DE1765370A1 - Vacuum switch for alternating currents - Google Patents

Description

Vacuum switch for alternating currents.

The invention lies in the field of vacuum holders for alternating currents and specifically refers to the level of overvoltages that occur when the switch is operated.

At, most circuit breakers the interruption process is initiated by two relatively movable contacts are separated from each other and thereby an electrical Liohtoogen between these contacts arise. If it is an alternating current * circuit, this arc remains until the next control zero crossing of the stream. Immediately afterwards, tension again arises between the contacts. When the dielectric The strength between the two halves of the contact can be rebuilt faster than the tension between the two halves of the contact If the contact halves are formed, the interruption is finally ended. If, however, the dielectric strength slows down when the tension builds up between the contact halves, the arc ignites again.

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While it is generally desirable to use the dielectric Strength build up again as quickly as possible, however, under certain conditions, a very quick build-up of the dielectric Strength lead to excessively large overvoltages.

For example, this can occur when the arc gap repeatedly ignites and interrupts ^ after the first extinction has taken place when the current has passed through zero. in the In the case of the first such new ignition, a high-frequency current is discharged through the arc lines as a result of vibrations of local capacitances and inductances. If the dielectric strength is very high after opening the switch contacts arises again quickly, this high-frequency current can already uei go out at its first zero crossing and, if necessary, go out at least at its second zero crossing. This fast one Current under-research can lead to a relatively high overvoltage between the contacts if the mentioned local Vibrations persist. This voltage can even assume higher values if the light arc section is shortly after the Interruption of the high-frequency current ignites again and the high-frequency current is immediately interrupted again after the new ignition will. Such a voltage, which builds up ever higher, can be the result of short successive ignitions and Interruptions of the high frequency current and is detailed in a work by Concordia and Skeats, AIEE Transactions,

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Volume 58, 1939, pages 371-376. There the writers have explains what conditions for the inductors and Capacities must be available to bring about such repeated ignition and extinguishing. However, these conditions only occur in relatively rare forms of circuits and are therefore quite rare themselves. However, if these forms of circuits are present, such a voltage build-up can also be observed with vacuum switches when the vacuum switch is at its Contacts shortly before a Stronfä passage opens. Since the opening of the Contacts has just started, the contact range is extraordinary briefly when the voltage increases as a result of the high frequency oscillations builds up and it may therefore happen that the contact path is not able to withstand this voltage. Then a new ignition occurs, which is followed by a new high-frequency current follows. Because of the very fast build-up of the dielectric Strength, which is characteristic of many vacuum switches, is normally this high-frequency current in a vacuum switch already extinguish at its first zero crossing, so that possibly further ignitions and interruptions of the arc can take place, which are accompanied by an increasing build-up of tension. This build-up of tension in the separating Contact can result from, is referred to below as a "short arc".

One purpose of the invention is to prevent the creation of excessive overvoltages in vacuum switches as a result of a.

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prevent rapid development of dielectric strength.

Another purpose of the invention is to provide simple and inexpensive means of controlling dielectric strength of a vacuum switch.

Another purpose of the invention is to prevent excessive overvoltages from being generated by repeated ™ to prevent ignition and extinguishing during an interruption process .

Another purpose of the invention is to provide a simple trigger circuit that can be used even after repeated Always respond if the same voltage value is triggered.

In one embodiment of the invention, a vacuum switch for alternating currents is used, which is within his Vacuum vessel has two contacts which are movable relative to one another. In this vacuum switch there are also triggering means proposed, which consist of a tripping path which, when it breaks down, creates an arc in the primary Arc gap initiates. Means are also provided which, when a voltage occurs on the primary arc path cause a flashover of the tripping path when the voltage at the primary light-arc path has a value . reached, which is about twice to 5.5 times the maximum voltage the line to earth.

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In a preferred embodiment of the invention the following components are available:

1) A voltage divider on the primary arc path, which contains series-connected capacities,

2) A trigger circuit with a bilateral conductive Diode thyristor, the resistance of which changes from a very high value to a very low value, when the voltage applied to the thyristor predetermined one Assumes value

5) Devices for parallel connection of the trigger circuit to one of the capacitors, so that a certain percentage of the voltages on the primary trip path is fed to the trigger circuit,

4) Means for supplying a voltage pulse to the tripping path after the thyristor is small Has accepted resistance.

The invention is described below with reference to the drawing.

Pig. I represents a section through a vacuum switch with closed contacts.

;. 2 shows the cl..icheri switch with open contacts.

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Fig. 5 shows another embodiment of the invention represent.

In FIG. 1, a vacuum switch is designated as a whole by 10, which has a vacuum-tight piston 11 which is evacuated to a pressure of 10 mm Hg or less. The designated as a whole with 11 vacuum envelope oesteht in detail ^ of a cylinder 12 of a suitable insulating material and from two metal caps 1J> and 14 that are fused at the edges 15 with the cylinder 12th

Within the vacuum switch housing 11 there are two contacts 17 and 18 which are movable relative to one another and which, according to FIG. 1, touch one another. The upper contact 17 is a fixed contact and is attached to the lower end of a tube 17 a, which is connected to the cap 13 at its upper end. The lower contact 18 is attached to the upper end of a floating * conductive Staoes 18a. This rod 18 a can move freely within an opening located in the lower cap 14 and is sealed by a metal bellows 20.

The vacuum switch 10 is used to initiate or interrupt the current transfer between the lines 8a and 8b.

An opening spring located outside the switch housing 24 moves the contact 18 downward, i.e. into the position shown in FIG

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depicted situation. The lower switch electrode is activated by a locking bar 26, which can be detected by a coil 27 however, held in the position shown in FIG. When the trip circuit 28 is closed, the Coil 2? energized, so that the spring 24, the lower switch electrode can move down.

To open the vacuum switch in the event of an overcurrent in

the lines 8a and 8b are provided with a current transformer which | a secondary winding 29 on line 8b. At the terminals of the winding 29 there is an overcurrent relay JO. If the current within the lines Sa and 8d exceeds a certain value, the relay J50 closes its contacts ~ $ Qa. and thus completes the circuit 28 for opening the vacuum switch 10.

The vacuum switch 10 can also be done by hand by means of a Switch 22 open v / earth, which is parallel to the contacts ^ Oa des iielais JJO lies. When switch j52 is closed, the trip circuit 28 is also closed and the vacuum switch 10 is opened again.

When contact 18 separates from contact 17, an arc is created in the primary arc path 21. Through Part of the contact material is evaporated from this light,

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so that a so-called plasma is formed within it the arc burns. The arc lasts until the next current passage through NulJl ^, after which it is extinguished. After this When the arc is extinguished, the vacuum path resumes its dielectric strength. If this dielectric Strength arises at a higher speed than the voltage builds up on the arc path, so there is no new one fc ignition of the arc instead. If this is not the case, however, the arc ignites again and the one described The process takes place again with each new zero crossing of the current until the arc path can withstand the new voltage able.

During the interruption process described above, metal vapors arise that can condense on the cool surfaces of the switch. Around a suitable condensation surface a tubular shield 25 is to be created around the arcuate arc 21 arranged around. This shield is preferably electrically isolated from both contacts.

It is, in general, desirable to use the dielectric Restore strength as quickly as possible, but in certain exceptional cases a quick restoration the dielectric strength lead to extraordinary overvoltages. One such case is the case of the so-called

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"Short Arc", which has already been spoken of above. As already explained there, if an ignition of the short arc path takes place at the first zero crossing, the vacuum switch because of the quick recovery of its dielectric strength interrupt the high-frequency current at the first zero crossing. This can lead to the formation of a lead to high voltages, which can increase even further if repeated ignitions and extinguishing operations occur.

To prevent such high overvoltages, a release section 50 is built into the vacuum switch. This triggering section 50 is preferably carried out in the same way as it is described in the American patent specification J5.087.092 (Lafferty). This Lichtoogen distance namely has a cylindrical ceramic body 52 which is built into a recess 51 within the fixed contact half. Two thin metallic layers 54 and 56 are placed on the outside of the ceramic body with a distance from each other reasonable λ. These two thin layers 5 ^ and 56 represent the electrodes of the trigger path. They are separated from one another by a V-shaped groove 57 which surrounds the entire circumference of the ceramic body. The trigger electrode 5 ^ is connected to the main electrode 17. The other trigger electrode 56 is isolated from electrode I7.

The layers 5 ^ and 50 consist of metal for example

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wisely made of titanium, which is a good getter for active gases such as hydrogen and can absorb considerable amounts of it. In a preferred embodiment of the invention, each of the two layers of titanium are loaded with a large amount of hydrogen, as in the above-mentioned patent is described. It is well known that the electric field lines favor at the interface between a metal and a ceramic body, which is in intimate contact with the metal is located, a breakdown at this interface. As a result, a relatively small voltage can be applied to the release path cause a rollover of one of the parting surfaces over the release path. When the trigger distance rollover 50, the arc releases hydrogen in trigger electrodes 54 and 56. This hydrogen is used by the arc ionized and the ionized hydrogen quickly penetrates into the main discharge path 21 and reduces its dielectric there Strength, so that as a result of the voltage which is then between the main electrodes 17 and 18, this distance is overturned.

In order to generate a voltage at the triggering path 50 a line is provided through the ceramic body 52 therethrough. At its lower end, this line 58 is welded to a metal cap 59, which is in contact with the trigger electrode 56 is located. The metal cap 59 is at the lower end of the ceramic

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Body t> 2 by means of a conventional metal-ceramic fusion Consolidated.

A voltage divider 60 is attached to the primary path 21 in order to feed a triggering pulse to the triggering section 50 when the voltage generated at the primary arc section 21 reaches a predetermined value. This voltage divider 60 includes two capacitors 62 and 6J5 etc. within seconds rien circuit. A certain fraction of the total voltage across the primary discharge path 21 occurs across the capacitor 62.

The voltage appearing at the capacitor 62 is applied to a trip circuit 65. This circuit 65 contains the series circuit the tripping path 50 and the diode thyristor 67 · This diode thyristor, which is sometimes also a double-sided diode switch is called is a semiconductor with a resistance that is controlled by a voltage applied to it can be changed between a very high value and a very low value ". This very low value can be called an avalanche value are designated. Regardless of the polarity that is fed to the thyristor 67, it switches on both sides Diode thyristor to low resistance when the voltage applied to it reaches the mentioned low voltage value. The two-part diode thyristor is marked. "through a breakdown voltage, even after numerous breakdowns remains constant. These thyristors are in detail

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on page 139 to I4l of the book "Semiconductor Controlled Rectifiers "by Gentry, Prentice-Hall, Inc., 1964.

When switch 10 is open, the voltage across capacitor 62 is generally not high enough to cause thyristor 67 to break through. If, however, the voltage at the switch exceeds a certain value, the thyristor 67 switches on suddenly its low resistance so that practically all of the voltage across the capacitor 62 is applied to the trigger path 50 sets. The release path f? O therefore ignites as a result of this Voltage pulse, before the capacitor 62 discharges through the triggering path and that for triggering the Vacuum switch required current so formed fc

The voltage at the primary discharge path 21, at which the thyristor 67 breaks down, is determined by the size of the capacitors 62 and 63 . By changing the size of the capacitor 62 relative to that of the capacitor 6j5, the amount of the total voltage at which the thyristor 67 breaks down and triggers the tripping path 30 can be influenced. Sometimes a high ohmic resistance can still be placed in parallel with each of the capacitors and leave the total voltage at which tripping occurs

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influence each other by adjusting these resistance values. Such resistances are indicated by dotted lines 68 and 69 in FIG.

For a vacuum interrupter of the type described, a relatively high tripping current is required to achieve the To ignite the vacuum section when the trigger section breaks down. A tripping current of the required level can also be achieved by the circuit 65 are supplied, even if the capacitor 62 is relatively low, because of the resistance of the thyristor 07 falls extremely sharply after its breakthrough. if that is, the triggering path 50 ignites, a high current flows through the triggering circuit öp, v / which only through the small inductance this circuit is limited.

Since the thyristor Öj has a symmetrical characteristic, it always works in the same way regardless of the polarity of the voltage on the capacitor Ö2.

It is now assumed that the circuit through the vacuum switch 10 is underexposed and that the contacts 1 / and Io due to the phenomenon described above the so-called Lichtoogen a voltage builds up. Under the. worst conditions of repeated ignition and extinguishing the voltage on the vacuum holder can be as large as five -

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times the peak voltage of the AC voltage curve and assume even higher voltage values. Such high tensions but are absolutely unsustainable for most supply systems.

In order to avoid such high overvoltages, the tripping path 50 is triggered when the voltage is applied to the vacuum switch a size between 2.0 times and j >.5 times the maximum voltage between line and earth. So if the first erasure of the high frequency current is a new ignition follows and the voltage on the primary discharge path then rises to a high value, the trigger path ignites 50 at its set value and causes a Lights in the primary discharge path 21. This ignition of the primary discharge path 21 has the effect that the self-capacitance the load on the circuit 8a, 60 over the vacuum switch discharges before the voltage applied to this switch reaches a value that corresponds to the overvoltage mentioned above would lead.

The first re-ignition of the triggering path 50 should start can be avoided because the vacuum switch 10 can normally interrupt the circuit without re-igniting If you put the trip circuit on a voltage of twice the normal peak voltage to earth or on The triggering path 30 sets an even higher voltage do not ignite yet, as the peak value of the high-frequency voltage, which is normally available for the first re-ignition,

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a little bit less than double the opitzensspannung ge _o en J ^ rde. Despite the presence of the trigger path $ 0 , the vacuum holder 10 can thus interrupt its circuit without causing a new ignition. Only if a first ignition has already taken place is the triggering path 50 used to avoid the creation of excessively high voltages during the sub-ordinance process.

As in the American patent specification 2,391,672 '

(Boehne et al.), A capacitance circuit represents another type of switching process in which repeated ignition and repeated interruption can lead to excessively high voltages. The triggering path 50 can also be used to avoid the creation of such high overvoltages with repeated ignition, a switch which carries out such a training process is switched into a predominantly capacitive circuit between a power source and a capacitive load. The triggering distance 50 tons is set in such a way that it only ignites when at least twice the normal peak voltage to earth occurs at the vacuum switch and therefore does not trigger an initial re-ignition. If, however, a first re-ignition occurs and higher voltages arise as a result of a first re-ignition and the immediately following examination of the high-frequency current, the triggering path breaks through and therefore also causes the primary path 21 to zin. This ignition of the

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Primary route 21 allows the loading capacity to be discharged via the vacuum switch, so that there is no charge left behind on the load capacity and no excessively high one Tensions in a manner similar to that described above can occur.

There is another pail in which the release path 50 has to bring about an ignition of the primary discharge path 21 when the vacuum switch 10 has an oesonders hoKhen S ^ rome lessons. This power interruption that too is marked as a tear-off process, it is due to the premature interruption of its current shortly before the zero crossing. if If such a surge of the current takes place at a relatively high value, relatively high overvoltages can also occur occur at the relevant switch. However, the described release device can cause such high voltages in their formation are prevented and the triggering device calls an arc on the primary discharge path 21 again what this burns down to a smaller value of the current.

A basic task of vacuum switches 10 is to interrupt inductive circuits. The maximal The voltage that builds up when such a circuit is interrupted is slightly less than twice the peak voltage against earth. The working voltage of the release device should

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then set v / earth high enough to prevent arcing in the tripping path 50 oei such inductive switching voltages.

In certain cases it is desirable to equip a vacuum switch with a separate tripping path on each main electrode in order to generate a breakdown of the primary discharge path in the event of a flashover of the triggering path. This ensures that a trigger arc is generated in the vicinity of the respective cathode regardless of the respective polarity of the voltages. This is shown in Figure ~ $ , which essentially corresponds to the representation according to Figure 1 and differs from it only in that an additional triggering path 150 is attached to the lower electrode.

A voltage divider 160, which contains the capacitors 162, 163 and 104 connected in series, is connected in parallel to the vacuum (switch
Trip circuit in Figure 1 corresponds. This trip circuit again contains the thyristor 67 sliding in both current directions
and the release distance ^ O. In parallel with the lower capacitor
164 is a similar trip circuit I65 with the thyristor
167 and the Ausiösestrecke 15O.

In a preferred embodiment of the invention
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The capacitors 1Ö2 and 164 have the same size and the thyristors have the same breakdown voltage. If an overvoltage occurs at the primary jintcharging path 21 If a certain size appears, there is sufficient output at capacitors 162 and 104 and therefore also at thyristors 67 and I67 high voltages, so that the thyristors are current-permeable. This calls for an instantaneous ignition of the release links 50 and 150, so that the primary charge path 21 in the same way as on the basis of FIG. 1 oeschrieoen vmrde, ignites.

In the embodiment according to FIG. 1, the capacitors have 102 and lo) and Io4 of such a size that tripping of the vacuum switch 10 at the same total voltage on Vacuum switch takes place as in the embodiment of Figure 1, i.e. oei twice to .2.5 times the normal Peak voltage to earth.

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Claims (11)

1765310 P a t e η t a η s υ ΐ · ü c π e l) Va.,. uui.nscha ± wr for alternating currents, _o e, ce η η ζ eic h- n υ t through
^) ο in VaivUUMjefäiS with an interior di'uciv by v.eni ^ er as IG "hihi Hj odor utilizer; ο) a dl eictrodenpaar intra halo of the vacuum _t; ei'äiBes whose 3cirnflachen finishing a primary rjitlauungsstrecke de- f; c) trigger means including a trigger path for Initiation of an electric arc in the primary discharge section as the result of a blow in the triggering distance; α) Means for the creation of a joystick in the tripping position: e, v. ^r hen the opannunj üntladun at the primary ^ sotrecke a fourth voroestitnmten achieved ^ NaEM lent: j I) IIIn voltage divider at the primary i ^ ntladun _a sstrecke, oestehend from iieihe in switched-capacitor;
II) in trip circuit with an in oeiden current r: chtun.jen permeable diode thyristor, the changes from a very high value to a very low value when the thyristor applied voltage exceeds a predetermined value; 10 9 3 3 1/0720 ° - 10 III) Means for connecting the trip circuit to one of the capacitors, which adds a certain percentage to the primary line of charge occurring voltages are fed to the trip circuit, IV) and means for supplying a voltage pulse to the tripping path at the transition of the thyristor in its low resistance. 2) Vacuum switch according to claim 1, characterized in that the in oeiden current directions The permeable thyristor and the trip circuit are in harmony with one another in the trip circuit. '$) Vacuum switch according to claim 1, characterized in that the electrodes are movable relative to one another and that the primary discharge path exists between their end faces. 4) Vacuum switch for carrying out capacitive switching operations, which in the interruption of a predominantly capacitive current between a current source and a capacitive load ostaren, wooei the vacuum switch contains the following components: N -4 a.) A vessel evacuated to at least 10 mm Hg, b) a pair of electrodes, the electrodes of which are movable relative to one another within the evacuated vessel 10 9 8 3 1/0720 bad original 21st and which, when touched, can transport electricity between the power source and the load, c) one of the contacts is free to move towards the other and creates a primary discharge path with it, d) Release devices including a release path to initiate a flashover in the primary discharge path as a result of a flashover I. in the release path, e) control devices which respond to a voltage on the address the primary load path and a flashover the trigger path after the first re-ignition during the capacitive switching operation, f) and means for shutting down these control devices. 5) Vacuum switch for carrying out capacitive switching j operations that confess in it, the predominantly capacitive ones Interrupting current between a current source and a capacitive load is marked by a) a vessel evacuated to at least 10 ~ mm Hg, υ) a pair of electrodes with oewegli- Chen innerhalü contacts of the vacuum vessel, c) a contact which gegenüuer the other contact oe is woglich and soft oei between the con- oeiden BATH 109831/0720 tact control surfaces a primary discharge path O- ■ is d) tripping means including a tripping path for initiating an arc in the primary discharge path as a result of an overturn in the release path, e) Means for generating an overburden in the triggering path, when the voltage at the primary discharge path has a predetermined value, which is kMner than 2.5 times the normal peak voltage to earth assumes f) that the predetermined value is high enough for a first re-ignition by the triggering means during a capacitive To prevent switching operation. 6) Circuit arrangement with vacuum switch, characterized by _2y. a) A colonist evacuated to at least 10 mm Hg, b) a first contact within this colony, c) a second contact within this colo, which is movable with respect to the first contact and can be brought into contact with the first contact, as well as can be detached from it in order to form a primary discharge path between the two contacts, d) Release devices with inclusion of a release path within the Koloens for the creation of a light oogen - 109831/0720 BATH ORIGINAL üoergan ^ s in the first discharge path as a result of a kickback in the release path., e) control devices. " responsive to üchaltspannungen, ground-v the erzeuigt by opening of the vacuum switch and a Lichtoogenüoersehlag in the trip route as a result of achieving a voroestirnmten Minuestspannung by the Schdtspannungen to Fol ₀ e haoen, f) that the minimum voltage is vorgegeoene gonügend high, similar to the Steuereinrichtunöen for r-raeugung a Uoerschla ^ s in aer release section as a result of switching voltages oeim to make zero slack unv / irksarn. 7) Circuit arrangement with vacuum switch consisting of: —4
a) a Koloen evacuated to at least 10 mm H ^, o) a first contact within this Koloens, c) a second contact inside this piston, the opposite one the first contact is possible and can be brought into and out of contact with it, so that a primary discharge path between the oeiden Contacts are established, d) Triggering means for initiating a Lichtuogenüoerschlags in the primary discharge path, e) control means which respond to switching voltages that oei the Opening of the vacuum switch arise and the triggering means as a result of an increase in the switching voltages BAD ORiQiNAL 109831/0720 24 - 24 - enter a predetermined minimum value, f) such a size of the minimum voltage that the control devices the triggering means oei the -oe in the zero crossing switching voltages occurring during the investigation unable to operate from inductive currents. 8) Vacuum switch according to claim J _1, characterized in that the tripping means contain ein.Auslösestrecke in the Koloen, which flips over when the tripping device arrows, wooei the primary discharge path flips over as a result of the spark transition in the tripping path. 9) vacuum switch according to claim 7. » characterized, that the control means are actuated by the switching voltages which are applied to the primary charge path appear. 10) Vacuum switch according to claim J, characterized in that devices for maintaining the contacts are present in a predetermined mutual position, which enables the passage of current through the contacts and that overcurrent-sensitive means for separating the contacts are present oeim occurrence of overcurrents. 10 9 8 3 1/0720 ^{BAD 0RIGINAL} 25th 11) Vacuum switch according to Anspruoh ¹ J _3, characterized in that the vacuum switch does not have a parallel branch with a resistor Desitzt, which would affect the voltage rise on the vacuum switch. 109831/0720