Improved Means for Protecting Electrical and Magnetic Apparatus against the Disturbing Effects of Electric Railways Passing in Proximity thereto.
Year: 1895

page_text: Date of Application, 21st Nov., 1895
Complete Specification Left, 23rd July, 1896-Accepted, 29th Aug., 1396
Communicated from abroad by SIEMENS AND HALSKE, of Berlin, in the Empire
of Germany, Electrical Engineers.]
Improved Means for Protecting Electrical and Magnetic Apparatus
against the Disturbing Effects of Electric Railways Passing in
Proximity thereto.
We, SIEMENS BROS. & Co. LIMITED, of 12 Queen Anne's Gate, Westminster,
in the County of London, Electrical Engineers, do hereby declare the nature of
this invention to be as follows:-
As is well known, electrical railways passing in the neighbourhood of buildings
in which electrical and magnetic observations are carried on have a disturbing effect
upon such observations.
The present invention relates to means whereby such disturbing action is obviated
or neutralised.
The main causes of such disturbances are, firstly the so called truant earth
currents which pass from the rail which constitutes the return conductor, into the
surrounding ground, and secondly the action at a distance of the conductors through
which the current is passing upon the instruments in the adjacent building.
Protective devices have been previously proposed against the above action,
which consist, firstly, in collecting a portion of the earth currents by means of
earth plates which are imbedded in the ground in the vicinity of the building to
be protected, and leading these currents through conductors surrounding the
building in such manner that the action of the earth currents upon the instruments
is thereby neutralised, secondly, in taking off a portion of the current flowing
through the rails of the electric railway by means of a conductor which is applied
to the rails near the building to be protected, and is led over such building to the
pole of the current generator that supplies the railway, the conductor being so
arranged as to neutralise the earth currents produced.
The first named method was intended to compensate for all earth currents
occurring in the vicinity of the building; the second one to compensate only for
the earth currents resulting from the electric railway.
The present invention consists in a farther development of the second method.
Experiments have shewn that by this method the disturbances caused by the
electric carriage can only be compensated for a single position thereof, but as
the disturbances vary considerably for different positions of the carriage, the
compensation obtained by these means only has a very small practical value.
If however in place in employing a single compensating conductor, a number
thereof be employed, which are connected side by side at certain distances apart
to the rail and are arranged according to the following method relatively to the
locality to be protected, an almost perfect compensation can be obtained.
Referring to Fig. 1 of the accompanying drawing, M represents the primary
current generator, Ŏ an elevated conductor, S the rails of the line, W an electrical
carriage, A B C D the connecting points of the compensation wires K' K' K³,
and U U Us, the parts of these wires that are carried over the locality to be
protected. If now the electric carriage passes from A to B and beyond, and the
strength of the main current remains constant, then, when the carriage is situated
[Price 8d.]

page_text: at A the current in the loop K¹ will be zero, but when the carriage is at B such
current will have a certain value, which it will retain during the farther motion
of the carriage.
During such motion of the carriage from A to B, the compensating current
in K' will increase regularly, its value being proportional to the distance of the
carriage from A.
In the loop K' on the other hand the current is zero until the carriage arrives
at B; it then increases regularly until the position C is attained, and then remains
constant during the farther motion of the carriage.
In a similar manner in the loop K³ the current commences when the carriage is
at C, increases till the position D is attained, and then remains constant.
If each of these loops be carried by the windings U₁ U' U' round the locality
to be protected and, for example, the winding Us be carried in the contrary
direction to the others, the sum of the effects of the separate compensating currents
will act upon the instruments in the locality. If therefore in Fig. 2 the curve of
the total effect be drawn which the electric carriage travelling along the line will
exercise upon the instruments, then there will be obtained for such curve the broken
line L passing through the points A b c d d.
If the disturbance curve T be drawn which gives the disturbance exercised on
the instrument at each position of the carriage, it will be evident that if this
curve, as shewn, is similar in form to that of the broken line L, then the
disturbances caused by the carriage will be neutralised by the system of com-
pensating wires K' KK with the exception of a small rest, which is caused by
the differences between the curves T and L.
In order therefore to obviate the disturbances caused by an electric railway, the
disturbance curve is first determined, that is, the series of disturbances caused by
a carriage travelling along the line; for this curve is then substituted a broken
line, that is, a line composed of a series of straight lengths, and as many com-
pensating wires K' K' &c. are applied as there are straight lengths, the points of
connection being determined by the abscissæ of the intersection points 6 c, and the
number of windings and the resistance of each loop are so adjusted that for a
certain position of the carriage between the points of connection of the loops, the
disturbance caused by the carriage is neutralised.
b
The disturbances within the locality to be protected caused by the motion of the
carriage will then be neutralised with the exception of a small rest resulting from
the difference between the curve and the broken line, and which can be reduced
at will by increasing the number of compensating loops.
It will be evident that this compensation can be effected for any form of the
railway, and that by means thereof all the disturbances caused by the railway,
whether the truant earth currents, or the distant action of the conductors of the
line, and of the electromotor, will be neutralised with the exception of a small
rest.
If the strength of the current of the electrical carriage is not constant, the non-
compensated rest of the disturbance will vary correspondingly; the arrangement
for the compensation however remains the same for all strengths of current.
This compensation holds good not only for a single carriage but also for a
number thereof; the non compensated rest will even frequently be less with several
carriages than with one; because such disturbance rests may be of different sign
and thus may neutralise each other.
It is furthermore to be observed that the truant earth currents are dependent
upon the resistance of the soil, and consequently also upon the weather.
In order to obtain the compensating action not withstanding such variations, each.
loop K is made to contain a resistance, and in addition, the resistance of the earth
between two sunk earth plates or between the rails and a water main is continually
determined by measurement.
If it be determined by experiment how the regulating resistances have to be
adjusted according to the observed earth resistance, and a table be worked out,

page_text: then the regulating resistances can be always so adjusted that the compensation will
also be correct with variable earth-resistance.
Dated this 21st day of November 1895.
ABEL & IMRAY,
Agents for the Applicants.
Improved Means for Protecting Electrical and Magnetic Apparatus
against the Disturbing Effects of Electric Railways Passing in
Proximity thereto.
We, SIEMENS BROS. & Co. LIMITED, of 12 Queen Anne's Gate, Westminster,
in the County of London, Electrical Engineers, 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 :-
As is well known, electrical railways passing in the neighbourhood of buildings
in which electrical and magnetic observations are carried on have a disturbing
effect upon such observations.
The present invention relates to means whereby such disturbing action is obviated
or neutralised.
The main causes of such disturbances are, first, the so called truant earth
currents which pass from the rail which constitutes the return conductor, into the
surrounding ground, and secondly, the action at a distance of the conductors
through which the current is passing upon the instruments in the adjacent building.
Protective devices have been previously proposed against the above action,
which consist, first, in collecting a portion of the earth currents by means of earth
plates which are imbedded in the ground in the vicinity of the building to be
protected, and leading these currents through conductors surrounding the building
in such manner that the action of the earth currents upon the instruments is thereby
neutralised, secondly, in taking off a portion of the current flowing through the
rails of the electric railway by means of a conductor which is applied to the rails
near the building to be protected, and is led over such building to the pole of the
current generator that supplies the railway, the conductor being so arranged as to
neutralise the earth currents produced.
The first named method was intended to compensate for all earth currents
occurring in the vicinity of the building; the second one to compensate only for
the earth currents resulting from the electric railway.
The present invention consists in a farther development of the second method.
Experiments have shewn that by this method the disturbances caused by the
electric carriage can only be compensated for a single position thereof, but as the
disturbances vary considerably for different positions of the carriage, the com-
pensation obtained by these means only has a very sinall practical value.
If however instead of employing a single compensating conductor, a number be
employed, connected side by side at certain distances apart to the rail and arranged
according to the following method relatively to the locality to be protected, an almost
perfect compensation can be obtained.
Referring to Fig. 1 of the drawings accompanying the Provisional Specification
M represents the primary current generator, an elevated conductor, S the rails
of the line, W an electrical carriage, A B C D the connecting points of the
compensation wires K' K' K³, and U¹ U U³, the parts of these wires that are
carried over the locality to be protected. If now the electric carriage passes
from A to B and beyond, and the strength of the main current remains constant,
then, when the carriage is situated at A the current in the loop K¹ will be zero,

page_text: but when the carriage is at B such current will have a certain value, which it will
retain during the farther motion of the carriage.
During such motion of the carriage from A to B, the compensating current
in K will increase regularly, its value being proportional to the distance of the
carriage from A.
In the loop K' on the other hand the current is zero until the carriage arrives
at B; it then increases regularly until the position C is attained, and then remains
constant during the farther motion of the carriage.
In a similar manner in the loop K³ the current commences when the carriage is
at C, increases till the position D is attained, and then remains constant.
If each of these loops be carried by the windings U¹ U' U³ round the locality to
be protected and, for example, the winding Us be carried in the contrary direction
to the others, the sum of the effects of the separate compensating currents will act
upon the instruments in the locality. If therefore in Fig. 2 the curve of the total
effect be drawn which the electric carriage travelling along the line will exercise
upon the instruments, then there will be obtained for such curve the broken line L
passing through the points A b c d d.
If the disturbance curve T be drawn which gives the disturbance exercised on
the instrument at each position of the carriage, it will be evident that if this curve,
as shewn, is similar in form to that of the broken line L, then the disturbances
caused by the carriage will be neutralised by the system of compensating
wires K K K with the exception of a small residue which is caused by the
differences between the curves T and L.
In order therefore to obviate the disturbances caused by an electric railway, the
disturbance curve is first determined, that is, the series of disturbances caused by
a carriage travelling along the line; for this curve is then substituted a broken
line, that is, a line composed of a series of straight lengths, and as many com-
pensating wires K₁ K' &c. are applied as there are straight lengths, the points of
connection being determined by the abscissæ of the intersection points 6 c, and the
number of windings and the resistance of each loop are so adjusted that for a
certain position of the carriage between the points of connection of the loops, the
disturbance caused by the carriage is neutralised.
The disturbances within the locality to be protected caused by the motion of the
carriage will then be neutralised with the exception of a small residue resulting
from the difference between the curve and the broken line, and this can be reduced
at will by increasing the number of compensating loops.
It will be evident that this compensation can be effected for any form of the
railway, and that by means thereof all the disturbances caused by the railway,
whether the truant earth currents, or the distant action of the conductors of
the line, and of the electromotor, will be neutralised with the exception of a small
residue.
If the strength of the current of the electrical carriage is not constant, the
non compensated residue of the disturbances will vary correspondingly; the
arrangement for the compensation however remains the same for all strengths of
current.
This compensation holds good not only for a single carriage but also for a number
thereof; the non compensated residue will even frequently be less with several
carriages than with one; because such disturbance residues may be of different
sign and thus may neutralise each other.
It is furthermore to be observed that the truant earth currents are dependent
upon the resistance of the soil, and consequently also upon the weather.
In order to obtain the compensating action notwithstanding such variations,
each loop K is made to contain a resistance, and in addition, the resistance of the
earth between two sunk earth plates or between the rails and a water main is
continually determined by measurement.
If it be determined by experiment how the regulating resistances have to be
adjusted according to the observed earth resistance, and a table worked out, then the

page_text: regulating resistances can be always so adjusted that the compensation will also be
correct with variable earth-resistance.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
For protecting electric and magnetic apparatus against the disturbances caused
by a neighbouring electric railway, an arrangement at determined points of the
rail of a number of compensating wires which are led to the locality to be protected
and have their positions, windings, and resistances so chosen that their action
opposes and approximately equals the disturbing currents proceeding from the
electrical car in all its positions within a certain range.
Dated this 23rd day of July 1896.
ABEL & IMRAY,
Agents for the Applicants.