Remote power supply system for a coaxial line with repeaters subjected to the influence of external electric fields

A remote power supply system is disclosed which is particularly for monocial transmission lines equipped with repeaters. It comprises at least one current transformer inserted between two sections of line in a local power supply circuit at each repeater. The transformer has two identical primary windings one inserted in a first branch connection connecting the inner conductor of a line section to the outer conductor of the other line section, the other inserted in a second branch circuit connecting the other conductors of the line sections.

The present invention relates to the remote AC power supply of repeaters in 
a monocoaxial transmission line equipped with repeaters. 
In a monocoaxial line with repeaters requiring remote AC power supply, the 
transmission signals and the remote supply current propagate along the 
same conductors, but in different frequency bands: a frequency of 50 Hz 
for the remote supply current and frequencies higher than approximately 
ten kilohertz for the signal current. These currents are separated at the 
repeaters by band filters. 
The remote supply current flows in a monocoaxial line along two opposite 
paths, the outgoing path and the return path forming a loop. Between each 
repeater, one of the paths is constituted by the inner conductor of the 
line and the other is constituted by the outer conductor. In general, 
there is no break in the metallic circuit of the outer conductor of the 
line at each repeater, while the internal conductor is cut, its ends being 
connected to separate connections, one transmitting the signals at the 
input-output element of the repeater in question and the other for 
conveying the remote supply current through the primary winding of a 
current transformer that forms part of the local power supply circuit of 
the repeater. 
The penetration of an external electromagnetic field into a monocoaxial 
line decreases as the frequency increases. Hence, the influence of 
electromagnetic fields of industrial origin results essentially in 
low-frequency currents in the inner conductor of a coaxial line which do 
not interfere with the transmission of the signals but which do perturb 
the AC power supply current, being added to or subtracted from this 
current. The mode of connecting the primary windings of the transformers 
of the local power supply circuits of the repeaters as has been described 
in the preceding paragraph is sensitive to these perturbations. 
Preferred embodiments of the present invention reduce the influence of 
currents induced by external electromagnetic fields on the remote power 
supply of the repeaters of a coaxial transmission line. 
The present invention provides a remote AC power supply system for 
repeaters of a coaxial transmission line in which the remote supply 
current flows through the line along an outward path and a return path 
which form a remote supply loop and are constituted between the repeaters 
by the inner conductors and the outer conductors of the intervening 
section of the coaxial line and in which the local power supply circuit of 
each repeater is inserted between first and second sections of the coaxial 
line connected to the repeater, the local power supply circuit including 
at least one current transformer having a first primary winding and a 
second primary winding respectively inserted in the outgoing path and in 
the return path of the power supply loop so as to take the power necessary 
for supplying the repeater in equal proportions from each of the said 
paths and to ensure the continuity of the remote power supply loop at the 
repeater.

FIG. 1 is a conventional (prior art) remote power supply system. A repeater 
1 is inserted between two sections A and B of a monocoaxial transmission 
line whose respective outer conductors have been referenced by the 
numerals 2 and 3 and whose respective inner conductors have been 
referenced by the numerals 4 and 5. The ends of the inner conductors 4 and 
5 of the sections A and B of the monocoaxial line are connected to the 
input-output elements of the repeater 1 via high-pass filters constituted 
by series connected capacitances 6, 7 followed by isolation transformers 
8, 9. The high-pass filters allow the transmission of the signals in the 
direction of the input-output elements of the repeater 1 because of their 
high frequencies and block the remote power supply current because of its 
low frequency. The inner conductors 4 and 5 of the section A and B of the 
monocoaxial line are also connected by a shunt connection formed by the 
series connection of two current transformers 10, 11 belonging to the 
local power supply circuit of the repeater 1 and of two inductances 12, 13 
forming low-pass filters which block the transmission of the signals and 
allow the remote power supply current to pass. The outer conductors 2 and 
3 of sections A and B of the coaxial line are electrically connected by a 
connection 14. The low-value capacitors 24 and 25 are used for fixing the 
potential of the equipments in relation to earth potential at the 
frequencies of the transmission signals. 
FIG. 1 has two current transformers 10, 11 in order to represent the fairly 
common case where it is necessary to have two supply sources available, 
but it is quite evident that there need be only one current transformer. 
In the circuit shown in FIG. 1, an inductance 15 is connected between the 
interconnection point of the primary winding of the current transformers 
10 an 11 and the connection 14 interconnecting the outer conductors 2 and 
3 of sections A and B of the monocoaxial line. It is intended to 
compensate the capacities of the monocoaxial line and of the repeater 1 at 
the frequency of the remote power supply current to improve the power 
factor of the remote supply loop. 
External electromagnetic fields generated e.g. by a power transport grid 
line or by the overhead wires of an electrified railway line in the 
vicinity of the monocoaxial transmission line induce different 
longitudinal currents in the inner and outer conductors which are 
essentially at low frequency. These induced longitudinal currents do not 
reach the input-output elements of the repeater 1 because they are stopped 
by the series-connected capacitances 6, 7. However, they do pass through 
the shunt connection formed by the series connection of the primary 
windings of the current transformers 10, 11 and of the inductances 12 and 
13 and thereby provoke overvoltages and undervoltages in the local power 
supply circuit of the repeater 1 which are detrimental to the proper 
operation of the repeater. 
The remote supply circuit shown in FIG. 2 embodies the invention and 
enables this defect to be reduced to a great extent. The elements of the 
circuit of FIG. 2 are unchanged with respect to those in FIG. 1 and the 
same reference numerals are used therein. This figure also shows the 
repeater 1 inserted between two sections A and B of a monocoaxial 
transmission line whose inner conductors are referenced 4, 5 and whose 
outer conductors are referenced 2, 3. As in FIG. 1, the inner conductors 
4, 5 of the sections A and B of the monocoaxial line are connected to the 
input-output elements of the repeater 1 via high-pass filters which are 
constituted by the series-connected capacitances 6, 7 followed by 
isolation transformers 8, 9 and allowing the transmission of the signals 
but stopping the remote power supply current. 
The local supply circuit of the repeater 1 comprises two current 
transformers 16, 17, since, as in the circuit of FIG. 1, it is presumed 
that the repeater 1 includes two supply sources. Each of these current 
transformers 16, 17 has two identical primary windings respectively 18 and 
19, and 20 and 21. 
The primary winding 18 of the current transformer 16, the primary winding 
20 of the current transformer 17 and an inductance 22 are series connected 
in a first shunt connection connecting the inner conductor 4 of section A 
of the monocoaxial line to the outer conductor 3 of section B of the 
monocoaxial line. The primary winding 19 of the current transformer 16, 
the primary winding 21 of the current transformer 17 and an inductance 23 
are series connected in a second shunt connection connecting the outer 
conductor 2 of section A of the monocoaxial line to the inner conductor 5 
of section B of the monocoaxial line. 
The inductance 15 fulfills the same function as in FIG. 1; it is matched 
with the capacitances of the monocoaxial line and of the repeater 1 at the 
frequency of the remote power supply current to improve the power factor 
of the remote power supply loop. In the case where the local power supply 
circuit of the repeater 1 comprises only one current transformer, it is 
sufficient to replace the primary winding 18, 19 or 20, 21 of the 
eliminated transformer by shorts. 
The inductances 22 and 23 form low-pass filters which prevent the 
transmission of the signals through the first and second shunt connections 
but allow the remote power supply current to pass. At the repeater, these 
shunt connections respectively constitute an outgoing path and a return 
path of the remote supply loop. As they are connected on one side of the 
repeater to the inner conductor of the monocoaxial line and on the other 
side of the repeater to the outer conductor of this line, on either side 
of the repeater 1 they provide permutation between one section and another 
of the outgoing path and return path roles in the remote power supply loop 
of the inner conductor and outer conductor of the monocoaxial line. 
The primary windings 18 and 19 or 20 and 21 of the respective current 
transformers 16 and 17 are wound and connected in directions such that the 
flux generated by the remote power supply currents which flow through them 
in opposite directions add together. In this way, the power necessary for 
supplying the repeater 1 and available to the secondary winding of the 
current transformers 16 and 17 is taken in equal parts from the outgoing 
and return paths of the remote supply loop. Further, the longitudinal 
currents which are induced in the outer and inner conductors of the 
monocoaxial line by external electromagnetic fields and which flow through 
these conductors in a same direction generate induction flows in the 
current transformers 16 and 17 in opposite directions which substract. 
The longitudinal currents induced in the outer and inner conductors of the 
monocoaxial line by outer external electromagnetic fields do not have the 
same intensities because of the shielding effect of the outer conductor on 
the inner conductor. The results of this is that compensation cannot be 
made on a single section of the monocoaxial line. It is made on the two 
half-sections of line on either side of the repeater 1 due to the 
permutation from one section to the other at the repeater 1 between the 
outgoing path and return path functions fulfilled by the inner and outer 
conductors of the monocoaxial line. 
Without going beyond the scope of the invention, some dispositions can be 
modified or some means can be replaced by equivalent means. In particular 
one of the transformers used in the local supply circuit of a repeater can 
be eliminated. Further, it is possible to insert an isolation transformer 
between the transformers 16 and 17 to break the metallic continuity and 
consequently to limit the length of a section subjected to the perturbing 
fields.