Compact Pulse Transformer with Transmission Line Embodiment

Abstract

An arrangement of coaxial windings is provided. The arrangement includes primary and secondary windings as air-core pulse transformers having insulation and winding arrangement for efficient energy transfer to the secondary winding. The secondary winding is wound with a central metallic core to include a coaxial transmission line with it and is configured to deliver a rectangular pulse across its terminals. The arrangement also includes a coaxial feeding arrangement for the primary winding with a central coaxial terminal connecting to one end of an adjustable primary closing switch electrode so as to have variable voltage feed input corresponding to its load requirement.

Claims

1. An arrangement of coaxial windings comprising primary and secondary as air core pulse transformer having insulation and winding arrangement for efficient energy transfer to secondary winding, the secondary winding so wound with the central metallic core to include a coaxial transmission line with it and so configured to deliver rectangular pulse across its terminals; and a coaxial feeding arrangement for the primary winding with central coaxial terminal connecting to one end of an adjustable primary closing switch electrode so as to have variable voltage feed input corresponding to the load requirement.

2. The arrangement of coaxial winding as claimed in claim 1, comprising a plurality of conductors of even length and insulated from one another but arranged in parallel, so as to form two multi-conductors end terminals wound coaxially with single or many turns and terminated at one end in helical fashion on the metal cylinder comprising of outer housing and the other terminal terminated helically across central return conductor.

3. The arrangement of coaxial conductors as claimed in claim 2, wherein the total parallel conductor requirement is generated to further provide the complete coaxial coverage to the secondary winding to achieve needed coupling coefficient in an air-core transformer.

4. The arrangement of winding as claimed in claim 1, wherein the insulation between the primary and secondary winding and central metallic core of stepped nature on a tapered cylinder, is formed using thin insulation sheets cut as sectors of circles to cover without wrinkles the tapered cylindrical core in many layers with sufficient axial overlapped and axial length decreasing/increasing, as to give the needed insulation requirement of transformer winding when the voltage builds along its winding length.

5. The arrangement of winding as claimed in claim 1, comprising multi-turn single layer secondary winding wound to achieve desired turns ratio as an air-core transformer and required pulse width as transmission line formed with the central metallic core of constant impedance, as required by the load.

6. The arrangement as claimed in claim 5, wherein the secondary winding having a common termination with primary winding at the external cylindrical and the other terminal connected to the central metallic tapered cylindrical core forming the high voltage end of the output along the central axis.

7. The arrangement of central axis secondary winding terminal as claimed in claim 6, wherein the fixed electrode having toroidal end-section, of the high voltage end of the secondary side closing switch to be comprised in a housing with pressurization of the high-voltage spark-gap as the closing switch.

8. The arrangement as claimed in claim 1 or 6, wherein the central tapered cylindrical metallic core is an axially slit cylinder to permit the interaction of magnetic flux generated by primary winding with the secondary winding without inducing eddy-currents.

9. the arrangement as claimed in claim 8, wherein the axial slits of the metallic cylindrical core are covered by thin conducting adhesive tapes to ensure that the thickness of the adhesive tape is sufficient to permit the diffusion of relatively slowly time varying primary winding flux ensuring good coupling through the central axis of the windings and also ensuring the central conductor's circumferential continuity so as to form the central axis conductor of the transmission line during the start of the fast rise-time energy discharge cycle with the closing of the secondary side spark-gap switch.

10. The arrangement as claimed in claim 9, wherein resistive or/and thin continuous metal cylinder are employed as central core without axial slitting.

11. The arrangement as claimed in claim 3, wherein two cylindrical parts are axially connected to form electrical continuity, but mechanically separable to ensure ease in winding.

12. The arraignment as claimed in claims 1 to 11, wherein sufficient electrical isolation/insulation between central metallic core and the external cylindrical housing are made through dielectric end-supports made of Acetal Homo-polymer block machined to size and fixed circumferentially at the two ends.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0031] FIG. 1 (a,b)illustrate, through Block diagram schematic, the functional aspect and the sequential arrangements of components in a Pulse Power System. FIG. 1a, shows the arrangement for LINAC and Radar applications, whereas, FIG. 1b, shows the arrangement in case of an FXR and HPM applications.

[0032] FIG. 2illustrates how the embodiment of line within the pulse transformer will transform the pulse power schematic.

[0033] FIG. 3Shows the sectional view of the inventiona half section of Compact Pulse Transformer with all the necessary embodiments and circuit connections at the input and the output ends with enumerative description of all the constituent elements.

[0034] FIG. 4shows a typical waveform at the secondary output of the Compact Pulse Transformer.

[0035] FIG. 5shows the input waveform of the capacitor bank discharge, after the primary end closing switch is operated.

[0036] FIG. 6 (a,b)shows the two different polarities (FIG. 6(a) showing negative polarity pulse and FIG. 6(b) showing positive polarity pulse) of waveforms achieved by tuning of the primary closing switch and/or changing the charging voltage of the capacitor bank.

DETAIL DESCRIPTION OF THE INVENTION

Constructional Steps of the Device

[0037] (i) Sectional details show a central shaft, part no. 1, made up of non-magnetic stainless steel (SS) with taper in 1:20, having an axial length of 250 mm for the winding. Shaft has a diameter of 75 mm at one end and 100 mm at the other end. The SS shaft also has 6 mm wide axial slits, 4 nos., at 90 intervals, all around the shaft. [0038] (ii) Shaft is vertically fixed at one end, the right side in the section shown, to a flange by thread screwing circumferentially on the shaft. [0039] (iii) The assembly of step (ii), in turn is attached to the flange end of external SS cylindrical body, again in vertical position, and the SS flanged end is made the base reference for all the following steps. [0040] (iv) SS shaft is cleaned by Acetone to remove any dust and grease. The slits are then covered by <0.3 mm thick, 25 mm wide Aluminium/Copper adhesive tapes, all along the length of the shaft. [0041] (v) Shaft is the laid with secondary insulation that is put in stepped manner with reducing axial length from 250 mm at the start to 50 mm at the end. Each set comprises of 3 mil thick Mylar sheet with twelve layers-cut to size of a corresponding circles sector for a non-crimpled tapered cylindrical layering. Thus, for a 25 mm thick maximum tapered portion, about 33 such layered sets are put. Mylar insulation is secured in place by 50 mm wide room temperature vulcanized (RTV) taped wound on top of the finished Mylar layer with 50% overlap. This makes the secondary insulation complete. [0042] (vi) Single layer secondary winding, comprising of 100 turns of 1.2 mm diameter silver plated copper, double layer Teflon insulated EE grade wire, is then laid on top of the finished insulation of step (v). The continuous conductor length required to wind the secondary is approximately of 45 meters. This covers an axial helically wound length of 250 mm on the insulated central SS shaft. Secondary winding is terminated with one end at the central shaft-having minimum side of the insulation, and the other end on the external SS cylinder forming the common terminal with the primary winding. [0043] (vii) After securing the secondary winding, a layer of RTV tape is put again. There after, as reported in step (v), insulation between secondary and primary windings is built in a complementary fashion, to finally have a cylindrically finished top layer with maximum thickness of 25 mm. [0044] (viii) Mylar layer is again secured in place by RTV tape laid as reported in step (v). [0045] (ix) Primary winding, comprising of 36 numbers of the same conductor as reported in step (vi), but the cut length of only 1.5 m length. All the conductors are first terminated on the outer SS housing (constituting of two cylinders threaded to each other and formed in two parts to help during winding) of the transformer in a helical fashion. The given length permits only three turns to this multi-conductor primary winding to be put covering the entire secondary winding's axial length of 250 mm to ensure even coupling. The other ends (36 numbers) of the primary winding are terminated on the central SS adapter threaded to part number 6 and supported by block separating the central SS shaft and this adopter, as shown in FIG. 3. The block also has notches to help secure the primary winding conductors through them before their termination on the SS adopter. [0046] (x) 1 mil thick tape of 50 mm width is finally laid on top of the primary insulation with care being taken to minimize the wrinkling during the winding. Winding is now ready for subsequent RTV potting (if required) but the transformer now has sufficient insulation to be tested for at least 250 kV insulation level. [0047] (xi) The second cylinder, as reported in (ix), as two part constituent of external SS cylindrical housing, is now threaded on the first as to enclose the completed winding in the external housing. Delrin end flange is now secured to the central shaft and the external housing with neoprene gasket to help absorb shocks and vibrations. [0048] (xii) The assembly is now ready for testing the transformers electrical parameters, viz., (i) Primary inductance, (ii) Secondary inductance (iii) mutual inductance, and (iv) corresponding winding capacitances, etc., [0049] (iii) How does the device operate? [0050] Device operation is in similar manner as a pulse transformer with any pulse power system. Electrically, it is a passive device and has to be powered to exploit its functional featuresthat of a transformer and that of the transmission line, in this invention. Primary stored energy of a capacitor bank is discharged in the low inductance primary of the transformer through a self breakdown primary switch. This generate sufficient high rate of rise large flux density, to induce across the secondary winding very large transient voltage. The secondary switch, set to break at the required output voltage through a preset gap setting or through the pressure adjustment of the gap-switch; thereby couples the primary energy to the load impedance. The extent of match/mismatch decides the net power transferred to the load. This matching extent, in the reported invention, is decided by the transmission line characteristic impedance embodiment within the transformer winding and the extent of this impedance match with the load. Device may be operated in single shot or repetitive manner. It is tested at 3 Hz for five minutes duration, with no adverse performance deterioration, giving a tested life shots of about 1000, without failure.

[0051] A few typical examples to illustrate how the invention is carried out in actual practice:

[0052] In one of the applications, typical requirement was to generate high voltage from a low impedance (<1 ohm), high current source (>500 kA). As the system is finally required to power high impedance load (>10 Ohm) with the purpose of generating high power microwaves, need for a high voltage pulse transformer became imperative. Typically, to drive an REB (Relativistic Electron Beam) Diode, pulse generator has to give a fast rise-time (<10 ns) flat-top pulse of about 100 ns pulse wide. This requirement indicates employment of transmission line or an equivalent network. Direct embodiment of very high voltage coaxial transmission line by using high power co-axial cables, is a possible solution, but was found to be cumbersome. Incidentally, the embodiment required coaxial flow of return currents and hence the need for a central return conductor was imperative. The idea to employ this central conductor within the pulse transformer core and multi-turn secondary windings configuration, intuitively suggested the topology of a delay line. The limitation was the central conductor which would generate large eddy currents and associated losses, thereby significantly reducing the available power at the load. The solution to this problem was to design the central conductor, in a fashion, as to permit relatively low frequency flux coupling during the primary winding excitation. This was made possible by axially slitting the central core and covering these slits by thin conducting tapes. This incorporation permitted diffusion of the slower rise-time primary excitation and yet permitted conductor continuity for transmission line modes for fast rise-time output discharge.

Main advantages of the invention are the following: [0053] (i) A compact embodiment comprising of pulse transformer and a transmission line features in one element, thereby significant reduction of linear dimensions of the pulse power system. This size reduction, and incidental reduction of weight, will be significant for airborne and portable pulse power systems and significantly adds to the commercial and strategic value of the system. [0054] (ii) An embodiment of tapered insulation system in a co-axial configuration, giving optimum high voltage withstand capacity and ensures good transformer coupling. The graded nature of the insulation scheme adopted will help transformer industry for better implementation of the insulation requirement of pulse transformer.