GB2228622A - Electric circuit switching method - Google Patents

Description

r 1 BLECTSIC CIRCUIT SWITCHING METHOD AND DEVICE THEREOF This invention

relates to electrical equipment, and more specifically to a method for switching electric circuits and a device thereof.

The invention can be successfully used in electrical switching equipment for switching heavy-duty circuitry, including emergency operation to limit and interrupt shortcircuit ouxrents.

Known in the art Is the method for switching A0 cir- cuits (I.S.Taev, A.G.Gadzhello et al. "Oenovi teorii electricheskikh apparatoyll (Electrical apparatus basics), 1987, Visshaya Shkola Publishers (Moscow), pp.184-187. - In Russian)l residing in Interrupting electric circuits by included into them contacts linked to a drive and inserting a dielectric medium, such as air, vacuum, etc., into the gap between the contacts.

With this method, an arc is generated between separating contacting parts of the contacts and this are has to be extinguished with the aidy for Instance, of a deio- nizing chamber with grids separating it into a number of connected In series gaps between plates of the deionization chamber. Arc extinguishing Is achieved after the circuit current passes through zero. due to the large number of gaps between plates of the deionizing grid. This method is widely used in switching equipment.

However. switching heavy currentsy in particular under emergency conditions during interrupting shortcircuit currents. the are energy becomes sufficiently high to cause excessive wear of main switching and switched elements. such as switching equipment, power supplies, power distribution lines, etc. Improving the switching speedy reliability and durability of switching equipment based on this known in the art method, with the aid of traditional techniques appears to be impossible, because the are generated during contacts breaking can be extinguished only when the are current passes through zero. Consequently, the arcing time cannot be reduced to less than a half-period of the switched current frequency, and just this is the reason of the low reliability of this known switching method, when applied to heavy-current eircuits.

Also known in the art is the electric circuit switching method (FR, Ay 2338561)g Comprising opening of the main contacts of the circuit being switched and insertion of a dielectric member into the intercontact gap.

The principal feature of this method is that contact opening is acomplished with the air of the dielectric member, which may be made lightweight and positioned in the direct vicinity of the contacts being switched. This allows pro- viding a relatively higgh switching speed. The method also allows automation of electric circuit switching, including Ar t breaking several contacts simultaneously with the aid of a single dielectric member.

However. this known switching method allows switching of only weakcurrent circuits, due to a number of causes preventing its application in heavy-current circuits.

The contact interrupting rating In case the circuit is broken by a single contact Is 0.9A, with two contacts the rating is increased to 4A, and with simultaneous breaking of three connected in series contacts - to 16A. A rise in switched circuit current results In an arc between the contacts being separated and the dielectric member Inserted into the intercontaot lwap stretches this arc and shifts its electrode points along the contacting parts,, but is, however. unable to extinguish the are. The arc thus developed can be extinguished only when its current passes through zero. At the same time, are extinguishing by introducing a dielectric into it is further hampered by that the arc Is only stretched out, rather than being broken up Into separate sections. and the arc current is not limited. This known circuit switching method does not take into account the time characteristics of dielectric member insertion Into the intercontact gap (the speed of dielectric filler displacement), does not specify the parts and contacts configuration, the width of the gap between the contacting parts of the contacts being parteds the necessity of wiping and contacting with the drawing points of the ig- c 13 2 nited are. Drives, used to displace the dielectric member (hydraulic, electromagnetic, pneumatic) are essentially incapable of providing the required speed of dielectric member insertion into the intercontaotgap to prevent arc ignition. At the same time, If the above conditions where met and arcing were prevented. the circuit being switched would nevertheless be submitted to overvoltages of unacceptable magnitude and rise speed, which are extremely difficult to suppress.

Also known the art Is the electric circuit switching device (G.N.Aleksandroy (Bd.). 'ITeoriya elektricheskikh apparatoyll' (Electrical Apparatus Theory). Visshaya SbLkola Publishers (Moscow) 1985, pp.178-180. - In Russian), essentially an automatic circuit breaker, comprising main contacts connected into the circuit being switched, a contact drive, and deionizing grids. Arrival of an interrupt command causes the main contacts to part under the action of the drive (embodied with sprin6s) and the ignited arc is shifted into the deionizing Srids, separated into a number of sections and Is extinguished at the next passage of current through zero value.

Are ignition leads to contact wearoutl this effect abruptly progressing with a rise in current, so that when interrupting limiting current values the breaker may be completely worn out by 3 to 5 interruption operations. Moreover, heavy emergency currents damage both power sup- plies and cables, so that -an electric circuit with such a switching device does not feature adequate reliability and safety of power supply to loads.

Also known in the art is the electric circuit switching 3 device (FR9 Aq 2338561)g comprising main contacts with movable and stationary contacting parts and a dielectric member linked to a drive. The dielectric member is shaped as a wedge with the sharp end entering the intercontact gap between the contacting parts under the action of the drive, to which It Is linked by a holder. The drive may be hydraulic, electromagnetic, or pneumatic. Arrival of an interrupt command the dielectric wedge member is inserted into the intercontact gap by the action of the drive and provides contacts opening. At low currents con- I- tact opening is achieved without arcing, this beint an undoubtable advantageous feature of these switching devices.

At the same time, at high currents an arc is ignited between parting contacting parts and Is stretched and pushed out of the contact zone by the dielectric wedge member, which, however, Is unable to extinguish it. The arc is directly between two contacting parts, Is not broken up into sections, and therefore does not practically limit the current. so that contact wearout is greatly enhanced.

At the same time, the contacts and dielectric member f configurations specified do not prevent spark and are craters, whereas the drives used cannot provide-the speed of the dielectric filler insertion, necessary to prevent are ignition.

It is an objective of this Invention to provide an electric circuit switching method, wherein Introduction of complementary operations and their sequenoing would allow switched current limiting and provide and provide areless switching of main and supplementary contacts In lo switching equipment, and a device thereof with a circuit confi-uration and design allowing optimal embodiment of this method.

The invention resides In that in the electric circuit switching method each main contact in the switched cir- cuit is shunted by at least one network of supplementary contacts, with each main and supplementary contacts shunted by at least a double number of supplementary contacts and the last network of supplementary contacts shunted by current-limiting resistorsq the main contacts are opened, a dielectric member Is inserted-into the intercontact gap by displacing it,, maintaining its contact with the entire surface of at least one of the contacting parts in each contact pair, with dielectric member insertion into the Intexcontact gap executed sequentially by first inserting 251t into the gap between the main contacts and thereafter .r t -7 into the gap between the supplementary contacts of each network after the contacts of the preceeding network have been parted, the insertion lasting less than the time of explosive breakdown build-up of the metallic bridge formed during contact opening, and interrupting the electric circuit after opening the last network of supplementary contacts.

The invention resides also In that the device of the abovecited electric circuit switching method comprises main contacts having movable and stationary contacting parts, at least one network of supplementary contacts with movable and stationary contacting. partsq connected In parallel to the main contacts, and having at least a double number of contacts, wherein the movable contacting parts of the main and supplementary contacts are mounted on an insulating panel pairwise, on opposite sides thereof, facing one another, and interconnected in parallel. current-limiting resistors connected in parallel to the last network of supplementary contacts, and a dielectric filler linked to a drive.

It Is expedient, that the time of total insertion of the dielectric filler between all the main and supplementary contacts be less than 1 ms, with circuit breaking taking place in air.

It is suitable. that the section of the dielectric 41 - k 13 member facing contacts be of stepwise configurations with the main contacts-and each network of supplementary contacts lined up against respective steps of the dielectric filler.

It is also advantageous that the section of the dielectric member facing the contacts be of line.ar profile, with the main contacts and each network of supplementary contacts arranged stepwise relative to this section of the dielectric filler.

It is preferable that the movable contacting parts of the contacts outside the zone of their contacting the stationary contacting parts be enclosed in insulating envelopes.

It is desirable that the networks of supplementary contacts be connected to the main contacts via threshold elements.

It is advisable that each threshold element be embodied by semiconductor devices arranged in parallel-opposition connection.

Furthermore. each threshold element may be embodied as a contact, to be closed prior to opening the main contacts.

The design configuration of this invention allows an Improved reliability of switching equipment performance an their higher wear-re a! stance 9 provides a multifold reduction of the switched current under emergency conditions 1 t.

in power distribution systems, thus enhancing the safety of their use.

These and other objeotives of the invention will become apparent from the following detailed description of specific embodiments thereof and the accompanying drawings, wherein:

Fig. 1 shows the schematic diagram of the electric circuit switching device with one main contact, according to the Invention; 1D Fig. 2 shows the schematic diagram of an embodiment of the switching device with two main contacts, according to the Invention; Fig. 3 shows the mutual positioning of the contacting parts of the main or supplementary contacts and the die- lectric member prior to switching, according to the invention; Fig. 4 shows the general view of the design of the switching device with a stepped configuration of the dielectric member, according to the invention; Fig. 5 shows the general view of the design of the switching device with stepped positioning of the networks of supplementary contacts, according to the invention; Fig. 6 shows the design arrangement of a three-pole switching device, according to the Invention; Fig. 7 shows threshold elements embodied with parallelopposition connected diodes, according to the invention; c -1u- Pig. 8 shows threshold elements embodied with parallelopposition connected thyristors, according to the Invention; F1g. 9 shows threshold elements embodied with the contact of a circuit breakerg according to the Invention.

The electric circuit s..jitohing method of this invention is as follows.

The switchin6 method of the invention Is based on preliminarly quickly limiting the current In the switched circuit prior to its final interruption. In its turny fast current limiting is based on the difference between the intercontact voltage, necessary to maintain a live arc across the contacts, and the breakdown voltage of the intercontact gap insulation, required to ignite an arc between open contacts. The former should exceed the voltage drop across the contacts, which is 15V to 20V with contact materials usually empljyed (such as copperg silver). whereas arc ignition across open contacts, parted for instance to a gap of 1 mm, requires a voltage over 15OV. At the same time it should be noted, that a low voltage (Of some 3V to 5V) across the contacting parts of contacts being parted may lead to sparkover of the intercontact gap. With a rise in switched current, and therefore In the voltage drop, the spark may turn into an arc dischargeg if additional preventive measures are not taken.

The herein above cited widely known effects are used as the basis for selection of the switching operation time W characteristics and parameters for heavy-current circuit Switching applications With the switching method of this Invention.

To prevent sparking developing into an arc discharge between parting contacting parts of the contact, I.e. to prevent explosive breakdown of thenetallio bridge, It Is necessary that the voltage drop across the switching contacts be lower than that of are ignition, and to eliminate electrode sparking sites by erasing, cooling, and smoothing out the contact surfaces and overlap them with a dielectric member, thus ensuring contact opening without arcing. To exclude voltages above that of arc ignition on the contacts being switched, to reduce overvoltage in the electric circuit, and to facilitate shearing of crater points, where- at the arc is ignited, main contact 1 (FI-. 1) is shunted 0 by two networks 293 of connected in series supplementary contacts 4. Network 2 comprises two supplementary contacts 4, each in turn shunted by four supplementary contacts 4 of network 3. Each supplementary contact 4 of network 3 is shunted by current-limiting resistors 5.

Networks 2,3 of supplementary contacts 4 and currentlimiting resistors 5 are connected to main contacts 1 via threshold elements 6.

Another embodiment of the electric circuit switching method of this invention Is presented in Fig. 2 and allows reliable switching of currents up to several kAg this being f -12acomplished by shunting each main contact 1 and:each supplementary contact 4 of network 2 by a double number of supplementary contacts 4. The electric circuit Is switched by sequentially 6pccontacting parts 7y8 (Pig. 3) of main contacts 1 (Fig. 1) and thereafter opening contacting parts V, 81 (Fig. 3) of supplementary contacts 4 (Fig. 1) of networks 2J. Due to main contacts 1 being shunted by qonnected in parallel networks 2 and 3 of supplementary contacts 4 and current-limiting resistors 5, after their opening the current being switched is passed to said shunting networks 2,3 and resistors 59 so that main contacts 1 Open without arcing, whereias the spark generated during switching is sheared off by dielectric member 9 (Fig. 3). Supplementary contacts 4 (Fig. 1) of network 2 are opened next and turn out to be shunted by network 3 and resistors-5. After opening supplementary contacts 4 of network 3 the current being switched is passed by resistors 5 and limited thereby to the specified value. 20 Final interruption of the electric circuit, wherein the active current is thus limited, is executed by contact 10, for instance a circuit breaker or switch, opened after opening supplementary contacts 4 of the last network 3. The preferable application of the electric circuit switching method of the invention is switching under emer- Q gency statesq i.e. interruption of short-circuit currents. Therefore, the method will be effective, if the shortoircuit current is limited to the critical value providing tripping of safety devices and simplicity of Its final interruption.

At the same time. to meet the requirement of avoiding voltages above that of arc ignition across the main and supplementary contacts 1,4 being switched, contacts 1,4 of networks 2,3 have to be opened 'when passing a current 1 1,j via contactsy 1,4, the value whereof is defined as:

I = nu/Rp where: U is the arc ignition voltage across a pair of contacts 1 or 4 (specified in reference books as a function of contact material); n is the number of simultaneously switched contacts 1 or 4; R is the equivalent resistance of networks shunting the circuit being switched.

Knowing the characteristics of current flow in the 2,3 circuit being switched under short-circuit conditions, it is quite easy to determine the time for the current to attain Its critical value, this time defining the required supplementary contacts 4 opening time. For instance, with an electric circuit powered by a 1UJUM supply, the 2,, switching time in air for main contacts 1 and supplementary contacts 4 should not exceed 1 ms.

The switching device of the switching method of this invention comprises main contacts 1 (P16s. 495) having movable and stationary contacting parts 7 and 8, respectively, and supplementary contacts 4 also having movable and stationary contacting parts 71,81, respectively, mounted pairwise on insulating panel 11 (Fig. 3) on opposite sides thereof. Movable contacts parts 7 and 71 are enclosed in insulating envelopes 12 at areas outside the zone of their contact to stationary contacting parts 8 and 81.

Current-limiting resistors of a high-resistivity material are connected across the last network 3 (Fig. 1) of supplementary contacts 4. The contact zones of main and supplementary contacts 194 (Fig. 4) are lined up, with dielectric member 9 positioned in the direct vicinity of this line.

13) Member 9 is of stepwise shape and mounted on movable member 13 of drive 14, the coil whereof is provided with terminals 15. Movable contacting parts 7 are loaded by springs 16.

An embodiment with dielectric member 9 featuring a linear profile and networks 293 of supplementary contacts 49 arranged stepwise relative to this profile is shown in P ig 5.

A three-pole embodiment of the device is shown in Fig. 6, wherein pairwise positioning of movable and stationary Contacting parts 798 of contacts 1 (Fig. 1) Is illust- 2P rated. Movable contacting parts 7 (Fig. 6) are retained against stationary contacts 8 by springs 16 mounted on Ar, k.

axles 17. Terminals 18 to connect the switching device to external circuitry are linked to movable contacting parts by flexible stays 19.

Dielectric members 9, the number whereof equals that of the switching devices poles, are mounted on movable member 13 of inductive drive 14.

Networks 2,3 (Fig. 1) of supplementary contacts 4 and current-limiting resistors 5 are connected to main contacts 1 via threshold elements 6, each designed either as lj parallel-opposition connected diodes 2j,21 (Fig. 7) or thyristors 22, 23 (Fig. 8) controlled by resistors 24,25 and Zener diodes 26, 27, or as contacts 28 (Fig. 9) connecting networks 2,3 (Fig. 1) of supplementary contacts 4 to main contact 1 prior to opening this latter.

The switching device of the electric circuit switching, method of this invention functions as follows.

Under normal operating conditions main contacts 1 (Pigs. 1 to 4) are closed and carry the full electric circuit current. Current flow through supplementary contacts 4 of networks 2,3 and through current-limitin6 resistors 5 is inhibited by threshold elements 6.

On arrival of a command from safety devices, signalling an emergency state in the power distribution system and the presence of an emergency current, movable member 13 (Fig.4) of Inductive drive 14 inserts dielectric member 9 Into the contact zone of main and supplementary contacts 1,4. Main 1 c and supplementary contacts 194 are designed so as to carry current of one direction via their movable contacting parts 7,71, I.e. the connection thereof is parallel as shown in Fig. 6. This ensures movable contacting Parts 797' being pressed to their respective stationary counterparts 8981 by electrodynamic forces generated with a rise in the current. thus preventing contact bounce when carrying emergency currents and eliminating the need of expensive contact weld-ons.

Dielectric member 9 first enters the intercontact gap of main contacts 1 and causes their opening, with spark craters forming during this operation being sheared off by dielectric member 9 and cooled, thus preventing the spark developing Into an arc. This is achieved by that dielectric member 9 is passed over the entire contacting surfaces of parts 7,8 (Fig. 3) with friction, and thereafter is shifted onto insulation panel 11 and insulating envelope 12 of movable contacting Part 7 or 7, also with friction.

The path of dielectric member 9 movement coincides with the configuration of stationary contacting parts 8,81 and therefore dielectric member 9 is moved mith friction along the entire surface of contacting parts W' and encompasses the entire surface of contacts 1, thus preventing arc regeneration. After main contacts 1 are openeds current Is passed by supplementary contacts 4 of networks 2,3 and by ourzent-limiting resistors 5, the total equivalent resistance whereof exceeds that of main contacts 1.

c Further displacement of dielectric member 9 (Pio..4) causes its next step to interrupt the first network 2 of supplementary contacts 4, which are in turn shunted by the second network 3 of supplementary contacts 4 and by current-limiting resistors 5. Openizig the first sta-e of supplementary contacts 4 is also arcless, with spark craters being sheared off by dielectric member 9. Supplementary contacts 4 of the last network 3 are opened in a similar way and the circuit current is passed by current-limiting retistors 5. As evident from the schematic diagram, each consecutive shuntin6 network 2,3 comprises a progressively greater number of supplementary contacts 4, so there is a correspondinG rise in resistance. This allows the rising switched current to be reduced in stages, whereas cascaded openimg of connected in series supplementary contacts 4 substantially reduces their load and ensures their arcless opening.

Under normal operating conditions networks 2,3 of supplementary contacts 4 carry no current, such current flow being inhibited by threshold elements 6. Fig. 6 illustrates threshold elements designed with connected in parallel-opposition diodes 20, 21. The voltage drop across 0 closed main contacts 1 is several dozen millivolts, so that diodes 20, 21 axe cut off and therefore pass no current to networks 2,3 of supplementary contacts 4. 0Dening main contacts 1 produces a larger voltage drop across themg I,-diodes 20, 21 are enabled and the full circuit current is passed to. supplementary networks 2J. The voltage drop across diodes 20. 21 does not affect the processes taking place, because it does not exceed some 0.7V to 1V.

Threshold elements 6 designed with parallel-opposition connected thyristors 22, 23 (Fig. 8) function in a similar Q way. Opening main contacts 1 enables thyristors 229 23 by voltage passed from control networks - resistor 25, Zener diodes 2% or resistor 24, Zener diode 26, respectively.

Zener diode 26, 27 breakdown voltage Is selected, taking into account the voltage drop across main contatts 1.

Threshold element 6 desig-ned with contact 28 (Fig-9) is normally open, and is closed Immediately prior to opening main contact 1 to connect networks 2,3 of supplementary contaots 4.

Final transfer of circuit current to current-limiting resistors 5 (Fig. 1) limits this current to the specified value, reduces the angle between this current and the supply voltage, this allowing subsequent easy electric circuit interruption under emergency conditions.

The residual limited current may be interrupted, for instance, by a lowrating -(low power) automatic circuit breaker connected in series with networks 2,3 or supplementary contacts 4 and current-limiting resistors 5. since under normal operating conditions they carry no load current and are operated only for short time intervals. It is 9 c also possible to use threshold element 6 designed as contact 28 (Fig. 9)g which connects and then disconnects networks 2,3 or supplementary contacts 4, or use controllable threshold elements 6, to be out off after the load current is transferred to current-limiting resistors 5.

It is also feasible to connect a supplementary contact with arc extinction facilities or automatic circuit breaker into the main electric circuit.

Implementing effective current limiting allows fast shorting of the switching device output circuits without a rise In the switched current, this being especially Important when designing safe high-speed protective Interruption systems.

Oonsequently, the circuit switching method of the invention and the device thereof allow:

- a multiple increase in switching equipment wear resistance, this being achieved by ensuring arcless opening of switched contacts 1,4 (Fig. 1) with shunting them by networks 2,3 or supplementary contacts 4 and by currentlimitin, resistors 5, and implementing shearing off spark craters by dielectric member 9 (Fig. 3) during its insertion beteen parting contacting parts 7,7t and 8,81; - an improved reliability of the main components of a heavy duty electric circuit, such as power trans- formers, protected switching equipment. cablesq loads. This is achieved by multiple reduction emergency state c currents and excluding short-circuit shock currents; - stable assured switching of high currents (up to dozens of kA). without arcing, this provided by the switching circuit design and by sequencing the operations executed; - significantly ease the opearting conditions of Protected electrical installations and degrade the requirements specified for them. This is achieved by reliable substantial reduction of the current carried under emergency 10 conditions, this reducing their required heat resistance; - Improved safety of power distibution systems ope ration. This is achieved by Improving the reliability of the heavy-duty circuit components and by reducing their current loads; - a wider field of electric equipment applications due to the possibility of using it under especially dangerous operating conditions; - designing advanced power distribution systems, in particular high speed systems with Interruption times of 1 ms to 2 ms. based on the switching method of this invention; modular design of high speed current-limiting devi ces intended for diverse applications, in particular to protect semiconductor converters.

K p

Claims (11)

WHAT WE CLAIM IS

1. An electric circuit switching methodg comprising shunting each main contact with at least one network of supplementary contacts, with-each main and supplementary contact shunted by at least a double number of supplementary contacts and with the last network of supplementary contacts shunted by current-limiting resistors. opening of the main contacts, insertion of a dielectric member into the intercontact rap, with.the dielectric member die- placement accompanied by its contacting the entire surface of at least one of the contacting parts of each contact and the dieleotrit-. member insertion being executed sequentially, first inserting it into the gap between the maincontacts and thereafter into the gap between supplementary contacts of each network after opening the contacts of the preceeding network, insertion taking a time interval less than that of explosive breakdown of the metallia bridge formed during contact opening, and with final electric circuit interruption after opening the last network of supplementary contacts.

2. An electric circuit switching method substantially as set forth In Claim 1, wherein total insertion of the dielectric member between all main and supplementary contacts takes less than 1 me, when the electric circuit is switched in air.

1 C 9

3. A switching device of the switching method as substantially set forth in the preceeding Claims l or-?comprising main contacts having movable and stationary contacting parts. at least one network of supplementary contacts with movable and stationary contacting parts, connected in parallel to the main contacts and comprising at least a double number of contacts, with the movable contacting, parts of the main and supplementary contacts mounted pairwise. one facing the other, on opposite sides of an insulating panel, and connected in parallel, currentlimiting resistors connected in parallel to the last network of supplementary contacts, and a dielectric member linked to a drive.

4. A switchiu6 device substantially as set forth in Claim 3. wherein the dielectric member section facing the contacts is of stepped configuration, with the main contacts and each network of supplementary contacts lined up facing the corresponding steps of the dielectric tiller.

5. A switching device substantially as set forth in Claim 3, wherein the dielectric member section f acing the contacts is of linear configuration, with the main contacts and each network of supplementary contacts positioned stepwise relative to this linear section of the dielectric member.

6. A switching device substantially as set forth in Claims 3 to 5, wherein the movable contacting parts, out- X side their contact zones with stationary contacting parts. are enclosed in insulating envelopes.

7. A switching device substantially as set forth In the preceeding Claims 3 to 6, wherein the networks of supplementary contacts are connected to the main contacts via threshold elements.

8. A switching device substantially as set forth In Claim 7, wherein each threshold element Is a contact, to be closed prior to opening the main contacts.

9. A switching device substantially as set forth in Claim 7, wherein each threshold element is embodied by parallel- opposition connected semiconductor devices.

10. An electric circuit siUtching method substantially as set forth in any one of the preceeding Claims and as j_5 described herein above with reference to the accompanying drawings.

11. A switching device of the above electric circuit switching method, substantially as set forth In any of the preceeding Claims and as described herein above with re- ference to the accompanying drawings.

Published 1990atThe PatentOffice, State House. 8671 1LghHolborn. London WC1R4TP.Purther copies MaY be obtainedfrom The PatentOffice. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD- Printed by Multiplex techniques ltd. St MW7 Cray. Kent, Con. 1,87