Apparatus for deicing of trolley wires

In a power transmission system comprising at least two trolley wires for supplying an alternating current power to an electric vehicle, and at least two feeder lines coupled to the trolley wires at feeding points of the corresponding trolley wires spaced apart a given interval for feeding a voltage to the trolley wires, with a closed loop formed between a portion of the trolley wires and a portion of the feeder lines through two adjacent feeding points, a throughtype current transformer is provided for each feeder line such that the feeder line extends through the transformer and the primary winding of the transformer is connected to receive an alternating current voltage between the above described at least two trolley wires, whereby a secondary alternating current induced in the feeder lines serving as a secondary conductor of the transformer flows through the above described closed loop, which causes a Joule heat along the trolley wires, thereby to deicing of the trolley wires. Preferably, an alternating voltage between the above described at least two trolley wires is selectively applied to the primary winding of the transformer, such that a supply of the alternating current voltage to the primary winding is controlled manually or automatically responsive to meteorological conditions. Such an automatic control of a supply to the primary winding of the transformer may be selectively effected, in association with the temperature of the trolley wires being lower than a preset temperature, a predetermined meteorological condition being met by an ambient temperature, water, snow and the like, a current normally flowing through the trolley wires being less than a predetermined value, and the like, singly or in combination.

BACKGROUND OF THE INVENTION 
1. Field of the Invention; 
The present invention relates to an apparatus for deicing of trolley wires. 
More specifically, the present invention relates to an apparatus for 
deicing trolley wires in a power transmission system comprising at least 
two trolley wires for supplying an alternating current power to an 
electric vehicle. 
2. Description of the Prior Art; 
Water, snow etc, if any, on trolley wires installed in a power transmission 
system for supplying an alternating current power to an electric vehicle 
is frozen to form a ice layer on the trolley wires when the ambient 
temperature or the temperature of trolley wire becomes lower than the 
freezing point. The ice layer prevents an electrical contact with a 
pantograph of an electric vehicle. As a result, a supply of an electric 
power from the trolley wires to an electric vehicle is disturbed and a 
pantograph is broken. For this reason, the operation of electric vehicles 
is often obstructed. 
A prior art system for deicing of trolley wires which is of interest to the 
present invention is disclosed in Japanese Published unexamined utility 
model application No. 131601/1974, laid open Nov. 12, 1974 for public 
inspection. FIG. 1 shows a schematic diagram of the prior art system for 
deicing of trolley wires as disclosed in the above referenced Japanese 
Utility Model Laying Open Gazette. Referring to FIG. 1, a trolley wire 11 
for supplying an electric power to an electric car is suspended from a 
stringing wire 13 by means of a plurality of electrically insulating 
hangers 12 and electrically conductive hanger 12'. The plurality of 
hangers 12 are provided to hang the trolley wire 11 from the stringing 
wire 13, with the trolley wire 11 electrically insulated from the 
stringing wire 13, while the hangers 12' are set in the vicinity of the 
feeding points 14 and 14' so as to electrically connect the corresponding 
points at the trolley wire 11 to the feeding points 14 and 14'. The 
feeding points 14 and 14' are connected to a feeder wire cable 15 at 
predetermined intervals of distance for the purpose of feeding a voltage 
to the trolley wire 11, thereby to compensate for a voltage drop along the 
trolley wire 11. As a result, a closed loop is formed by means of a 
portion of the feeder line 15 and the trolley wire 11, coupled to each 
other at the feeding points 14 and 14' through the hangers 12'. A rail 
installed beneath and along the trolley wire 11 forms a return circuit of 
a current flowing from the trolley wire 11 through a pantograph of an 
electric car and wheels thereof to the rail 16. A primary winding 171 of a 
transformer 17 is connected between the feeder line 15 and the rail 16. A 
secondary winding 172 of the transformer 17 is provided to transform the 
voltage applied to the primary winding 171 to a lower voltage and is 
connected to a full wave rectifier 18. The full wave rectifier 18 
comprises a bridge circuit of diodes, connected in a well known fashion, 
and the direct current output is applied to the above described closed 
loop formed by the feeder line 15 and the trolley wire 11. The direct 
current output terminals of the full wave rectifier 18 may be shunted with 
an alternating current bypassing diode 19. With such a circuit 
configuration, a direct current is caused to flow through the above 
described closed loop comprising the feeder line 15 and the trolley wire 
11 and the said direct current is superposed on the alternating current 
flowing through the trolley wire 11. As a result, the current flowing 
through the trolley wire 11 is increased and a Joule heat is produced 
along the trolley wire 11, thereby to deicing of the trolley wire 11. 
However, the above described prior art system requires the transformer 17 
and the full wave rectifier 18 for the purpose of applying a direct 
current to the trolley wire 11 to deicing of the trolley wire, with the 
result that the circuit configuration becomes complicated and expensive. 
In such a power transmission system where a single trolley wire and the 
rails are utilized for supplying an electric power to an electric vehicle, 
a very high voltage power of such as several thousand volt to several ten 
thousands volt should be transmitted and this necessitates transformation 
of the said very high voltage to an appropriate voltage suited for 
rectification into a direct current voltage to be supplied to the trolley 
wire for the purpose of deicing of the trolley wire, with the result that 
the transformer 17 should be extremely large sized and becomes expensive. 
In addition, in order to apply the output of the full rectifier to the 
feeder line and the trolley wire, some connections for such direct current 
circuit need be separately provided, which makes installation complicated 
and expensive. Furthermore, as the output direct current from the 
rectifier is divided into two parts at the connection point of feeder 
line, only one part of the divided current is effective to increase a 
Joule heat in the trolley wire 11. As a result, deicing of the trolley 
wires need much electric power, resulting in lower efficiency. 
Another example of interest to the present invention for an apparatus for 
deicing of trolley wires is seen in Japanese Published examined patent 
application No. 42805/1976, published Nov. 18, 1976 for opposition. More 
specifically, the referenced Patent Publication Gazette discloses that 
both a trolley wire for an up line and a trolley wire for a down line of a 
double track are connected at the terminations to form a closed loop and a 
separate power source for supplying a power for deicing is provided in a 
power source for supplying an electric power to both trolley wires, such 
that an alternating current is applied from the substation to the closed 
loop formed by the trolley wires of the up and down lines, whereby an 
additional electric power is applied to the trolley wires and a icing of 
the trolley wires is prevented or unfreezed. However, the above described 
deicing apparatus requires a double track including an up and down lines. 
For this reason, the apparatus disclosed in the referenced Japanese Patent 
Publication cannot be applied to a single track. In addition, the closed 
loop formed by the up and down lines becomes so large as to cover a 
distance between two adjacent substations coupled to the double track. As 
a result, a deicing operation should be effected in such a large closed 
loop and a localized deicing operation cannot be effected such that a 
freeze of the trolley wires is prevented only in a relatively short span 
of the trolley wires where prevention of a icing is required by virture of 
meteorological conditions in such a local area. For this reason, the 
system disclosed in the latter referenced Patent Publication involves a 
problem of an increased power loss. 
SUMMARY OF THE INVENTION 
Briefly described, in a power transmission system comprising at least two 
trolley wires for supplying an alternating current power to an electric 
vehicle and at least two feeder lines coupled to the trolley wires at 
feeding points of the corresponding trolley wires spaced apart a given 
interval for feeding a voltage to the trolley wires, with a closed loop 
formed between a portion of the trolley wires and a portion of the feeder 
lines through two adjacent feeding points, a through-type current 
transformer is provided for each feeder line such that the feeder line 
extends through the transformer and the primary winding of the transformer 
is connected to receive an alternating current voltage between the above 
described at least two trolley wires, whereby a secondary alternating 
current induced in the feeder lines flows through the above described 
closed loop, which causes a Joule heat along the trolley wires, thereby to 
deice of the trolley wires. 
Preferably an alternating voltage between the above described at least two 
trolley wires is selectively applied to the primary winding of the 
through-type current transformer, such that a supply of the alternating 
current voltage to the primary winding of the through-type current 
transformer is controlled manually or automatically responsive to ambient 
meteorological conditions. Such an automatic control of a supply of the 
alternating current voltage to the primary winding of the through-type 
transformer is selectively effected, in association with various 
conditions, singly or in combination, such as the temperature of the 
trolley wires being lower than a predetermined temperature, a 
predetermined meteorological condition being met by an ambient 
temperature, water, snow and the like, a current normally flowing through 
the trolley wires being less than a predetermined value, and the like. 
Therefore, a principal object of the present invention is to provide an 
apparatus for preventing a icing of trolley wires, which is simple in 
structure, easy of maintenance and inexpensive in cost, and of higher 
efficiency. 
Another object of the present invention is to provide an apparatus for 
deicing of trolley wires, wherein a icing can be prevented selectively in 
a relatively short span of trolley wires, where deicing of the trolley 
wires is most required in the light of the meteorological conditions in 
such a local area. 
A further object of the present invention is to provide an apparatus for 
deicing of trolley wires, wherein a power consumption required for deicing 
of the trolley wires is reduced and thus a icing of the trolley wires can 
be prevented with a less power loss and with a higher efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 is a block diagram showing the principle of the present invention. 
As described previously, the present invention is characterized by 
employment of a through-type current transformer. Therefore, it would be 
appropriate to describe the through-type current transformer, before the 
explanation of the principle of the present invention with FIG. 2. 
FIG. 3 is a perspective view of a through-type current transformer to be 
employed in the present invention. Referring to FIG. 3, the through-type 
current transformer 30 comprises a primary winding 31 wound around the 
portions of an O letter shaped core 32 having a through aperture 33. 
According to the present invention, the through-type current transformer 
30 is utilized such a manner that a feeder line 15 extends through the 
through aperture 33 of the core 32 of the transformer. Therefore, when an 
alternating current voltage is applied to the primary winding 31, an 
alternating current flux is induced in the core 32 and accordingly an 
alternating current is induced by the alternating current flux to flow 
through the feeder line 15. 
With simultaneous reference to FIGS. 2 and 3, the principle of the present 
invention will be described in the following. With particular reference to 
FIG. 2, the embodiment is shown comprising three trolley wires 11R, 11S 
and 11T which are installed along a path for travel of electric vehicles, 
such as electric cars, to supply a three-phase alternating current power 
to the electric vehicles. The three trolly wires 11R, 11S and 11T are 
electrically connected to three feeder lines 15R, 15S and 15T installed 
along the above described three trolley wires 11R, 11S and 11T, 
respectively, at predetermined intervals of distance l for the purpose of 
supplying a three-phase alternating current power from the feeder lines 
15R, 15S and 15T to the corresponding trolley wires 11R, 11S and 11T at 
the above described intervals l. The three feeder lines 15R, 15S and 15T 
are connected at the ends thereof through three supply lines 150R, 150S 
and 150T, respectively, to a substation 20. Thus, it would be appreciated 
that for each span of the above described intervals l a closed loop is 
formed for each phase by the corresponding portion of the respective 
trolley wire and the corresponding portion of the respective feeder line 
as coupled to each other at the adjacent two feeding points. Thus, for 
each span of the above described intervals l, three closed loops are 
formed, the closed loop for the phase R including the corresponding 
portions of the trolley wire 11R and the feeder line 15R, the closed loop 
for the phase S including the corresponding portions of the trolley wire 
11S and the feeder line 15S, and the closed loop for the phase T including 
the corresponding portions of the trolley wire 11T and the feeder line 
15T. 
At each span of the above described intervals l, through-type current 
transformers 30R, 30S and 30T structured as shown in FIG. 3 are set such a 
manner that the feeder lines 15R, 15S and 15T extend through the through 
apertures 33 of the transformers 30R, 30S and 30T, respectively. It is 
pointed out that in FIG. 2 the through-type current transformers are 
identified by the reference numeral 30 as affixed with postscripts R, S 
and T to represent the corresponding phases R, S and T, although in FIG. 3 
such postscripts were not employed. As best seen in FIG. 2, the primary 
windings 31 of the through-type current transformers 30R, 30S and 30T are 
connected to two supply lines among three supply lines 150R, 150S and 150T 
or alternatively connected to two trolley wires among the three trolley 
wires 11R, 11S and 11T. So as to receive a single phase alternating 
current power. Preferably, a switch means 21 is set for each span to 
selectively supply the above described three sets of single phase 
alternating current powers to the primary windings of the through-type 
current transformers 30R, 30S and 30T from the supply lines 150R, 150S and 
150T or from the trolley wires 11R, 11S and 11T. The switch means 21 may 
be a manual switch selectively operable by an operator. Alternatively, the 
switch means 21 may be an automatic circuit breaker automatically operable 
according to a predetermined condition such as a meteorological condition, 
such as an ambient temperature, water, snow and the like, and/or a 
physical condition of the trolley wires, such as the temperature, the 
current and the like of the trolley wires. 
In operation, when an ambient meteorological condition becomes worse, i.e. 
an ambient temperature becomes lower than the ice point when the water 
and/or snow exist, so that trolley wires 11R, 11S and 11T are placed in a 
condition where a freeze is likely to occur, the switch means 21 is closed 
manually or automatically according to detection of such meteorological 
condition, whereby an alternating current voltage is applied to each of 
the primary windings of the through-type current transformers 30R, 30S and 
30T. Accordingly, an alternating current flux is induced in each of the 
cores 32 of the through-type current transformers 30R, 30S and 30T and 
thus an alternating current is induced in each of the feeder lines 15R, 
15S and 15T extending through the through apertures 33 of the 
transformers. The alternating current thus induced in each of the feeder 
lines 15R, 15S and 15T by virtue of the alternating current flux of the 
respective through-type current transformers 30R, 30S, and 30T is caused 
to flow through the corresponding closed loop. As a result, in each of the 
trolley wires 11R, 11S and 11T, there flows a sum of a load current to be 
caused to flow through each of the feeder lines 15R, 15S and 15T in order 
to operate the electric vehicles and the above described induced current 
caused to flow through each of the above described closed loop. 
Because of superposition of the above induced current and load current 
usually flowing through the trolley wires during the operation of the 
electric vehicles, a Joule heat is generated in each of the trolley wires 
11R, 11S and 11T which serves to deice the trolley wires. When no electric 
vehicles is operated, then no load current flows through the trolley wires 
and accordingly only the above described induced current is caused to flow 
through each of the trolley wires. 
It should be pointed out that the direction of flow of the load current in 
each of the trolley wires 11R, 11S and 11T by virtue of the operation of 
the electric vehicles and the direction of flow of the above described 
induced current in each of the trolley wires 11R, 11S and 11T induced by 
means of the corresponding through-type current transformers 30R, 30S and 
30T are selected to be the same and thus the direction of flow of the 
above described induced current in each of the feeder lines 15R, 15S and 
15T is opposite to the direction of flow of the current normally flowing 
therethrough, with the result that a much more Joule heat is produced in 
each of the trolley wires as compared with that in each of the feeder 
lines. 
In a preferred embodiment of the present invention, the switch means 21 is 
adapted to be on/off controlled automatically according to an ambient 
meteorological condition, the condition of the trolley wires per se, and 
the like. Such embodiment will be described in the following. 
FIG. 4 is a block diagram of a preferred embodiment of the present 
invention and FIG. 5 is a block diagram of a decision circuit 50 employed 
in the FIG. 4, wherein decision is made automatically as to whether a 
icing of the trolley wires should be prevented in response to an ambient 
meteorological condition, such as an ambient temperature, water, snow and 
the like, and a trolley wire condition, such as a trolley wire 
temperature, trolley wire current and the like. 
The above described trolley wires 11R, 11S and 11T for supplying a 
three-phase alternating current power are connected to one side terminals 
of an electromagnetic switch serving as the above described switch means 
21 through a molded case circuit breaker 411. The other side terminals of 
the electromagnetic switch 21 are connected to the primary windings of the 
through-type current transformers 30R, 30S and 30T, such that a single 
phase power is taken from two of the three other side terminals in 
different combinations. A current transformer 431 is coupled to any one 
line, such as 15S in the embodiment shown, among the feeder lines 15R, 15S 
and 15T, for detecting an overcurrent flowing in the feeder lines. Among 
the power supply lines 150R, 150S and 150T, another current transformer 
432 is coupled to the same phase 150S as that of the feeder line 15S 
wherein the current transformer 431 is coupled, for detecting an 
overcurrent flowing through the supply lines. The current transformer 432 
may also be utilized to detect a current to be supplied from the 
substation 20 to the transmission system being less than a predetermined 
value such as in case where the number of operations of the electric 
vehicles is reduced in a night time, for example, which is taken into 
consideration in determining whether a freeze of the trolley wires should 
be prevented. 
A voltage between the trolley wires 11R and 11S obtainable through the 
molded case circuit breaker 411 is applied through another molded case 
circuit breaker 412 to a primary winding of a transformer 42. The 
secondary winding of the transformer 42 is connected to a control unit 40 
for the purpose of energization thereof. The control unit 40 comprises a 
parallel connection coupled to the secondary winding of the transformer 42 
including a delay relay 1D for a delay operation responsive to initiation 
of energization, an overcurrent detecting circuit 44 responsive to the 
overcurrent detected output of the current transformer 431 and 432 for 
energizing a relay 1R, decision circuit 50 responsive to an ambient 
temperature detector 471, a water detector 472, a snow detector 473, a 
trolley wire temperature detector 48 and the current transformer 432 for 
determining a condition of necessity for deicing of the trolley wires, a 
relay 21R for closing the electromagnetic switch 21, a pilot lamp 491 for 
displaying a state of supply of the power, and a lamp 492 connected in 
series with a normally open auxiliary contact 21a of the electromagnetic 
switch 21 for indicating the closed state of the electromagnetic switch 
21. 
In a normal state of operation where the meteorological condition is 
better, when the molded case circuit breakers 411 and 412 are closed, the 
secondary voltage of the transformer 42 is applied to the control unit 40 
and thus the pilot lamp 491 is lit to indicate a supply state of the power 
and with a delay of a predetermined period of time after initiation of 
energization the contact 1Da of the delay relay 1D is closed, whereby a 
voltage is applied to the overcurrent detecting circuit 44, and the 
decision circuit 50 for energization thereof. Since various circuits such 
as 44 and 50 are supplied with an energization power after the contact 1Da 
of the delay relay 1D is closed, any information which is liable to occur 
until a steady state is reached after initiation of energization can be 
prevented. The overcurrent detecting circuit 44 is structured such that 
unless the current in the feeder line 15S as detected by the current 
detector 431 and 432 exceeds a predetermined current value a connection 
between the terminals a and c is opened so that the relay 1R may not be 
energized. Therefore, the normally closed contact of the relay 1Rb is 
remains closed. However, since the relay 2R is not energized in such a 
situation, the contact 2Ra of the relay 2R is opened. Accordingly, the 
relay 21R is not energized, whereby the electromagnetic switch 21 is kept 
opened and the through-type current transformers 30R, 30S and 30T are not 
supplied with a power. 
Now description will be made of how an iced trolley wires is deiced in 
response to detection of an ambient meteorological condition. As the above 
described temperature detector 471, a transistor coupled to be variable of 
the characteristic as a function of an ambient temperature, a thermocouple 
or the like may be used. The above described water detector 472 may be 
structured such that it's impedance is varied as a function of presence or 
absence of water and thus the output voltage thereof is decreased 
responsive to presence of the water. The above described snow detector 473 
may comprise a heater for heating a portion of snow for melting the same 
and a water detector similar to the water detector 472 for detecting the 
presence of the water produced as a result of melting of the snow for 
providing a decreased output voltage responsive to the snow. The trolley 
wire temperature detector 481 may comprise a thermocouple provided 
associated with one of the trolley wires, the output voltage of which is 
variable as a function of the temperature of the trolley wire. The current 
detector 432 may comprise a current transformer. 
The detected outputs of the temperature detector 471, the water detector 
472, the snow detector 473, the trolley wire temperature detector 481 and 
the current detector 432 are applied to the amplifiers 511, 512, 513, 514 
and a decision circuit 526, respectively, in the decision circuit 50. The 
output voltage of ambient temperature as amplified by the amplifier 511 is 
applied to decision circuits 521 and 522. The decision circuit 522 is 
structured to level detect the above voltage of ambient temperature at a 
predetermined level, say a level corresponding to the ambient temperature 
of +2.degree. C., so that the high level output signal is obtained when 
the ambient temperature is lower than the above described temperature of 
+2.degree. C. The output of the decision circuit 522 is applied to an AND 
gate 541. A decision circuit 523 is connected to the amplifier 512 to 
receive the output of the amplifier 512 and is structured to determine 
whether the output voltage of the water detector 472 has become lower than 
a predetermined voltage due to the presence of the water, thereby to 
provide the high level output to an OR gate 531. A decision circuit 524 is 
connected to the amplifier 513 to receive the output of the amplifier 513 
and is structured to determine whether the output voltage of the snow 
detector 473 has become lower than a predetermined voltage due to the 
presence of snow, thereby to provide the high level output to the OR gate 
531. A decision circuit 525 is connected to the amplifier 514 to receive 
the output of the amplifier 514 and is structured to level detect the 
voltage of trolley wire temperature at a predetermined level, say the 
temperature of +2.degree. C., so that the high level output is applied to 
the OR gate 532, when the trolley wire temperature is lower than the 
temperature of +2.degree. C. On the other hand, the decision circuit 526 
is structured to level detect the trolley wire current at a predetermined 
level, say the current value of 50A, so that the high level output siganl 
is obtained when the trolley wire current is smaller than the current of 
50A and is applied to the other input of the OR gate 532. 
Accordingly, when the ambient temperature is lower than the predetermined 
temperature of say +2.degree. C. under the presence of water or snow and 
the trolley wire temperature is lower than the predetermined temperature 
of say +2.degree. C. or the trolley wire current is smaller than the 
predetermined value of say 50A, the AND gate 541 is enabled to provide the 
high level output signal as a command for additional heating of the 
trolley wires for deicing of the trolley wires. 
The decision circuit 521 is structured to level detect the above described 
voltage of ambient temperature at another given level corresponding to 
another different predetermined ambient temperature of say -1.degree. C. 
which is 3.degree. C. lower than the above described predetermined 
temperature of +2.degree. C., so that the high level output signal is 
obtained when the ambient temperature becomes lower than the above 
described another predetermined temperature of -1.degree. C. Accordingly, 
when the ambient temperature is lower than the above described another 
predetermined temperature of -1.degree. C. and the trolley wire 
temperature is lower than the above described predetermined temperature of 
+2.degree. C. or the trolley wire current is smaller than the above 
described predetermined current value of 50A, the AND gate 542 is enabled 
to provide the high level output as a command for additional heating of 
the trolley wires. 
The outputs of these AND gates 541 and 542 are applied through an OR gate 
55 to the relay 2R for energization thereof. Therefore, when the high 
level output is obtained from the OR gate 55, the terminals a and c of the 
decision circuit 50 is connected and the normally open contact 2Ra of the 
relay 2R is closed, whereby the relay 21R is energized. Therefore, the 
electromagnetic switch 21 is closed. Since the normally open contact 21 is 
closed, an alternating current voltage is applied to each of the primary 
windings 31 of the through-type current transformers 30R, 30S and 30T, 
whereby an alternating magnetic flux is induced in each of the magnetic 
cores 32 of the transformers and accordingly an induced current flows 
through each of the closed loops comprising the corresponding portions of 
the feeder lines 15R, 15S and 15T and the trolley wires 11R, 11S and 11T 
for the span now in discussion. A flow of the above described induced 
current in each of the trolley wires causes an additional Joule heat, 
thereby to prevent or deice the trolley wires. At the same time the 
normally open auxiliary contact 21a of the relay 21R is closed and the 
lamp 492 is lit to indicate that the trolley wires are being heated. 
In the foregoing description, the decision circuit 50 was described as 
structured to make coordinated decision responsive to detection of the 
meteorological condition such as an ambient temperature, water, snow and 
the like and the detection of a trolley wire condition such as the trolley 
wire temperature, the trolley wire current, and the like to determine 
whether a command for additional heating by the induced current should be 
provided. Besides the above decision circuit 50, such a decision circuit 
may also be used, wherein among the above described conditions, inasmuch 
as a condition such as meteorological condition, trolley wire condition 
etc, may be utilized to make separate decision to determine whether a 
command for additional heating should be provided responsive individually 
to each detection. In addition to the detectors 471, 472, 473 or in place 
of the detector 472 in the decision circuit 50, another detector such as a 
humidity detector, fog detector and the like may also be used. Either of 
the trolley wire temperature detector 481 and the current detector 432 may 
be omitted, because there is a certain relationship between the trolley 
wire temperature and the current of the feeder lines in some conditions. 
Now description will be made of the operation in case where an overcurrent 
flows through the trolley wires. When at least any one of the detectors 
471, 472, 473, and 481 is in disorder and thus the temperatures are not 
detected correctly, in spite of the fact that a command for additional 
heating has been obtained and the induced current has been caused to flow 
through the trolley wires as well as the feeder lines of the closed loops 
by means of the throughtype current transformers, the total of the 
currents in the current transformers 431 and 432 increases to exceed a 
predetermined current value of say 600 A. The overcurrent detector 44 is 
structured such that the terminals a and c is closed to energize the relay 
coil 1R when the total of the currents in the current transformers 431 and 
432 exceeds the above described predetermined value of say 600 A. 
Accordingly, in such a situation, the normally open contact 1Ra of the 
relay 1R is closed and the relay 1R is energized to be selfretained, while 
the normally closed contact 1Rb is opened. Therefore, the relay 21R is 
deenergized and the electromagnetic switch 21 is opened. Therefore, the 
alternating current voltage applied to the primary windings of the 
through-type current transformers 30R,30S and 30T is interrupted and the 
induced current by the through-type current transformers is accordingly 
interrupted, with the result that additional heating of the trolley wires 
by means of the through-type current transformers is discontinued. 
As described in the foregoing, according to the embodiments of the present 
invention, additional heating of the trolley wires is achieved by an 
alternating current induced by the through-type current transformers 
rather than utilizing a transformer and a rectifying circuit for supplying 
an additional direct current power to the trolley wires. As a result, a 
large sized transformer and a rectifying circuit of a large capacity can 
be dispensed with. Thus, according to the present invention, an apparatus 
for deicing of the trolley wires is provided, which is simple in 
structure, easy of maintenance and is inexpensive in cost. According to 
another aspect of the present invention, the through-type current 
transformers are provided to induce an additional current only in the 
closed loops formed in a relatively shorter span of the trolley wires by a 
portion of the trolley wires and a portion of the feeder lines. As a 
result, only a portion of the trolley wires included in the closed loop 
can be selectively heated to deice the trolley wires which is likely to 
occur in a relatively narrow local area. As a result, deicing of the 
trolley wires can be achieved with less electric power and thus with 
higher efficiency. According to another aspect of the present invention, 
the condition for deicing of the trolley wires is determined by an 
coordinated or individual decision of an ambient meteorological condition, 
a trolley wire condition and the like and an automatic control is effected 
responsive to such decision. According to further aspect of the present 
invention, the present invention can also be employed even in a single 
track system as well as a double track system including an up and down 
lines. 
Although in the foregoing description, the embodiments were described as 
employing a power transmission system comprising three trolley wires 
combined with three feeder lines for supplying a three-phase electric 
power to electric vehicles, it is pointed out that the present invention 
can be equally applied to a power transmission system comprising only two 
trolley wires combined with two feeder lines for supplying a single phase 
alternating current power to electric vehicles. Thus, it is intended that 
the present invention also covers such changes and modifications. 
Originally, the feeder lines 15R, 15S and 15T are provided to feed at 
intervals l to the trolley wires 11R, 11S and 11T an alternating current 
electric power of the respective phases to eliminate a voltage drop along 
the trolley wires 11R, 11S and 11T because of the load current flowing 
therethrough. Therefore, the present invention can be advantageously 
employed in such a power transmission system comprising a plurality of 
trolley wires for supplying an alternating current power to electric 
vehicles and the corresponding plurality of feeder lines already installed 
to be coupled to the trolley wires at feeding points of the corresponding 
trolley wires spaced apart a given interval for the purpose of only 
feeding a voltage to the trolley wires, by additionally providing a 
through-type current transformer for each feeder line such that the feeder 
line extends through the transformer and connecting the primary winding of 
the transformer to receive an alternating current voltage between two 
trolley wires or feeder lines. Thus, according to the present invention, 
skillful use is made of the feeder lines already installed to be coupled 
to the trolley wires for the purpose of feeding a voltage to the trolley 
wires. On the other hand, the present invention can also be advantageously 
employed in a power transmission system comprising only trolley wires for 
supplying an alternating current power to electric vehicles, by 
additionally providing feeder lines to be coupled to the trolley wires at 
feeding points of the corresponding trolley wires spaced apart a given 
interval for the purpose of feeding a voltage to the trolley wires and 
also for the purpose of forming a closed loop between a portion of the 
trolley wires and a portion of the feeder lines through two adjacent 
feeding points, and by further providing a through-type current 
transformer for each feeder line such that the feeder line extends through 
the transformer and the primary winding of the transformer is connected to 
receive an alternating current voltage between at least two trolley wires 
or two feeder lines. In the latter situation, the distance l is selected 
to be most suited for dividing the trolley wires into a plurality of 
closed loop areas which should be individually selected in consideration 
of the meteorological condition peculiar to that area. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and the scope of the present invention being limited only by the terms of 
the appended claims.