JPH043612B2 - - 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 grid line and the ground potential of the intermediate shield, and captures changes in the phase difference of the detection signals. In addition to determining the presence or absence of a decrease in the degree of vacuum, a vacuum gap is created between the grid potential member and the intermediate shield that discharges only on either the fixed side or the movable side, which reaches an unbreakable region when the degree of vacuum decreases. By configuring the sensor to detect a decrease in the degree of vacuum, it is possible to reliably detect a decrease in the degree of vacuum at a time when the degree of vacuum is still high (early stage of leakage), and furthermore, the degree of vacuum can be detected at all times while the power is on. This system is designed to enable monitoring, and can be disconnected if a decrease in the degree of vacuum 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, if the degree of vacuum deteriorates to around 10 ^-1 mmHg (13.33 Pa), flashing will occur at 500V.

Conventionally, means for detecting a decrease in the degree of vacuum of 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, and this intermediate shield 2 is 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 provided. 21 is an impedance, 22 is a detector, and the intermediate shield 2 is an impedance 21.
and the ground via a detector 22.
3a, 3b are auxiliary shields, 40 is a bellows, 4
1a 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.

Incidentally, in order to improve the withstand voltage characteristics when the contact is opened, vacuum interrupters are generally constructed so that the electric field distribution state is approximately symmetrical between the fixed side and the movable side. That is, the intermediate shield 2, the auxiliary shields 3a and 3b, and the metal end plate 4.
1a, 41b, etc., the fixed side and the movable side have the same size gap.

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 with 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.

In addition to these problems, since the detection is based on the potential rise of only the intermediate shield 2, in order to avoid the influence of voltage fluctuations in the grid circuit, it is necessary to keep the ground potential _E3 of the intermediate shield 2 almost at the grid potential. It must be detected when the temperature rises to _E1 . Therefore, at the time when 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.

Also, the electrodes 42a, 42b shown in FIG.
In this method, a voltage is applied in that state, and the presence or absence of a decrease in the degree of vacuum is determined by comparing the voltages (see Japanese Patent Publication No. 114-1983). In other words, in the figure, C _V is in an open circuit state. The capacitances of the vacuum interrupter, D _A and C _B are the ground capacitances of the fixed electrode rod 4a and the movable electrode rod 4b, respectively. Now, if vacuum interrupter 1 is in an open state and a ground voltage E _p is applied to it, the terminal voltage E _a between a and e is E _a = E _p The terminal voltage E _b between b and e is E _b = C _V /C _V +C _B E _p . 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 shown in Fig. 7 and Fig. 8 are combined, that is, in Fig. 7, the vacuum I tried to determine the degree.

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 sixth
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 poles are 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, where the load current cannot be cut off even when a drop in the vacuum level is detected, the detection voltage must be increased, and when a drop in the vacuum level is detected, the vacuum level reaches such a level that it cannot be cut off any longer. There is. There is a problem in that the degree of vacuum cannot be constantly monitored while electricity is 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 short gap has a higher discharge starting voltage than the long gap. The short gap had sufficient withstand voltage in the region of around 10 ^-2 mmHg (1,333 Pa).

Based on this knowledge, the present invention first provides a metallic intermediate shield insulated from the electrode,
A vacuum gap is formed between this intermediate shield and either the fixed side or the movable side grid potential member, which discharges when the degree of vacuum is lowered and in a region where it can be disconnected. Then, provide impedance and capacitance between grid potential members, such as between the grid line and the ground, and between the intermediate shield and the ground, respectively,
Furthermore, the detection signal of the ground potential of the grid line obtained through impedance and the detection signal of the ground potential of the intermediate shield obtained through capacitance are compared in terms of phase, and based on the phase difference, it is determined whether the degree of vacuum has decreased. A determining section is provided to perform the determination.

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 space between the intermediate shield and the grid potential member is equivalent to a parallel circuit of a capacitor and a resistor. When the degree of vacuum is normal, the resistance value of the resistor is close to infinity, so for example, the detection signal of the grid potential member obtained via impedance and the detection signal of the intermediate shield obtained via capacitance are in phase. It's on. Here, when the degree of vacuum decreases, the resistance value decreases, so that the phase of the intermediate shield detection signal obtained through the capacitance is delayed, and a phase difference occurs between the detection signals. When this phase difference exceeds a predetermined value, the determining section determines that the degree of vacuum has decreased.

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.
The same reference numerals as 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 short plate 41a side is made to protrude sufficiently longer in the axial direction than the end of the auxiliary shield 3a. The portion is configured to directly face the fixed electrode rod 4a via a gap without sandwiching the auxiliary shield 3a. 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,
This is the maximum distance between members of different potential within 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.

Reference numeral 5 denotes an impedance voltage divider for detecting the ground potential _E1 of the system electric line, and is provided, for example, in the vicinity of the vacuum interrupter 1 between the power supply side electric line and the ground. This impedance voltage divider 5
is the impedance component Z ₁ such as capacitor resistance,
Z ₂ , and in this example a capacitor is used.

6 is a capacitor voltage divider that detects the ground potential of the intermediate shield 2, for example, 0, 2μF,
Consists of 200PF capacitors C ₁ and C ₂ . In addition, a capacitor C ₃ is connected between the intermediate shield 2 and the fixed electrode rod 4a of the vacuum interrupter 1 as shown in FIG.
and a resistor R, and the capacitance of capacitor _C3 when closed is 20PF to 100PF.

Reference numeral 7 denotes a determination unit, and this determination unit 7 generates a square wave that shapes each waveform of the detection potential e ₁ detected by the impedance voltage divider 5 and the detection potential e ₃ detected by the capacitor voltage divider 6 into a square wave. Shaping circuit 71, 7
2, and extract the zero point deviation of the pulse signals output from these square wave shaping circuits 71 and 72.
A zero point deviation pulse generation circuit 73 equipped with a NAND circuit, and a pulse width determination that determines that the degree of vacuum has decreased when the pulse width of the pulse signal from this pulse generation circuit 73 exceeds a predetermined value and issues a determination signal, for example, an alarm. It has a circuit 74.

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 an impedance voltage divider 5 and a capacitor voltage divider 6, respectively, and the detected potentials e ₁ and e ₃ are input to square wave shaping circuits 71 and 72, respectively. When the degree of vacuum is normal, the resistance value of the resistor _R in _the equivalent circuit of FIG.
The zero points of each pulse signal from 2 are aligned. Therefore, since the pulse width of the pulse signal from the pulse generation circuit 73 is less than a predetermined value, the pulse width determination circuit 74 does not output a determination signal for lowering 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 Patsien curve shown in FIG. Since this is the maximum distance between members with different potentials, discharge first begins at this gap. As a result, the resistance value of the resistor R decreases, and the phase of the detected potential _e3 of the capacitor voltage divider 6 becomes delayed as shown in FIG. As a result, the pulse signals from the square wave shaping circuit 72 are as shown in FIGS.
As shown in FIG. 3, the phase is delayed with respect to the pulse signal from the square wave shaping circuit 71,
As shown in FIG. 4C, a pulse signal having a pulse width corresponding to the zero point deviation of each pulse signal is output. When the pulse width of this pulse signal exceeds a predetermined value, the pulse width determination circuit 74 outputs a determination signal for lowering the degree of vacuum.

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, it is possible to avoid flash shorting on the fixed side or the movable side. If it is either one of the movable sides, it is not limited to the electrode rod, but the metal end plate 41
A vacuum gap may be provided between the system potential members such as a and 41b and the intermediate shield 2, which discharges in a vacuum region that can be cut off when the degree of vacuum is reduced. 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, since the configuration compares the phase 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 the change in the phase difference to detect a decrease in the degree of vacuum, voltage fluctuations in the grid electrical circuit can be detected. It can be detected at the stage of local discharge due to a decrease in the degree of vacuum, without being affected by noise or weight noise. As a result, it is possible to detect the initial stage of a leaf when the degree of vacuum decreases, so it can be handled in a vacuum region with a withstand voltage higher than the operating voltage range (voltage that can be shattered), so it can be shattered after detecting a decrease in vacuum. 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. 1, and Fig. 3 is a waveform diagram showing detected potentials from an impedance voltage divider and a capacitor voltage divider. , Figures 4A to C are
Figure 5 is a curve diagram showing the relationship between the degree of vacuum and the discharge starting voltage between gaps when the vacuum gap is different, Figure 6 is a curve diagram showing Patsien's law, and Figure 7 is a diagram of pulse waveforms in each judgment section. , and FIG. 8 are principle diagrams showing the principle of a conventional vacuum level drop detection device. 1...Vacuum interrupter, 2...Intermediate shield, 3a, 3b...Auxiliary shield, 4a...Fixed electrode bar, 4b...Movable electrode bar, 5...Impedance voltage divider, 6...Capacitor voltage divider, 7... ...Judgment unit, 71, 72...Square wave shaping circuit, 73...
Zero point deviation pulse generation circuit, 74...Pulse width determination 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 electrode 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, and at least the above-mentioned 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, and the intermediate shield is connected to either the fixed side or the movable side. A vacuum gap is formed between one of the grid potential members, which discharges in a vacuum region that can be cut off when the degree of vacuum decreases, and an impedance provided between the grid potential member and the ground is connected to the A capacitance provided between the intermediate shield and the ground, a detection signal of the ground potential of the grid potential member obtained via the impedance, and a detection signal of the ground potential of the intermediate shield obtained via the capacitance are determined in terms of phase. A device for detecting a decrease in the degree of vacuum of a vacuum interrupter, comprising a determination unit that compares the phase difference and determines whether or not the degree of vacuum has decreased based on the phase difference.