Operation circuit and power switching device employing the operation circuit

In an operation circuit of an electromagnetic switching device, when electric energy is discharged by discharge switches connected in series, respectively, to opening coils and closing coils, an induction current flowing in a direction opposite to a current of the coil of the excitation side is generated. The current flows through the coil on the non-excitation side due to magnetic coupling, and a magnetic flux necessary for driving is cancelled, thereby inhibiting generation of a driving force. The operation circuit includes first and second opening and closing coils, so that a moving element may be driven between those coils. This circuit includes a circuit for suppressing an over-voltage at the moment of interrupting an excitation current of a first coil and for interrupting an induction current generated through the first coil at the time of exciting the second coil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an operation circuit for use in, for example, a power switching device.

2. Description of the Related Art

Hitherto, in an operation circuit for use in an operation mechanism to drive a power switching device, as shown on page 4 andFIGS. 9to11of the Japanese Patent Publication (unexamined) No. 033034/2002, two discharge switches such as thyristors are provided and controlled from outside, and turned ON in synchronization with an opening command or a closing command, and are turned OFF at the moment of completion of such opening operation or closing operation.

In the mentioned conventional operation circuit for use in an operation mechanism to drive a power-switching device of above arrangement, there exist the following problems.

In the conventional operation circuit, an opening coil and a closing coil are connected in parallel to capacitors, and electric energy is discharged by discharge switches connected in series to these two coils, respectively. In this known arrangement, the mentioned opening coil and closing coil are disposed adjacent to each other within the operation mechanism. Accordingly, a problem exists in that any induction current, which flows in a direction opposite to a current direction of the coil of the excitation side, is generated through the coil of the non-excitation side due to magnetic coupling when current is carried. Thus a magnetic flux necessary for driving is cancelled, and the generation of a driving force is inhibited.

Moreover, since the state of the magnetic coupling changes in a supersensitive manner depending on a relative positional relation between a moving element being in the stopped state and the mentioned opening coil and closing coil, another problem exists in that the operation is not stable.

SUMMARY OF THE INVENTION

The present invention was made to solve the above-discussed problems, and has an object of providing a highly reliable operation circuit in which driving characteristics are improved, as well as a stable performance is achieved. Another object of the invention is to provide a power-switching device employing this operation circuit.

In an operation circuit of an operation mechanism according to the invention that includes a pair of coils and is arranged so that a moving element may be driven between the mentioned coils; there is connected means for suppressing an over-voltage at the moment of interrupting an excitation current of one of the coils as well as for interrupting an induction current generated through the one coil at the time of exciting the other coil.

As a result, it is possible to significantly improve operation efficiency of the operation mechanism, as well as to protect the coils from being in conditions of the over-voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several preferred embodiments according to an operation circuit relating to the present invention are hereinafter described referring to the accompanying drawings.

FIG. 1is a circuit diagram showing an example of an operation circuit according to the invention. An operation circuit1according to the invention is comprised of opening coils2-4, closing coils5-7, an opening capacitor8that is a source of current for exciting an opening operation, a closing capacitor9that is a source of current for exciting a closing operation, a DC power supply10for charging the capacitors and converters11,12for rectifying a charge voltage of the capacitors, a discharge switch13discharging an electric energy of the opening coil, a discharge switch14discharging an electric energy of the closing coil, a diode15protecting the opening coils from being in over-voltage conditions generated upon making an electric energy of the opening coils OFF with the use of the mentioned switch13, an diode16protecting the closing coils from being over-voltage conditions generated upon making an electric energy of the closing coils OFF with the use of the mentioned discharge switch14, an induction interruption switch17causing a current path of the diode15to be ON at the time of excitation, and an induction interruption switch18causing a current path of the diode16to be OFF at the time of non-excitation.

As the current sources8,9, a capacitor is used, for example.

Further, in the drawing, the diode16and the induction interruption switch18are connected in parallel to the coils and connected in serial to each other, as means for suppressing the over-voltage upon interrupting an excitation current for the closing coils as well as for interrupting an induction current generated through the closing coils at the time of exciting the opening coils.

Likewise, the diode15and the induction interruption switch17are connected in parallel to the coils and connected in serial to each other, as means for suppressing the over-voltage upon interrupting an excitation current for the opening coils, as well as interrupting an induction current generated through the opening coils at the time of exciting the closing coils.

FIG. 2is a perspective view showing an example of an operation mechanism19for carrying out an opening and closing operation using the mentioned operation circuit.FIG. 3(a) is a cross sectional view of an internal part of this perspective view taken along the line IIIa—IIIa of FIG.3(b). FIG.3(b) is a cross sectional view taken along the line IIIb—IlIb of FIG.3(a).

In the drawings, the opening coil and closing coil are disposed in such a manner as to be surrounded at an outer circumferential portion thereof by a yoke in an axial direction of a connection rod21, as well as to be substantially in parallel to each other with a space formed therebetween via the yoke20; and to surround the outside of this connection rod21coaxially therewith in a direction perpendicular to an axis of this connection rod.

In addition, a moving element22is fixed to an outer circumferential portion of the connection rod21, and is in the state of being capable of performing a reciprocating motion in an axial direction of this connection rod.

A permanent magnet23to hold the foregoing moving element22when the mentioned operation mechanism19is in the opening state or the closing state is disposed in such a manner as being fixed to the inside portion of the mentioned yoke with a space formed with respect to this moving element right outside of the moving element22.

Further, the operation mechanism19arranged like this drives the mentioned moving element22to be in the opening or closing state with the use of the mentioned operation circuit1.

Besides, FIGS.3(a) and3(b) show conditions in which the moving element22is driven to be in the opening state and to be held in this state with the mentioned operation circuit1using the operation mechanism19.

FIG. 4is a perspective view showing an example of a power switching device24performing interruption and application of current with the use of the mentioned operation mechanism19.FIG. 5is a cross sectional view of an internal part of the power switching device24on which the mentioned operation mechanism19is mounted.

Referring to theFIGS. 4 and 5, the mentioned operation mechanism19is connected to a vacuum valve26via an insulator25.

In addition, referring toFIGS. 4 and 5, three operation mechanisms19a,19b,19care mounted respectively relative to each phase of a three-phase switching device. However, even in the case where a three-phase linkage is disposed and one operation mechanism19is mounted relative to the three phases, the device effectively acts as a power switching device to perform operations of interrupting and carrying current.

Now, an opening operation is described with reference toFIGS. 1,3(a) and3(b).

A charge voltage of the capacitor8is charged to be a set value by a DC power supply10.

The discharge switch13is a switch capable of being controlled from outside, for example, by a thyristor switch, which is made ON in synchronization with an opening command whereby current is discharged to the opening coils2-4connected in parallel to the capacitor8. Then the moving element22moves from the closing state to the opening state due to an electromagnetic force, and is held in the opening state by the force of a magnetic flux provided by the permanent magnet23.

At this time, at the opening coils2-4, to protect the opening coils2-4from being in conditions of an over-voltage Vo that is generated based on the under-described Expression (1) upon making a discharge current OFF with the discharge switch13, the diode15and the induction interruption switch17for the circulation are disposed in parallel to the opening-coils. The induction interruption switch17is in ON state.
Vo=Lcoil·di/dt(1)
Where: Lcoil denotes inductance of the coil, and di/dt denotes the rate of falling of current at the moment of making current OFF.

In the case of, e.g., thyristor switch, since current comes to be zero instantaneously, di/dt becomes an extremely large value, and voltage Vo generated between the coil terminals becomes significantly large, thereby making it possible to result in dielectric breakdown of the coils. Therefore, the induction interruption switch17is made ON.

Likewise, at the closing coils5-7, which are connected in serial to the other closing capacitor9, the diode16and the induction interruption switch18for the circulation are disposed in parallel to the closing coils. Further, the induction interruption switch18is ON state.

At this time, by making OFF the mentioned induction interruption switch18before the discharge switch13for opening is ON, it is possible to cut an induction current generated through the closing coils5-7that are coupled to the opening coils2-4due to magnetic coupling.

Since this induction current cancels a magnetic flux to excite an opening operation, operation efficiency can be enormously improved by cutting the mentioned induction current.

Furthermore, one capacitor is disposed respectively corresponding to each of the excitation side and the non-excitation side, so that an individual operation becomes possible relative to each of the opening side and the closing side.

Now, a closing operation is described with reference toFIGS. 1 and 6.

A charge voltage of the closing capacitor9is charged to be a set value by the DC power supply10.

The discharge switch14is a switch capable of being controlled from outside, for example, a thyristor switch, which is made ON in synchronization with a closing command whereby current is discharged to the closing coils5-7connected in serial to the closing capacitor9. Then the moving element22moves from the opening state to the closing state due to electromagnetic force, and is held in the closing state by the force of a magnetic flux provided by the permanent magnet23.

At this time, at the closing coils5-7, to protect the closing coils5-7from being in conditions of an over-voltage Vo that is generated according to the mentioned expression (1) upon making a discharge current OFF with the discharge switch14, the diode16and the induction interruption switch18for the circulation are disposed in parallel to the closing coils5-7. The induction interruption switch18is in ON state.

Lcoil in the foregoing expression (1) denotes inductance of the coil, and di/dt denotes the rate of falling of current upon making current OFF.

In the case of, e.g., thyristor switch, since current comes to be zero instantaneously, di/dt comes to be an extremely large value, and voltage Vo generated between the coil terminals becomes significantly large thereby making it possible to result in breakdown of the insulating film of the coil. Therefore, the induction interruption switch18is made ON.

Likewise, at the opening coils2-4, which are connected in parallel to the other opening capacitor8, the diode15and the induction interruption switch17for the circulation are disposed in parallel to the opening coils. Further, the induction interruption switch18is in ON state.

At this time, by making OFF the mentioned induction interruption switch17before the discharge switch14for closing is ON, it is possible to cut an induction current generated at the opening coils2-4that are coupled to the closing coils5-7due to magnetic coupling.

Since this induction current cancels a magnetic flux to excite a closing operation, operation efficiency can be enormously improved by cutting the mentioned induction current. The other effects are the same as those having been described in the case of the opening operation.

In addition, referring toFIG. 1, providing only one charge circuit including the DC power supply10with respect to the opening capacitor8and the closing capacitor9enables reduction in cost.

Further, referring toFIG. 1, the serial connection between the closing coils5-7results in no conduction of current to any of the closing coils5-7in the case of occurring any fault at the mentioned closing coils5-7or at the wiring to the mentioned closing coils. Thus, it is possible to prevent conditions that any of the three phases is not closed.

Furthermore, the serial connection makes impedance in the circuit larger and makes the flow of current smaller, and therefore acceleration is decreased thereby enabling to reduce shock exerted on the vacuum valve62at the time of closing.

Any of the mentioned advantages allows for improvements in reliability as a circuit breaker.

Although connecting the closing coils in series is shown herein, the serial connection of the opening coils in like manner enables to bring the same advantages as described above.

Although not described in this first embodiment, the charge circuit of a capacitor may be either connected or be disconnected by means of a switch at the time of discharging electric energy to the coils. There is no difference in advantages of the invention between the two states.

An example of connecting the closing coils in series is shown in the foregoing first embodiment, however, the serial connection of the opening coils likewise enables to achieve the same advantages as described above.

By connecting the opening coils2-4in,parallel as shown inFIG. 1, a total impedance of the circuit can be reduced, are smaller capacity of the capacitor8and an opening operation requiring a high-speed operation can be achieved, thus reduction in cost of the power supply and a higher-performance of the opening operation being attained. Although connecting the opening coils in parallel is shown herein, the parallel connection of the closing coils in like manner enables the same advantages as described above.

As shown inFIG. 7, a capacitor27and a resistor28are disposed in parallel to the opening coil2, and a capacitor29and a resistor30are disposed in parallel to the closing coil5. Thus, in response to any change in current of which falling is sharp in the case of making an excitation current OFF with the use of the discharge switch13or the discharge switch14(not shown), a composite impedance of the capacitor27and resistor28and a composite impedance of the capacitor29and resistor30come to be smaller than impedances of the mentioned opening coil and closing coil respectively.

Therefore, for example, at the moment of making the discharge switch13OFF, current comes to circulate between the opening coil2, thereby the capacitor27and the resistor28resulting in gradual attenuation of current in accordance with impedance of the circulation circuit.

As a result, voltage generated across both terminals of the opening coil2can be suppressed in accordance with the expression (1).

On the other hand, as for an induction current through the closing coil5on the opposed non-excitation side, the change in current is so slow as that in excitation current. In this case, since a composite impedance of the capacitor29and resistor30becomes larger than the impedance of the mentioned closing coil, no current flows into the circulation circuit. Therefore there is no generation of an induction current.

In the drawing, to act as means for suppressing the over-voltage at the moment of interrupting an excitation current of the opening coil, as well as for interrupting an induction current generated through the opening coil at the moment of exciting the closing coil, there are provided the capacitor27and the resistor28that are connected in parallel to the coil and connected in serial to each other.

Further, it is shown in the drawing that there are provided the capacitor29and the resistor30that are connected in parallel to the coils, and connected in serial to each other to act as means for suppressing the over-voltage at the moment of interrupting an excitation current of the closing coil, as well as for interrupting an induction current generated through the closing coil at the moment of exciting the opening coil.

FIGS.8(a) and8(b) show results, which are obtained on the test of effects by a circuit analysis.

As an example, FIG.8(a) shows waveforms of voltage across the terminals of the opening coil2and across those of the opposed closing coil5in the case of discharging electric energy to the opening coil2. FIG.8(b) shows conduction current through the opening coil2and the opposed closing coil5.

It is understood from FIG.8(a) that in the case of receiving an emergency interruption command and instantaneously interrupting current through the opening coil2, voltage31between the terminals of the opening coil2is suppressed to a degree of about −100V, whereby the opening coil2is protected from the over-voltage. It is further understood from FIG.8(b) that current34through the closing coil5during current-carrying through the opening coil2is suppressed to substantially zero, whereby an induction current due to magnetic coupling is cut.

Furthermore, although one opening coil and one closing coil are respectively shown in the foregoing explanation, it is a matter of course to achieve the same effects even in the case of a plurality of coils As shown in FIG.1.

In case ofFIG. 1, there are disposed the discharge switches13,14respectively on each of the opening and closing sides. However, even when the discharge switches are disposed individually at each phase and at each electrode, for example, as shown with the discharge switches13a-13c, and14a-14cinFIG. 9, there is no difference in effects according to the foregoing embodiments 1 to 3.

Furthermore, arrangement of the discharge switches located individually at each phase and at each electrode enables the control of individually opening or closing each phase, resulting in advantage that application of this device to a phase control breaker becomes possible.

FIG. 10shows an arrangement in which diodes35-40are disposed in serial respectively to each of the opening coils2-4and the closing coils5-7

By this arrangement, for example, it becomes possible to prevented an induction current from circulating within the three-phase coils due to difference in self-impedances of the opening coils2-4, resulting in advantage of suppressing fluctuation in operation between the three phases.

In the mentioned embodiments 1-5, a capacitor is employed as excitation means of a coil. However, a direct excitation from a DC power supply brings about the same effects.

As shown inFIG. 7, there are provided capacitors respectively one on each of the whole opening side and the whole closing side with accompanying construction in which there is provided only one charge circuit with respect to the unit of both sides, thereby enabling to reduce number of parts of the circuit resulting in improvement in reliability.

FIG. 11shows layout of commons41a,41b,41c,42a,42b,42cof a circuit according to this invention.

As shown inFIG. 11, the commons are disposed on the side of a positive electrode of the discharge circuit, thereby making insulation of the common circuit unnecessary. This brings about reduction in number of parts resulting in advantage of higher reliability and cost reduction.

FIG. 12shows, as an example of conditions of the change over time of each component of the present switching device at the time of a closing operation, a change43in displacement of the moving element22, a conduction current waveform44of the closing coils5-7, a timing chart45of the discharge switch14, and a timing chart of the induction interruption switch18.

In the drawing, ti denotes a conduction time period; t2denotes a time period from the completion of the closing operation until the discharge switch14is made OFF; and t3denotes a time period from OFF of the discharge switch14until the conduction current comes to be a value of substantially zero (value regarded as zero).

When a closing command is received by the power switching device24, the induction interruption switch18, which is connected in parallel to the closing coils5-7, is made ON, at the same time or thereafter, the discharge switch14is made ON, and current is discharged from the closing capacitor9to the closing coils5-7. However, since this current is gradually increased by degrees, it is possible to prevent the coils from occurrence of the over-voltage.

The discharge of current to the closing coils5-7causes the moving element22to move from the opening state to the closing state by an electromagnetic force and to be held in the closing state due to magnetic flux provided by the permanent magnet23.

At this moment, since there is provided in the operation circuit1means for making current OFF after a predetermined time width such as timer or delay switch having a time width sufficient to complete the closing operation, the discharge switch14is made OFF, and conduction through the closing coils is brought into OFF. Thus, OFF of the discharge switch14can be carried out without any special current detector.

At the moment of making the mentioned discharge switch14OFF, the induction interruption switch18is in the ON state, and therefore the OFF current circulates to the side of the induction interruption switch18and the diode16, and comes to attenuate by degrees. Accordingly, no over-voltage occurs between terminals of the closing coils5-7, thereby enabling to prevent the closing coils5-7from dielectric breakdown.

On the other hand, when the induction interruption switch18is brought into OFF during dropping of current at the time of OFF of the closing coils5-7, current at the moment of making the closing coils OFF comes instantaneously to be zero. Therefore, it is possible that the over-voltage occurs between the terminals of the closing coils5-7.

In the operation circuit according to the invention, the induction interruption switch18is set to be OFF with a predetermined time width from OFF of the discharge switch14until current through the closing coils5-7comes to a value substantially zero (value regarded as zero). Thus, the closing coils5-7can be prevented from over-voltage. It is possible to easily calculate these predetermined time widths by inspection at the time of dispatching products.

The induction interruption switch18is set so as to be still kept in the OFF state after the whole conduction sequence has completed, thereby enabling to prevent an induction current from flowing through the closing coils5-7, which is located on the side of non-excitation, without need to make the induction interruption switch18OFF at the time of the next interruption operation. Consequently, efficiency at the time of the opening operation can be improved.

Further, for manually operating the interruption at the time of power outage, it is possible that magnetic flux of the permanent magnet23changes due to movement of the moving element, and an induction current is excited through the closing coils5-7. However, since the induction interruption switch18has been in the OFF state when there is no conduction after the last closing operation has completed, no induction current flows through the closing coils5-7, thereby enabling to carry out manual interruption operation smoothly as well as reliably.

FIG. 13shows change47in displacement of the moving element22and a conduction current waveform48of the closing coils5-7at the time of the closing operation.

In general, a large shock is applied to the vacuum valve26at the moment of the closing operation, so that it is necessary in the normal circuit breaker to suppress the moving rate of the moving element22at the time of the closing operation to be not more than a predetermined level for the purpose of assuring a high durability of the vacuum valve26.

On the other hand, in the operation mechanism19, an electromagnetic force exerted on the moving element becomes larger, and acceleration of the moving element is likely to increase as it approaches to the closing state.

To cope with this, as shown inFIG. 13, the discharge switch14is once made OFF and the conduction current is interrupted after the moving element has been accelerated sufficiently, thereby suppressing the acceleration due to electromagnetic force. Then, the discharge switch14is made ON again, and current is carried again immediately before closing, thereby enabling to prevent chattering that is a bounding phenomenon at the time of closing.

Consequently, the shock applied to the vacuum valve26can be suppressed to the minimum, thereby assuring a longer operation life of the breaker and a higher reliability.

In the foregoing embodiments, an operation circuit of the power-switching device is mainly described as an example. This invention, however, is not limited to this example, and it is a matter of course that the invention can be applied to any other operation circuit for an operation mechanism such as valve control, fuel pump control or linear oscillator for use in an automobile.

Furthermore, in the embodiments, an operation mechanism, which is different in arrangement from the conventional embodiments, is referred and described. However, a targeted operation mechanism may have any other configuration. As far as it is an operation mechanism driven by a plurality of coils with magnetic coupling through the action of an electromagnetic force, this invention can be applied to any other mechanism as a matter of course.