DC Interrupting apparatus

A DC interrupter unit as provided between a DC power source unit and a load unit. The DC interrupter unit includes a DC interrupter section having at least one interrupter to interrupt a DC current and a saturable reactor connected between the interrupter section and one terminal of the load unit. The interrupter unit further includes a series circuit having a resistor and capacitor in series, the series circuit being connected between the junction of the interrupter section and the saturable reactor and the other terminal of the load unit.

BACKGROUND OF THE INVENTION 
The present invention relates to a DC interrupting apparatus having a DC 
power source unit, a DC interrupter unit, and a load unit and, more 
particularly, a DC interrupting apparatus for preventing surge voltage 
from being propagated from a DC power source unit to a load unit and vice 
versa. 
For a better understanding of the present invention, some problems involved 
in the conventional DC interrupting apparatus will be described with 
reference to FIGS. 1 and 2. FIG. 1 shows a conceptional view of a 
conventional interrupting apparatus for transmitting electric energy from 
a DC power source unit 1 to a load unit 3, through a DC interrupter unit 
2. A DC current I fed from a DC power source unit 1 including an AC power 
source 4 and a rectifier 5 is supplied to the load unit 3, through an 
interrupter 6, for example, a vacuum interrupter. The load unit 3 is 
comprised of a resistor 7, an inductance coil 8 with a low resistance 
connected across the resistor 7, an inductance coil 9 magnetically coupled 
with the inductance coil 8, and a resistor 10 connected in series with the 
inductance coil 9 and consuming energy. When a DC current I is rapidly 
interrupted by the interrupter 6, a current flowing through the inductance 
coil 8 flows into the resistor 7. The current flowing through the resistor 
7 attenuates in accordance with a time constant determined by an 
inductance of the inductance coil 8 and the resistor 7. The energy 
produced by a change of the current is propagated to the inductance coil 9 
so that energy is supplied to the load 10. For the energy supply, a large 
current at a high voltage must be interrupted by the interrupter 6. To 
this end, usually, a plurality of interrupters are connected in series in 
the interrupter unit 2. Alternately, a plurality of groups each including 
a plurality of interrupters connected in series are connected in parallel. 
Because of the interruption of a large current, a steep surge voltage is 
frequently produced in the DC power source unit 1 and the load unit 3. 
Such a surge voltage is preferably absorbed in a unit at which the surge 
voltage is produced so as not to be transmitted to other units. 
FIG. 2 shows a circuit diagram of a interrupter unit inserted between 
points A and B shown in FIG. 1. Inserted between the points A and B, a 
saturable reactor 11, a first interrupter 12a, a second interrupter 12b in 
series fashion. A series circuit including a capacitor 13a and a resistor 
14a is connected across the interrupter 12a. Another series circuit having 
a capacitor 13b and a resistor 14b is connected across the interrupter 
12b. Those series circuits are provided to absorb transient voltages 
applied across the interrupters 12a and 12b. Between the points A and B, a 
series circuit including a capacitor 15 and a normally opened switch 16 is 
connected and the capacitor 15 is previously charged by a charging device 
17 to have polarities as shown. 
In the interrupter unit shown in FIG. 2, when the DC current I is 
interrupted, the interrupters 12a and 12b are simultaneously opened to 
produce arcs across the respective interrupters. After a predetermined 
time lapse since these interrupters are begun to open, the switch 16 is 
closed and the capacitor 15 is discharged through the interrupters 12a and 
12b and the saturable reactor 11. The discharging current is denoted as Ir 
(commutation current). When Ir&gt;I, a zero point occurs in a current flowing 
through the interrupters 12a and 12b. At the time that the zero point 
occurs, the current I is interrupted. In order that the interrupters 12a 
and 12b may easily interrupt the current I, it is desirable that the 
inclination (a changing rate of current) of a current flowing through the 
interrupters immediately before the current flowing through the 
interrupters becomes zero is small, and that a rate of increase of the 
voltage (recovery voltage) applied between the electrodes of each 
interrupters after the current is interrupted, is small. The saturable 
reactor 11 serves to make the inclination of the current small. That is, 
after the current is interrupted, the current flows through the saturable 
reactor is extremely small so that the reactor serves as a large 
inductance. 
In FIG. 2, after a current flowing through the interrupters 12a and 12b is 
interrupted, an oscillating voltage is applied across terminals of 
respective interrupters for a relatively long time. As a result, after the 
DC current is interrupted and the time of several hundreds milliseconds is 
lapsed, the interrupter 12a, for example, is refired, while the 
interrupter 12b is not refired. At this time, the entire of the 
oscillating voltage is applied as an excessive voltage across the 
interrupter 12b. As a result, there possibly occurs a situation where the 
interruption is impossible in worst case. 
During the period from the instance that an excessive voltage is applied 
across an interrupter until the interrupter is refired, much time is 
required. The time taken for the interrupter to be refired depends on the 
extinguish medium or the amplitude of the excessive voltage. This time may 
be several tens milliseconds or more in a vacuum interrupter. Within this 
several tens milliseconds, the insulation of the interrupter 12a first 
refired is recovered. With respect to the excessive voltage applied across 
the interrupter 12b, however, since charges stored in the capacitor 13b 
are not rapidly discharged, the excessive voltage applied to the 
interrupter 12b when the interrupter 12a is refired is continuously 
applied across the interrupter 12b. On the other hand, no voltage is 
applied across the interrupter 12a even if the insulation is recovered. 
Accordingly, when the interrupter 12a is insulation-recovered following 
the refiring, it is desirable that a part of an excessive voltage having 
been applied across the interrupter 12b is shifted to the terminals across 
the interrupter 12a and that the voltage applied across the interrupters 
12a and 12b are equalized as rapidly as possible. A case where the 
interrupters 12a and 12b are connected in series has been described. When 
the number of the series-connected interrupters increases, the problems 
relating to the refiring, the insulation recovery and an excessive voltage 
being applied across an interrupter are more complicated. 
The interrupter unit shown in FIG. 2 has additional following problems. A 
steep surge voltage occurring in the power source unit is propagated to 
the load unit, through the capacitors 13a and 13b. A steep surge voltage 
occurring in the load unit is likewise propagated to the DC power source 
unit. As a result, the performance of a DC interrupting apparatus may 
possibly be deteriorated. 
In order to equalize the recovery voltage being applied across each of the 
interrupters 12a and 12b as rapidly as possible, it is conceivable that 
the resistors 18a and 18b are connected across the interrupters 12a and 
12b, respectively, as shown in FIG. 3. In FIG. 4A, there is shown a 
relation between a voltage value (a relative value) applied across each 
interrupter in FIG. 2 and the lapse of time. Further, FIG. 4B shows a 
relationship between a voltage value (a relative value) applied across 
each interrupter shown in FIG. 3 and the lapse of time. In the figures, an 
original "0" of time represents a time point immediately after the DC 
current is shut off. At the time point "0", the interrupters 12a and 12b 
are both supplied with recovery voltages. At the time T1, for example, if 
the interrupter 12a is refired and the interrupter 12b is not refired, a 
recovery voltage is applied fully across the interrupter 12b as shown by 
V12b and no part of the recovery voltage is applied across the interrupter 
12a as shown by V12a (FIGS. 4A and 4B). In FIG. 2, i.e. FIG. 4A, the 
capacitor 13b holds charges for a relatively long time. Accordingly, even 
if the insulation of the interrupter 12a is recovered, the voltage V12b 
across the interrupter 12b is held as it is, as shown in the figure. In 
FIG. 3, i.e. FIG. 4B, the interrupter 12a is refired at time T1 and, at 
time T2, is insulation-recovered, the charge in the capacitor 13b of the 
interrupter 12b is discharged so that the voltage across the interrupter 
12b becomes V1 at the time T3. With this, the voltage across the 
interrupter 12a becomes V1 at time T3. In this case, it is desirable that 
the time constant of the circuit including the capacitor 13a and resistors 
14a and 18a and that of the circuit including the capacitor 13b and the 
resistors 14b and 18b are small. When the capacities of the capacitors 13a 
and 13b are small, however, it is difficult to decrease the rising rate of 
a recovery voltage which is applied to respective interrupter after DC 
current interruption. Also, it is difficult to make the resistance of each 
resistor small in the light of the heat capacity of each resistor. 
Further, the FIG. 3 circuit can not prevent a surge voltage produced at 
the power source unit from being propagated to the load unit and the surge 
voltage produced at the load unit from being propagated to the power 
source unit. 
Accordingly, an object of the present invention is to provide a DC 
interrupting apparatus which can prevent a surge voltage produced at the 
DC power source unit from being propagated to the load unit and a surge 
voltage produced at the load unit from being propagated to the power 
source unit. 
Another object of the invention is to provide a DC interrupting apparatus 
which may shorten the time necessary to distribute a recovery voltage over 
series connected interrupters in an equal value. 
SUMMARY OF THE INVENTION 
According to the invention, there is provided a DC interrupting apparatus 
having a DC interrupter unit connected between a DC power source unit and 
a load unit, in which the DC interrupter unit comprises: a DC interrupter 
section including at least one DC interrupter to interrupt a DC current 
supplied from the DC power source unit to the load unit; and at least one 
saturable reactor connected between the DC interrupter section and one 
terminal of the load unit; and a series circuit having a resistor and 
capacitor in series and connected between the connection point of the 
interrupter section and the saturable reactor and the other terminal of 
the load unit. 
Other objects and features of the invention will be apparent from the 
following description taken in connection with the accompanying drawings, 
in which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the respective embodiments, like reference symbols in FIGS. 1 and 3 will 
be used to designate like or equivalent parts or portions, for simplicity 
of explanation. In FIG. 5, a DC interrupter unit 2 coupled between a DC 
power source unit 1 and a load unit 3 has the following construction. 
Inserted between the positive terminal of a rectifier 5 and one of the 
terminals of the load unit 3 are a normally closed switch 20, a first 
interrupter 12a, a second interrupter 12b, and a saturable reactor 11 in 
series in this order. As previously described referring to FIG. 2, one end 
of a series circuit including a normally opened switch 16 and a 
commutation capacitor 15 previously charged by the charging device 21 as 
shown in the polarity, is connected to the positive terminal of the power 
source unit. The other end of the series circuits is connected to the 
connection point of the load unit and the saturable reactor 11. Resistors 
18a and 18b are connected across the interrupters 18a and 18b, 
respectively. A first series circuit having a capacitor 22a and a resistor 
23a is connected across the power source unit. A second series circuit 
having a capacitor 22b and a resistor 23b is connected between the 
connection point between the interrupter 12b and the saturable reactor 11, 
and the ground. One of these series circuits may be omitted. 
In the embodiment shown in FIG. 5, when the DC current I is interrupted, 
the electrodes of the interrupters 12a and 12b are simultaneously opened 
to produce arcs between each pair of electrodes. After the electrodes of 
the interrupter are begun to open and a given time is lapsed, the switch 
16 is closed. At this time, the capacitor 15 has already been charged with 
the polarity as shown, a current Ir flows through the interrupters in the 
direction opposite to that of the DC current I. If Ir&gt;I, a zero point is 
formed in the current flowing through the interrupters 12a and 12b. After 
a given time following the openings of the interrupters 12a and 12b, the 
normally closed switch 20 is opened. More precisely, the switch 20 is 
opened at a time point that the zero point is formed in the current 
flowing through the interrupters 12a and 12b. The given time is determined 
depending on the circuit condition. 
Also in this embodiment, it is assumed that after the interrupters 12a and 
12b interrupted the DC current, one of these interrupters, for example, 
12a is refired and the entire of a recovery voltage is applied across the 
interrupter 12b, and that the interrupter 12a is insulation-recovered. 
Since the components connected across the interrupters 12a and 12b, 
respectively, are resistors 18a and 18b and not the capacitors (13a and 
13b in FIG. 2), immediately after the refired interrupter 12a is 
insulation-recovered, recovery voltages applied across the interrupters 
12a and 12b are equalized. Further, the first series circuit including a 
capacitor 22a and a resistor 23a absorbs a steep surge voltage produced in 
the power source unit. The second series circuit including a capacitor 22b 
and a resistor 23b absorbs a steep surge voltage produced in the load 
unit. Because of the presence of these series circuits, the propagation of 
a surge voltage from the power source unit to the load unit or form the 
load unit to the power source unit is prevented. The propagation of the 
surge voltage may be substantially prevented even if the switch 20 is not 
provided. However, the provision of the switch 20 more reliably prevents 
the surge voltage propagation. The first and the second series circuits 
cooperate with the saturable reactor 11 to decrease the rising rate of a 
recovery voltage applied across each of the interrupters 12a and 12b after 
the DC current is shut off. In sometimes, after the interrupters 12a and 
12b shut off the DC current, both interrupters are refired. In such case, 
it is impossible to interrupt the DC current. The switch 20 prevents such 
a situation. 
In an embodiment shown in FIG. 6, three series circuits each including 
interrupters 12a, 12b and 12c, a branch resistor 25, and a saturable 
reactor 26 are connected in parallel between the switch 20 and the load 
unit 3. Three series circuits each including a capacitor 22c and a 
resistor 23c are connected in parallel between ground and the connection 
points between the saturable reactors 26 and the branch resistors 25. A 
series circuit including a capacitor 22a and a resistor 23a is connected 
across the power source unit, as like the embodiment shown in FIG. 5. 
Three series circuits each including the capacitor 22c and the resistor 
23c, and the saturable reactor 26 are provided to prevent an interference 
at the time of the DC current interruption. The branch resistor 25 is 
provided to equalize the current flowing through the series-interrupter 
groups. The operation and the effects of the embodiment shown in FIG. 6 
are the same as those of the embodiment of FIG. 5. Therefore, explanation 
of those will be omitted. 
An embodiment shown in FIG. 7 uses a single series circuit having a 
capacitor 22b and a resistor 23b in place of three series circuit each 
including the capacitor 22c and the resistor 23c. In this embodiment, 
resistors 27 are further used each to separate the adjacent 
series-interrupter groups, as shown. The operation and the effects of the 
embodiment is the same as those of the embodiment shown in FIG. 5. 
Therefore, explanation of those will be omitted.