EP0239783A2 - High-tension electrical switch installation - Google Patents

Abstract

Electrical switching device for high switching voltages. The invention relates to a circuit breaker for high-voltage networks with at least 2 switches (S 1) and (S 2) connected in series with mutually different interruption principles. The switch (S 1) interrupts all ohmic and inductive load currents with short arcing times on its own, while the switch (S 2) opens a period (Δ t) of a few milliseconds after switch (S 1) and in series with switch ( S 1) causes the interruption of capacitive currents and interference currents with high switching voltages. Switch (S 1) is preferably a vacuum load switch with a comparatively low nominal voltage, while switch (S 2) can be a gas or liquid load switch with low switching capacity, which at the same time also fulfills the function of an isolating switch.

Description

The invention relates to an electrical switching device for high switching voltages according to the preamble of the first claim.

Such switches have hitherto become known as breakers for direct current circuits. For example, DE OS 23 50 584 describes a DC power switching device that works with voltage dividers, in which a first circuit breaker, which can be designed as a vacuum switch, in series with a parallel circuit comprising a second circuit breaker, which can be an SF6 switch, and one electronic switch. The known switching device enables a current interruption at a return voltage that is greater than the dielectric strength of each of the two circuit breakers, essentially controlled by the current-voltage characteristic of the electronic switch in conjunction with capacitors lying in parallel with the switches

According to DE OS 31 31 271, a switchgear for interrupting high-voltage direct current has also become known, in which a series connection of a vacuum and a gas jet switch is provided, to which the Voltage control, a voltage-dependent resistor or a capacitor are connected in parallel. On the one hand, the ability of the vacuum switch to interrupt currents when the current is steep and the return voltage is used, and on the other hand the high dielectric strength of SF6 switches, which they have in the low-frequency range of the return voltage, is used. The two switches open at the same time, and the capacitor in parallel with the SF6 switch causes a delayed rise in the return voltage.

The known switching devices have a relatively complex structure because they use additional switching devices and control elements in addition to the two circuit breakers. Both circuit breakers also work synchronously and are charged with arc times of the same length.

In addition, DE-OS 29 34 776 medium-voltage switch disconnectors are described, which consist of a vacuum interrupter and an air circuit breaker. The vacuum switch height is designed so that it can withstand the interruption of operating currents with inductive and capacitive. citing recurring voltages, while the air disconnect switch only has to open the de-energized high-stress isolating section.

The invention has for its object to provide a particularly cost-effective switching device with a small space requirement and a long service life, with which the currents that are essential for power switchgear, particularly in line operation, can be safely interrupted even with high values of the transient voltage in relation to the line voltages. With the new switching device, it should also be possible to switch off all fault currents in networks with low short-circuit power. The switching device should also be particularly suitable for installation in switchgear encapsulated on all sides and insulated with gas or liquid.

This object is achieved by the features of the first claim. Advantageous further developments can be found in the subclaims.

The inventive concept can be implemented particularly effectively in multi-purpose circuit breakers. The essence of the invention is explained in the following figures.

• Figur 1 Zeitlicher Verlauf der Lastkennlinie der erfindungsgemäßen Schalteinrichtung und verschiedener Schaltspannungen.
• Figur 2a Prinzipieller Aufbau der erfindungsgemäßen Schalteinrichtung.
• Figur 2b Schematischer Bewegungsablauf zu Fig. 2a.
• Figur 3 Schaltfolge bei der Unterbrechung eines teilweise induktiven Laststromes.
• Figur 4 Schaltfolge bei der Unterbrechung eines kapazitiven Stromes.
• Figur 5 Integrierte Ausführung der Schalter S 1 und S 2 in einer geschlossenen Kapselung.

Show it:

• Figure 1 Time course of the load characteristic of the switching device according to the invention and various switching voltages.
• Figure 2a Basic structure of the switching device according to the invention.
• Figure 2b Schematic sequence of movements to Fig. 2a.
• Figure 3 switching sequence in the interruption of a partially inductive load current.
• Figure 4 switching sequence when interrupting a capacitive current.
• Figure 5 Integrated version of the switches S 1 and S 2 in a closed encapsulation.

The basic considerations of the inventive concept are illustrated in a diagram in FIG.

The time profile of the load characteristic curve LS 1 starting at the contact separation KT 1 of the switch S 1 is due to a steep increase in the first milliseconds and a peak value reached after about 10 ms, which for load switch systems, for example, is about twice the phase voltage Up _h ( Peak value) should be marked.

The contact separation KT 2 of the switch S 2 is later by the interval Δt; the associated load characteristic curve LS 2 begins at time KT 2, it increases linearly with a comparatively low slope to a final value that is significantly greater than that of LS 1. The maximum value of the load characteristic curve LS 1 is in turn significantly higher than the switching voltages U _{WL '} occurring in the first interrupting phase in a three-phase system when load currents i _{L are} provided with inductive components, as can also be seen from FIG. 1. Such load currents are therefore interrupted by switch S 1 alone. Inexpensive vacuum circuit breakers with a small nominal voltage can advantageously be used for this. Vacuum load switches with a nominal voltage of 7.2 kV or 12 kV are suitable for use in networks with a nominal voltage of 24 kV.

If a capacitive current i is interrupted, however, the return voltage u _WC in the first quenching phase swings up with a low steepness and would lead to a renewed ignition of the arc at the intersection A with the load characteristic LS 1 and thus to a re-ignition of the switch. Through the series circuit of the switch S 1 to the switch S 2, opens by an interval .DELTA.t later, leaves a load characteristic LS _ges produce, which allows a safe interruption of capacitive currents. According to the invention, Δt is set in the order of magnitude of the arc time that occurs when inductive currents are interrupted and is several milliseconds.

For a better understanding of the switching voltages that occur during switching processes in capacitive circuits, see the article: "Switching high-voltage capacitors on and off with compressed air switches", BBC-Nachrichten Okt./Nov. 1956, pages 128-135. From this work it can be seen that when capacitor batteries are interrupted, peak values of the mains-frequency switching voltage U _w occur which, compared to the peak value of the phase voltage Up _{h, have} an amplitude factor U _W / Up _h of 2.5 in the first quenching phase and even with single-phase earth fault of 3.6.

Conventional switching devices for the switching tasks described above must withstand these switching voltages, which in the medium-voltage networks are in the order of magnitude of the standardized AC test voltage. For vacuum circuit breakers, this means the use of relatively large switching chambers, which cause high costs.

In Figure 2a, the basic structure of the switching device according to the invention is given in a single-phase representation. FIG. 2b shows the temporal sequence of movements of the two switches S 1 and S 2 with x ₁ as the contact path of the switch 1 and x ₂ as the contact path of the switch 2. A small vacuum load switch is provided as switch S 1 with a low dielectric strength in relation to the operating voltage of the system, which is controlled by a drive S 11. Load switches of simple design, which work with a high-quality insulating medium, such as SF6, N ₂ or switch oil, can be provided as switch S 2. They are actuated via the crank mechanism S 21 by a drive, not shown. Since the switch S 2 opens later according to the inventive concept by the time difference dt, it is not loaded by weak inductive currents or only briefly in the last quenching phases. This also applies to the interruption of capacitive currents effective arc time, as can be seen from Figure 1, in the first quenching phase only in the falling part of the current i _c . In many cases, the switch S 2 will therefore not need an actual extinguishing device. However, in order to be able to promise the longest possible maintenance intervals for the entire switching device, it is advisable to equip the switching contacts of switch S 2 with contact parts 21 and 22 made of erosion-resistant material. (Figure 5).

According to an additional feature of the invention, the insulating medium of the switch S 2 can simultaneously be used to increase the external insulation strength of the switch S 1. This makes it possible to use listed vacuum switches with a relatively low nominal voltage for S 1. Since the arc load in switch S 2 is very low due to the contact opening being delayed by Llt, there is no significant reduction in the insulating capacity of the switching device even after many switching operations.

The drives of the switches S 1 and S 2 are synchronized via known mechanical or electrical means, which are not shown because they are not essential to the invention, in such a way that the contact openings differ by the time interval dt.

In order to further clarify the mode of operation of the switching device according to the invention, FIGS. 3 and 4 each show a sequence of the positions of the switches S 1 and S 2 which are characteristic when a partially inductive load current i _L or a capacitive current i _{c is} interrupted.

With switch position I both switches are closed, the operating current flows via switches S ₁ and S ₂ to consumer V or to capacitor -C.

In switch position II, switch S 1 has opened while switch S 2 is still closed, an arc Li is burning at the electrodes of switch S 1 (see FIG. 1).

In FIG. 3, the arc is extinguished in switch position IIIa and i _L = 0. The switch S 1 is almost completely open and controls the switching voltage U _WL . The interruption process has ended, although switch S 2 is still closed. At the end of the switch movement in switch position IV, both switches are open.

In Figure 4, the switch position IIIb is shortly after the contact separation KT 2 of the switch S 2, the current i _c has not yet been interrupted by the switch S 1 been. Arcs Li therefore burn in both switches. After the next zero crossing, i _{c is} interrupted, the switches S 1 and S 2 connected in series withstand the peak value Û _{We of} the capacitive switching voltage.

The idea of the invention of the gradual interruption of different types of load cases in consumer networks can also be applied sensibly with other coordination of the switching voltages to the load characteristics. So it can be advantageous in some cases to set the upper limit of the characteristic curve LS 1 to a value that is greater than 2.5 x Û _ph , while after the contact separation of switch S 2 additional faults with earth faults are interrupted with even greater switching voltages. With an appropriate design of the voltage values, the switching device according to the invention can also be used to advantage for single or two-phase networks.

In order to be able to equip particularly small-volume switchgear with the advantages of the inventive concept, the switches S 1 and S 2 can be combined in a combined switching device with a common drive. 5 shows in a three-field circuit breaker system with the switches X, Y and Z how the switch S 1 is integrated as a vacuum switch in the switch S 2 provided with a swivel arm 13. With reference to FIGS. 1 and 4, for the switch X, the switched-on position I of the switching device with a fixed contact 11, which is connected to the busbar 12, the swivel arm 13 with its contact piece 14, the vacuum load switch 15 arranged in the swivel arm, and the fixed fulcrum contact 16, which connects the switch to a bushing 17 or a socket of a high-voltage connector, shown schematically. The fulcrum contact 16 carries the fulcrum 18 of the swivel arm 13 and a link 19 with which the opening movement of the vacuum switch 15 is controlled so that it takes place in its essential part before the galvanic separation of the swivel arm 13 from the fixed contact 11.

In the middle switch Y, the switching device can be seen in a position which corresponds to the position IIIb in FIG. 4 shortly before the interruption of a capacitive current. The fixed contact 11 and the swivel arm 13 can be reinforced by the contact parts 21 and 22 made of erosion-resistant contact material. The switch Z is shown in the open position of the switching device. (Position IV on Figure 4).

The switching device just described is preferably used with at least three three-pole switching units in a completely encapsulated, gas- or liquid-insulated switchgear assembly, the encapsulation 23, as well as a moisture absorber 24, which is recommended for SF6-insulated systems, also being indicated in FIG. 5 is.

Terms

• i, i _L , i _c ....... current; induct., capacitive current
• u, U ............. voltage
• ^u _WL , ^U _WL ......... switching voltage with inductive load
• ^u _toilet . ^U _WC ......... switching voltage with capacitive load
• U _ph .............. phase voltage
• t ............... time
• Δt .............. time interval
• A ............... intersection
• S1, S2 ........... switch 1, switch 2
• KT1, KT2 ......... contact separation of switches S1, S2
• LS1, LS2 ......... load characteristic of switches S1, S2
• LSg _es ............ Load characteristic of the series connection S1 and S2.
• ^X, X ₁ , X ₂ ........ contact path
• S11 .............. drive from S1
• S21 .............. crank mechanism for S2
• V ............... partially inductive consumer
• C ............... capacity
• Li ............... arc

B e g r i f f e

• 11 ............ fixed contact
• 12 ............ busbar
• 13 ............ swivel arm
• 14 ............ Contact piece on the swivel arm
• 15 ............ Vacuum load switch
• 16 ............ pivot point contact
• 17 ............ Implementation
• 18 ............ pivot point
• 19 ............ backdrop
• 21, 22 ........ Contact parts made of erosion-resistant contact material.
• 23 ........... encapsulation
• 24 ........... moisture absorber

Claims (11)

1. Electrical switching device for high switching voltages, which consists of at least two circuit breakers connected in series with control elements for voltage distribution, different extinguishing principles with different dielectric behavior immediately after the zero crossing of the current to be interrupted, of which a first interrupter has a steep increase in dielectric strength at a maximum value thereof of a fraction of the required total voltage and is preferably a vacuum switch, and a second interrupter has a comparatively flat increase in dielectric strength with a maximum value which is higher than that of the first interrupter and is preferably a gas switch,
characterized,
that in a network of certain nominal voltage - The first interrupter is a switch (S 1) with a small operating voltage in relation to the mains voltage, the load and fault currents provided with inductive components in particular at comparatively small switching voltages without the involvement of second interrupt, the second interrupter is a switch (S 2) for comparatively smaller load currents, the switch contacts of which open a time interval (Δt) of several milliseconds after the first interrupter, - The series connection of both interrupters can interrupt capacitive currents even under earth fault conditions with comparatively large switching voltages, the voltage distribution over the two open interrupters preferably being controlled by their intrinsic and earth capacitances. 2. Electrical switching device for high switching voltages according to claim 1
characterized,
that the time interval (Δt) is equal to the average arc time for load currents provided with inductive components. 3. Electrical switching device for high switching voltages according to claim 1 and 2
characterized,
that as a switch (S 1) a vacuum load switch with a relatively low operating voltage relative to the mains voltage and as a switch (S 2) a load switch of low power with a gaseous extinguishing agent, preferably SF6, is used. 4. Electrical switching device for high
Switching voltages according to claims 1 to 3
characterized,
that the second interrupter has no closed extinguishing path and that its extinguishing agent simultaneously increases the external insulation of the first interrupter. 5. Electrical switching device for high switching voltages according to claim 4
characterized,
that the second interrupter also has the function of a disconnector. 6. Electrical switching device for high switching voltages according to claim 1
characterized,
that the two switches (S 1) and (S 2) have separate, mechanically or electrically coupled drives. 7. Electrical switching device for high switching voltages according to claim 1,3 and 5
characterized,
that the switch (S 1) is integrated in the swivel arm (13) of the switch (S 2) and is inevitably actuated depending on its position. 8. Electrical switching device for high switching voltages according to claim 1, 5 and 7
characterized,
that several, preferably three three-pole switching units are installed in a common gas or liquid-tight encapsulation. 9. Electrical switching device for high switching voltages according to claim 1, 4, 5, 7 and 8
characterized in that the switch (S 2) uses an insulating liquid, preferably switch oil, as an extinguishing agent. 10. Electrical switching device for high
Switching voltages according to claim 1, 5, 7, 8 and 9
characterized,
that the switch (S 2) in addition to the operating and disconnected position also has a third position for earthing and that the earthing process is carried out by successively closing the switches (S 2) and (S 1). V shows 11. Electrical switching device for high switching voltages according to claim 8
characterized ,
that a moisture absorber (24) is provided in the gas-tight enclosure (23) of the switching device.

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