JPH043613B2 - - 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.

B. Summary of the Invention The present invention is a device for detecting a decrease in the degree of vacuum in a vacuum interrupter equipped with an intermediate shield, which detects the ground potential of a system line and the ground potential of an intermediate shield, and detects a change in waveform distortion between the detected signals. In addition to determining the presence or absence of a decrease in the degree of vacuum by detecting By installing a vacuum gap to detect a decrease in vacuum level, it is possible to reliably detect a decrease in vacuum level while the vacuum level is still high (early stage of leakage). The vacuum level can be monitored at all times, and it can be turned off even after a decrease in the vacuum level is detected.

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 a decrease in the degree of vacuum due to an increase in the number of shear breaks, the degree of vacuum may also decrease due to vacuum leakage from bellows, airtight joints, etc., although this is very rare. A vacuum interrupter (current interrupter) has a reduced degree of vacuum, resulting in a decrease in interrupter performance as a vacuum interrupter, and eventually becomes unable to interrupt the interrupter. Therefore, it is required to regularly or constantly check the degree of vacuum. Moreover, it is desired that the vacuum interrupter can accurately and easily test the degree of vacuum in the energized state after being assembled with an operating mechanism to form a vacuum interrupter.

On the other hand, 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 FIG. 6, the horizontal axis shows the internal pressure of the vacuum interrupter, and the vertical axis shows the discharge starting voltage. In the figure, the solid line (partially broken line) m shows the characteristics when the vacuum gap is 10 mm. As can be seen from FIG. 6, if the degree of vacuum inside the vacuum interrupter is a high vacuum of 10 ^-4 mmHg (13.33 mPa) or less, the discharge starting voltage is extremely high. However, when the degree of vacuum deteriorates to around 10 ^-1 mmHg (13.33Pa)
It flashes at 500V.

A conventional means for detecting a decrease in the degree of vacuum in a vacuum interrupter using such a law is known, and an example thereof is shown in FIGS. 7 and 8.

First, the system shown in FIG. 7 attempts to determine the degree of vacuum by detecting the rise in ground potential of the intermediate shield.

In the figure, 1 is a vacuum interrupter, and 2 is an intermediate shield. This intermediate shield 2 is provided insulated from grid potential members (members having the same potential as the grid circuit) such as the fixed electrode rod 4a and the movable electrode rod 4b. It is being 21 is an impedance, 22 is a detector, and the intermediate shield 2 is connected to the ground via the impedance 21 and the detector 22. 3
a, 3b are auxiliary shields, 40 is a bellows, 41
A and 41b are metal end plates, and 42a and 42b are electrodes. Further, 43 and 44 are an insulating cylinder and a sealing fitting, respectively, and constitute a vacuum container together with the metal end plates 41a and 41b.

In such a configuration, when vacuum deterioration occurs, the insulation between the intermediate shield 2 and the grid potential member is broken, the potential of the intermediate shield 2 rises to almost the grid potential, and as a result, the detector 22 receives electricity. A signal is provided so that a decrease in vacuum can be detected.

By the way, vacuum interrupters are generally constructed so that the electric field distribution state on the fixed side and the movable side is almost symmetrical in order to improve the withstand voltage characteristics when the contact is opened. That is, the intermediate shield 2, the auxiliary shields 3a and 3b, and the metal end plate 41.
A, 41b, etc., the vacuum gap has the same size gap on the fixed side and the movable side.

For this purpose, in the means shown in FIG. 7, the fixed side and the movable side are constructed symmetrically as described above, so that the intermediate shield 2 and both the fixed side and the movable side can be connected at almost the same degree of vacuum. Discharge occurs in each case. Therefore, even if a decrease in the degree of vacuum is detected in a vacuum region that can be cut off and the operating mechanism (not shown) is activated to open the electrodes 42a and 42b, the fixed side and the movable side are connected via the intermediate shield 2. In the end, the current cannot be cut off because the current is flashing.

Furthermore, in addition to these problems, intermediate shield 2
Since the detection is based on a rise in the potential of the grid, in order to avoid the effects of voltage fluctuations in the grid circuit, detection should be performed when the ground potential _E3 of the intermediate shield 2 rises to approximately the grid potential _E1 . I have to take care of it. For this reason, the current situation is that by the time a decrease in the degree of vacuum is detected, the degree of vacuum has already decreased to such an extent that even the rated load current cannot be cut off.

In addition, the one shown in FIG. 8 opens the electrodes 42a and 42b, applies a voltage in that state, and compares the voltages to determine whether or not the degree of vacuum has decreased (Japanese Patent Publication No. 114-1981). In other words, in the figure, C _V is the capacitance of the vacuum interrupter in the open state, and C _A and C _B are the ground capacitances of the fixed electrode rod 4a and the movable electrode rod 4b, respectively. Vacuum interrupter 1 is now open,
If we apply the ground voltage E _p to this, the terminal voltage _E a between a and e is E _a = E _p and the terminal voltage E _b between b and e is E _b = C _V / C _V + C _B E _p . Become. That is, E _a > E _b . However, if the vacuum interrupter 1 has a vacuum failure, there will be an arc discharge between a and b and conduction will occur, and the arc voltage in this case is less than a few tens of volts, which is sufficiently small compared to the applied voltage E _p , so E _a ≒ E _b It can be considered as Therefore, when the vacuum interrupter is open, if E _a > E _b , it is normal, and if E _a ≈ E _b , it can be determined that the vacuum is defective. In practice, each terminal voltage is measured using a capacitor voltage divider for safety reasons.

However, this method has a problem in that it is impossible to constantly monitor the degree of vacuum while electricity is being applied because the detection is performed in an open state.

By the way, the state in which the techniques of FIG. 7 and FIG. 8 are combined, that is, in FIG. 7, not only the potential of the intermediate shield but also the grid potential is considered, and based on both the intermediate shield potential and the grid potential, An attempt was made to determine the degree of vacuum.

In other words, by taking the grid potential into consideration and detecting the intermediate shield potential using this as a reference, it is attempted to eliminate the adverse effects of voltage fluctuations.

However, even with this, the seventh
A similar problem arose as in the case of the means shown in the figure. That is, since the fixed side and the movable side are constructed symmetrically, electric discharge occurs between the intermediate shield 2 and both the fixed side and the movable side at approximately the same degree of vacuum, causing the electrodes 42a and 42b to Even if the circuit is opened, a flashover occurs between the fixed side and the movable side via the intermediate shield 2, and the current cannot be cut off.

D Problems to be Solved by the Invention As described above, in the conventional technology, as the degree of vacuum decreases, flashover occurs between the intermediate shield and both the fixed side and the movable side at approximately the same degree of vacuum. In order to avoid the effects of voltage fluctuations, etc., the load current cannot be cut off even when a drop in the vacuum level is detected, and the detection voltage must be increased, and when a drop in the vacuum level is detected, the vacuum level has reached such a level that it cannot be cut off anymore. . There was a problem in that the degree of vacuum could not be constantly monitored while electricity was being applied.

The present invention has been made to solve these problems.

E Means for Solving the Problems The inventors of the present invention studied the discharge phenomenon in a vacuum interrupter and obtained the characteristics shown in FIG. 5. FIG. 5 shows the vacuum interrupter internal pressure on the horizontal axis and the discharge starting voltage on the vertical axis. In FIG. 5, solid line m ₁ , solid line m ₂ and solid line m ₃ indicate the characteristics of vacuum gaps A, B and C, respectively, and 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 5, 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. The short gap had sufficient withstand voltage in the region of around 10 ^-2 mmHg (1.333Pa).

Based on this knowledge, the present invention first provides a metallic intermediate shield insulated from the electrode, and creates a space between the intermediate shield and the system potential member on either the fixed side or the movable side to reduce the degree of vacuum. Once in a while, a vacuum gap is formed that discharges in the area where it can be disconnected. Then, a first impedance and a second impedance are provided between the grid potential members, for example, between the grid line and the ground, and between the intermediate shield and the ground, respectively, and further, the ground potential of the grid line obtained through the first impedance. A determining unit is provided for extracting a waveform distortion component of a detection signal of the ground potential of the intermediate shield obtained through the second impedance in response to the detection process, and determining whether or not the degree of vacuum has decreased based on the waveform distortion component. .

F. Effect When the degree of vacuum in the vacuum interrupter decreases during energization, discharge begins at the long gap provided on either the fixed side or the movable side before reaching the uninterruptible region. At this time, no discharge occurs in the other vacuum gap (short gap), and the short gap is not induced to discharge by the discharge in the long gap. On the other hand, the discharge occurs intermittently within one cycle of the grid voltage. That is, one cycle includes a discharge time and a discharge stop time, and therefore the waveform of the ground potential of the intermediate shield is distorted with respect to the waveform of the ground potential of the grid line. Since the proportion occupied by the discharge time increases as the degree of vacuum decreases, it is possible to determine whether or not the degree of vacuum has decreased by extracting the waveform distortion between detected potentials.

G Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an equivalent circuit of the circuit in FIG. 1. The same reference numerals in FIG. 7 indicate the same parts. In this embodiment, the axial length of the auxiliary shield 3a is made small, and the end of the intermediate shield 2 on the fixed end plate 41a side is made to protrude sufficiently longer than the end of the auxiliary shield 3a in the axial direction. Part is auxiliary shield 3
The fixed electrode rod 4a is directly opposed to the fixed electrode rod 4a through a gap without sandwiching the electrode rod 4a. The gap length l of the gap is a length that allows discharge in a vacuum region that can never be cut off when the degree of vacuum decreases, and is the maximum distance between members of different potentials in the vacuum interrupter 1.

Note that when electrons fly between members with different potentials, they fly in a direction perpendicular to the equipotential lines, so the distance described here means the flight distance of the electrons. In the figure, 4b is a movable electrode rod.

5 is a first circuit that detects the ground potential _E1 of the grid line.
The impedance voltage divider is provided, for example, in the vicinity of the vacuum impedance 1 between the power supply side electric circuit and the ground. This impedance voltage divider 5 is composed of impedance components Z ₁ and Z ₂ such as capacitors and resistors, and in this example, a capacitor is used.

6 is a second circuit for detecting the ground potential of the intermediate shield 2;
are impedance voltage dividers, e.g.
It consists of capacitors C ₁ and C ₂ of 0.2μF and 200P ^F.
Note that the second impedance voltage divider 6 is not limited to using a capacitor. Also, the intermediate shield 2 and the fixed electrode rod 4 of the vacuum interrupter 1
A is represented by a parallel circuit of a capacitor _C3 and a resistor R, as shown in FIG. 2, and the capacitance of the capacitor _C3 when closed is ^20PF to ^100PF .

Reference numeral 7 denotes a determination unit, which takes out the waveform distortion of the detection potential e 3 detected by the second impedance voltage divider 6 with respect to the detection potential e ₁ detected by the first impedance voltage divider 5, and converts the waveform distortion into the detection potential e ₃ detected by the second impedance voltage divider 6. It has a function to determine whether the degree of vacuum has decreased based on this. In this example, this determination section includes an amplifier 71 that amplifies the detected potential e ₃ , and when the detected potential e ₁ and the output from the amplifier 71 are inputted, a differential amplifier 72 and the peak value of the output voltage from the differential amplifier 72 . It has a determination circuit 73 that issues a determination signal, for example, an alarm, to determine whether the degree of vacuum has decreased when the value exceeds a predetermined value.

Next, the operation of the above embodiment will be described.

The ground potential of the grid circuit and intermediate shield is
The voltages are divided by impedance voltage dividers 5 and 6, respectively, and the detected potential e ₁ of the first impedance voltage divider 5 is input to the differential amplifier 72 as is. The detected potential _e3 of the second impedance voltage divider 6 is amplified by the amplifier 71 so that the amplitude is equal to that of the detected potential _e1 , for example.
e ₃ ′=k×e ₃ , and the difference between this potential e ₃ ′ and the detected potential e ₁ is amplified by the differential amplifier 72 and sent to the determination circuit 7.
3 is input. When the degree of vacuum is normal, no discharge occurs between the intermediate shield 2 and the system potential member, so the waveforms of the detected potentials e ₁ and e ₃ are uniform, and the output voltage from the differential amplifier 72 is approximately zero. be. Therefore, in this case, the determination circuit 73 does not output a determination signal indicating a decrease in the degree of vacuum.

When the degree of vacuum decreases now, discharge begins in the gap between the intermediate shield 2 and the fixed electrode rod 4a.
The reason for this is that in the region around 10 ^-2 mmHg of the pressure curve shown in Fig. 5, discharge occurs from a place where the gap length is large, and the gap length l is the same as the vacuum interrupter 1. Since this is the maximum distance between members of different potential within the gap, discharge first begins at this gap. Regarding this discharge, rather than discharging continuously, there is a discharge time and a discharge stop time in one cycle of the grid voltage, and as the degree of vacuum decreases, the proportion occupied by the discharge time increases. FIG. 3A is a waveform diagram showing the detected potentials e ₁ and e ₃ , and the waveform of the detected potential e ₃ is distorted due to discharge. Figure 3B is a waveform diagram of the difference voltage between the potential e ₃ ' obtained by amplifying the detection potential e ₃ and the detection potential e ₁ , and the waveform of the potential e ₃ ' is different from the waveform of the detection potential e ₁ . Because of the distortion, a waveform approximating a trapezoid appears. The sloped portion of the voltage waveform shown in FIG. 3B is a portion caused by waveform distortion of the detected potential _e3 , and therefore corresponds to the discharge time, and the remaining horizontal portion corresponds to the discharge stop time. Regarding this voltage waveform, as the discharge time increases, the horizontal portion becomes shorter and its height increases, approaching a sine wave.

Figure 4 A and B are vacuum levels of 1.2×10 ^-2 Tor and 2×, respectively.
This is an output waveform diagram of the differential amplifier 72 at 10 ^-2 Torr, and it can be seen from this diagram that the amount of waveform distortion increases as the degree of vacuum decreases. Therefore, the differential amplifier 7
Since the peak value of the output voltage from 2 increases as the degree of vacuum decreases, by setting a reference value in the determination circuit 73, when the peak value exceeds the reference value, it is possible to detect the decrease in the degree of vacuum. A determination signal is output.

In extracting the waveform distortion in the above, instead of managing the peak value of the output voltage from the differential amplifier 72, the constant voltage (horizontal portion) time of the output voltage may be managed; The integral amount of the output voltage may also be managed.

In the above-mentioned embodiment, a gap having the maximum distance is provided between the fixed electrode rod 4a and the intermediate shield 2, but in the present invention, in order to avoid flash shorting on the fixed side and the movable side, the gap is provided between the fixed electrode rod 4a and the intermediate shield 2. If it is either one of the movable sides, it is not limited to the electrode rod, but the metal end plate 41
System potential and members such as a and 41b and intermediate shield 2
A configuration may also be provided in which a vacuum gap is provided between the two and the vacuum gap that discharges electricity in a vacuum region that can be cut off when the degree of vacuum decreases. Note that in the present invention, detection can be performed not only in the closed state but also in the open state, and in this case, it is necessary to provide the gap on either the fixed side or the load side, which is the charging part side.

H. Effects of the Invention As described above, according to the present invention, a discharge occurs between the intermediate shield and the grid potential member on either the fixed side or the movable side in a region where the degree of vacuum is reduced and it is possible to Since a vacuum gap is formed, an electric discharge occurs on either the fixed side or the movable side at the beginning of a leak (high vacuum) when the degree of vacuum decreases. At this time, the other vacuum gaps have sufficient withstand voltage. Moreover, the configuration compares the waveforms of the detection signal of the ground potential of the grid potential member and the detection signal of the ground potential of the intermediate shield, and detects a decrease in the degree of vacuum by capturing the change in waveform distortion between the detection signals. It can be detected at the stage of local discharge due to a decrease in the degree of vacuum without being affected by voltage fluctuations in the electric circuit or weight noise. As a result, it is possible to detect the initial stage of a leak due to a decrease in vacuum level, so it can be handled in a vacuum range with a withstand voltage higher than the working voltage range (voltage that can be interrupted), so it can be interrupted after detecting a decrease in vacuum level. be able to. Furthermore, since a decrease in the degree of vacuum can be detected in the closed state, the degree of vacuum can be constantly monitored while electricity is being supplied.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit to the circuit in FIG. Waveform diagram showing , Figure 4 A, B
5 is a waveform chart showing an example of the detected potential difference, FIG. 5 is a curve chart showing the relationship between the degree of vacuum and the discharge starting voltage between the gaps when the vacuum gap is different, FIG. 6 is a curve chart showing Patsien's law, and FIG. FIG. 7 and FIG. 8 are principle diagrams showing the principle of a conventional vacuum level drop detection device. DESCRIPTION OF SYMBOLS 1... Vacuum interrupter, 2... Intermediate shield, 3a, 3b... Auxiliary shield, 4a... Fixed electrode bar, 4b... Movable electrode bar, 5... First impedance voltage divider, 6... Second Impedance voltage divider, 7... Judgment section, 71... Amplifier, 72...
... Differential amplifier, 73 ... Judgment circuit.

Claims (1)

[Scope of Claims] 1. A vacuum container is formed by closing both ends of a cylinder with end plates, and a fixed electrode rod is airtightly introduced into the vacuum container from one end plate, and a fixed electrode rod is inserted from the other end plate. A movable electrode rod that can be moved toward and away from the vacuum chamber is airtightly introduced through a bellows, and a pair of fixed and movable electrodes that can be moved toward and away from each other is provided at each inner end of these electrode rods. In a device for detecting a decrease in the degree of vacuum in a vacuum interrupter capable of freely opening and closing a power grid circuit, the intermediate shield made of metal surrounding the outer periphery of an electrode is provided insulated from the electrode, the intermediate shield and either a fixed side or a movable side. A first impedance is provided between the grid potential member and the ground, forming a vacuum gap that discharges in a vacuum region that can be disconnected when the degree of vacuum is reduced, and the grid potential member and the ground. and a second impedance provided between the intermediate shield and the ground, and a signal obtained through the second impedance in response to a detection signal of the ground potential of the grid potential member obtained through the first impedance. 1. A vacuum level drop detection device for a vacuum interrupter, comprising a determination unit that extracts a waveform distortion component of a detection signal of a ground potential of an intermediate shield and determines whether or not there is a vacuum level drop based on the waveform distortion component.