JPH03205717A - Vacuum down detecting apparatus for vacuum valve switchgear - Google Patents

Abstract

PURPOSE:To detect vacuum down presicely in early stage by determining that vacuum down is caused when multirecurring arc current is not detected while receiving an output signal of a multirecurring arc surge detecting sensor installed in vacuum valves and a switching control signal of the vacuum valve switchgear. CONSTITUTION:Vacuum down of a vacuum valve 1 of a vacuum valve switchgear 21 connected to an A.C. power source system is detected according to whether there is multirecurring arc surge caused by current cutting or high frequency extinguishing phenomena. There are installed multirecurring arc surge detecting sensors 23 installed correspondingly to vacuum valves 1 of each phase and a determining part 30 which determines vacuum down in the vacuum valves 1 and puts out a signal when a multirecurring arc current is not detected during switching operation of the vacuum valves 1 while receiving each output signal of the multirecurring arc surge detecting sensors 23 and a switching control signal of a vacuum valve switchgear 21. In this way, vacuum down is detected in early stage before withstand voltage between poles of vacuum valves loweres greatly.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention detects a decrease in the degree of vacuum of a vacuum valve and multiple re-ignition surges in a switching device such as a vacuum circuit breaker or a vacuum switch using a vacuum valve. This article relates to a device for detecting a decrease in the degree of vacuum. [Conventional technology]
Taku vacuum circuit breakers and vacuum switches have highly degassed parts that correspond to the arc extinguishing chambers of other circuit breakers. A completely sealed vacuum valve is used. Vacuum is an ideal insulating medium, but if the vacuum deteriorates, it cannot perform its function, so the degree of vacuum of the vacuum valve plays a large role in the reliability of vacuum circuit breakers and vacuum switches. ．． Therefore, in order to ensure high reliability when manufacturing vacuum valves, we control the manufacturing process such as material selection, purchasing, processing accuracy and degassing treatment, and perform performance confirmation tests.
Strict quality control is implemented from inspection and other procurement of materials to product shipment. In particular, the control of the vacuum level of the vacuum valve is the most important, and thorough management is carried out to prevent complete failure. Figure 8 is a principle explanatory diagram of the factors that reduce the degree of vacuum in a vacuum valve.
-Internal gas release and vacuum in which gas molecules remaining inside the vacuum vessel, electrodes, and conductors that make up the vacuum valve are gradually released from their surfaces, although they are maintained at a high vacuum of about Torr. It gradually decreases due to slow leakage, where air gradually enters from the outside through small holes in the valve's construction materials and joints. Among these, the one caused by gas release is a curved change with a saturation value, while the one caused by slow leak is a linear change depending on the pore size. Therefore, the overall change is shown as the total gas by superimposing these. In order to manage the vacuum life of a vacuum valve, it is necessary to take appropriate measures to address these deterioration factors. FIG. 9 is a schematic cross-sectional view showing a conventional vacuum valve equipped with a sensor that directly detects a decrease in the degree of vacuum.
is supported by a cylindrical insulating container 5, a fixed contact 2 supported by a metal end plate 4A connected to one end thereof, and an end plate 4B and a metal bellows 6 connected to the other end of the insulating container. By using the movable contactor 3 as a main structural element and driving the movable contactor 3 by an operation device (not shown), a circuit breaker or a switch having the function of switching a load current or a charging current is constructed. Further, inside the vacuum valve l, a metal shield 7 is provided concentrically inside the insulating container 5, and metal vapor generated by an arc when the current is cut off adheres to the inner wall of the insulating container 5, reducing insulation performance. It is designed to prevent this from happening. Reference numeral 10 denotes a magnetron element as a vacuum sensor, which is airtightly attached to the end plate 4A and detects the vacuum inside the vacuum valve. However, this method has the disadvantage that a new slow leak occurs at the airtight joint between the vacuum valve and the vacuum sensor, which impairs the $1 performance of the vacuum valve. Furthermore, it is almost impossible to attach a vacuum sensor to an existing vacuum valve by post-processing. FIG. 10 is a characteristic diagram showing the relationship between the internal pressure of the vacuum valve and the alternating current Franciover voltage between the poles. When the degree of vacuum inside the vacuum valve decreases to an extent approaching the 10-" Torr order, the Franciover voltage increases. Started to drop, 10-”
to the lower limit value (1G-'K) on the order of 10-' Torr
V order), and above the order of 10 Torr, the franchisee voltage gradually increases and recovers to the franchisee voltage in atmospheric pressure air. In general, when the degree of vacuum in a vacuum valve drops to the order of 10-'' Torr, it becomes unable to withstand the voltage of the power system, and in the open state, abnormal discharge occurs between the contact poles or between the contact connected to the power system and the metal shield. occurs, and in the closed state, an abnormal discharge occurs between the pair of contacts and the metal shield. Therefore, the conventional technology also has the above characteristics and detects the abnormal discharge electrically from the outside of the vacuum valve. There are several known devices for detecting a decrease in the degree of vacuum that indirectly detect the decrease in the degree of vacuum by detecting the decrease in the degree of vacuum. A circuit breaker provided between l1 and the load system 12,
A vacuum valve 1 such as a switch has a lightning arrester 13 on its load side.
, CR type surge absorber 14, etc. are provided, and paying attention to the fact that a discharge current (3) flows due to abnormal discharge between poles, a current sensor 15 is installed on the ground wire side of the lightning arrester l3 or surge absorber 14, and the current sensor 15 is installed on the ground wire side of the surge arrester l3 or surge absorber 14 to detect the discharge current that occurs when the poles are opened. It is designed to detect a decrease in the degree of vacuum by detecting the discharge current. FIG. 12 is a structural diagram showing the second prior art, in which high-frequency noise generated along with an abnormal discharge 100 between electrodes of the vacuum valve 1 is connected to the power supply system side of the vacuum valve via a high-voltage capacitor 16. The detector 17 is configured to detect the high frequency noise generated by the noise. FIG. 13 is a structural diagram showing the third prior art, in which the electric potential of the metal shield 7 that increases due to the abnormal discharge 101s that occurs between the metal shield 7 and the contact during opening and closing is insulated. A voltage dividing capacitor l8 is connected to the external terminal 7^ of the metal shield drawn out through the container 5 via a high voltage capacitor l6, and the voltage detector 19 is configured to measure the potential of the voltage dividing capacitor l8. There is. FIG. 14 is a configuration diagram showing a fourth conventional technique, in which the potential rise of the metal shield 7 due to the abnormal discharge 101s that occurs similarly to the third conventional technique is suppressed by providing a gap between the metal shield 7 and the outer surface of the insulating container 5. It is configured to be detected by a potential sensor 20 that is held and arranged. [Problems to be Solved by the Invention] In the first prior art, abnormal discharge can be detected using a lightning arrester or a surge absorber, but the discharge current and abnormal discharge 100 caused by abnormal voltage at cut-off or turn-on are detected.
It is necessary to provide a discrimination circuit on the output side of the current sensor 15 to discriminate between the discharge current and the discharge current generated by the current sensor, which causes a problem that the detection circuit becomes complicated. In the second conventional technology, it has been experimentally verified that when an abnormal discharge occurs between the poles, it immediately changes to an arc discharge, and because the arc drop between the poles is small, the detected high-frequency noise charge is There is a problem in that the amount is extremely small, only a few PCs, making it difficult to perform highly reliable detection.Also, it is necessary to provide a high-voltage capacitor 16 for high-frequency noise detection for each vacuum valve, which increases the size of the device. Furthermore, like the second conventional technique, the third conventional technique requires a high-voltage capacitor 16, and an external terminal must be provided by penetrating the insulating container, which poses a risk of adversely affecting the performance of maintaining the degree of vacuum. There is. In the fourth conventional technology, since the coupling capacitance between the metal shield and the potential sensor is small, capacitance coupling easily occurs between the vacuum valve of the other phase, etc., and the judgment accuracy of the detection result is low, leading to erroneous judgments. There are flaws that are easy to make. Furthermore, the above-mentioned four conventional technologies have a common feature that abnormal discharge does not occur unless the withstand voltage performance between the poles of the vacuum valve decreases to the extent that it cannot withstand the normal ground voltage of the grid, and therefore abnormal discharge is detected. At this point, vacuum valves have the disadvantage that they have lost their ability to withstand voltage. An object of this invention is to detect a decrease in the degree of vacuum in a vacuum valve at an early stage and with high accuracy without decreasing the degree of vacuum to the extent that the vacuum valve cannot withstand the voltage between its electrodes. [Means for Solving the Problems] In order to solve the above problems, according to the present invention, the vacuum valve reduces the vacuum degree of the vacuum valve of the vacuum valve type switchgear connected to the AC power system by cutting the current. phenomenon. The system detects multiple re-ignition surges based on the presence or absence of multiple re-ignition surges generated based on a high-frequency arc-extinguishing phenomenon. When the multiple re-ignition current is not detected during the opening/closing operation time of the vacuum valve in response to the output signals of the respective detection sensors and the opening/closing control signal of the vacuum valve type switching device, a decrease in the degree of vacuum is detected in the vacuum valve. It shall be equipped with a determination section that determines that a phenomenon has occurred and issues a signal, and the detection sensor is composed of either a current sensor, a current sensor, or a voltage sensor, and is insulated and supported on the outer periphery of the insulating container of each phase vacuum valve. It also includes those in which each phase vacuum valve is connected to the load side via a power cable having a ground conductive layer, and a detection sensor is arranged on the ground line side of the ground conductive layer. [Operation] Due to the strong arc-extinguishing power of vacuum, vacuum valves have current interruption phenomena and high-frequency arc extinguishing phenomena that cannot be seen in air circuit breakers or gas circuit breakers. Long multiple re-ignition surges occur. However,
These phenomena become unstable when the degree of vacuum decreases to the order of 10 Torr, and the withstand voltage between electrodes begins to decrease.
-" Torr, it almost never occurs. The above-mentioned means are designed to utilize the above-mentioned phenomenon for detecting a decrease in the degree of vacuum. That is, it is usually caused by the resonance of the inductance and free capacitance of the load circuit. As a detection sensor for multiple re-ignition surges with a determined vibration frequency of 100 KHz to several MHz, a high-frequency current sensor or high-frequency voltage sensor is installed corresponding to each phase vacuum valve of the opening/closing equipment 1 to detect and judge multiple re-ignition surges. The section determines whether multiple re-ignition signals are detected within the opening and closing time of the vacuum valve, and when no signal is detected, it issues an alarm signal indicating a decrease in the degree of vacuum. As a result, the decrease in the degree of vacuum causes the generation of multiple re-ignition surges to become unstable at 10-' T, which is close to 10-' Torr.
orr order. In other words, it is possible to detect this at an early stage before the vacuum valve's interelectrode withstand voltage drops significantly. In addition, the amplitude of multiple re-ignition surges is several KV, which is several times larger than that of other circuit breakers, and the duration is also 1 S.
It is about 10 times longer than other circuit breakers in terms of length, so it can be easily distinguished from the preceding discharge between the poles and the re-ignition surge that occurs when the vacuum valve opens and closes. , it is possible to improve the detection accuracy of multiple re-ignition surges. Furthermore, the Rogowski coil is used as a current sensor. Alternatively, by installing a voltage divider as a voltage sensor on the outer periphery of the insulating container of the vacuum valve or on the ground wire side of the load-side power cable, the ground capacitance of the insulating container or the ground capacitance of the power cable can be reduced. It can also be used as a high-voltage capacitor to make the detection sensor small and inexpensive. [Example] This invention will be explained below based on an example. FIG. 1 is a schematic diagram showing a vacuum level drop detection device for a vacuum valve type switchgear according to an embodiment of the present invention, and shows an example in which a current sensor is used as the detection sensor. In the figure, each phase vacuum valve IU, IV.
The fixed contact 2 side of each of the 1st class 1 is connected to the Sanwa AC power system 11, and the movable contact 3 side is connected to the external load 12, and opening/closing is controlled by a control section (operation section) 22. Current sensor 23U as a multiple re-ignition surge detection sensor. 23V. 23- is in the form of a Rogowski coil, and is insulated and supported on the outer periphery of a psossing device (not shown) located close to the load side of each phase vacuum valve. Additionally, the Rogowski coil may be installed on the power supply side of each phase vacuum valve. Reference numeral 30 denotes a determining section, which receives, for example, an opening control signal 22T. A trigger pulse generation circuit 25 receives the closing lIl1II signal 22C and emits a trigger pulse 25S synchronized with the start point of the opening/closing operation of the contact, and a signal that is turned on in response to the trigger pulse 25S and rectifies the detection signal 23S of the current sensor. A noise discrimination circuit 26 determines that multiple re-ignition pulses have occurred when the time integral value exceeds the level specified by the setting signal 313 and emits a pulse signal 263, and a pulse signal 26S is generated during the opening/closing operation time of the contact. There is a no-signal detection circuit 27 that issues an ON signal 27S when the ON signal 27S is not detected, and a no-signal detection circuit 27 that determines whether a decrease in the degree of vacuum has occurred in the vacuum valve when the ON signal 27S is detected, and outputs the notification signal 29 for each phase vacuum valve. The system is equipped with a vacuum degree drop detection circuit 28 to detect a decrease in the degree of vacuum, and is configured to be able to specify which of the phase vacuum valves 10, IV, and 1%1 a decrease in the degree of vacuum has occurred based on the notification signal 29. FIG. 2 is a sectional view of a main part showing different arrangement states of the detection sensor in the above-mentioned embodiment. It is formed into an annular shape so as to surround the outer periphery of the insulating container 5, and is insulated and supported by the wA green container 5. Further, a ground conductive layer 5^ is formed on the outer peripheral surface of the insulating container 5 as necessary to eliminate the influence of the alternating current electric field on the Rogowski coil 23. In addition, when the multiple re-ignition surge detection sensor is a voltage sensor, the ground conductive layer 5A is grounded via a Cera Q7 capacitor having good high frequency characteristics, for example, and this Cera ξ
If we use a power capacitor as a detection capacitor to detect multiple re-ignition surge voltages, the capacitance that the charging part of the vacuum valve 1 has with respect to the ground conductive layer 5A can be used as a voltage dividing capacitor to generate a small and inexpensive voltage. You can get a sensor. Next, the principle and operation of the vacuum level drop detection device constructed as described above will be explained. Figure 3 is a characteristic diagram showing the maintenance or cutting characteristics of vacuum arc discharge using copper electrodes as an example. In the case of copper electrodes, there is a region where maintenance of vacuum arc becomes unstable in the range of about 10 to 30A. However, in a current region larger than the unstable region, the vacuum arc is maintained stably, and the lower limit current in the unstable region is called the cutting current io, and in the current region below Io, the vacuum arc cannot be maintained. This is the cause of current interruption phenomena and high frequency arc extinguishing phenomena in vacuum valves. Note that the value of the cutting current 1o varies greatly depending on the electrode material, but the value of the cutting current 1o also varies greatly depending on the degree of vacuum, and as shown by the broken line in FIG.
When the degree of vacuum decreases to the Torr order, the current cutting phenomenon is almost no longer observed. This invention attempts to detect a decrease in the degree of vacuum before the degree of vacuum decreases to the extent that the franchisee voltage between the poles decreases significantly by utilizing the vacuum degree dependence of this current cutting phenomenon. be.
By the way, if a vacuum valve type switchgear connected to an inductive load is turned on or the contacts are opened just before the current zero point, the distance M between the contacts (distance between the poles) is small and the voltage applied between the poles cannot be withstood. As a result, preliminary discharge and re-ignition occur. Transient vibrations are induced by LC resonance in the load circuit. This transient oscillation also creates a current zero point. Figure 4 is a waveform diagram showing the occurrence of a re-surge due to the current cutting phenomenon of an air circuit breaker. Even if a zero point occurs, it cannot be interrupted, the arc is maintained, and it is interrupted at the next current zero point of the commercial frequency current i. Also, when the switch is turned on, the contact closes in a continuous arc state. In this way, a circuit breaker with a weak arc-extinguishing force does not cut off a preceding discharge or a re-striking surge, so multiple re-striking surges, which will be described later, do not occur, and therefore the duration of the opening/closing surge that occurs is also zero. .It is short, less than 1ms. Figure 5 is a waveform diagram showing the occurrence of a re-sparking surge of the arc-extinguishing gas.A vacuum bulb with high arc-extinguishing power can withstand several cycles of transient vibrations, usually from 100 KHz to several MHz, that occur with preceding discharge or re-sparking. This causes LC resonance to be induced on the load side, which causes the voltage between the contacts to rise again, causing repeated re-ignition. This is the mechanism by which multiple re-triggering surges occur.As shown in the figure, their duration is usually as long as about 10, and their amplitude is several times larger than that of the re-triggering surge of an air circuit breaker as shown in Figure 4. , for example, reaches near IOKV. Furthermore, when the degree of vacuum of the vacuum valve decreases to the order of 10-'' Torr, the occurrence of multiple re-ignition surges is no longer recognized, and the situation approaches that of the preceding discharge and re-ignition surge in the air circuit breaker described above.
It is possible to detect a decrease in the vacuum level of the vacuum valve by the presence or absence of multiple re-ignition surges. FIG. 6 is a time chart showing the operation of the above-mentioned embodiment, and its operation will be explained in conjunction with the structural diagram of the vacuum drop detection system shown in FIG. In the figure, the control unit 22
From time h to time h, the vacuum valve opening operation command signal 22
It is assumed that the contact starts opening at time t0, which is delayed by Δt, and is fully opened at time t#, when the opening operation time T has elapsed. The trigger pulse generation circuit 25 receiving the control signal 22T from the control section 22 generates Δ1. Time delayed t. A trigger pulse 25S is generated in synchronization with the point in time (the point in time when the contact starts to open), and a signal 275 at H level is outputted, which turns on the no-signal detection circuit 27, which is constituted by a memory circuit such as a flimp-frosov circuit. If the vacuum degree of each phase vacuum valve is a normal value, multiple re-ignition pulses 23
5 is output to the noise discrimination circuit 26. Upon receiving this, the noise discrimination circuit 26 rectifies the multiple re-ignition pulse 235 using, for example, an integrating circuit, a quantizing circuit, etc., and then integrates it over time, and when the integrated value Vt exceeds the threshold level v3 of the setting signal 31S. When the pulse signal 26S is output. Therefore, a re-ignition pulse with a small time integral value Vi and a multiple re-ignition pulse with a large time integral value Vt are discriminated.
Only multiple re-ignition pulses are converted into pulse signal 26S. The pulse signal 26S is input as a recent signal to the no-signal detection circuit 27, thereby causing the H level signal 27S to return to the L level. The vacuum degree drop detection circuit 28 that receives the signal 273 may be, for example, a timer switch circuit that turns on and issues the notification signal 29 when the signal 27S continues for the opening operation time T1 or more. The duration of the detected H level signal 27S is T,
As the result is as follows, the notification number 29 is not output. Next, at time tl1, the closing operation inn signal 22C is output, and from this, Δ1. Initial time t of closing operation time Tx of delayed contact
Assume that trigger pulse 255 occurs at lm. At this time, if the degree of vacuum of each phase vacuum valve is normal, the determination unit 30 operates in the same manner as in the opening operation, so the notification signal 29 is not generated. However, it is assumed that the degree of vacuum of one of the vacuum valves of each phase has decreased to the order of 10-'' Torr, multiple re-ignition surges have not occurred, and only the preceding discharge pulse has been detected as the detection signal 23S at time tax. case,
The time integral value Vt of the preceding discharge pulse is small, and the setting signal 3
Since it is below the threshold level Vs of 1, the noise discrimination circuit 2
6 does not generate the pulse signal 26S, so the output signal 27S of the no-signal detection circuit If}27 continues even after the time t when the contact closes the H level. As a result, the vacuum level drop detection circuit 28 detects t. The signal 29U. for each phase is turned on by detecting an H level signal that continues even after the point in time, and notifies the decrease in the degree of vacuum. 29V. Output either of 29-. Note that when the degree of vacuum decreases to the order of 10-'Torr, multiple re-ignition surges may or may not be detected due to repeated opening and closing of the vacuum valve, and the degree of vacuum may decrease to 10-' Torr.
Multiple re-ignition surges almost no longer occur as they approach 0-''Torr. Therefore, by replacing the vacuum valve when multiple re-ignition surges occur irregularly, you can prevent problems caused by a decline in withstand voltage performance. Note that in the above-described embodiment, the authority of the judgment section does not limit the details of the circuit; for example, in the noise discrimination circuit, the detection signal is simply rectified and the fact that its absolute value is large is utilized. It is also possible to use a configuration in which the digital signal is compared with a set signal using a microprocessor, or a configuration in which digital signal processing is performed using a microprocessor. Each phase vacuum valve IU of the opening/closing device 2l,
1v and 1v each have a ground conductive layer 44, and the power cable 42U. 42V. A Rogowski coil 43U.42W is conductively connected to the external load 12 through the grounding wire 45 of each phase cable, and serves as a current sensor for detecting multiple re-ignition surge currents. 43V. 43- is provided, and the Rogowski coil detects the surge current included in the ground charging current of each phase cable, and the detection signal 42- is sent to the judgment unit 30. Output to. In this configuration, the ground capacitance of the power cable can be used as a high-voltage capacitor for surge detection, and the insulating support structure of the Rogowski coil can be greatly simplified, making the detection device smaller and smaller. It has the advantage of being inexpensive to form. Note that when attempting to detect multiple re-ignition surge voltages, it can be easily detected by connecting a surge detection capacitor whose one end is grounded to the ground conductive layer 44. [Effects of the Invention] As described above, in this invention, a sensor for detecting multiple re-ignition surges that occurs when each phase vacuum valve is opened/closed is provided corresponding to each phase vacuum valve, and multiple re-ignition pulses are detected by the determination section. When it did not, it was determined that the vacuum level of the vacuum valve had decreased and an alarm signal was issued. As a result, by utilizing the property that multiple re-ignition surges no longer occur when the vacuum level of the vacuum valve decreases to the order of 10-' Torr, we have succeeded in reducing the vacuum level before the withstand voltage of the vacuum valve significantly decreases. This enables early detection of each phase vacuum valve. This eliminates the drawback of conventional technology for detecting abnormal discharges, which is that they cannot be detected unless the degree of vacuum drops to such an extent that the withstand voltage performance required for a vacuum bulb cannot be maintained. It is possible to provide a vacuum level drop detection device for a vacuum valve type opening/closing device that can detect a vacuum level drop in the state. In addition, the insulating container of the vacuum valve can also be used as an insulating support material to provide a current sensor or voltage sensor, or the relative ground capacitance of each power cable on the load side can also be used as a high-voltage capacitor and a current sensor or voltage sensor can be installed on the ground wire side. If a voltage sensor is provided, the insulation of the detection sensor for multiple re-ignition surges will be greatly simplified, and the advantage will be that the detection sensor can be made small and inexpensive.

[Brief explanation of drawings]

Figure 1 shows a vacuum valve type opening/closing VT which is an embodiment of this invention.
Fig. 2 is a cross-sectional view of the main parts showing the arrangement of the current sensor in the embodiment, Fig. 3 is a vacuum arc diagram for explaining the principle of the invention. 4 is a waveform diagram showing the generation state of re-ignition surge of an air circuit breaker, Figure 5 is a waveform diagram showing the occurrence state of multiple re-ignition surge of vacuum valve, and Figure 6 is a waveform diagram showing the occurrence state of multiple re-ignition surge of vacuum valve. A time chart showing the operation of the embodiment, Fig. 7 is a schematic diagram showing a different embodiment of the present invention, Fig. 8 is a characteristic line diagram showing factors for reducing the vacuum level of the vacuum valve, and Fig. 9 is a vacuum sensor. 10 is a characteristic line diagram showing the relationship between the degree of vacuum of the vacuum valve and the AC Franciover voltage. FIG. 11 is a configuration diagram showing the first conventional technique. FIG. 13 is a block diagram showing the second conventional technique, FIG. 13 is a block diagram showing the third conventional technique, and FIG. 14 is a block diagram showing the fourth conventional technique. 1: Vacuum Halp, Ill, IV, IN
: Vacuum hull for each phase, 2.3: Contactor (contact) 5: Insulating container, 7: Metal shield, 11: AC power system, 12
: External load, 21: Switchgear, 22: Control unit, 15.2
3.43: Current sensor (detection sensor) 30: Judgment section, 42: Power cape, 44: Ground conductive layer, 45: Ground wire. 11 Figure 3 j A + group 5th piece N C B Tou (Okihi 1st grade) Figure F3 Figure 89 Sacred grass bar 7゛ yen @F pressure (Toke) '$10 Figure 11 cut] l5i3tshiJ certain 14tomo

Claims (1)

[Scope of Claims] 1) Presence or absence of multiple re-ignition surges generated by the vacuum valve based on a current cutting phenomenon and a high frequency arc extinguishing phenomenon to reduce the degree of vacuum in a vacuum valve of a vacuum valve type switchgear connected to an AC power system. The multiple re-ignition surge detection sensor provided corresponding to each phase vacuum valve, the output signal of each of the multiple re-ignition surge detection sensors, and the output signal of the multiple re-ignition surge detection sensor and the vacuum valve type switching device. and a determination unit that receives the opening/closing control signal and determines that a decrease in the degree of vacuum has occurred in the vacuum valve and issues a signal when the multiple re-ignition current is not detected during the opening/closing operation time of the vacuum valve. A device for detecting a decrease in the degree of vacuum of a vacuum valve type switching device, characterized by the following. 2) The degree of vacuum of the vacuum valve type switchgear according to claim 1, wherein the detection sensor comprises either a current sensor or a voltage sensor, and is insulated and supported on the outer periphery of an insulating container of each phase vacuum valve. Drop detection device. 3) Each phase vacuum valve is connected to the load side via a power cable having a ground conductive layer, and a detection sensor is arranged on the ground line side of the ground conductive layer. Item 2. A vacuum degree drop detection device for a vacuum valve type opening/closing device according to item 2.