JPH03219514A - Vacuum-type circuit-breaker - Google Patents

Abstract

PURPOSE:To suppress surge electric voltage generated by arcing at the shutting time of low current of delay power factor by installing a ferrite ring on an electrically conducting axle which is a part of a loop in which high frequency electric current flows at the time of arc regeneration. CONSTITUTION:A ferrite ring 10, which is ferromagnetic, is attached to electrically conducting axles 4, 5 of a vacuum 6, which is a part of a loop where high frequency electric current flows at the time of arc regeneration. Then, corresponding to the high frequency electric current flowing in a circuit, magnetic fluxes are generated in the inside of the ring 10 and the number of crossing magnetic fluxes increases. Inductance in the part thus becomes large so that time constant of a rising part becomes large. Since the same effect is achieved even if the ring 10 is installed in any point of the current loop, it is inserted in the electrically conducting axle 5 of the valve 6 and thus an insulation distance between a pair of electrodes 2, 3 of the ring 10 and the valve 6 is kept sufficiently. Since reactance increases, sharp surge electric voltage generated by arc generation between contacts at the shutting time of low current of delay power factor is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention particularly relates to a vacuum circuit breaker that suppresses surge voltage during switching.

(Prior art) The switching surge voltage that occurs when switching a small current of an inductive load in a vacuum circuit breaker is composed of a surge voltage of several kHz associated with current interruption and a surge voltage of several MHz associated with re-ignition. In order to suppress these surge voltages, C
R suppressor, lightning arrester.

Nonlinear resistors are used. However, all of these surge suppression devices are aimed at suppressing ground voltage.
It does not target the surge voltage of several M) Iz that accompanies re-ignition (however, by suppressing the ground voltage, the effect of suppressing the peak value of the surge voltage of several MHz that accompanies re-ignition occurs. Journal of the Institute of Electrical Engineers of Japan) , Vo12.93.Refer to No.8)
.

By the way, since high-voltage motors and the like are connected to the end of the system, there is no standard for impulse withstand voltage. If a switch that generates high-frequency surge voltage, such as a vacuum circuit breaker, is connected to open and close such a high-voltage motor,
Problems may arise in insulation coordination with high-voltage motors. That is, when a surge voltage having a steep wavefront length enters the high-voltage motor, the high voltage is shared by the coil at the outlet of the high-voltage motor.

(Problem to be Solved by the Invention) Then, not only the insulation between the coil and the ground (main insulation) but also the insulation between the layers becomes a problem. When the alternating current voltage is at a commercial frequency, the voltage distribution between the coils is approximately equal, so only a low voltage is applied between the layers inside the coil, and therefore the interlayer dielectric strength voltage may be at a low level. However, when a surge voltage with a short wavefront length enters, the voltage shared by the coil at the sunrise part increases.Moreover, this shared voltage becomes larger as the wavefront length becomes shorter.For example, when a surge voltage with a wavefront length of 0.2μS When the invasion occurred, the ratio of the shared voltage in the sunrise section was 9.
It is known that it is about 0%.

As described above, when considering the insulation coordination with interlayer-insulated equipment, where there is a large unbalance in voltage sharing among various parts in response to a sudden surge, the sudden surge voltage becomes a big problem.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a vacuum circuit breaker that can suppress the steep surge voltage that occurs due to arcing between contacts when interrupting a small current with a lagging power factor.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a vacuum valve in which a pair of electrodes are provided facing each other in a vacuum container with a high degree of vacuum of 10-" Pa or less and are movable toward and away from each other via current-carrying shafts. This vacuum circuit breaker is a built-in vacuum circuit breaker, characterized in that an annular magnetic body is provided in the vacuum container, the axis of which is penetrated by a current-carrying shaft.

(Function) The wavefront length of the steep surge voltage when the vacuum circuit breaker re-ignites is determined by the inductance around the vacuum circuit breaker and the surge impedance of the line. In addition, the wavefront length at that time is relaxed as the inductance around the vacuum circuit breaker increases, so the ferromagnetic material with good saturability characteristics provided in the current-carrying part of the vacuum circuit breaker through which the high-frequency surge current flows. The apparent inductance around the vacuum circuit breaker increases, making it possible to alleviate the sudden rise in surge voltage at the time of re-ignition.

(Example) Hereinafter, one example of the vacuum circuit breaker of the present invention will be described with reference to the drawings.

In FIG. 1, a vacuum valve 6 in which a pair of electrodes 2, 3 facing each other in a vacuum vessel 1 are disposed so as to be freely accessible and separable via current-carrying shafts 4, 5, respectively, is connected to a vacuum circuit breaker 7. The current-carrying shafts 4 and 5 are connected to the main circuit disconnecting parts 8 and 9 of the main circuit. Here, the ferrite 1-ring 10 is extrapolated onto the current-carrying shaft 5.

The operation of the vacuum circuit breaker configured in this way will be explained.

When the vacuum circuit breaker 7 interrupts the small current of the motor load, the second
Repeated re-ignition (multiple re-ignition) as shown in the figure may occur (note: the broken line indicates the voltage between the electrodes). This phenomenon occurs because the current is cut off immediately after the contacts in the vacuum valve open.
Moreover, this occurs when the contacts are not sufficiently opened. For this reason, the transient recovery voltage accompanying the current interruption exceeds the withstand voltage between the contacts, and discharge occurs between the contacts, and at this time, the high frequency current flowing between the contacts is extinguished at its current zero point. These phenomena occur repeatedly and the voltage gradually rises, but if you zoom in on the vicinity of the re-ignition point where this phenomenon occurs, it will generally look like the one shown in Figure 3. That is, since the voltage changes rapidly at the moment of re-ignition, it is necessary to consider the line as a distributed constant.

In a general in-house power distribution system, a vacuum circuit breaker and an electric motor are generally connected by an electric cable. When focusing on one vacuum breaker here, a similar feeder breaker is connected to the power supply side of the vacuum breaker, and the surge impedance seen from the vacuum breaker is small. Furthermore, the vacuum circuit breaker and the busbar of the closed switchboard in which it is housed have stray inductance. Further, a power cable is connected to the load side of the vacuum circuit breaker, and its surge impedance is several tens of ohms. Furthermore, the surge impedance of the motor connected to the other end of the power cable is generally approximately Ω. Taking the above into consideration, the equinodal circuit at the time of re-ignition is found as shown in Figure 4. In the figure, the power supply side is a strain capacitance 11 to ground, and the discharge between the contacts is simulated by closing the switch 12. The inductance around the vacuum circuit breaker is represented by the power supply side stray inductance 13 and the load side stray inductance 14,
The power cable is represented by a cable 15, and since the surge impedance of the motor is large compared to the surge impedance of the power cable, steep surge voltages can be ignored, so the circuit shown in Figure 4 does not need to be considered. First, one end of the cable 15 is open.

In the equivalent circuit shown in the figure, when the switch 12 is closed, the voltage waveform generated between the stray inductance 14 and the connection point of the cable 15 to the ground is as shown in Fig. 5, assuming that the line length of the cable 15 is sufficiently long. It becomes like this. The time constant J of the rising portion of this voltage waveform can be expressed by the following equation.

J” (Lxa + Li4)/Z is the surge impedance of the cable 15, L□3 is the inductance of the straight inductance 13 on the power supply side, Li4
is the inductance of the load side straight inductance L□4.

As is clear from the above formula, in order to alleviate the steep rise at the time of re-ignition, either increase L131L14 or change Zc
It is possible to reduce Zc, but it is often wasteful to reduce Zc just for surge suppression.
Since L14 is determined by the generatrix shape and arrangement, it is difficult to change this. Therefore, as in the above configuration,
A ferrite ring 1 made of ferromagnetic material is attached to the current-carrying shaft 5 of the vacuum valve, which is part of the loop through which high-frequency current flows during re-ignition.
By attaching 0, a magnetic flux corresponding to the high frequency current flowing in the circuit is generated inside the ferrite ring 10, increasing the number of flux linkages between the high frequency current and the magnetic flux in the magnetic path of the ferrite ring 10, and reducing the inductance of this part. By increasing the value of L13+L14 apparently shown in FIG. 4, the time constant J of the rising portion can be increased.

According to this method, the same effect can be expected no matter where the ferrite ring 10 is placed in the current loop through which the high-frequency current flows. However, such a ferrite ring 10
Since it is a problem to install the ferrite ring 10 in the live part and ensure sufficient insulation distance depending on the location, in the present invention, it is inserted into the current carrying shaft 5 inside the vacuum valve used in the vacuum circuit breaker. A sufficient insulation distance between the bulb 6 and the shield 16 provided at 7- surrounding the pair of electrodes 2 and 3 can be ensured.

As a result, according to the present invention, a vacuum circuit breaker is provided which can alleviate the steep rise voltage at the time of re-ignition, prevent interlayer dielectric breakdown of the motor, and achieve insulation coordination for re-ignition surge.

In the above embodiment, the magnetic path cross-sectional area of the ferrite ring 10 may be determined based on the severing current value of the load that generates a small current.Furthermore, the ferrite ring 10 may be installed through an insulator at the installation location. The shield 16 shown in FIG. 1 may also be made of ferrite.

〔Effect of the invention〕

As described above, according to the present invention, a vacuum circuit breaker has a built-in vacuum valve in which a pair of opposing electrodes are provided in a vacuum container with a high degree of vacuum of 10-2 Pa or less and can be freely connected to and separated from the other via the current-carrying shaft. In the vacuum chamber, an annular magnetic body is installed in the vacuum chamber, and the current-carrying shaft passes through the center of the vacuum chamber.The vacuum chamber is capable of suppressing the sudden surge voltage that occurs due to arcing between contacts when interrupting a small current with a lagging power factor. You can get a circuit breaker.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view showing one embodiment of the vacuum circuit breaker of the present invention, and FIGS. 2, 3, 4, and 5 are diagrams showing the operation of the vacuum circuit breaker of the present invention. . 1... Vacuum container 2, 3... Electrodes 4, 5
...Electric shaft 6...Vacuum valve 10.
...Ferrite ring (8733) Agent Patent attorney Yoshiaki Inomata (and 1 other person) JP-A-3 219514 (4) 2nd AkiP details Figure 3

Claims (1)

[Claims] In a vacuum circuit breaker with a built-in vacuum valve in which a pair of electrodes are provided facing each other in a vacuum container with a high degree of vacuum of 10^-^2 Pa or less and can be freely connected and separated via current-carrying shafts, A vacuum circuit breaker, characterized in that an annular magnetic body is provided at the center of the axis through which the current-carrying shaft passes.