WO2010058401A2

WO2010058401A2 - System for producing high intensity electric current pulses

Info

Publication number: WO2010058401A2
Application number: PCT/IL2009/001094
Authority: WO
Inventors: Oren Gafri; Yuri Livshitz
Original assignee: Pulsar Welding Ltd .
Priority date: 2008-11-20
Filing date: 2009-11-19
Publication date: 2010-05-27
Also published as: WO2010058401A3

Abstract

A system for producing a high intensity electric current pulse is described. The system includes a plurality of discharge modules connected in parallel to a load device. Each discharge module comprises a capacitor bank and a high current switch connected in series to the load device. The system also includes a high voltage supply device coupled to the capacitor banks for charging thereof. Any two of the discharge modules are coupled to each other through a resistive element so as to prevent sharp voltage decrease across the capacitor banks, and thereby to enable a concurrent operation of the high current switches.

Description

System for producing high intensity electric current pulses

FIELD OF THE INVENTION

This invention relates to an apparatus producing high intensity electric current pulses required for inducing strong electromagnetic fields, light, ultraviolet and acoustic waves in gas, liquid, solid and/or plasma medium, and more particularly to an electromagnetic forming apparatus.

BACKGROUND OF THE INVENTION

Systems and methods for producing high intensity electric current pulses are used in the art for inducing strong electromagnetic fields, light, ultraviolet and acoustic waves in gas, liquid, solid and/or plasma medium. For example, these electric current pulses can be used in electromagnetic working sheet or tubular metal work pieces. The term "working", within the present invention implies to a process which is a result of work applied on the surface of the work piece or on a portion thereof. Working can result in forming, joining, welding, crimping and/or swaging of the work pieces.

Electromagnetic working is based on placing a work-coil in close proximity to the metal to be formed and running a brief, high intensity current pulse through the coil. If the metal to be formed is sufficiently conductive the change in magnetic field produced by the coil will develop eddy currents in the work piece. These eddy currents also have associated with them a pulse magnetic field that is repulsive to that of the coil. This natural electromagnetic repulsion is capable of producing very large pressures that can accelerate the work piece at high velocities (typically 1-500 meters/second). This acceleration is produced without making physical contact to the work piece.

Examples of prior art patents involving electromagnetic working include U.S. Pat. Nos. 2,976,907 to Harvey et al., 4,143,532 to Khimenko et al., 4,656,918 to Rose, 4,5,353,617 to Cherian et al., and 5,824,998 to the Inventors of the present Application, the disclosures of which are hereby incorporated by reference into this description.

Fig. IA shows an electric scheme of a typical prior art system 10 for producing one or more high intensity electric current pulses. The system 10 includes a high- voltage supply device 11 connected to a high voltage capacitor bank 12 (comprising one or more capacitors) through a switch 13. The supply device 11 and the capacitor bank 12 form together a charge circuit A.

The system 10 further includes a high current switch 14 in series with the capacitor bank 12 and a load device 15. Here, the load device is not considered as a part of the system 10, but it should be taken into account for understanding the functionality of the system. The capacitor bank 12, together with the high current switch 14, the load device 15 and all interconnection cables therebetween form a discharge circuit B. For example, when the load device is an electromagnetic working apparatus, it includes commonly one or more single- or multiturn work-coils.

For safety reasons, one of the terminals of the high- voltage supply device 11 is permanently grounded; while another terminal (energized or potential terminal) can also be grounded through a grounding switch 17, when the system is out of operation. A current limiting resistor 18 is usually included into this chain for limiting the discharge current, when closing the switch 17.

When the switch 13 is closed and the high current switch 14 is open, the capacitor bank 12 is charged by the voltage supply device 11. The capacitor bank 12 can then be discharged by opening the switch 13 and closing the switch 14, to supply a high voltage to the load device 15 and thereby generate an electric current pulse therethrough. The closing of the high current switch 14 is usually activated by an ignition circuit 19 launching an ignition electric pulse to the switch 14.

Despite the apparent simplicity, the system 10 suffers from a number of limitations. For example, although the electric capacity of the capacitor bank 12 can be practically adjusted to any desired value, the high current switch 14 is limited by the magnitude of the breakdown current that for the commercially available high current switches typically does not exceed 150 kA.

Furthermore, the reliability and service lifetime of the high current switch decrease when the discharge current is close to the current breakdown. The reliability of the switch is, in turn, critical for most industrial applications, especially for mass production machinery.

Attempts were made of parallel installation of a number of switches for enabling the currents to attain the magnitudes of about 1000 kA. Referring to Fig. IB, an electric scheme of an exemplary system 100 for producing high intensity electric current pulses is illustrated. The system 100 is based on a parallel installation of a number of equivalent discharge modules 101 coupled to the load device 15. Three such discharge modules 101 are presented in the system shown in Fig. IB. Each discharge module 101 includes the discharge circuit B (shown in Fig. IA) that includes the corresponding capacitor bank 12 and the high current switch 14. The system 100 includes an activation means 102 coupled to the switches 14 and assuring substantially simultaneous activation thereof. For example, when the high current switches are vacuum switches (ignitrons), all the switches can be initiated by a common ignition circuit, so as to provide substantially simultaneous ignition thereof.

However, it was found that in practice the switches 14 cannot operate simultaneously. Thus, even a miserable ignition advance of one of the switches can lead to such a voltage decrease on the capacitor bank 12, that the ignition of the rest of the switches will be prevented. As a result, all the current will pass through this operating switch, thereby damaging it.

SUMMARY OF THE INVENTION

There is still a need in the art for, and it would be useful to have, novel system for producing high intensity electric current pulses and supplying them to a load device. The apparatus should be sufficiently reliable and efficient for industrial applications, including mass production machinery, for example, for pulse magnetic forming of metals. The load device can be installed in fixed position providing an easy approach and positioning work pieces relatively to the tool, or alternatively, it can be movable enabling robot-manipulated positioning thereof relatively to a fixed work piece; anyway, the system should be able to supply the current pulses to the load device.

The present invention partially eliminates disadvantages of the conventional techniques and provides a new system producing higher electric current pulses than conventional systems, at higher frequency when needed, and having reliability and efficiency level, satisfactory for industrial applications, including mass production lines. According to an embodiment of the invention, the system for producing a high intensity electric current pulse includes a plurality of discharge modules connected in parallel to a load device. Each discharge module comprises a capacitor bank and a high current switch connected in series to the load device. The system also includes a high voltage supply device coupled to the capacitor banks for charging thereof. Any two of the discharge modules are coupled to each other through a resistive element so as to prevent sharp voltage decrease across the capacitor banks, and thereby to enable a concurrent operation of the high current switches.

According to an embodiment of the invention, the resistive element between each two discharge modules includes two resistors each connected to a potential terminal of the corresponding capacitor bank and to a common energized bus connected to a potential terminal of said high voltage supply device.

According to an embodiment of the invention, the high voltage supply device is coupled to each capacitor banks through at least one diode open in the capacitor bank direction.

According to an embodiment of the invention, the system further comprises at least one sensor configured for contactless measurements of the high electric discharge current provided by the discharge modules. For example, the sensors can be based on a Rogovsky coil.

According to another embodiment of the invention, the system further includes a voltage divider configured for coupling at least one of the capacitor banks to a voltmeter unit for measurements of the high voltage across the capacitor bank. For example, the voltmeter unit can be based on a computer-based device configured for collecting the data indicative of the high-voltage from the voltage divider and display the data on a monitor.

According to an embodiment of the invention, the load device is coupled to at least one of the capacitor banks through an electro-conductive screen surrounding the corresponding high current switch. For example, the electro-conductive screen can be arranged in a grounded part of the corresponding discharge module. According to another example, the electro-conductive screen can be arranged in an energized part of the corresponding discharge module. According to this embodiment, the discharge current in the electro-conductive screen is directed oppositely to the current in the switch.

According to another aspect, the present invention provides ignition unit configured for providing an ignition electric pulse to the high current switches. The ignition unit comprises a coaxial cable loop having a center conductor and an outer conductor separated by a dielectric, an ignition system resistor connected to two ends of the center conductor, and a discharge circuit formed by said outer conductor connected in series to an ignition system capacitor and an ignition system switch. The ignition system resistor can be coupled to the high current switch of each discharge module through one or more connecting cables. Each connecting cable has a center conductor and an outer conductor separated by a dielectric. The center conductor is connected to a trigger electrode of the high current switch, whereas the outer conductor is connected to one of the switching electrodes of said high current switch.

The ignition system comprises an amplifying transformer and a rectifier. A secondary coil of the amplifying transformer is coupled through the rectifier to said ignition system capacitor for charging thereof, whereas a primary coil of the amplifying transformer is fed by mains voltage.

The ignition system further comprises another amplifying transformer. The ignition system switch is operated by a high voltage pulse provided by a secondary coil of this amplifying transformer to a trigger electrode of the ignition system switch. Accordingly, a primary coil of this amplifying transformer is coupled to another capacitor that is charged by mains voltage trough another half-wave rectifier.

According to an embodiment of the invention, each discharge module is coupled to a collector of the load device through a predetermined number of coaxial cables. The predetermined number is obtained by

where /_/ is a maximal magnitude of an electric current pulse provided by said system, and /_? is a limiting current pulse admissible for one cable; where the magnitude of // is obtained by //=«/3, where /₃ is the limiting current pulse admissible for one switch, and n is the total number of the discharge modules in the system.

According to another embodiment of the invention, each discharge module is coupled to a collector of the load device through at least one pair of bus-bars. The bus- bars are separated from each other by a predetermined distance. Moreover, the bus-bars can be insulated one from another by a dielectric material having an electric strength higher than 20 kV/mm.

According to an embodiment of the invention, the system comprising a technological table that includes a collector having a pair of bus-bars terminated by a first pair of symmetrically opposed contact plates at one end and by a second pair of symmetrically opposed contact plates at the other end. The contact plates extend outwardly from opposing sides of a gap defined between the bus-bars. The first pair of the contact plates is located vertically on one of the sides of the table, whereas the second pair of the contact plates is located horizontally within a rectangular opening arranged in a top plate of the table. A slot is defined between edges of the rectangular opening and the second pair of contact plates. The slot has a width that is higher than a predetermined threshold value B (in mm) that can be obtained by the empirical equation: B= 2U/3, where U is a total voltage provided by the capacitor banks (in kV).

The gap between the bus-bars has a width in the range of from about 0.5mm to about 5mm, and preferably between 0.5mm and 2mm. According to an embodiment of the invention, the gap between the bus-bars is filled with a dielectric material having an electric strength higher than about 20 kV/mm. According to another embodiment of the invention, the bus-bars are covered by a dielectric coating.

Thus, according to one broad aspect of the invention, there is provided a system for producing a high intensity electric current pulse, comprising: a plurality of discharge modules connected in parallel to a load device, each discharge module comprising a capacitor bank and a high current switch connected in series to the load device; and a high voltage supply device coupled to the capacitor banks for charging thereof; wherein any two of the discharge modules are coupled to each other through a resistive element so as to prevent sharp voltage decrease across the capacitor banks, and thereby to enable a concurrent operation of the high current switches.

According to another broad aspect of the invention, there is provided an ignition unit for providing an ignition electric pulse to a high current switch, said ignition unit comprising: a coaxial cable loop having a center conductor and an outer conductor separated by a dielectric, an ignition system resistor connected to two ends of the center conductor, a discharge circuit formed by said outer conductor connected in series to an ignition system capacitor and an ignition system switch.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figs. IA and IB are electric schemes of prior art systems for producing a strong electric pulse;

Fig. 2 is an electric scheme of a system for producing a strong electric pulse, according to an embodiment of the present invention;

Fig. 3 is an electric scheme of an alternative embodiment of the system of the present invention;

Fig. 4A is an example of a configuration of a single discharge module of the system of the present invention;

Fig. 4B is another example of a configuration of a single discharge module of the system of the present invention;

Fig. 5 is an electric scheme of a system for producing a strong electric pulse, according to a further embodiment of the present invention;

Fig. 6 illustrates an electric scheme of the ignition unit of the system of the present invention for producing a strong electric current pulse, according to one embodiment of the present invention; Fig. 7 illustrates a schematic diagram of connection of the discharge modules of the system of the invention to a collector of a load device, according to an embodiment of the invention; and

Fig. 8 illustrates an implementation of the collector of the load device, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The principles and operation of the system for producing high intensity electric current pulses according to the present invention may be better understood with reference to the drawings and the accompanying description, wherein like reference numerals have been used throughout to designate identical elements, where it is convenient for description. It is understood that these drawings are given for illustrative purposes only and are not meant to be limiting.

The electric schemes in Figs. IA and IB have already been described the introduction, so further detailed discussion of these arrangements is considered unnecessary here.

Referring to Fig. 2, an electric scheme of a system 20 for producing strong (high intensity) electric current pulses is shown, according to one embodiment of the invention. Similar to the system 100 shown in Fig. IB, in order to provide a strong electric current pulse to the load device 15, a plurality of equivalent discharge modules 21 is employed connected in parallel to the load device 15. For the purpose of simplicity of illustration, only three discharge modules 21 are shown in Fig. 2. Each discharge module 21 comprises the corresponding capacitor bank 12 and the individual high current switch 14 connected to a potential terminal 121 of the corresponding capacitor bank 12. Thus, the resulting current in the load device 15 can be equal to the sum of the currents in all individual discharge circuits.

According to an embodiment of the present invention, ground terminals 122 of all the capacitor banks 12 can be connected together by a common grounded bus 123 coupled to the grounded terminal 112 of the high- voltage supply device 11. Preferably, the grounded bus 123 is implemented on the basis of a conductive bus-bar. Examples of the materials suitable for the common conductive bus-bar include, but are not limited to, copper and aluminum. It should be appreciated by a person skilled in the art that each discharge modules 21 corresponds to a series RLC circuit. In general, the current resonant frequency / (in Hertz) of a tuned RLC resonance circuit can be obtained by:

f-ττ≡ ⁽¹⁾ where C is the capacitance (in Farads) of the capacitor bank 12 and L is the inductance (in Henrys) of the discharge circuit, which, in turn, can be obtained by: L = L_U + L_dc, (2) where Ly is the inductance of the load device, and Lj_c is the inductance of the rest of the discharge circuit. It should be kept in mind that the capacities C and the inductances L of all the individual discharge circuits must be substantially equal, to assure their common frequency and to prevent any interference among the discharge modules 21.

Preferably, the high current switch 14 is a three electrode spark-gap switch including two switching electrodes 141 and 142 forming the switching paths and a third electrode (trigger electrode) 143 configured for providing passage of high current between the two switching electrodes. Examples of the high current switch 14 include, but are not limited to, vacuum switch, spark gap switch filled with a gas (trigatron), ignitron, thyratron, etc. The operation of these switch devices is known per se, and therefore will not be expounded hereinbelow.

The system 20 also includes an ignition unit 19 configured for closing the high current switch 14 by launching an ignition high voltage electric pulse to the trigger electrode 143. A detail description of the ignition unit 19 according to one embodiment of the present invention will be described hereinbelow.

As noted in the Background section, it would be harmful to operation of the system when an ignition advance of one of the switches 14 will result at a voltage decrease on the capacitor bank 12 and prevention of the ignition of the other the switches.

In order to exclude such a possibility, the present invention teaches to couple each discharge module 21 to another discharge module 21 through a current resistive element. Various embodiments of the current resistive element will be described hereinbelow. According to the embodiment shown in Fig. 2, such a resistive element between each two discharge modules 21 includes two resistors 22 each connected to the potential terminal 121 of the corresponding capacitor bank 12 and to a common energized (potential) bus 23. The bus 23 is connected to a potential terminal 111 of the high voltage supply device 11. The purpose of the resistors 22 is to separate the discharge modules 21 from each other as will be described herebelow.

Let us consider a case when one of the switches 14 comes in action ahead of the other switches. The changes of the voltage U over time t across the capacitor banks 12 in the discharge modules 21 in which the switches were not yet activated can be estimated by

U ≡ U_maxexpf-t/RC), (3) where U_max is the maximal voltage, R is the electrical resistance of the resistor 22 and C is the capacitance of the capacitor bank 12. According to an embodiment of the present invention, the magnitude of the electrical resistance R is such that the ignition delay τ between the switches 14 would be less than or equal to the relaxation time RC of the capacitor bank 12, to wit: τ <RC. Such a provision can prevent too sharp voltage decrease across the capacitor banks 12, and thus enables the concurrent operation of all the switches 14.

An additional functionality of this separation is to direct all the discharge current of each capacitor bank through its respective switch, thus to prevent switch overloading. Nevertheless, some degree of the current non-uniformity is possible, and it is recommended to use switches having the magnitude of the breakdown current at least 10% higher than the discharge current of the capacitor bank.

For safety reasons, the terminal 112 of the high- voltage supply device 11 is permanently grounded; while another terminal (potential terminal 111) can also be grounded through the switch 17, when the system is out of operation. The resistors 22 can also function as a current limiting resistor to restrict the discharge current when the switch 17 is closed.

For example, typical values for the components of the system 20 and the parameters of its operation are as follows. The number of the discharge modules 21 is 8, the nominal voltage provided by the high-voltage supply device is 2OkV, the electrical resistance of the resistor 22 is 4kθhm and the capacitance of the capacitor bank 12 is 40 microfarads; the electric current pulse provided across the load device 15 can have a value of about 1.5χ 10⁶ A.

Referring to Fig. 3, an electric scheme of a system 30 for producing strong electric current pulses is shown, according to another embodiment of the invention. Similar to the systems shown in Fig. IB and Fig. 2, in order to provide a strong electric current pulse to the load device 15, a plurality of equivalent discharge modules 21 is employed connected in parallel to the load device 15, each discharge module 21 comprising the corresponding capacitor bank 12 and the individual high current switch 14.

According to this embodiment of the invention, the system 30 includes a plurality of charge circuits; each charge circuit couples a high- voltage supply device 11 in series to the corresponding high voltage capacitor bank 12 through the switch 13 and a diode 31. Notwithstanding that the term "diode" usually implies a small signal device with current typically in the milliamp range; and the term "rectifier" is a power device, operating from IA to IOOOA or even higher, in this description the term diode and the term rectifier are equivalent. The diodes 31 are open in the capacitor charge direction and closed in their discharge direction, so as to prevent the discharge current through an energized bus 33.

Similar to the embodiment shown in Fig. 2, the resistors 22 separate the discharge modules 21 from each other, thereby assuring the concurrent ignition of the switches 14 within the time period equal to the product of the electrical resistance R of the resistor 22 by the capacitance C of the capacitor bank 12. Likewise, the switch 17 enables the safety grounding of the energized charge circuits via the resistors 22 when the apparatus is out of operation.

In this design, energy losses on the resistors 22 over the charging time are prevented. In this case, it is also recommended to use switches 14 with breakdown current at least 10% higher than the discharge current of the capacitor banks 12.

It should be noted that the modular structure of the system of the present invention enables advanced reliability of the high intensity electric current pulse supply. Firstly, the number of the modules can be chosen such that if one of them is damaged, the pulse received by the load device is still enough for proceeding to the required action. Secondly, a spare discharge circuitry can be installed but not connected, so that when one of the operating circuitries is damaged, it can be disconnected and the spare circuitry connected in place of it.

According to an embodiment of the invention, an additional improvement can be achieved by providing a sensor (not shown) for each capacitor bank 12 for contactless measurements of the high electric discharge current. According to an example, the sensor suitable for such measurements can be based on a Rogovsky coil placed around the conducting terminal of the capacitor bank 12. An operating principle of the Rogovsky coil is based on sensing the magnetic field in the space around the conductor that carries the current. The operation and utilization of the Rogovsky coil is known per se, and therefore will not be expounded herein. The measurement results can be gathered and analyzed in real time by a computer unit (not shown), producing a report and/or signal representative of the system behavior.

According to still another embodiment of the invention, an additional improvement can be achieved by conducting measurements of the high electric voltage across each capacitor bank 12. For this purpose, each capacitor bank 12 can be coupled to a voltmeter unit (not shown) through a voltage divider (not shown). For example, the voltmeter unit can be based on a computer-based device (not shown) adapted for collecting the data indicative of the high- voltage from the voltage divider and display these data on a monitor, when required. The operation of the voltage divider and the computer unit for such purposes is known per se and will not be expounded herebelow.

The electric pulse frequency of the electromagnetic forming apparatuses usually does not exceed 100 kHz. However, there are some applications, such as the electromagnetic forming of relatively low electro-conductive materials, e.g., steel and other ferrous alloys, when higher frequencies than 100 kHz can be required.

More specifically, the skin layer thickness A of conductivity of the workpiece can be estimated by

where pis the specific resistance of the workpiece material,/ is the pulse current frequency obtained by Eq. (1), and μo is the magnetic constant (JJQ = 4π 10 ^~7 HnJm). When the skin layer thickness A exceeds the thickness of the workpiece, the workpiece becomes transparent for the electromagnetic field, and the energy brought thereto by the electric pulse can be partially lost.

According to Eq. (3), the decrease of Δ can be achieved by using the pulses of high frequencies/ As can be understood from Eqs. (1) and (2), the frequency /varies inversely with the capacity C of the capacitor bank 12 and with the inductance L = Ly + L_dc of the discharge module 21. It can be noted that capacity C of the capacitor bank, preferably, should not be decreased, because the capacity C defines the amount of the energy provided to the load device 15. Therefore, the preferential way to increase the frequency is to reduce the inductance of the discharge circuit L_dc-

It should be also noted that efficiency η of the discharge module 21 can be obtained by

η^" L + L ^{■ (5)}

Therefore, the decrease of the inductance L_dc can also result at the enhancement of the efficiency^.

The circuit inductance L_d0 includes inductances of the circuit elements, such as the switch and all the current conductors. Some ways to diminish their inductance will be disclosed hereinbelow.

It should be noted that the modular discharge circuitry structure of the system of the present invention provides a decrease of the system inductance.

Moreover, special configurations of the discharge circuitry shown hereinbelow can also result at a further decrease of the inductance L_dc-

Referring to Fig. 4A, an example of the configuration of the discharge module 21 providing the decrease of the inductance L_d0 is schematically illustrated. According to this embodiment, the discharge module 21 includes the capacitor bank 12 coupled to an energy supply (not shown) through an energized line 42 and a grounded line 43. The discharge module 21 also includes the vacuum discharge switch 14 coupled to the potential terminal 121 of the capacitor bank 12 through an energized connection line 44 (at one end of the switch) and to an energized terminal 151 of the load device 15 through an energized connection line 45 (at the other end of the switch). According to this embodiment of the invention, in order to decrease the inductance of the switch the coupling of the load device 15 to the ground terminal 122 of the capacitor bank 12 is implemented through an electro-conductive screen 46 formed as a tube surrounding the switch 14. More specifically, the electro-conductive

! screen 46, arranged in the grounded part of the discharge circuitry, is coupled to the load device 15 through a grounded connection line 47, and to a ground terminal 122 of the capacitor bank 12 (e.g., to the grounded line 43) through a grounded connection line 48. hi such a configuration, the discharge current in the electro-conductive screen 46 is directed oppositely to the current in the switch 14. The direction of the discharge current

I in the circuitry is indicated by the arrows.

The connection lines 45 and 47 are terminated by terminals 49 A and 49B. Preferably, but not mandatory, the terminals 49A and 49B are placed close enough to each other. Such a provision enables to use a common coaxial cable for connecting these both terminals to the load device 15.

' Preferably, but not mandatory, the connection lines 45 and 47 as well as the connection lines 44 and 48 are formed of coaxial cables (schematically shown by reference numerals 491 and 492, respectively), either single or bundled. The center conductors of the coaxial cables can be selected for the energized connection lines 44 and 45, while the outer conductors of the coaxial cables can be selected for the i grounded lines 47 and 48.

Preferably, the discharge switch 14 is produced with the electro-conductive screen 46 being an integral part of the switch and having connectors (not shown) at both sides thereof, thus enabling connection of the switch 14 to the outer conductor of one or more co-axial cables, while the center conductors of these cables are connected to the discharge switch electrodes.

Referring to Fig. 4B, another example of the configuration of the discharge module 21 providing the decrease of the inductance Lj₀ is schematically illustrated. This embodiment differs from the embodiment shown in Fig. 4A in that the electro- conductive screen 46 surrounding the switch 14 is arranged in the energized part of the

¹ discharge circuitry. Specifically, the electro-conductive screen 46 is connected to the switching electrode 141 of the switch 14 through the energized connection line 401 and to the load device 15 through an energized connection line 402. The potential terminal 121 of the capacitor bank 12 is coupled to the switching electrode 142 of the switch 14 through the energized connection line 44. In turn, the grounded terminal 122 of the capacitor bank 12 is coupled to the load device 15 through a grounded connection line 403. Similar to the embodiment shown in Fig. 4A, the discharge current in the electro- conductive screen 46 is directed oppositely to the current in the switch 14. The direction of the discharge current is indicated by the arrows.

Referring to Fig. 5, an electric scheme of a system 50 for producing a strong electric pulse is shown, according to yet another embodiment of the present invention. The system includes a plurality of discharge modules 51 coupled to the load device 15. Specifically, each discharge module 51 includes a resistor 53 connected in series to an energized electrode 111 of the high- voltage supply device 11 and a capacitor bank 52. The capacitor banks 52 of all the discharge modules 51 are connected to a capacitor bus 56 connecting the capacitor banks 52 to an energized terminal 151 of the load device 15. The load device 15 is connected to a grounded electrode 112 of the high- voltage supply device 11 through a grounded bus 55 that is common to all the discharge modules 51. Each discharge module 51 also includes a high current switch 54 connected to the grounded bus 55 and to a junction 56 of connection the resistor 53 to the capacitor bank 52. Preferably, the capacitor bus 56 is insolated from the grounded bus 55 by a dielectric plate (not shown) made of a dielectric material having an electrical strength grater than about 20kV7mm. Examples of suitable dielectric materials include, but are not limited to, epoxyglass, polyethylene, MYLAR^®, Teflon, Silicon rubber, etc.

When the switch 54 is open, the capacitor bank 52 is charged by the voltage supply device 11 through the resistor 53 and the load device 15. The capacitor bank 52 is then can be discharged by closing the switch 54, to supply a high voltage to the load device 15 and thereby generate an electric current pulse therethrough. The closing of the switch 54 is performed by providing an ignition high-voltage electric pulse from the ignition unit 19 to a trigger electrode 543 of the switch 54.

Referring to Fig. 6, an electric scheme of the ignition unit 19 of the system of the present invention for producing a strong electric current pulse is illustrated, according to one embodiment of the present invention. The ignition system 19 includes a coaxial cable loop 61 having a center conductor 611 and an outer conductor 612 separated by a dielectric. The coaxial cable loop 61 can be formed of one or more turns having a diameter of about 10cm to 30cm. Two ends 613 and 614 of the center conductor 611 are connected to two ends 621 and 622 of an ignition system resistor 62, respectively. In turn, two ends 615 and 616 of the outer conductor 612 are connected in series with an ignition system capacitor 63 and two switching electrodes 641 and 642 of an ignition system switch 64, thereby to form a discharge circuit.

The high current switch 14 is coupled to the resistor 62 through a connecting cable 65 having a center conductor 651 and an outer conductor 652 separated by a dielectric. At one end, the center conductor 651 is connected to the trigger electrode 143 of the switch 14, whereas the outer conductor 652 is connected to the switching electrode 142 of the switch 14. At the other end, the center conductor 651 and the outer conductor 652 are connected to the two ends 621 and 622 of the resistor 62.

The capacitor 63 is charged by a charging module 630 that includes an amplifying transformer 66 and a rectifier (diode) 67. Specifically, the capacitor 63 is coupled to a secondary coil 661 of the amplifying transformer 66 through the rectifier (diode) 67. A primary coil 662 of the amplifying transformer 66 is fed by mains voltage.

The switch 64 is operated by a high voltage pulse provided by a second ignition unit 640. The second ignition unit 640 includes an amplifying transformer 68 and a rectifier module 69. A second a secondary coil 681 of an amplifying transformer 68 is connected to a trigger electrode 643 of the switch 64. A primary coil 682 of the amplifying transformer 68 is fed by the rectifier module 69 that includes a capacitor 691 in series with a switch 692. The capacitor 691 can, for example, be charged by mains voltage trough a half- wave rectifier (diode) 693.

In operation, when required, the capacitor 691 can be discharged through the primary coil 682 by closing the switch 692. In this case, the voltage across the primary coil 682 will be amplified by the transformer 68 and fed to the trigger electrode 643 of the switch 64. In turn, this will result at the closing of the switch 64, and thereby providing the discharge of the capacitor 63 through the outer conductor 612 of the coaxial cable loop 61. It can be appreciated that the outer conductor 612 is linked to the center conductor 611 by an alternating magnetic field created therebetween. Thus, the electric pulse created across the center conductor 611 is fed to the trigger electrode 143 of the switch 14 through the connecting cable 65, thereby to close the switch 14. It should be noted that the provision of the embodiment of the ignition system 19 provides an electric separation of the discharge circuit of discharge modules (21 in Fig. 2) from the discharge circuit of the ignition system 19. In particular, because there is no direct electrical connection between the center conductor 611 and the outer conductor 612, the high voltage across the switch 14 will not interfere with the high voltage across the switch 64.

In one reduction to practice, typical values for the components and parameters of operation of the ignition system 19 are as follows: the electrical resistance of the resistor 62 is in the range of lMohm to 3Mohm, the capacitance of the capacitor 63 is in the range of 0.2 microfarads to 2 microfarads, the capacitance of the capacitor 691 is in the range of from about 0.1 microfarads to about 2 microfarads, the voltage provided across the capacitor 63 is in the range of from about 6kV to about 9kV, the voltage provided to the trigger electrode 643 is in the range of from about 6kV to about 9kV.

Reference is now being made to Fig. 7 illustrating a schematic diagram of connection of the discharge modules 21 to a collector 71 of the load device 15 by means of connection lines 72, according to an embodiment of the invention.

According to this embodiment, the connection lines 72 connecting discharge modules 21 to the collector 71 include coaxial cables. Fig. 7 shows the example in which the number of the connection lines 72 equals 3. A working coil 73 of the load device 15 is mounted on the collector 71. Each discharge module 21 is connected to the collector 71 through one or more coaxial cables. Number N of the coaxial cables connecting each discharge module 21 to the collector 71 has a predetermined value. T According to an embodiment of the invention, the number N can be obtained by N=I]/l₂, where /_/ is the maximal magnitude of the electric current pulse provided by the system of the present invention, and /_? is the limiting current pulse admissible for one cable. In turn, the magnitude of /_/ can be obtained by

where /₃ is the limiting current pulse admissible for one switch (14 in Fig.l), and n is the total number of the switches (or discharge modules) in the system.

Preferably, all the coaxial cables for each discharge module have the same length, which is determined by technological requirements. For example, a machine with 25 kJ output can be equipped with 10 cables, each having length of about 2.5m. The radius of the cable bending can be about 0.3 m. The total length can be about 2.5 m. A workstation (working table) can have dimensions of about Im by about 0.6m. The distance between a voltage supply device and the workstation can be about 0.8m. In general, the distance between the system and the workstation should be minimized in order to reduce the losses along the coaxial cables. In the cases where the workstation is placed at a greater distance from the magnetic pulse system, connecting as many as possible coaxial cables in parallel may compensate the losses along the cables.

According to another embodiment, the connection lines 72 connecting the discharge modules 21 to the collector 71 include one or more pairs of bus-bars (not shown). These bus-bars can, for example, be made of copper or aluminum. Preferably, the bus-bars should be separated from each other by a distance of lmm to 3mm, and be insulated one from another by a dielectric material having an electric strength higher than about 20kV/mm. Examples of the dielectric material include, but are not limited to, epoxyglass and polycarbonate.

Referring to Fig. 8, an implementation of the collector 71 of the load device (not shown) is illustrated, according to an embodiment of the invention. The collector 71 includes a pair of bus-bars 71a and 71b made of a conductive material, e.g., copper or aluminum. The bus-bars 71a and 71b are arranged within a technological table 81. The bus-bars 71a and 71b are terminated by a pair symmetrically opposed contact plates 83 and 84 at one end and by another pair symmetrically opposed contact plates 85 and 86 at the other end, extending outwardly from opposing sides of a gap 87 defined between the bus-bars 71a and 71b. Generally, the bus-bars 71a and 71b can take any shape which would be convenient for connection the connection lines (72 in Fig. 7) to the contact plates 83 and 84 and the load device, e.g. external inductor, to the contact plates 85 and 86. According to this embodiment of the invention, the contact plates 83 and 84 are located vertically on one of the sides of the table 81. The contact plates 85 and 86 are located horizontally within a rectangular opening 811 arranged in a top plate 811 of the table 81. A slot 812 defined between edges 813 of the opening 811 and the contact plates 85 and 86 has a predetermined width. Specifically, the width B should be higher than a predetermined threshold value B (in mm) that can be obtained by the empirical equation: B= 2U/3, where U is the total voltage provided by the capacitor banks (in kV). The contact plates 83, 83, 85 and 86 each includes bolt openings 88 for attaching connection lines to the contact plates 83 and 84, and the load device to the contact plates 85 and 86.

According to an embodiment of the invention, the gap 87 has a width in the range of from about 0.5mm to about 5mm (preferably, between 0.5mm and 2mm), and is filled with a dielectric material having an electric strength higher than about 20 kV/mm. It should be noted that this gap should be as small as possible in order to get a minimal self inductance of the system, thereby to increase its efficiency. Examples of the dielectric material include, but are not limited to, MYLAR™, epoxyglass and polycarbonate.

According to another embodiment of the invention, the gap 87 has a width in the range of from about 0.5mm to about 5mm (preferably, between 0.5mm and 2mm), and the bus-bars 71a and 71b are covered by a dielectric coating, such as a TEFLON™ or other dielectric material.

According to yet an embodiment of the invention, the collector (71 in Fig.7) and the load device can be mounted on an automatic robot manipulator (not shown). In such a case, the connection lines (72 in Fig. 7) connecting the discharge modules to the collector are based on flexible coaxial cables moving together with the robot manipulator.

As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures systems and processes for carrying out the several purposes of the present invention.

It is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims.

Claims

CLAIMS:

1. A system for producing a high intensity electric current pulse, comprising: a plurality of discharge modules (21, 51) connected in parallel to a load device (15), each discharge module (21) comprising: a capacitor bank (12, 52) having a potential terminal (121) and a ground terminal (122); and a high current switch (14, 54) connected in series to the load device (15); and a high voltage supply device (11) coupled to the capacitor banks (12) for • charging thereof; wherein any two of the discharge modules (21) are coupled to each other through a resistive element so as to prevent sharp voltage decrease across the capacitor banks, and thereby to enable a concurrent operation of the high current switches (14).

2. The system according to Claim 1, wherein said high voltage supply device (11) has an energized terminal (111) and a grounded terminal (112), the system comprises a grounding switch (17) for grounding said energized terminal by means of said grounding switch when the system is out of operation.

3. The system according to Claim 2, wherein the grounding of said energized terminal is implemented through said resistive element.

¹ 4. The system according to any one of the preceding claims, wherein said resistive element between each two discharge modules (21) includes two resistors (22) each connected to the potential terminal (121) of the corresponding capacitor bank (12) and to the common energized bus (23) connected to the potential terminal (111) of said high voltage supply device (11).

5. The system according to any one of the preceding claims, wherein an electric capacity of the capacitor banks (12) and an inductance of discharge circuits of all said discharge modules are essentially equal.

6. The system according to any one of the preceding claims, comprising at least one diode (31), said at least one diode being coupled in series to said high voltage

¹ supply device (11) and to at least one capacitor bank (12), and is open in the capacitor bank direction.

7. The system according to Claim 1, wherein the ground terminals (122) of the capacitor banks (12) are connected together by means of a common grounded bus (123) coupled to the grounded terminal (122) of said high-voltage supply device (11).

8. The system according to Claim 1, wherein each high current switch (14) has magnitude of the breakdown current at least 10% higher than the discharge current of the corresponding capacitor bank (12).

9. The system according to Claim 1 comprising sensor for at least one capacitor bank (12), the sensor configured for contactless measurements of the high electric discharge current provided by the discharge modules.

10. The system according to Claim 9, wherein the sensors is based on a Rogovsky coil.

11. The system according to Claim 1 comprising a voltage divider configured for coupling at least one of the capacitor banks (12) to a voltmeter unit for measurements of the high voltage across the capacitor bank.

12. The system according to Claim 11, wherein said voltmeter unit is based on a computer-based device configured for collecting the data indicative of the high- voltage from the voltage divider and display the data on a monitor.

13. The system according to any one of the preceding claims, wherein the load device (15) is coupled to at least one of the capacitor banks (12) through an electro- conductive screen (46) surrounding the corresponding high current switch (14).

14. The system according to Claim 13, wherein said electro-conductive screen (46) is arranged in a grounded part of the corresponding discharge module.

15. The system according to Claim 13, wherein said electro-conductive screen (46) is arranged in an energized part of the corresponding discharge module.

16. The system according to Claim 13, wherein the discharge current in the electro-conductive screen (46) is directed oppositely to the current in the high current switch (14).

17. The system according to any one of the preceding claims, comprising an ignition unit (19) configured for providing an ignition electric pulse to said high current switches (14).

18. The system according to claim 17, wherein said ignition unit (19) comprising: a coaxial cable loop (61) having a center conductor (611) and an outer conductor (612) separated by a dielectric, an ignition system resistor (62) connected to two ends (621) and (622) of the center conductor (611), and a discharge circuit formed by said outer conductor (612) connected in series to an ignition system capacitor (63) and an ignition system switch (64).

19. The system according to Claim 18 comprising a plurality of connecting cables (65) for coupling the high current switch of each discharge module to the ignition system resistor (62).

20. The system according to Claim 19, wherein each connecting cable (65) has a center conductor (651) and an outer conductor (652) separated by a dielectric, said center conductor (651) is connected to a trigger electrode (143) of said high current switch (14), whereas said outer conductor (652) is connected to one of the switching electrodes (141) and (142) of said high current switch (14).

21. The system according to any one of claims 18 to 20, wherein said ignition unit (19) comprises: an amplifying transformer (66) having a primary coil (662) and a secondary coil (661); and a rectifier (67).

22. The system according to Claim 20, wherein the secondary coil (661) of the amplifying transformer (66) is coupled through the rectifier (67) to said ignition system capacitor (63) for charging thereof, whereas the primary coil (662) of the amplifying transformer (66) is fed by mains voltage.

23. The system according to any one of claim 18 to 22, wherein said ignition unit comprises another amplifying transformer (68), wherein said ignition system switch (64) is operated by a high voltage pulse provided by the secondary coil (681) of said another amplifying transformer (68) to a trigger electrode of said ignition system switch (64), whereas a primary coil (682) of said another amplifying transformer (68) is coupled to another capacitor (691) that is charged by mains voltage trough another half- wave rectifier (693).

24. The system according to Claim 1, wherein each discharge module (21, 51) is coupled to a collector (71) of the load device (15) through a predetermined number of connecting lines (72).

25. The system according to Claim 24, wherein said connecting lines (72) are coaxial cables, wherein the predetermined number is obtained by

where // is a maximal magnitude of an electric current pulse provided by said system, and h is a limiting current pulse admissible for one cable; where the magnitude of/; is obtained by /₇=71/₃, where /_? is the limiting current pulse admissible for one switch, and n is the total number of the discharge modules in the system.

26. The system according to Claim 25 comprising an automatic robot manipulator, wherein said collector and said load device are mounted on said automatic robot manipulator.

27. The system according to Claim 1, wherein each discharge module (21, 51) is coupled to a collector (71) of the load device through at least one pair of bus-bars.

28. The system according to Claim 27, wherein the bus-bars in said at least one pair are separated from each other by a predetermined distance.

29. The system according to Claim 25, wherein the bus-bars in said at least one pair are insulated one from another by a dielectric material having an electric strength higher than 20 kV/mm.

30. The system according to any one of the preceding claims, comprising a technological table including a collector having a pair of bus-bars terminated by a first pair of symmetrically opposed contact plates at one end and by a second pair of symmetrically opposed contact plates at the other end, the contact plates extending outwardly from opposing sides of a gap defined between the bus-bars, said first pair of the contact plates is located vertically on one of the sides of the table, said second pair of the contact plates is located horizontally within a rectangular opening arranged in a top plate of the table.

31. The system according to Claim 30, wherein a slot is defined between edges of said rectangular opening and the second pair of contact plates, the slot has a width that is higher than a predetermined threshold value B (in mm) that can be obtained by the an empirical equation: B= IU β, where t/ϊs a total voltage provided by the capacitor banks (in kV).

32. The system according to Claim 30, wherein said gap between the bus-bars has a width in the range of from about 0.5mm to about 5mm.

33. The system according to Claim 30, wherein said gap between the bus-bars is filled with a dielectric material having an electric strength higher than 20 kV/mm.

34. The system according to Claim 30, wherein said gap between the bus-bars has a width in the range of from about 0.5mm to 5mm, and the bus-bars are covered by a dielectric coating.

35. An ignition unit (19) for providing an ignition electric pulse to a high current switch, said ignition unit comprising: a coaxial cable loop having a center conductor and an outer conductor separated by a dielectric, an ignition system resistor connected to two ends of the center conductor, a discharge circuit formed by said outer conductor connected in series to an ignition system capacitor and an ignition system switch.

36. The ignition unit according to Claim 35 comprising at least one connecting cable for coupling said high current switch to the ignition system resistor.

37. The system according to Claim 36, wherein each connecting cable has a center conductor and an outer conductor separated by a dielectric, said center conductor is connected to a trigger electrode of said high current switch, whereas said outer conductor is connected to one of the switching electrodes of said high current switch.

38. The system according to Claim 35 comprising an amplifying transformer and a rectifier, wherein a secondary coil of the amplifying transformer is coupled through the rectifier to said ignition system capacitor for charging thereof, whereas a primary coil of the amplifying transformer is fed by mains voltage.

39. The system according to Claim 35 comprising another amplifying transformer, wherein said ignition system switch is operated by a high voltage pulse provided by a secondary coil of said another amplifying transformer to a trigger electrode of said ignition system switch, whereas a primary coil of said another amplifying transformer is coupled to another capacitor that is charged by mains voltage trough another half-wave rectifier.