Leijon, Mats (Hävelvägen 6, S- Uppsala, SE-756 47, SE)
Lindblom, Adam c/o Skahlberg (Bävernsgränd 18 A, Uppsala, SE-753 19, SE)
Isberg, Jan (Kalsgatan 27, Västeras, SE-722 14, SE)
Bernhoff, Hans (Geijersgatan 56, Uppsala, S-752 31, SE)
Leijon, Mats (Hävelvägen 6, S- Uppsala, SE-756 47, SE)
Lindblom, Adam c/o Skahlberg (Bävernsgränd 18 A, Uppsala, SE-753 19, SE)
Isberg, Jan (Kalsgatan 27, Västeras, SE-722 14, SE)
| 1. | System for the generation of highpower pulses comprising an aircored transformer (10) provided with: a primary winding (11) intended for recharging of magnetic energy in the trans former (10) and a secondary winding (12) intended for discharging of the magnetic energy accumulated in the transformer (10) in the form of a highpower pulse to a load (16), means (13) for the generation of an energy pulse for accumulation of magnetic energy in the transformer (10) via the primary winding (11), a repetitive breaker (14) intended to break the current on the primary side of the transformer (10), characterized in that said primary and secondary winding (11,12) are coaxially arranged in relation to each other in a highvoltage cable. |
| 2. | System according to claim 1, characterized in that said primary and secondary windings (11,12) arranged coaxially in relation to each other comprise an inner conductor (30) enclosed by a first semiconducting layer (31), then said first semiconducting layer (31) is enclosed by a first layer (32) of fixed insulation, then said first layer (32) of fixed insulation is enclosed by a second semiconducting layer (33), then said second semiconducting layer (33) is enclosed by one outer conductor (34), then said one outer conductor (34) is enclosed by a third semiconducting layer (35), then said third semiconducting layer (35) is enclosed by a second layer (36) of fixed insulation, then said second layer (36) of fixed insulation is enclosed by a fourth semiconducting layer (37). |
| 3. | System according to the preceding claim, characterized in that said outer conductor (34) lengthwise is divided into a plurality of parts (34', 34"), which are connected in parallel to each other, the number of parts connected in parallel deciding the turns ratio between the primary and secondary winding (11, 12) in the transformer (10). |
| 4. | System according to claim 2, characterized in that said inner conductor (30) is divided into a plurality of parallel conductors (30a) insulated from each other. |
| 5. | System according to the preceding claim, characterized in that each parallel conductor (30a) is connected to a transmission line (17) with a transmissionline capacitance (18). |
| 6. | System according to any one of the preceding claims, characterized in that said repetitive breaker (14) comprises a capacitance (41), which capacitance is connected in series to a closing switch (42), as well as an inductance (43). |
| 7. | System according to any one of claims 15, characterized in that said repetitive breaker (14) is a combined breaker comprising at least one semiconductor switch (20) and at least two vacuum breakers (21 a, 21 b). |
| 8. | System according to the preceding claim, characterized in that said combined breaker comprises a semiconductor switch (20) that is con nected in parallel to a first vacuum breaker (21 a), which then are connected in series to a second vacuum breaker (21 b). |
| 9. | System according to any one of the preceding claims, characterized in that said primary and secondary winding (11,12) are arranged to step up voltage, the highpower pulse being generated in the form of a highvoltage pulse. |
| 10. | System according to the preceding claim, characterized in that the secondary winding (12) is connected to one or several transmission lines (17) with a transmissionline capacitance (18). |
| 11. | System according to any one of claims 9 or 10, characterized in that the system comprises a closing switch (15) arranged between the secondary side of the transformer (10) and said load (16). |
| 12. | System according to the preceding claim, characterized in that said closing switch (15) comprises a discharge gap. |
| 13. | System according to any one of claims 18, characterized in that said primary and secondary winding (11,12) are arranged to step up current, the highpower pulse being generated in the form of a highcurrent pulse. |
| 14. | Method of generating a highpower pulse, comprising: generation of an energy pulse for the recharging of the primary winding (11) in a transformer (10), breaking the current on the primary side of said transformer (10), characterized in that the magnetic energy stored in the transformer (10) is transformed from the primary winding (11) to the secondary winding (12) arranged coaxially in relation to the primary winding (11), subsequently to which the magnetic energy is dis charged from the secondary winding (12) in the form of a highpower pulse to a load (16). |
| 15. | Method of generating a highpower pulse according to the preceding claim, characterized in that the discharging from the secondary winding (12) to the load is effected via a subsequently is discharged from the transmissionline capacitance (18) in the form of a highvoltage pulse to the load (16) via a closing switch (15) comprised in the system. |
| 16. | Method of generating a highpower pulse according to claim 14, characterized in that the discharging from the secondary winding (12) to a load (51) is effected via a Blumline scheme (52) and a triggered discharge gap (53), the full voltage of the secondary winding being obtained over the load (51). |
| 17. | Method of generating a highpower pulse according to any one of claims 14, 15 or 16, current flowing on the primary side through the repetitive breaker (14) comprisingfirst and second vacuum breakers (21a, 21b), characterized in that the breaking of the current on the primary side is effected according to the following steps: separation of the contacts (22) of both of the vacuum breakers, turning on of a semiconductor switch (20) comprised in the breaker (14), commutation of the current flowing on the primary side from the first vacuum breaker (21 a) comprised in the breaker (14), this first vacuum breaker (21 a) turn ing off, turning off of said semiconductor switch (20), the second vacuum breaker (21 b) turning off. |
| 18. | Method of generating a highvoltage pulse according to any one of claims 14, 15 or 16, current flowing on the primary side through the repetitive breaker (14), characterized in that the breaking of the current on the primary side is effected by means of a counter or coinduction obtained from a capacitance (41), which capacitance is connected in series to a closing switch (42), as well as from an inductance (43), a zero crossing being obtained in an electrical arc in vacuum (44), the current in the primary circuit being broken. |
Field of the Invention Pulse generators intended for the generation of pulses of high power in the form of high voltage or high current are used in a number of different areas, such as laser technology, electronic weapons, biological applications such as purifica- tion of waste water, purification of gases, medical applications such as defibrillators, in the research concerning fusion technology, particle physics, extreme magnetic fields, etc. , etc.
Traditionally, so called Marx generators have been used for the generation of pulses of high voltage. The Marx generator comprises a number of condensators in which capacitive energy is stored under connection in parallel so as to subsequently being discharged simultaneously in serial, a high-voltage pulse being generated. Such pulse generators are expensive as well as very bulky.
By instead utilizing inductively stored energy being discharged in the form of a high-power pulse, a much more compact system in comparison with a system constructed by means of condensators is obtained. This is because inductively stored energy may be stored approx. 10 times denser than capacitively stored energy. However, discharging of inductively stored energy involves a great deal technical challenges.
Systems where inductively stored energy is utilized for the generation of a high-voltage pulse are known. The article"An economic compact high-voltage pulse generator"by B. M. Novac et al. describes such a system. The known sys- tem according to the published article comprises a primary capacitance C, which is connected to the primary winding of a transformer via a closing switch for the recharging of magnetic energy in the transformer. The energy stored magnetically in the transformer is transformed to the secondary winding of the transformer
wire. The energy is transmitted in the form of a high-voltage pulse to a load via a discharge gap.
The known system breaks the current on the primary side by means of the exploding wire. Hence, the system just manage to generate one pulse, before another pulse can be generated a new exploding wire has to be connected. Thus, the known system cannot generate several consecutive pulses. In order to gener- ate several consecutive pulses, it is required that the primary side is broken by a breaker having repetitive function. To break an inductive current requires much more from the proper breaker than at capacitive load.
In the article, the problem of electric puncture in the insulation between the turns in the secondary winding of the transformer at high voltages is further described. According to the article, by virtue of this, the known system does not resist more than approx. 100 kV.
Among many of the examples of fields of use mentioned above, the load has a low or very low impedance. At a quick and efficient generation of a pulse of high power to a load of low impedance, a matching in the system generating the pulse is desirable, i. e. a low-impedance coupling to the load for quick discharging of the pulse.
At discharging of a high-power pulse, large forces between the primary and secondary windings of the transformer arise. For several reasons, the above- described system does not manage to generate pulses of high power, on one hand breakdown in the insulation between turns of the windings will arise, and on the other hand the forces between the primary and secondary winding will become so large that the transformer has to be dimensioned in view of that. Thus, the described known system according to the article has a number of limitations.
Summary of the Invention The present invention is intended to provide a system for the generation of high-power pulses, which solves the problems mentioned above. The system comprises a transformer provided with a primary and a secondary winding. The primary winding is intended for recharging of magnetic energy in the transformer and the secondary winding is intended for discharging of the magnetic energy accumulated in the transformer in the form of a high-power pulse to a load.
The windings are arranged coaxially in relation to each other in the trans- former and comprise an inner circular conductor enclosed by a first semicon- ducting layer. Around the first semiconducting layer, a first layer of fixed insulation is then arranged. Next, said first layer of fixed insulation is enclosed by a second semiconducting layer. Around said second semiconducting layer, an outer con- ductor is then arranged. Next, said outer conductor is enclosed by a third semi- conducting layer, which then is enclosed by a second layer of fixed insulation.
Finally, a fourth semiconducting layer enclosing the second the layer of fixed insulation is arranged.
The insulation in this type of winding resists substantially more than the insulation in a traditional transformer winding.
By using a coaxial cable having the above-described included layers where both the primary and secondary winding are coaxially arranged, contained in one and the same cable, the forces that arise between the windings at the pulse gen- eration inside the proper cable are trapped. Hence, the forces arising at the pulse generation are concentrated to the insulation of the cable between the inner and the outer conductor, and thereby will not load the structure of the transformer. By means of this construction, the forces that arise between the primary and secon- dary winding will be carried by a large area along the length of the cable. The forces arisen on the windings will be contained in the proper cable.
By arranging the primary and secondary windings in this way in the trans- former, low leakage fluxes and a high coupling coefficient, >0,9, are obtained.
Hence, the charged magnetic energy will efficiently become transformed to the secondary winding and only a very small part of the energy has to be absorbed in the proper breaker.
Accordingly, this system enables pulses of significant higher voltage than the known system, without the risk of breakdown of the insulation in the secondary winding.
In addition, the system comprises a repetitive breaker intended to break the current on the primary side of the transformer.
The system further comprises means for the generation of an energy pulse for accumulation of energy in the primary winding.
Moreover, the invention relates to a method of generating a high-power
to the following : initially an energy pulse is generated for the recharging of the pri- mary winding in the transformer. Subsequently the current is broken on the pri- mary side of the transformer by means of a breaker, the energy stored magneti- cally in the primary winding being transmitted to the secondary winding from where discharging of the energy then takes place to the load.
Brief Description of the Drawings Fig. 1 shows a known system for the generation of high-voltage pulses.
Fig. 2 shows a preferred embodiment of a system for the generation of high-voltage pulses according to the present invention.
Fig. 3 shows a combined breaker, which in a preferred embodiment is com- prised in the system.
Fig. 4 shows the embodiment of primary and secondary winding of the transformer in the system according to the present invention.
Fig. 5 shows the embodiment of primary and secondary winding of the transformer seen in cross-section in the longitudinal direction.
Fig. 6 shows the embodiment of primary and secondary winding of the transformer seen in cross-section in the cross direction.
Fig. 7 shows an embodiment having an alternative breaker.
Fig. 8 shows an alternative embodiment where the load is fed via a Blum- line configuration.
Detailed Description of Preferred Embodiments The present invention will now be described in detail by means of accom- panying figures.
Fig. 1 shows a system according to prior art for the generation of high-volt- age pulses. The known system comprises a primary capacitance C 1 that is con- nected to the primary winding 2 of a transformer 3 via a closing switch 4 for the recharging of magnetic energy in the transformer. The energy magnetically stored in the transformer is transformed to the secondary winding of the transformer 5 when the circuit on the primary side is broken by the activation of an exploding wire 6. The energy is transmitted in the form of a high-voltage pulse to a load 7 via a discharge gap 8.
Fig. 2 shows a preferred embodiment of a system for the generation of high-power pulses according to the present invention. The system comprises a transformer 10 having a primary winding 11 and a secondary winding 12. Means 13 for the generation of an energy pulse to the primary winding 11 is further com- prised. A breaker 14 having repetitive function breaks the current on the primary side after that the primary winding has been recharged and magnetic energy has been stored in the transformer 10. When the primary circuit is broken by the breaker 14, the magnetic energy stored in the transformer is forced out in the sec- ondary winding 12. A closing switch 15 is arranged between the secondary side of the transformer and a load 16. In a preferred embodiment, the closing switch is a <BR> <BR> discharge gap. Other types of closing switches may be used, such as, e. g. , a con- trolled laser switch.
In a preferred embodiment, the transformer used in the system is of trans- mission-line type having a transmission line 17 with a transmission-line capaci- tance 18. In this embodiment, the energy forced out in the secondary winding 12 is charged in the transmission-line capacitance 18 of the transformer and is subse- quently discharged from the transmission-line capacitance in the form of a high- voltage pulse to the load 16 via the closing switch 15. Discharging in this way, via a transmission-line capacitance, is particularly suitable for quick generation of high-voltage pulses to loads of low impedance. By connecting a plurality of trans- mission lines in parallel, any capacitance may be obtained for a given pulse length. Thereby it is possible to match the impedance against the impedance of the load in question. By means of a plurality of transmission lines connected in parallel, pulses of high power can be generated very fast, since the lines con- nected in parallel become much shorter than when only one line is used for a cer- tain given capacitance.
Fig. 3 shows a repetitive breaker 14, which is comprised in an additional preferred form of the system according to the present invention. The breaker shown in the figure is a combination of a semiconductor switch 20 and two or more vacuum breakers 21. The combined breaker shown in the figure comprises a first vacuum breaker 21 a that is connected in parallel to a semiconductor switch 20, which then are connected in series to a second vacuum breaker 21 b. When cur- rent flows on the primary side for the recharging of energy in the primary winding,
first and the second vacuum breaker, while the semiconductor switch 20 is unloaded.
When generation of a pulse is desired, the current is broken on the primary side by means of the combined breaker according to the following step. The elec- trodes 22 in both of the vacuum breakers 21 separate, the current going in electri- cal arc 23 between the electrodes 22 in both of the breakers 21. Subsequently, the semiconductor switch 20 is turned on. The current is commutated in a suitable way from the first vacuum breaker 21 a to the semiconductor switch 20, the current going through the semiconductor switch 20. Thereby, the first vacuum breaker 21 a turns off. Subsequently, the semiconductor switch 20 is turned off. Hence, the second vacuum breaker 21 b will be turned off. Since the semiconductor switch 20 as well as the vacuum breaker 21 a is very fast, the voltage across the semicon- ductor switch will not advance to any high level. instead, the-voltage will be carried by the second vacuum breaker 21 b. By means of this configuration, the semicon- ductor switch 20 does not need to be dimensioned to continuously withstand the currents that flow in the primary circuit, but current flows through the semiconduc- tor switch 20 only a short moment before it is turned off. After breaking, the largest part of the voltage will be carried by the second vacuum breaker 21 b, for what reason the semiconductor switch 20 only needs be dimensioned for a part of the high voltage.
Fig. 4 shows the winding system of the transformer comprised in the sys- tem according to the present invention. An inner circular conductor 30 is enclosed by a first semiconducting layer 31. The first semiconducting layer 31 is then enclosed by a first layer 32 of fixed insulation. Next, this first layer 32 of fixed insulation is enclosed by a second semiconducting layer 33. The second semiconducting layer 33 is enclosed by an outer conductor 34. The outer con- ductor 34 is enclosed by a third semiconducting layer 35. Then the third semi- conducting layer 35 is enclosed by a second layer 36 of fixed insulation. Next, the second layer 36 of fixed insulation is enclosed by a fourth semiconducting layer 37.
Fig. 5 shows the winding system in cross-section in the longitudinal direc- tion. In the preferred embodiment, the outer conductor 34 is lengthwise divided into a plurality of parts that are connected in parallel to each other. The number of
dary winding in the transformer. Where the conductor is divided and connected in parallel, the connection may be enclosed by insulation 34'or be made without insulation 34". By choosing the number of parts connected in parallel and by choosing the inner and outer conductor, respectively, as primary and secondary winding, respectively, step-up transformation of voltage as well as current can be obtained with any winding factor.
Fig. 6 shows the embodiment of the primary and secondary winding of the transformer, seen in cross-section in the cross direction. The inner conductor 30 is divided into a plurality of parallel conductors 30a insulated from each other and enclosed by semiconducting layer 31 a. When the inner conductor is used as secondary winding, the insulated parallel conductors can be connected directly to separate parallel transmission lines.
Figure 7 shows an embodiment having a breaker that is an alternative to the combined breaker comprising semiconductor components as shown in figure 3. A capacitance 41, being connected in series to a closing switch 42, and an inductance 43 are arranged to bring about counter or co-induction, a zero crossing being obtained in an electrical arc in vacuum 44, the current in the primary circuit being broken and a high-power pulse being generated. Advantages of this configu- ration are that it provides a very compact and cost-efficient solution of breaking of large currents against high voltage.
Figure 8 shows an alternative embodiment where the load is fed via a Blumline configuration. In the Blumline scheme 52, a first and a second coaxial cable having earthed and partly earthed casing, respectively, are included, which is shown in the figure. The first cable is wound up on an earthed cable coil, which provides a compact construction, while the second cable is wound up on an insu- lated coil.
When the discharge gap 53 is closed, reflections occur in the cables that are added to each other, the full transformer voltage feeding the load 51. By feed- ing the load 51 via the scheme with Blumline 52 shown according to the figure and a triggered discharge gap 53, accordingly full voltage to the load is obtained instead of half voltage, which is the case in the previously described embodiments.
Said cables may consist of semicon cable, a cable having double semicon- ducting layers, between which fixed insulation is arranged. The resistivity in the
pure resistive layer, while it during the course of discharging acts as a dielectric.
These properties is controlled, on one hand, by the addition of different degree of filling in the semicon, which for instance may be carbon black in PE plastic, silicon carbide, zinc oxide, chromium oxide, iron oxide, aluminium oxide, and on the other hand by adjustment of the thickness of the various layers. Thus, during the course of recharging the semicon acts as a resistive layer, which smoothes the electric field, thereby enabling a very high voltage. On the other hand, during the course of discharging the semicon acts as a dielectric, which results in a higher effective s being obtained in the insulating material of the cable, which in turn gives rise to a slower wave velocity at discharging of a pulse. The insulation material between the mentioned semiconducting layers may be filled in the same way, in order to modify the discharging properties of the cable. Consequently, a longer discharging by time at a given cable length is obtained when--this type of cable is used in compari- son with a usual transmission cable. Thus, by means of an adapted cable, a sub- stantial shorter cable is required for a certain predetermined pulse length.
Moreover, said scheme opens the possibility of obtaining very short pulses to the load as well as the possibility of the pulses having square-topped shape.
When effected in cable technology, the Blumeline may consist of a plurality of parallel cables to increase the capacitance and decrease the impedance.
The invention is not limited to the above embodiments given as examples, but may be made as modifications within the scope of the general idea according to the invention described in the appended claims.
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