Feeder voltage compensating apparatus for electric railway

This invention serves to reduce the drop of feeder voltage in an electric railway, and relates to a feeder voltage compensating apparatus for electric railways wherein an accumulator and a thyristor rectifier are connected by a thyristor switch circuit which can change-over the charging and discharging directions of the accumulator.

BACKGROUND OF THE INVENTION 
This invention relates to a D.C. power supply apparatus which prevents a 
feeder voltage drop in an electric railway power line adopting a D.C. 
feeding system. 
In the electric railway power line which adopts a D.C. feeding system, 
rectifier substations have heretofore been installed at intervals of 
several kilometers to about 10 kilometers. In a high capacity substation, 
electric power is received at an extra-high voltage of at least 20 kV and 
is converted into a predetermined D.C. voltage, which is fed to an 
overhead line. 
However, in the case where an extra-high voltage feeder does not exist near 
a site for installing the substation, feeding facilities for the 
extra-high voltage must be disposed over a long distance to the position 
of the substation, and the installation cost of the rectifier substation 
including the expenses of the feeding facilities becomes very high. On the 
other hand, when as a countermeasure, the rectifier substations are 
installed in places accessible to receiving electric power of the 
extra-high voltage, the intervals of the rectifier substations become very 
long in some cases. This leads to the problem that the D.C. overhead line 
voltage at an intermediate point between two adjacent substations or at an 
end point (remotest point from the last substation) lowers abnormally 
during the running of an electric vehicle or train. 
SUMMARY OF THE INVENTION 
This invention has been made in order to solve the above mentioned 
problems, and provides a D.C. power supply apparatus which can effectively 
relieve a voltage drop at the intermediate points between substations 
without disposing extra-high voltage feeding facilities over a long 
distance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described with reference to 
the drawings. 
Referring to FIG. 1, a main substation 1 is constructed of a rectifier 11 
and a transformer 12, and has a power receiving line 13 for receiving 
electric power at an extra-high voltage of e.g., 60 kV. Further 
illustrated are a feeder and trolley line 2, a rail 3, an electric vehicle 
or train 4, a feeder voltage compensating apparatus 5 according to the 
present invention. The compensating apparatus comprises an accumulator 6, 
a thyristor switch circuit 7 which includes thyristor switches 71-74 and 
terminals 75-78 and a rectifier 8 which is constructed of a smoothing 
reactor 80, thyristors 81-86, a transformer 87, an A.C. circuit breaker 
88, a power receiving line 89 which receives electric power at a high 
voltage of, e.g., 6 kV, a mechanical or thyristor type high-speed circuit 
breaker 91, and disconnecting switches 92, 93. The operation of the above 
embodiment will be described hereinbelow. 
First, for the case where thyristor switches 72 and 73 are in the "on" 
state, current is permitted to flow in the direction of discharging the 
accumulator 6 along a path consisting of the rail 3.fwdarw.disconnecting 
switch 93.fwdarw.thyristor switch 73.fwdarw.rectifier 8.fwdarw.thyristor 
switch 72.fwdarw.accumulator 6.fwdarw.high-speed circuit breaker 
91.fwdarw.disconnecting switch 92.fwdarw.feeder line 2. Utilizing the 
voltage control of the rectifier 8, the output of the feeder voltage 
compensating apparatus 5 can be subjected to a control for providing a 
constant voltage having a current limiting function, etc. 
On the other hand, when thyristor switches 71 and 74 are turned "on", 
current is permitted to flow in the direction of charging the battery 6 
along a path consisting of the feeder and trolley line 
2.fwdarw.disconnecting switch 92.fwdarw.high-speed circuit breaker 
91.fwdarw.accumulator 6.fwdarw.thyristor switch 71.fwdarw.rectifier 
8.fwdarw.thyristor switch 74.fwdarw.disconnecting switch 93.fwdarw.rail 3. 
Utilizing the voltage control of the rectifier 8, it is possible to 
control the charging current to be a desired constant current value or to 
establish a voltage limiting function so as to control the terminal 
voltage of the accumulator 6 as well as preventing the overcharge of this 
accumulator. 
A specific example for the present invention for the above described 
arrangement will be explained below. 
It is assumed that the rated voltage of the feeder line 2 is 1,500 v, that 
the capacity of the main substation 1 is 1,500 kW, and that the voltage - 
current characteristic of the main substation is as follows: 
##EQU1## 
where E.sub.ss : main-substation voltage, 
I.sub.ss : main-substation current, 
E.sub.do : main-substation no-load voltage, 
R.sub.ss : main-substation equivalent resistance. 
It is also assumed that the distance between the main substation 1 and the 
feeder voltage compensating apparatus 5 according to the present invention 
is 15 km, that the electric vehicle line resistance (the overall 
resistance of the feeder line, trolley line, rail, etc.) is 0.04 
.OMEGA./km, and that the peak value I.sub.p of the vehicle current is 
1,000 A. Further, the characteristic of the feeder voltage compensating 
apparatus 5 according to the present invention will be studied on an 
operation in which the output voltage E.sub.B of the apparatus is constant 
at 1,150 V for an output current I.sub.B below 300 A, while the output 
voltage E.sub.B is not limited to 1,150 V when and after the output 
current I.sub.B has reached 300 A, that is, for the case where constant 
voltage control having a current limiting function is performed. 
This characteristic is illustrated in the right upper part of FIG. 2 
depicted for explaining the effects of the present invention. Since the 
rectifier 8 is constructed of a thyristor bridge, it is capable of, not 
only a converter operation for providing a voltage in the positive 
direction, but also an inverter operation for providing a voltage in the 
negative direction. Therefore, it can control voltages in a wide range. 
Supposing now that the position of the vehicle 4 is represented by a 
distance x km from the main substation 1 and that a starting current of 
1,000 A is flowing at the point, the pantograph point voltage E.sub.p of 
the vehicle 4 becomes the value indicated by the dot-and-dash line in the 
graph of FIG. 2, in the absence of the feeder voltage compensating 
apparatus 5. That is, the voltage at the farthest point from the main 
substation 1 (a point of x=15 km) drops down to 900 V. 
When the feeder voltage compensating apparatus according to the present 
invention is therefore disposed at the point of x=15 km, the pantograph 
point voltage E.sub.p of the vehicle 4 becomes a value indicated by the 
solid line in the graph of FIG. 2, and good vehicular pantograph point 
voltages are obtained throughout the 15 km distance. In addition, the 
feeder voltage compensating apparatus 5 may have an output capacity of 
1,150 V.sub.D.C. x 300 A=345 kW, and it can receive electric power at a 
voltage as high as, e.g., 6 kV as stated before. It is accordingly 
understood that the compensating apparatus is economical and is highly 
effective. Conversely, for the case of charging the accumulator, the 
charging current is usually lower than about 1/10 of the discharging 
current and therefore affects the electric vehicles' line very little. 
In FIG. 2 the region A is in a range where the pantograph point voltage can 
be held above 1,150 V when supplying electric power from the main 
substation 1 and no output current I.sub.B from the feeder voltage 
compensating apparatus 5 is required. Further, in region B the pantograph 
point voltage is held at approximately 1,150 V by supplying power from the 
main substation 1 and the feeder voltage compensating apparatus 5, wherein 
the output voltage E.sub.B of the feeder voltage compensating apparatus 5 
is 1,150 V, while the output current I.sub.B is not greater than 300 A. 
Further, a region C is a range in which the output current I.sub.B of the 
feeder voltage compensating apparatus 5 is limited so as not to exceed 300 
A. 
The case of supplying power from one main substation 1 has been described 
above. However, it is understood that the present invention is also 
applicable to cases of a section between two main substations, etc. 
Hereafter, the change-over control of the thyristor switch circuit 7 will 
be considered. 
In the case where the thyristor switches 71 and 74 are "on" (charging 
state) and the case where thyristor switches 72 and 73 are turned "on" 
(discharging state), the following method may be relied on. The gates of 
the thyristor switches 71 and 74 are first turned "off", and the 
mechanical or thyristor type high-speed circuit breaker 91 is subsequently 
opened, to cause the charging current to be 0. Thus, the thyristor 
switches 71 and 74 are turned "off". Thereafter, the high-speed circuit 
breaker 91 is closed, and the gates of the thyristor switches 72 and 73 
are turned "on" so as to turn "on" these thyristor switches. The 
change-over from the discharging state to the charging state can be 
executed by a similar method. Regarding the change-over methods, since the 
switching frequency of the high-speed circuit breaker 91 is high, the 
thyristor type contactless circuit breaker is useful, whereas there is a 
mechanical limitation in lifetime in case of mechanical type circuit 
breaker. 
The present invention therefore provides also means for changing-over the 
charging and discharging directions of the thyristor switch circuit 7 
without the opening and closure of the high-speed circuit breaker 91. 
FIG. 3 is a simplified circuit connection diagram showing a method for 
turning "off" the thyristor switches 71 and 74 under the charging state. 
The path of current flow is indicated in a solid line and indicates a 
charging current. 
As is apparent from FIG. 3, the thyristor bridge constructed of the 
thyristors 81-86 performs the inverter operation, and the charging current 
therefrom can be reduced to zero, by controlling the thyristor switches 71 
and 74 which can be readily turned "off" by turning their gates "off". 
That is, the desired specification constants of the circuit arrangement may 
be set and the phase control of the rectifier 8 may be determined so as to 
hold the following relationship among the no-load voltage E.sub.do of the 
main substation 1, the voltage E.sub.BD of the battery at the time at 
which this battery is going to discharge, and the maximum value E.sub.DR 
of the inverter operation voltage of the rectifier 8 so that: 
EQU E.sub.DR &gt;E.sub.do -E.sub.BD Equation (2) 
The same applies to a method for turning "off" the thyristor switches 72 
and 73 under the discharging state. As seen from FIG. 4 showing a 
simplified circuit connection diagram, the following relationship may be 
held among the pantograph point voltage E.sub.p of the vehicle, the 
battery voltage E.sub.BC at the time at which the battery is going to 
charge, and the maximum value E.sub.DR of the inverter operation voltage 
of the rectifier 8 so that: 
EQU E.sub.DR &gt;E.sub.BC -E.sub.p Equation (3) 
The current indicated by the solid line in FIG. 4 is a discharging current. 
According to these methods, the high-speed circuit breaker 91 is normally 
in the closed state and can be used for an interrupting operation in case 
of an accident, and the thyristor switches 71-74 can be turned "off" by 
bringing the rectifier 8 into the inverter operation through a phase 
control, so that the change-over from the charging and discharging states 
can be smoothly effected. 
Further, the present invention provides different means for changing-over 
the charging and discharging states. 
FIGS. 5 to 7 show other embodiments of this invention. In FIG. 5, a 
thyristor switch with a forced commutation circuit which has a current 
interrupting capability is used as the thyristor switch 71, and the same 
symbols as in FIG. 1 indicate the same or corresponding parts. With the 
circuit of FIG. 5, the condition of Equation (2) need not always be met 
for turning "off" the thyristor switches 71 and 74 under the charging 
state, and the voltage of the inverter operation of the rectifier 8 need 
not be great, so that the installation capacity of the rectifier 8 can be 
reduced. This is useful particularly in a case where the output voltage of 
the rectifier 8 is predominantly determined by Equation (2). 
Likewise, in the case where the output voltage of the rectifier 8 is 
predominantly determined by Equation (3), it is useful to make the 
thyristor switch 73 the thyristor switch with the forced commutation 
circuit which has current interrupting capability, as illustrated in FIG. 
6. In addition, when both Equations (2) and (3) are predominant to the 
same extent, it is useful to make both the thyristor switches 71 and 73 
the thyristor switches with the forced commutation circuits which have 
current interrupting capability, as illustrated in FIG. 7. 
As set forth above, a feeder voltage compensating apparatus according to 
the present invention compensates for a drop in feeder voltage. 
Furthermore, the apparatus may be small in output capacity and can be 
driven by receiving electric power at a high voltage of, e.g., 6 kV 
without requiring the reception of electric power at an extra-high voltage 
as required in a main substation. Consequently, the apparatus is subject 
to few restrictions in installation and is useful. In addition, the 
apparatus is made more effective because methods permitting smooth 
change-over between charging and discharging states are provided.