JPH043614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a vacuum level drop detection device for a vacuum interrupter, and in particular detects a vacuum level drop using an impedance change between a grid potential member and an intermediate shield. Regarding equipment.

B. Summary of the Invention The present invention provides a vacuum level drop detection device for a vacuum interrupter that detects a vacuum level drop using an impedance change between a grid potential member and an intermediate shield. Determine the decrease in vacuum level based on changes in the waveform,
By storing this judgment signal in memory, it is possible to detect the decrease in the degree of vacuum before it reaches a pressure that cannot be cut off, and also to be able to reliably detect even a rapid decrease in the degree of vacuum.

C. Prior Art Vacuum interrupters inherently have a longer life both electrically and mechanically than other switching devices, and require almost no maintenance or inspection. However, in addition to the degree of vacuum decreasing over time due to an increase in the number of times the sheath is broken, the degree of vacuum may decrease rapidly due to vacuum leakage from bellows, airtight joints, etc., although this is very rare. .
The vacuum interrupter (current interrupter) has reduced interrupting performance due to a decrease in its degree of vacuum, and eventually becomes unable to interrupt the interrupter. Therefore, the vacuum interrupter is required to periodically or constantly check its vacuum degree.

Moreover, it is desired that the vacuum interrupter can accurately and easily test the degree of vacuum in a charged state after being assembled with an operating mechanism to form a vacuum interrupter.

By the way, the degree of vacuum of the vacuum interrupter and the discharge starting voltage of the vacuum gap have a relationship similar to Patsien's law, as shown in FIG. In Figure 2, the horizontal axis shows the internal pressure of the vacuum interrupter, and the vertical axis shows the discharge starting voltage.The solid line (partly broken line) in the figure shows the characteristics when the vacuum gap is 10 mm. As can be seen from Figure 2, if the degree of vacuum inside the vacuum interrupter is a high vacuum of 10 ^-4 mmHg (13.33mPa) or less, the discharge starting voltage is extremely high. However, when the degree of vacuum deteriorates to around 10 ^-1 mmHg (13.33Pa), the voltage drops to 500V.

Conventionally, in order to monitor the degree of vacuum in the charging state by utilizing such a law, the voltage between the open electrodes of the vacuum interrupter or between the grid potential members such as electrodes and the intermediate shield in the closed state has been proposed. There are devices that detect a decrease in the degree of vacuum from changes in ground voltage.

FIG. 3 shows a case where detection is performed from the voltage change of the load side electrode when the contact is opened. The vacuum interrupter 1 has a fixed electrode 2 on the grid line side and a movable electrode 3 on the load side. The vacuum level drop detection device for this vacuum interrupter 1 includes a voltage detector 4 which is a series circuit of impedance elements that detects the ground voltage _E2 level of the movable electrode 3, and A determination circuit 5 is provided which determines whether the degree of vacuum has decreased depending on whether the detection level has increased to a level corresponding to the system line voltage (voltage of the fixed electrode 2) _E1 .

In such a configuration, as the degree of vacuum in the vacuum interrupter 1 decreases, the discharge starting voltage between the electrodes 2 and 3 decreases, and eventually a flashover occurs between the electrodes 2 and 3. That is, as the degree of vacuum decreases, a discharge occurs between electrodes 2 and 3, and the voltage E ₂ of electrode 3 increases until it becomes almost equal to the voltage E ₁ of electrode 2, and the voltage
A decrease in the degree of vacuum is detected by detecting a rise in _E2 .

FIG. 4 shows a case where detection is performed from a change in the ground voltage of the intermediate shield. In the figure, the ground voltage E ₃ of the intermediate shield (made of metal) 6 is detected by the voltage detector 7, and based on the change in this detection level, an output for determining whether or not the degree of vacuum has decreased is obtained from the determination circuit 5.

Compared to the one shown in FIG. 3, this detection device can detect a decrease in the degree of vacuum as long as the electrode 2 is charged regardless of whether the electrodes 2 and 3 are in an open or closed state.

D Problems to be solved by the invention The conventional vacuum level drop detection device
It detects the voltage E ₂ or the voltage E ₃ of the intermediate shield 6, and in both cases, a decrease in the degree of vacuum is determined from the change in the absolute value of the ground voltage. For this reason, it becomes susceptible to fluctuations in the system potential and superimposed high-frequency noise, and there is a problem in that it is not possible to detect the early stage of a decrease in the degree of vacuum, which the vacuum interrupter has the ability to interrupt.

In other words, if the vacuum level drop detection sensitivity is increased, erroneous detection will occur due to system potential fluctuations and noise, and conversely, if the detection sensitivity is decreased, there will be a flash short between electrodes 2 and 3 or between electrode 2 and the intermediate shield. Since it cannot be detected until the vacuum interrupter is in the uninterrupted state, the vacuum interrupter is already in the uninterruptible state.

In addition, with conventional detection devices, if the degree of vacuum rapidly decreases due to vacuum leakage due to a pinhole, etc. in the bellows, and the pressure rises to near atmospheric pressure, there is a problem that detection of a decrease in the degree of vacuum may fail. It was hot. In other words, when the degree of vacuum decreases to near atmospheric pressure, as shown in the characteristics of the vacuum cleaner shown in Fig. 2, at the atmospheric pressure point P, the discharge starting voltage that once decreased recovers according to the characteristics, and the withstand voltage increases. Since the voltage characteristics are good to some extent, for example, if the operating voltage of the vacuum interrupter is lower than the system potential V in FIG. 2, the judgment output of the detection device will be an erroneous judgment that the degree of vacuum is good.

E Means for Solving the Problems The present invention has been made in view of the above problems.
a first detector that detects a ground voltage waveform of a grid potential member connected to the vacuum interrupter; a second detector that detects a ground voltage waveform of an intermediate shield;
A determination circuit that obtains a determination signal of a decrease in the degree of vacuum of the vacuum interrupter based on a change in the detection waveform of a second detector relative to the detection waveform of the first detector, and a memory holding circuit that stores and retains the determination signal of this determination circuit. This is a vacuum level drop detection device equipped with the following.

F Effect By storing the determination output of the determination circuit, the detection output is prevented from disappearing even when the degree of vacuum rapidly decreases to atmospheric pressure.

Further, by using the detected waveform of the grid potential member as a comparison standard for the detected waveform of the second detector, the effects of fluctuations in the grid potential and superimposed high-frequency noise are eliminated.

In addition, detection by comparing detection waveforms, that is, comparison of detection signals is not limited to amplitude (voltage), but also phase difference,
By comparative detection including waveform distortion, it is possible to detect a decrease in the degree of vacuum before it progresses to the point where it cannot be cut off. This point will be explained in detail below.

As a result of researching the correlation between the degree of vacuum and the voltage waveform of the intermediate shield in a vacuum interrupter, the inventors of the present invention found from experimental results that even in the early stages of decreasing the degree of vacuum, a phase change and a change in the amount of waveform distortion appear in the detected waveform. I was able to obtain it, and I was also able to obtain it as a calculation result from the equivalent circuit.

As an example of this experiment, the detected voltage waveform e ₃ of the intermediate shield 6 and the detected voltage waveform e ₁ of the electrode _{2 in} FIG. 4 mentioned above were observed. I got what is shown below. FIG. 5 shows waveforms e ₁ and e ₃ when a local discharge occurs at the beginning of a decrease in the degree of vacuum (degree of vacuum P ₁ shown in FIG. 2). In this case, the intermediate shield voltage waveform e ₃ has a smaller change in amplitude than the waveform e ₁ , causing waveform distortion and phase shift.

FIG. 6 shows waveforms e ₁ and e ₃ when the degree of vacuum is further reduced (degree of vacuum P ₂ shown in FIG. 2). At this time, discharge and flashover occur in each vacuum gap, and waveform _e3 with respect to waveform _e1 has waveform distortion and phase shift (delay), and the peak value increases, causing waveform _e3 to become close to waveform _e1. becomes the amplitude.

Regarding the relationship between these changes in waveform and the change in the degree of vacuum, the fact that it can be considered to be based on the change in impedance between the electrode 2 and the intermediate shield 6 is as follows.
This was also confirmed by computer calculations from the equivalent circuit shown in FIG. In FIG. 7, voltage E ₁ of electrode 2 is detected as voltage e ₁ by voltage division of impedance elements Z ₁ and Z ₂ , and impedance between electrode 2 and intermediate shield 6 is determined by capacitance C ₃ and discharge resistance R.
The voltage E ₃ of the intermediate shield 6 is divided into the voltage e ₃ by the capacitors C ₂ and C ₁ .
When the decrease in the degree of vacuum is assumed to be a decrease in the discharge resistance R, the phase shift of the voltage e ₃ with respect to the voltage e ₁ is C ₃ =100 pF, and the calculation results shown in FIG. 8 are obtained. In addition, the figure also shows the relative voltage due to the change in resistance R.
It also shows the level change of e ₃ (intermediate shield voltage). From the above experimental examples and the calculation results from the equivalent circuit, it is possible to detect a decrease in the degree of vacuum at its initial stage (when the vacuum interrupter has the ability to It was found that the detection can be performed at a certain degree (degree of vacuum).

G. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. Reference numeral 1 denotes a vacuum interrupter that includes a metal intermediate shield 6 insulated from the fixed electrode 2 and the movable electrode 3. As a vacuum level drop detection device for this vacuum interrupter 1, a first detector 8 is composed of a series circuit of impedance elements Z ₁ and Z ₂ that detects a partial voltage waveform of the ground voltage of the fixed electrode 2 connected to the system line.
and a second detector 7 consisting of a series circuit of capacitors C ₁ and C ₂ that detects the divided voltage waveform of the ground voltage of the intermediate shield 6, and a second detector 7 with the detected waveform of the first detector 8 as a comparison reference input a digital or analog phase shift determination circuit 9 that detects that the change in phase shift of the detected waveform of the detector 7 has exceeded a predetermined angle; and a storage circuit 10 that stores the determination output of the determination circuit 9. Simultaneously with the storage operation of the storage circuit 9, an alarm device 11 is provided which generates an alarm for a decrease in the degree of vacuum.

In such a configuration, as long as electrode 2 is in a charged state, a ground voltage appears on intermediate shield 6, regardless of whether electrodes 2 and 3 are in an open or closed state. A detected waveform appears at 7. The detection waveforms of these two detectors 8 and 7 are similar to the system line voltage waveform, and both detection waveforms change at the same rate when the line voltage fluctuates and superimposed high frequency noise occurs. Therefore, by using the voltage _e1 as a reference for determining the degree of vacuum reduction based on the change in the detected waveform by the determination circuit 9, detection is performed in which the effects of voltage fluctuations and noise are removed.

Then, the determination circuit 9 determines from the amount of change in the phase shift between the detected voltages e ₁ and e ₃ whether the vacuum level has already started to decrease before it can no longer be cut off (as shown in Figure 2).
Detected at around P ₁ ). Furthermore, memory holding circuit 1
By storing the judgment output from the judgment circuit 9 using 0, even when the vacuum level of the vacuum interrupter rapidly decreases and reaches atmospheric pressure, the judgment signal of the decrease in the vacuum level is maintained, and the alarm 11 Continue the alarm operation.

In addition, in the embodiment, a case is shown in which the determination of the degree of vacuum is determined from a change in phase shift, but this may be determined from a change in waveform distortion or a combination of both, or even a change in amplitude. Of course, a more reliable judgment can be obtained.

In addition, in the embodiment, the structure of the vacuum interrupter 1 is provided with a vacuum gap between the intermediate shield and the grid potential member that discharges in a vacuum range where the vacuum level can be cut off even when the vacuum level is low. can be made even more reliable. The reason for this will be explained in detail below.

The present inventors investigated the discharge phenomenon in a vacuum interrupter and obtained the characteristics shown in FIG. 9. FIG. 9 shows the vacuum interrupter internal pressure on the horizontal axis and the discharge starting voltage on the vertical axis. In FIG. 9, solid lines 14, 15, and 16 indicate the characteristics of vacuum gaps A, B, and C, respectively, and the gap lengths have a relationship of A>B>C.

In general, it was known that long gaps have a higher discharge starting voltage than short gaps, but as can be seen from Figure 9, this phenomenon occurs in high vacuum or near atmospheric pressure, and is 10 ^-2 mmHg. In the region around (1.333 Pa), on the other hand, the discharge start voltage is higher in the short gap than in the long gap.

Because of this phenomenon, that is, the phenomenon in which the discharge starting voltage between the long gap and the short gap is reversed, the gap length between the fixed electrode 2 and the intermediate shield 6 causes the discharge to occur in the vacuum range where the vacuum level can be cut off at the beginning of the vacuum level drop. The opening gap between the fixed electrode 2 and the movable electrode 3 and the gap between the movable electrode 3 and the intermediate shield 6 are assumed to be short gaps (for example, the solid line 16 in FIG. 9). By this,
As shown in Figure 9, it is possible to obtain a discharge to the intermediate shield in the vacuum region S ₁ or S ₂ , which can be cut off, and this results in a large change in the detected waveform at the beginning of the vacuum reduction. This makes detection even more reliable.

H. Effects of the Invention As described above, according to the present invention, a decrease in the vacuum degree of the vacuum interrupter is detected from the deformation of the ground voltage waveform of the intermediate yield with respect to the ground voltage waveform of the line, and this detection signal is stored and retained. , it is possible to detect the initial stage of vacuum deterioration (before it progresses to an unstoppable level). Furthermore, by storing the detection signal, it is possible to reliably obtain a detection output and an alarm even when the degree of vacuum drops rapidly. Furthermore, by using the vacuum interrupter with a vacuum gap that discharges at the beginning of a decrease in the degree of vacuum, detection of the beginning of a decrease in the degree of vacuum can be more reliably detected.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a characteristic diagram based on Patsien's law, Figures 3 and 4 are circuit diagrams of conventional detection equipment, and Figures 5 and 6 are intermediate shield voltage detection waveforms relative to line voltage detection waveforms due to progress of vacuum reduction. Figure 7 is an equivalent circuit diagram for determining changes in the detected waveform due to changes in impedance of the intermediate shield, Figure 8 is a characteristic diagram of phase and amplitude obtained from Figure 7, and Figure 9 is a diagram showing the change in the detected waveform due to impedance changes in the intermediate shield. FIG. 6 is a characteristic diagram showing the relationship between the internal pressure of the vacuum interrupter and the discharge starting voltage when the gap lengths are different. 1... Vacuum interrupter, 2... Fixed electrode, 3
...Movable electrode, 6...Middle shield, 7...Second
Detector, 8...first detector, 9...phase determination circuit, 10...memory holding circuit, 11...alarm.

Claims (1)

[Scope of Claims] 1. In a device for detecting a decrease in the degree of vacuum of a vacuum interrupter that is provided with a metal intermediate shield insulated from a grid potential member, the ground voltage waveform of a grid potential member connected to the vacuum interrupter is detected. A first detector detects the ground voltage waveform of the intermediate shield, a second detector detects the ground voltage waveform of the intermediate shield, and a vacuum is determined from the amount of change in the detected waveform of the second detector with respect to the detected waveform of the first detector. 1. An apparatus for detecting a decrease in the degree of vacuum of a vacuum interrupter, comprising: a determination circuit that obtains a determination signal of a decrease in the degree of vacuum of the interrupter; and a memory holding circuit that stores and retains the determination signal of the determination circuit. 2. Claim 1, characterized in that the vacuum interrupter is provided with a vacuum gap between the intermediate shield and the grid potential member, which discharges in a vacuum range where the vacuum level can be cut off when the vacuum level is lowered. A device for detecting a decrease in the degree of vacuum of a vacuum interrupter as described in 2.