Note: Descriptions are shown in the official language in which they were submitted.
1(~43435
OCCUPANCY DETECTING A . C . TR~CK
CIRCUIT APPARATUS
1. Back~round of the Invention
This invention relates to alternating current track
circuits for railroads, and while the invention is subject to a ,
wide range of applications, it will be particularly described as
being of the double rail type for application to a stretch of
railway track divided into track sections by insulated joints.
The present invention is particularly useful in the
use of alternating current track circuits for electrified rail-
raods having D.C. power propulsion. A system of this character
10. is disclosed in the Estwick U.S. Patent No. 1,822,572, issued
September 8, 1931, and assigned to the same assignee (by change
of name) as the present invention. This patent discloses in -
FIG. 1 a conventional alternating current track circuit for
frequencies of 25-60 HZ using a track and local phase detecting
relay for sensing occupancy of the associated track section.
The track feed energy and the energy for the local winding are
obtained from the same source, and the track winding current -
lags the input voltage in accordance with inductive reactance
of the track rails and of an adjustable reactance in series with
20. the track rails at the feed end of the track circuit. It is
the adjusted phase different between the currents in the track -
and local windings that makes the track relay, which can be
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of a vane type, operable. Optimum operating conditions are
obtained when there is a 90 difference in the phase relation-
ship of the track and local windings of the track relay.
It is pointed out in this patent that for long track
circuits it i8 difficult to obtain the optimum phase difference
in the track relay, and thus various remedies are proposed
including shifting the phase of the local winding of the track
30. relay. With the improvements according to this patent, there
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1043435
1. are still shunting sensitivity problems and phase shift pro-
blems involved for long track sections of electrified railroads,
where impedance bonds must be used, and particularly where
protection for broken down rail joints is provided by stagger-
ing the instantaneous polarities of adjoining track sections.
An object of the present invention is to provide an
alternating current double rail track circuit which substantially
obviates one or more of the limitations and disadvantages of
the described prior arrangements.
10. Another object of the present invention is to provide
an alternating current track circuit having improved shunting
sensitivity for long track circuits.
Summary of the Invention -
Alternating current track circuit apparatus is pro-
vided for a stretch of railway track divided by insulated
joints into adjoining double rail track circuits and having
impedance bonds at respective transmitting and receiving ends
of the track circuits permitting power propulsion direct
current to bypass the joints. An alternating current track -
20. feed is connected across the track rails at the transmitting
end of each of the track circuits through a circuit tuned to
resonance by a variable capacitor connected in series with a
wlnding of the impedance bond at that end of the track section -
for energization of the associated track circuit from a source
of alternating current. An alternating current receiver is
provided for the receiving end of each of the track circuits -
for connection across the track rails through a circuit tuned
to resonance by a variable capacitor in series with a winding -
of another of the impedance bonds and a track winding of a
30. receiving relay for sensing the presence of a vehicle in the -
a8sociated track section. The receiver comprises a local
source of energy derived from the same source as the track
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1043435
1. feed and connected to a local winding of the relay in series
with a variable capa~itor for adjustment of the phase difference
between energization of the track and local windings for provid-
ing optimum sensitivity of the relay.
For a better understanding of the present invention,
together with other and further objects thereof, reference is
had to the accompanying description, taken in connection with
the accompanying drawings, while its scope will be pointed out
in the appending claims.
10. In the Drawings
FIG. 1 illustrates schematically a typical alternat-
ing current double rail track circuit according to a preferred
embodiment of the present invention;
FIG. 2 illustrates by vector diagrams typical prior
art phase displacements of currents in a track winding as com-
pared to applied voltage for different lengths of track
circuits;
FIG. 3 illustrates by vector diagram typical phase
displacements of current in a track winding as compared to
20. applied voltage for different lengths of track circuits accord-
ing to the preferred embodiment of the present invention as
illustrated in FIG. l; and
FIG. 4 illustrates the affect of variable capacitance
in series with the local phase relay winding when the trans-
mitting and receiving ends of the preferred embodiment of the
pre8ent invention as illustrated in FIG. 1 are tuned to
resonance.
With reference to FIG. 1, alternating current track
circuit apparatus is provided for a stretch of railway track 10
30. divided by insulated joints 11 into adjoining double rail track
circuits 12, 13 and 14 respectively. These track circuits have
impedance bonds at respective transmitting and receiving ends ~ -
3 :
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~04343S
1. permitting power propulsion direct current to bypass the joints.
An alternating current track feed 16 is provided at ,
the transmitting end of each of the track circuits and is
connected to the track rails through a circuit tuned to
resonance by a variable capacitor Cl connected in series with
a winding 18 of bond 15 for energization of the associated
track circuit from a source of alternating current 19.
An alternating current receiver 20 is connected across
the rails at the right-hand end of each of the track sections
10. through a circuit tuned to resonance by a variable capacitor C2 - .
in series with a winding 22 of another of the impedance bonds
15. Also included in series in the receiving circuit is a track ~'
winding 23 of a track relay TR. The receiver 20 also comprises
a local source of energy 24 derived from the source 19 and
connected to a local winding 25 of the relay TR in series with a .
variable capacitor C3. The variable capacitor C3 is for adjust-
ment of the phase different between energization of the track :~
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and local windings of the track relay TR for providing optimum
sensitivity of this relay. A center tap of the primary winding -::
20. 17 of each of the bonds 15 is connected to a corresponding center
tap of the next adjoining bond 15 so that the D.C. propulsion .
return bypasses the insulated joints 11. .
It is a well known practice in alternating current track : -
circuits to guard against a possible failure due to breaking down
of the insulated joints by staggering the instantaneous polari-
ties of the track circuits as is illustrated in FIG. 1. Two
position A.C. vane relays such as is disclosed in the U.S. Maenpaa - -
Patent No. 2,559,448, issued July 3, 1951, are generally used for ..
track relays TR which are operable only when the phase differ-
30. ence between the track winding and local winding of the relay
is within a predetermined range. If the track circuit is so
long that the rail impedance plus the impedance of the bonds -
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104;~435
1. shifts the phase difference beyond this range, it is necessary
to reverse the polarity of the local winding in order to make
the relay responsive; but to do this, would make the relay also
responsive to the adjoining track circuit in case the rail
joints are broken down. Thus, where the normal A.C. track
circuit is used for a long track circuit wherein only the
bond at the relay end is tuned to resonance, broken down joint
protection cannot be provided.
FIG. 2 illustrates the phase shift of the track phase
lO. of a track relay TR relative to the supply voltage for differ-
ent lengths of track circuits, assuming that only the relay end
of the track circuit is tuned to resonance. It will be readily
understood from this diagram that there is considerable difficul-
ty in providing proper control for A.C. track circuits of varying x,
length, particularly where long and short track sections are
adjoining, and still provide broken down joint protection.
In the system according to the present invention,
however, it is possible to obtain much improved results as is
illustrated in FIG. 3 by tuning both the transmitting and
20. receiving ends of each track section to resonance to effect-
ively cancel the inductance of the impedance bonds, and to
obtain optimum phase difference between the local winding and
the track winding of each track relay by adjustment of
capacitor C3 in series with the local winding. This reduces
the phase shift spread for different length track circuits -~
from 119 according to a test of the prior art system as ~ -
illustrated in FIG. 2, to only 44 according to a test of the
preferred embodiment of the present invention as illustrated -
in FIG. 3. -
30. To obtain the optimum operating characteristics for
the track circuit according to the preferred embodiment of the -
present invention, the capacitor C3 in series with the local
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~043435
1. winding 25 of relay TR is adjusted, after first tuning both
ends of the track circuit to resonance. This adjustment is to
a value providing close to 90 phase displacement between the
track and local windings of the relay and to obtain a shunting
resistance within the track circuit requirement calling for
the track relay to be responsive to at least a .3 ohm resistance
rail shunt.
In FIG. 4, for a typical set of values in a 6,000
foot track circuit, shunt resistance and local-track phase
10. difference curves 26 and 27 are obtained respespectively. The
optimum adjustment of the capacitor C3 is to a value correspond-
ing to the point 26a of curve 26 corresponding to a .31 ohm
shunting resistance. This adjustment obtains a phase differ-
ence between the track and local windings 23 and 25 correspond-
ing to point 27a on curve 27. The curves 26 and 27 are for a
6,000 foot 75HZ track circuit having a ballast resistance of
5 ohms per thousand feet, and having the feed and relay ends of
the track circuit tuned to resonance wherein capacitor Cl is
adjusted to 2.24 mfd and capacitor C2 is adjusted to 2.3 mfd.
20. Shunting resistance at point 26a of curve 26 is .31 ohms, the
variable capacitor C3 is adjusted to 2.3 mfd, and the phase
difference between the local and track phases as represented
by the point 27a is 90.
The track circuit thus provided according to the
preferred embodiment of FIG. 1 can be adjusted for obtaining
high track voltage and good shunting sensitivity, and the local
phase of the relay TR can be adjusted independently for the
required operating characteristics, such adjustments all result-
ing in being able to provide full broken down joint protection
30. for diferent lengths of adjoining track circuits. It is to be
understood that the frequency of 75HZ has been chosen only ~or
example and that frequencies from 25HZ to lOOHZ could be used.
6 ~
104343S
1. While there is disclosed what at present is considered
to be the preferred embodiment of the present invention~ it will
be obvious to those skilled in the art that changes and modifica-
tions may be made therein without departing from the invention
and it is therefore aimed in the appending claims to cover all
such changes and modifications as fall within the true spirit
and scope of the invention.
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20.
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30.
