JPH0434247B2 - - 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 provides a device for detecting a decrease in the degree of vacuum in a vacuum interrupter equipped with an intermediate shield. In addition to providing a vacuum gap that discharges only on either the side or the movable side, the difference between the detected amount of ground potential of the intermediate shield and the detected amount of ground potential of the system line is corrected according to the open/closed state of the vacuum interrupter. By configuring the system to detect a decrease in the degree of vacuum based on the system, it is possible to reliably detect a decrease in the degree of vacuum at a time when the degree of vacuum is still high (at the beginning of a leak), and to detect whether the vacuum interrupter is open or closed. It is possible to accurately detect a decrease in the degree of vacuum regardless of the situation, and furthermore, it is possible to constantly monitor the degree of vacuum while the power is on, and it can be turned off even after a decrease in the degree of vacuum is detected. It is something.

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. 7, 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. 7, if the degree of vacuum in the vacuum interrupter is a high vacuum of 10 ^-1 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 mpa), flashover 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. 8 and 9.

First, the system shown in FIG. 8 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.

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. 8, 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.

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 equal to the grid voltage. 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.

Further, in the case shown in FIG. 9, the electrodes 42a and 42b are opened, a voltage is applied in this state, and the presence or absence of a decrease in the degree of vacuum is determined by comparing the voltages. (Refer to Special Publication No. 114 of 1973).

That is, 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. 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 of FIG. 8 and FIG. 9 are combined, that is, in FIG. 8, not only the potential of the intermediate shield but also the grid potential is taken into account, 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 8th
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. The load current cannot be cut off even if a drop in the vacuum level is detected.In order to avoid the effects of voltage fluctuations, 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. It is not possible to constantly monitor the vacuum level while the power is on.

There is a problem.

The present invention has been made to solve these problems.

E. Means for Solving the Problems The present inventors studied the discharge phenomenon in a vacuum interrupter and obtained the characteristics shown in FIG. 6. FIG. 6 shows the vacuum interrupter internal pressure on the horizontal axis and the discharge starting voltage on the vertical axis. In FIG. 6, 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.

It was generally known that long gaps have higher discharge starting voltages than short gaps, but as can be seen from Figure 6, this is a phenomenon in high vacuum or near atmospheric pressure, and is 10 ^-2 mmHg. In the region around (1.333pa), on the other hand, the discharge start voltage is higher in the 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 member, for example, between the grid line and the ground, and between the intermediate shield and the ground, respectively, and the ground potential of the intermediate shield obtained via the second impedance. a correction unit that corrects the detection signal of the vacuum interrupter so that the detection signal when the vacuum interrupter is open and the detection signal when the vacuum interrupter is closed are equal when the degree of vacuum is normal; A determination unit is provided that determines whether or not the degree of vacuum has decreased by comparing the detection signal of the ground potential of the system electric line obtained through the first impedance.

F Effect In the device configured as described above, when the detection signal obtained from the second impedance when the vacuum interrupter is opened and the detection signal obtained from the second impedance when the vacuum interrupter is closed are normal in vacuum, The correction amount of the correction section is set so that they are equal. As a result, the detected amount of ground voltage of the intermediate shield, which is input to the determining section when the degree of vacuum is normal, is corrected to the same value both when the vacuum interrupter is opened and when it is closed. In this state, if the degree of vacuum in the vacuum interrupter decreases while energizing (when closed), a discharge occurs in the long gap provided on either the fixed side or the movable side before reaching the uninterruptable area. begins. 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, by discharging with a long gap,
A fluctuation occurs in the peak value difference between the potential of the intermediate shield that has been corrected based on the correction amount corresponding to the closed state and the ground potential of the grid circuit, and this causes the judgment unit to immediately detect a decrease in the degree of vacuum. Detected. Since it is detected when only the long gap is discharging, the current can be quickly cut off by opening the electrodes immediately after that.

Furthermore, when the degree of vacuum in the vacuum interrupter decreases during opening, discharge begins in the long gap portion, similar to the case during closing. For this reason, a fluctuation occurs in the peak value difference between the ground potential of the intermediate shield corrected based on the correction amount corresponding to the open state and the ground potential of the grid circuit, and this causes a decrease in the degree of vacuum in the judgment section. is detected immediately.

G. Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as in FIG. 8 are indicated by the same reference numerals, and the explanation thereof will be omitted. 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. 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.

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

6 is a second impedance voltage divider for detecting the ground potential E ₃ of the intermediate shield 2, and is composed of capacitors C ₁ and C ₂ with capacitances of 0.1 μF and 1000 pF, respectively. Note that the second impedance voltage divider 6 is not limited to using a capacitor.
7 indicates the load. FIG. 2 shows an equivalent circuit when the vacuum interrupter 1 having the above structure is provided with the first and second impedance voltage dividers 5 and 6. In Figure 2, C ₄ is intermediate shield 2
and the movable electrode 4b. Although FIGS. 1 and 2 show the closed state, the circuit when the contacts are open is shown in FIGS. 3 and 4. In these figures, 8 is an installation device for short-circuiting both ends of the load 7 when the vacuum interrupter 1 is opened, and C ₅ indicates the interelectrode capacitance. In the equivalent circuit of FIG. 2 showing the closed pole, the detected voltage e ₃ is determined by the voltage division ratio as shown in the following equation.

e ₃ = 1/C ₁ / (1/C ₁ ) + (1/C ₂ ) + {1/(C ₃ +C ₄
)} ...(1) Also, in the equivalent circuit of Fig. 4 showing the open circuit,
The detection voltage e ₃ is determined by the voltage division ratio as shown in the following equation.

e ₃ = 1/C ₁ /1/C ₁ +1/C ₂ +1/C ₃ +C ₃ (C ₄ +C ₅ )
/C ₃ +C ₄ +C ₅ ...(2) As can be seen from the equivalent circuits in Figures 2 and 4, the detected voltage e 3 of the impedance voltage divider 6 when the vacuum interrupter 1 is closed and the detected voltage when the vacuum interrupter ₁ is opened e ₃ have different voltage values. Therefore, in the present invention, the intermediate shield 2
The detected voltage _{e 3 (} output voltage of the second impedance voltage divider 6) proportional to the ground voltage E 3 of is corrected as follows according to the open/closed state of the vacuum interrupter 1.
In other words, 10 of the voltage correction section 9 is an auxiliary switch for the breaker, and the auxiliary switch 10 converts the detection signal of the open/closed state of the vacuum interrupter 1 into the amplification factor determining circuit 1.
Send to 1. 12 is an auxiliary relay of the grounding device 8. A detection signal indicating the ON or OFF state of the grounding device 8 is sent to the amplification factor determining circuit 11. The auxiliary relay 12 can be omitted if the grounding device 8 is not provided as shown in FIG. The amplification factor determination circuit 11 is a circuit that determines the amplification factor of the preamplifier 13 according to the detection signals (signals representing the open/closed state) of the auxiliary switch 10 and the auxiliary relay 12, and for example, the amplification factor of the preamplifier 13 is The amplification factor is selected from the amplification factor according to the detection signal. Preamplifier 1
3 amplifies the detected voltage e ₃ of the second impedance voltage divider 6 by the amplification factor determined by the amplification factor determination circuit 11. Since the detected voltage e ₃ is corrected by amplifying with the amplification factor determined according to the open/closed state of the vacuum interrupter 1, the detected voltage e ₃ when the pole is closed is amplified by the preamplifier 13. It is possible to make equal the voltage e ₃ ′ obtained by amplifying the detected voltage e ₃ at the time of opening by the preamplifier 13. ₁₄ is a determination unit, and this determination unit 14 A differential amplifier 15 amplifies the peak value difference between the detected voltage e ₁ of the impedance voltage divider 5 and the output voltages e ₃ ′, E ₃ ″ of the preamplifier 13; It is comprised of a determination circuit 17 that determines a decrease in the degree of vacuum based on the output signals of the switch 10 and the auxiliary relay 12 and the detection signal of the voltage detector 16 that detects the presence or absence of power supply voltage. The determination circuit 17 issues a determination signal, for example, an alarm, for a decrease in the degree of vacuum when the deviation output of the differential amplifier 15 exceeds a predetermined value, and also issues an alarm when the power supply voltage detector 16 detects no voltage. It has a function of blocking the voltage and causing a display (not shown) to display that there is no power supply voltage.

Next, the operation of the above embodiment will be described. The grid line voltage and the intermediate shield voltage are detected by impedance voltage dividers 5 and 6, respectively, and the detected voltage _e1 is input to the differential amplifier 15, and the detected voltage
e ₃ is connected to vacuum interrupter 1 by preamplifier 13.
After being amplified with an amplification factor according to the open/closed state of the signal, the signal is input to the differential amplifier 15. When the degree of vacuum is normal, the detection voltage e ₁ and the output voltage e ₃ ' of the preamplifier 13,
There is a predetermined peak value difference between e ₃ ″ and the differential amplifier 15 outputs a signal corresponding to the deviation. At this time, the determination circuit 17 does not output a determination signal for a decrease in the degree of vacuum. When the degree of vacuum decreases, discharge begins in the gap between the intermediate shield 2 and the fixed electrode rod 4a.The reason for this is 10 ^-2 mmHg (1.333 Pa) of the Passien curve shown in Figure 6.
In the front and rear regions, the discharge occurs from a place where the gap length is large, and since the gap length l is the maximum distance between members with different potentials in the vacuum interrupter 1, the discharge occurs locally in this gap first. It begins to discharge. As a result, the potential of the intermediate shield 2 changes, and the peak value difference between the detection voltage e ₁ and the output voltages e ₃ ′ and e ₃ ″ of the preamplifier 13 changes, and the amount of the change increases to a predetermined magnitude. When the value exceeds the threshold, the determination circuit 17 outputs a determination signal indicating a decrease in the degree of vacuum.
Incidentally, FIG. 5 is a waveform diagram of each detected potential when the degree of vacuum decreases.

As described above, the determination circuit 17 of the above embodiment has a function of preventing the generation of a vacuum level lowering alarm when the power supply voltage detector 16 detects no voltage, so that a false alarm may not be issued. There is no.

In the above embodiment, a gap having the maximum distance is provided between the fixed electrode part 4a and the intermediate shield 2, but in the present invention, in order to avoid flashover on the fixed side and the movable side, the gap on the fixed side is Or if it is either the movable side, 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.

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.
In addition, the signal obtained by correcting the detection signal of the ground potential of the intermediate shield according to the open/closed state of the vacuum interrupter is compared with the detection signal of the ground potential of the grid potential member in terms of peak value, and the degree of vacuum is reduced by capturing the change in the peak value difference. Since it is configured to detect this, 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 grid 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 is possible to respond in a vacuum range with a higher withstand voltage than the operating voltage range (voltage that can be interrupted), and it can be interrupted after detecting a decrease in vacuum level. be able to.

Further, since the detection signal of the ground potential of the intermediate shield is corrected according to the open/closed state of the vacuum interrupter, the detection signals of the ground potential of the intermediate shield can be made equal when the contact is opened and when the contact is closed. This makes it possible to accurately determine the decrease in the degree of vacuum in either the open or closed state. Therefore, even if the vacuum interrupter is repeatedly opened and closed, the degree of vacuum can be constantly monitored.

[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, Fig. 3 is a main part circuit diagram of the embodiment of the invention, and Fig. 4 is A circuit diagram showing an equivalent circuit to the circuit in Fig. 3, and Fig. 5 a waveform diagram showing detected potentials from each impedance detector.
Fig. 6 is a curve diagram showing the relationship between the degree of vacuum and the discharge starting voltage between the gaps when the vacuum gap is different;
Figure 7 is a curve diagram showing Patsien's law, Figure 8
9 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...Load, 8...Grounding device, 9...Voltage correction section, 10...Auxiliary switch for breaker, 11
...Amplification factor determination circuit, 12...Auxiliary relay, 13
... Preamplifier, 14 ... Judgment section, 15 ... Differential amplifier, 16 ... Voltage detector, 17 ... 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 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, 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 detection signal of the ground potential of the intermediate shield obtained through the second impedance when the vacuum interrupter is opened. and a correction unit that corrects the detection signal when the pole is closed to be equal to that when the degree of vacuum is normal, and the signal corrected by the correction unit and the ground potential of the grid potential member obtained through the first impedance. A device for detecting a decrease in the degree of vacuum of a vacuum interrupter, comprising a determination unit that determines whether there is a decrease in the degree of vacuum by comparing the detection signal with a potential detection signal.