one another by main-
taining invariable the tension of the primary current, where it enters into the
secondary stations. To obtain an automatic regulation of alternating currents in a
satisfactory manner, that is to say, to receive an invariable tension of the current
in certain points of the net, even if the effect of the generator and the resistances
in the circuit are variable, the following new and simple means are applied.
The excitement of the reversed current machine is usually effectuated by a
current of a determined invariable electromotive power, either by the current of
a special dynamo-machine or by a current of the same direction, which is taken
from the alternating current generator itself. In reversed current machines with
permanent magnets the magnetizing is invariable by itself. To obtain a constant
intensity of the current or of the tension, the magnetizing ought to be invariable
and depend directly on the main current.
This purpose is attained by the following proceeding.
The main current to be regulated is made circulating through the bobbins of a
so called alternating current secondary generator or inductor, before it reaches the
working place. The second bobbin, which is wound parallelly to the first round, a
common iron core is intercalated in the exciting circuit. The alternating current
indirectly produced by the second spire, that is to say, secondarily induced by the
main current, is turned into the same direction by a commutator adapted to the
shaft of the machine.
It the secondary spire is intercalated in the exciting circuit in such a way, that
the current induced therein is added to the exciting current, the magnetizing will
change in the same sense as the intensity of the main current. The magnetizing
will change in the contrary sense, when the secondarily induced current is
circulating opposite to the exciting current.
The first arrangement serves for regulating the tension of the current, the second
arrangement for regulating the intensity thereof. The principle of the automatical
regulating method is therefore to excite the electromagnets by the combined action
of two currents of different origin. One current continuous or turned into the
same direction, is constant in consequence of its derivation, this is the true exciting
current, the other secondary induced current, which is produced indirectly by the
main current, and consequently dependent on it, must be variable according to its
nature. The first mentioned current is usually preponderating so much the more
as the variations to be compensated in the main current are less important. If the
variations are very important, the constant exciting current may be less important;
it may even entirely be spared unless it is without that superfluous, as it is the case
in generators with permanent magnets.
The new regulating method may be further illustrated by the following example.
Fig. 1 shows in a diagram a reversed current machine, in which the electro-
magnets S are rotating and the wires of the armature fixed. The magnetizing
current is taken from a separate wire ab and turned into the same direction by the
commutator C. A and B are the points where the working current leaves the
armature of the machine, a and b the points where the exciting current exits.
DE is the wire bobbin of the inductor intercalated in the main circuit and d e the
wire bobbin intercalated in the circuit of the exciting current.

page_text: The
The main current flows from A over D E to M and from N back to B.
exciting current flows from a to d, reinforces itself here with the secondarily
induced current of the bobbin d e, goes then to the commutator C and after having
circulated as a direct current through the bobbins S it returns to b.
Supposed the potential difference between M and N shall be maintained constant.
The arrangement is now made in that way, that the desired tension between M.
and N, will be obtained at the smallest intensity of the current in the main line,
and that at a normal or greatest allowed intensity of the current, the secondary
induction in de may be exactly great enough, to maintain, under otherwise the
same conditions, the tension between M and N the same as formerly, and that only
in consequence of the reinforced magnetizing.
Rather exactly the same tension will then exist in the interposed intensities of
the current. Besides the possibility of giving the induction bobbins the necessary
dimensions the movableness of the iron core K may also serve for obtaining the
necessary effect of the induction,
Fig. 2 shows in a diagram how the secondary generator A. is employed for
regulating the current in such a case, that the excitement is produced from the
exterior at D by a continuous current, by a separate dynamo-machine for instance
by a primary or secondary battery etc.
The main current S flows through the primary windings of the secondary
generator A and hence to the several applying places. The secondarily induced
current goes from A to the two contact brushes 6¹ and be of the commutator C,
which is fixed upon the shaft of the reversed current machine. To the same shaft
is also connected a collector B, consisting of two contact rings 3 and 4 and two
contact brushes 63 and 6. These contact brushes are in conducting connection with
the constant current source, that is to say, with the two pinching screws 6º and bª.
One end of the coil M is attached to a system of sectors c¹ of the commutator the
other end to the contact ring 3, while the contact ring 7 is in communication with
the other system of sectors c³ of the commutator. The exciting current follows
now the way from be to b₁ and from 3 to c² as a continuous current, from c² 62
over A until b¹ and c¹, a variable current of an uniform direction comes in addition
to it (resp. is to subtract from the first current) the exciting current is a continuous
one from cover M to and further from 6³ until 65.
In the two examples the electromagnets are supposed movable and the armatures
fixed. The arrangement can of course be carried out also in the inversed manner,
small modifications in the intercalation are only necessary for that purpose. The
essential of the regulation with the aid of secondary generators is sufficiently
explained by the above examples.
A great number of combinations of the disposable currents for the purpose of
exciting the electromagnets is possible. The constant exciting current can be
taken.
1) from an exterior current source,
2) from the armature itself of the reversed current generator, namely, from
separate wires of the armature, or as a branch current of the closing circuit, if a
constant tension is to be obtained, or as a portion of the main current if a constant
intensity of the current is desired, or
3) from a secondary generator, where it is induced by any one of the currents
mentioned under 2).
The variable exciting current is taken from the armature of the reversed current
generator as branch current of the closing circuit, when a constant intensity of the
current is to be obtained or as a portion of the main current, when the tension
shall be a constant one. These currents are taken therefore also either directly or
indirectly by secondary generators, the current being secondarily induced by one of
the above mentioned variable alternating currents.
Thence follows, that sometimes two secondary generators or one secondary
generator with three coils are employed, in such cases, namely, where the constant
exciting current as well as the variable one are indirectly produced.

page_text: An important advantage of this regulating method, especially in reference to
such cases, where alternating currents of a considerable tension are to be regulated
is, that in consequence of the transformation it will easily be avoided, that currents
of a high tension must be used for exciting the electromagnets. It is given on the
contrary, a comfortable mean for placing the currents which are to be commutated
and must serve for excitement, in any desired condition. It is thus obtained, that
in the current generators of the main station the force of the exciting magnets
changes always automatically in such a way, that the tension in question must rest
invariable at the entrance into the secondary stations.
The several places of consumption in the local circuits are independent from each
other in consequence of their distribution as branch lines of the secondary circuit
line, if only the interior resistance of the induced bobbins is proportionally small
and if the primary tension of the station does not change.
If the independence of certain lamp groups from each other shall be still more
complete, it is advantageous to supply these groups from a separate line; for an
optional number of secondary circuits insulated from each other can be taken from
a bobbin.
This system of distributing electricity is therefore based upon the circumstance,
that the tension of the current must reinain invariable in the primary distributing
net, as well as in all the local circuits.
To supply in the local circuits places of consumption of different tension, different
lamps for instance, the secondary station is subdivided, where it is necessary, in
several groups of bobbins, which form with their induced bobbins a tension series.
On the commencement and on the end of the induced series of bobbins, and also
on the points of subdivision (fig. 3, the roman numbers I to IV.) pinching screws
are applied. These pinching screws represent then different potential differences,
and in conducting a circuit from each pinching screw I II III and IV a local net is
produced, from which lamps etc. with different tension may be supplied. The
tension for instance between I and II or between II and III, or between III and IV
is 30 Volts, between I and III or between II and IV-60 Volts and between
I and IV-90 Volts.
In a thus arranged distribution of currents a different and variable intensity of
current will reign in each branch line of the large primary net, in contradiction to
the systems hitherto known, where also such induction apparatus for distributing
electricity have been proposed, but with a constant intensity in the entire distri-
buting circuit. The primary intensity changes in each branch circuit proportionally
to the increasing or decreasing of the number of places of consumption in the
corresponding branch stations. This comes from the increasing of the electromotive
counter-force of the induction bobbins, when the intensity of the secondary current
decreases and vice-versa. Thence follows, that the consumption of energy changes
for each secondary station in a similar proportion as the consumption of the current
in the corresponding local circuit. The whole expense of power and the consumption
of current is thus regulated in the whole distributing net. In order to regulate
still more exactly, if necessary, the primary current in any branch, or the secondary
current in a local circuit, or to modify intentionally the intensities of the current
in certain circuits the ordinary rheostats or resistances are not employed, instead
thereof special arrangements, consisting of induction bobbins as represented in
figure 4, are made.
One of the spires A B conducting with itself the current to be regulated, is
subdivided longitudinally. The points of subdivision are 1 to 11. The second
spire a b produces induced currents. This spire is also subdivided from 12 to 21.
In the interior of these two spires is the iron core K. The points 1 to 21 are
provided with connecting wires which are successively put into connection with a
contact C or separated from it. The body C is moved either by hand or auto-
matically according to the circumstances. The more wire points from 21 downwards
are touching the body C, the more windings of the spire ab are short circuited, and
the more points are touching C from 11 downwards, the more the way of the

page_text: current from A to B will be shortened. The short circuiting of the windings
from 21 to 12 effectuates a successive reduction of the electromotive counterforce
in the primary spire A B and the shortening of the current way from A to B
reduces also the resistance opposed to the current. This arrangement offers therefore
a very simple mean for changing the intensity of the current in a given circuit.
The efficacious mean is caused by the circumstance, that the electromotive counter-
force of a spire wound round an iron core is for alternating currents considerably
stronger than the proper resistance of the wire from which the spire is made.
Not only insulated copper wires are used for the spires A B and a b, but also
insulated wires made from another badly conducting metal.
Fig. 5 shows in a diagram how the branch stations are supplied from the main
circuit. O is the central station, between the two circuits of the main 'line M and N
reigns an invariable tension. There may for instance three secondary stations be
represented. Station I consists of a single induction bobbin, station II has two
induction bobbins, the primary spires whereof are arranged parallel to each other;
the secondary spires are disposed in the same way. Station III consists of three
induction bobbins, the primary spires are intercalated in sequence, but the secondary
spires parallel to each other. A regulating device is intercalated at C into the local
circuit of the third station, it is of a similar construction as described in fig. 4.
All the secondary stations of the distribution shown in fig. 5 are parallely
branched off from the main circuit line M N.
It will especially be understood that the inventors claim these improvements as
their invention whatever may be the shape and form of the employed induction
apparatus or secondary generators.

page_text: i
Improvements in Distributing Electricity, and Apparatus
therefor.
I WILLIAM PHILLIPS THOMPSON of 6 Lord Street Liverpool do hereby declare
the nature of this invention (a communication from Carl Zipernowsky and Max
Déri of Budapest, Austria) and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement:-
For sometime past induction coils consisting of two coils or layers of insulated
copper wires with a common iron core similar to the Ruhmkorff' apparatus, have
been used for the transformation of alternating electric currents.
By means of such transformation electric energy can be cheaply conveyed over
lines of considerable length and be utilized in a number of local circuits for lighting
and other purposes.
The distribution of electrical energy by such means, has however not succeeded
in such a manner as to satisfy the requirements of every day practice, because it
was not possible to increase or diminish the number of points of consumption in
operation, without affecting the working of the others in a marked degree, and
it was therefore necessary to use mechanically acting regulating devices at the
different points of consumption, to compensate for the variations caused by the
changes in the quantity of electrical energy used.
In the same manner the efficiency of the systems hitherto used was greatly
dependent upon the number of points of consumption in activity.
Now the object of this invention is to make all individual points of consumption
of electrical energy quite independent from one another, all necessary regulation
being made by or at the generator of electricity.
We group the induction coils or transformers so as to constitute secondary
distributing stations or local centres. The primary coils of the several transformers
of such a local centre may be arranged either in series or in multiple arc circuits.
In the former case the secondary or induced spires of all the transformers of the
respective station form a single local circuit irrespective of whether these induced
spires are connected up in quantity or in series. In the second case however,
i.e. when the primary coils of the several transformers constituting a local centre
are connected up in multiple arc, either each individual induced coil may form a
separate secondary circuit or any number or all of the induced coils of the trans-
formers of a local centre may be connected to form a single local circuit.
The apparatus for the actual utilization of electricity, as incandescent and arc
lamps, electro-motors etc, are in all cases connected up in multiple are in the local
secondary circuits.
But the distinctive feature of our system of distribution is, that each group of
induction coils or transformers or the several stations of second order shall merely
constitute branch circuits of the main line for the primary current i.e. the primary
circuits of the several local centres, any one of these being taken as a whole,. are
also connected in multiple arc.

page_text: In this manner we have conductors distributing the primary (niga tension
current in as many branch circuits as there are local centres and any desirablo
number of secondary (low tension) circuits.
Now the electromotive forces of the two coils of a transformer bear a constant
ratio to one another-Therefore if the internal resistance of such an apparatus is
very low, the secondary tension will remain almost unaltered, if we only have a
constant difference of potential at the terminals of the primary coil-But by
means hereafter to be shown we maintain an invariable tension at the points whero
the primary current enters the local centres-Therefore the secondary tension in
the several local circuits will remain almost unaltered in spite of any variations in
the number of lamps etc, in activity.
In order to maintain automatically a constant difference of potential with
alternating electric currents at certain points of the main or distributing line any
variations in the performance of the generator notwithstanding, we have devised
the following means.
Usually the magnets of alternate current machines are excited by a current of a
given uniform E. M. F. which current may be furnished either by a separate
dynamo (exciter) or by a reversed current derived from the alternating current
dynamo itself. In magneto-electric machines the magnetization is of course
unvariable.
To attain a constant tension or intensity it is however requisite that the
magnetization be variable and become directly dependent on the state of the main
current. This object we attain in the following manner.
The main current which is to be regulated passes through one of the spires of
an induction coil or alternating current transformer before ar ving at the points.
of consumption. The second spire or coil of the transformer is inserted in the
exciting circuit. The current induced in this second spire by the main-current
passing through the first is reversed by a commutator on the shaft of the
inachine.
Where the secondary spire of this transformer is so inserted in the exciting
circuit that the current indirectly induced therein is added to the otherwise
furnished exciting current, the magnetization will vary in the same sense with
the main current; if however, the secondary induced current counteracts the
exciting current, the variation of magnetization will take place in an inverse sense.
The first arrangement serves for regulating the tension of the main current, the
second for regulating its quantity-The leading principle of our selfacting
regulation consists in exciting the electromagnets by the combined action of two
currents of different origin. The one of these currents is, by reason of its origin
constant (or nearly so) and this is the exciting current properly so called; the
other is produced by the main current through induction in a transformer and
being naturally dependent of the main current is of course variable.
Ordinarily the first of these two currents preponderates and will be relatively
stronger, in proportion as the variations in the inain current to be balanced are
less. If the variations to be compensated are very considerable the constant
exciting current may become less preponderant and in some cases it may even be
entirely dispensed with if it is not, as in generators with permanent magnets,
otherwise superfluous. To illustrate our method we give two examples shown in
the adjoined drawings.
Fig. 1 is a diagram of an alternating current generator in which the electros S
rotate while the armature coils remain stationary. The magnetizing current is
supplied by special induced wires a. b and is reversed by the commutator C.
A and B are the points at wbich the working current issues from the armature
of the machine a and b are the terminals of the exciting current D E is the spire
of the regulating transformer inserted into the main line de is the spire inserted
into the exciting circuit. The main current passes from A over D E to the main M
then through the utilizing devices (indicated as incandescent lamps) to N and
returns to B. The exciting current flows from a to d; there it is reinforced by the

page_text: current induced in de, then proceeds to the commutator C and after having
traversed the electromagnet coils S as reversed current, returns to b. Assuming
now for instance that the difference of potential between M and N is to be main-
tained constant, we establish by the separate exciting coil a b the requisite tension,
when the main current is weakest, and provide for the induction in d e in such a
manner that when the main current attains its maximum intensity, the increase of
magnetization will (under otherwise equal conditions) still cause the same tension
to reign at M. N. Then the same tension will approximately be attained also for
intermediate current strengths.
In Figure 2 is shown one manner of employing a secondary generator A for
regulating the machine in case of the electros being excited by a separate con-
tinuous current supplied at D whether such a current be obtained from a separato
dynamo, or a primary or secondary battery or by other means whatever.
The main alternating current generated in the armature S traverses the primary
coil of the transformer A and thence proceeds to the various stations L where it is
utilized. The secondary induced current from A passes to two contact brushes b¹
and 6 of the commutator C attached to the shaft of the alternating current
machine. On the same shaft there are two contact rings 3 and 4 with two
brushes 63 and 6 these latter being connected with the source of the continuous
exciting current at 65 and 66. One end of the magnet coil wires M of the alter-
nating current generator is connected to one of the two systems of sectors of the
commutator i.e. with c¹ while its other end is fastened to the ring the second
ring being connected to the other segment c² of the commutator. The
magnetizing current therefore flows as a continuous current from 6 to b* thence
through M to c¹ where it meets the variable reversed current; this latter passes
through 6 A 62 as an alternating current to join at c² again the exciting current
reinforcing or weakening it as above stated and then further proceeds to ³ ³ and
returns to b. But each of these currents may also enter into separate magnet
coils, the continuous current entering through contact rings into one set of coils as
is usually the case, while the auxiliary current induced in the regulating trans-
former is reversed by a commutator and sent into another set of magnet coils In
both examples illustrated the electro magnets of the generator have been assumed
to be moving and the armatures stationary. Of course, however the arrangement
may also be reversed, this necessitating but slight alterations in the mode of con-
necting up the circuits. The essential features of the method of regulating by
means of secondary generators or transformers are sufficiently set forth in the
above examples.
Furthermore numerous combinations of the available currents may be employed
for the purpose of suitably exciting the magnets. The constant exciting current
may be taken from one of the following sources
1) from an extraneous source (dynamo battery &c).
2) from the armature of the alternating current machine itself, either from
special armature wires, or as a branch from the main circuit in case of constant
tension being aimed at or as a portion of the main current itself when this shall be
of constant intensity.
3) from a transformer in which it is induced by any of the currents indicated
sub 2).
The variable exciting current is obtained from the armature of the alternating
current generator, either as a branch circuit from the main line, where constant
intensity of the external working current is aimed at, or the main current itself
(i.e. part of it) is made use of, where constant tension is required.
This variable current, it will be seen, is also either obtained directly or by the
intervention of an induction coil or transformer.
Hence in some cases two transformers are used, or one with three different
spires This latter is the case when both the constant and the variable part of the
excitation are produced indirectly by induction coils.

page_text: An important advantage of this mode of regulation is realized in the particular
case of very high tension alternating currents, by use of the transformers as above
described the employment of the high tension for the excitation may be readily
avoided, as we can make the magnetizing current of any suitable potential or
intensity irrespective of what character the main current of the generator be.
We have by this means perfectly succeeded in causing the magnets of the
generator of electricity to vary automatically in such a manner and proportions,
that the difference of potential of the current on entering the local centres will
remain nearly constant.
The individual points of consumption in the several local circuits are inde-
pendent from one another by reason of their distribution as branch circuits
derived from the secondary line (i.e. connection in multiple arc), provided only
that the internal resistance of the transformers be relatively low, and the primary
tension at the station invariable.
Should the independence of individual groups of lamps be still more perfect, it
will be advisable to feed such a group by an independent line, as any desired
number of secondary circuits may be derived each separately from one transformer.
It follows from the foregoing that our system of distributing electrical energy
by means of alternating currents and induction coils or transformers is based upon
having a constant difference of potential in the primary conductors as well as in
the secondary ones.
For the purpose of feeding in one local circuit consumption points or devices
with currents of various tensions (as for instance lamps of different type) we may
where it is required subdivide the secondary spires of the transformers of one local
centre into several groups of coils constituting a tensional series. At both ends of
such a series of coils as well as at the points of subdivision (in fig. 3 the points
marked I, II, III, IV) we provide terminals-These terminals represent various
differences of potential and by connecting a line to each of the terminals I, II, III
and IV we obtain a local net, from which the different lamps or the like may be
supplied, so that for instance the tension between I and II (or II and III or III
and IV) be say 30 Volts between I and III (or II and IV) it be 60 Volts and
I and IV will furnish a current of 90 Volts.
In a distribution of current according to our system there will be a variable
intensity of current in the main line as well as in every branch circuit of it, in
contradistinction to the systems of distribution by inductional transformers
hitherto known or proposed, all of these being based upon constant intensity of
the primary current-In our system the intensity of the primary current varies in
the same way as the number of points of consumption in activity. This is caused
by the counter-electromotive-force of the transformers somewhat increasing when
the intensity of the secondary current diminishes and vice-versa. The consumption
of energy for each local station varies in the same manner as the current in the
corresponding local circuit and consequently the total consumption of power varies
in accordance to the total supply of current in the secondary circuits.
Fig. 4 is a diagram showing the manner in which we supply local centres from
the main line. At O is the central station-Between the main lines M and N the
tension is invariable.-Three local centres or secondary stations are shown-
Station I consists of a single transformer; at Station II there are two trans-
formers with their primary as well as their secondary coils connected up in
multiple are; at station III there are three transformers, with their primary coils
in series, the secondary ones in multiple arc-As it will be seen all the branch
circuits leading to the several local centres are derived as parallel circuits from the
main line; i.e. connected up in multiple arc.
We desire it distinctly to be understood that the form of the induction
apparatus or transformers used may be whatever, without departing from the
principle of our invention.

page_text: Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to
me by my foreign correspondent I declare what I claim is
1. In alternating current generators the above described combination of a
constant, or nearly constant, exciting current with a variable current, which
variable current by aid of a special induction coil or transformer is made directly
dependent upon the conditions of the current in the external circuit, and the
coinbination of these two currents in one, two or more separate windings of the
magnets; therefore the application of induction coils or transformers for this
combination as described above and partially shown in fig. 1 and 2, for the purpose
of regulating the alternating currents by means of an automatically variable
excitation of the magnets according to a certain low viz-in order to maintain
constant, within certain limits at a dettermined point of the circuit either the
tension or the intensity of the current nonobstant of variations in the quantity of
current supplied or in the resistance of the circuit and the application of this
regulation for distributing electricity.
2. In the application of induction coils or transformers for alternating electric
currents the arrangement of several stations of second order as branch circuits of
the main line, i.e. connecting up the local centres with the main line in multiple
are, to which main line is supplied an alternating electric current of a tension as
constant as possible substantially as described and shown in fig. 4.
3. In the application of induction coils or transformers for alternating electric
currents the groupment of the coils of these apparatus in each station of second
order as described with reference to Fig. 3 that is in such a way, that the induced
or secondary wires form a tensional series with several terininals of different
potential and the formation of a local net of conductors from the which lamps or
other devices may be supplied with currents of different tension.
n
.