Prolonging the lifetime of a compact multi-wire-layered secondary winding in the Tesla transformer.

A compact multi-wire-layered secondary winding for the Tesla transformer was proposed by Zhao et al. [Rev. Sci. Instrum. 88(5), 055112 (2017)]. The basic idea is to wind multiple layers of a metal wire around a polymeric base tube. However, the lifetime of this type of winding is only about 200 000 pulses, and thus it fails to meet the requirement of a lifetime of 1 × 106 pulses. In this study, two methods are developed to prolong the lifetime of this winding. One method involves replacing the original three-skin wire with a polytetrafluoroethylene (PTFE) wire. The results of small-scale experiments in different conditions show that the lifetime of the PTFE-covered copper wire is at least ten times longer than that of the three-skin wire. The other method involves improving the local structure of this winding. A strong mechanical stress is concentrated at the small end of the winding, and a highly intense electric field appears in this region, where both reduce the lifetime of the winding. Improving the local structure of the winding theoretically prolongs its lifetime by a factor of 4. Both methods were applied to the original secondary winding of a Tesla transformer and extended its theoretical lifetime by a factor of 40. The modified winding had a lifetime longer than 2 × 106 pulses without any traces of discharge. This is equivalent to a lifetime longer than that of the original winding by a factor of 10 and verifies the effectiveness of the proposed methods.

A quasi-coaxial HV rolled pulse forming line.

A quasi-coaxial high-voltage (HV) rolled pulse forming line (rolled PFL) is researched in this paper. The PFL is rolled n circles on a support cylinder simultaneously by two layers of copper foil electrodes and two layers of insulation dielectrics. The first circle of the two electrodes are elicited in opposite directions along the axis, acting as the quasi-coaxial output structure of the PFL, and the left n - 1 circles of the PFL form a complete rolled strip line of n - 1 circles. The rolled PFL is convenient to realize HV insulation and is able to output a pulse with good quality. Characteristic parameters of the PFL are designed theoretically. Besides, the pulse discharge process of the PFL is simulated by computer simulation technology (CST) modeling, and the simulation result verifies the correctness of theory design. Furthermore, a rolled PFL with a characteristic impedance of 4.4 Ω is developed. The test characteristic impedance of the developed PFL by the incident pulse method confirms to the theory design. The discharge voltage waveform with a full width at half maximum of 57 ns of the PFL is acquired, which has a rise time of 6.8 ns. The HV test of the rolled PFL is carried out, and a discharge current pulse with an amplitude of 7 kA is acquired when the PFL is charged to 70 kV. It is calculated that the developed PFL has an energy storage density of 2.5 J/l. A Tesla generator based on 13 stages of rolled PFLs is designed, which is expected to output a 450 kV pulse with a duration of 100 ns on a 40-Ω match load. The discharge waveform of the generator is simulated by the CST software. The simulative output pulse has a rise time of 5 ns, with a flattop jitter less than 5%.

A compact multi-wire-layered secondary winding for Tesla transformer.

A compact multi-wire-layered (MWL) secondary winding for a Tesla transformer is put forward. The basic principle of this winding is to wind the metal wire on a polymeric base tube in a multi-layer manner. The tube is tapered and has high electrical strength and high mechanical strength. Concentric-circle grooves perpendicular to the axis of the tube are carved on the surface of the tube to wind the wire. The width of the groove is basically equal to the diameter of the wire so that the metal wire can be fixed in the groove without glue. The depth of the groove is n times of the diameter of the wire to realize the n-layer winding manner. All the concentric-circle grooves are connected via a spiral groove on the surface of the tube to let the wire go through. Compared with the traditional one-wire-layered (OWL) secondary winding for the Tesla transformer, the most conspicuous advantage of the MWL secondary winding is that the latter is compact with only a length of 2/n of the OWL. In addition, the MWL winding has the following advantages: high electrical strength since voids are precluded from the surface of the winding, high mechanical strength because polymer is used as the material of the base tube, and reliable fixation in the Tesla transformer as special mechanical connections are designed. A 2000-turn MWL secondary winding is fabricated with a winding layer of 3 and a total length of 1.0 m. Experiments to test the performance of this winding on a Tesla-type pulse generator are conducted. The results show that this winding can boost the voltage to 1 MV at a repetition rate of 50 Hz reliably for a lifetime longer than 104 pulses, which proves the feasibility of the MWL secondary winding.

A low-jitter self-break repetitive multi-stage gas switch.

A megavolt low-jitter self-break repetitive gas switch is developed by the use of the corona stabilization and the multi-stage structure in this paper. This switch is multi-stage, consisting of one corona stabilization stage and subsequent rimfire stages. The corona stabilization stage breakdowns first, then the subsequent rimfire stages are self-fired by the over-voltage from the closure of the corona stabilization stage. SF6 is used in the switch. It has been proven by experiment that the multi-stage gas switch, which consists of one 1.3-cm gap corona stabilization stage and five 0.5-cm gap rimfire stages, can operate at repetition rate frequency (PRF) of 50 Hz with a voltage jitter less than 2% in 2000 discharges. The breakdown voltage of this multi-stage switch reaches 770 kV and the single discharge current is 8.50 kA at 4 bars.

A voltage-division-type low-jitter self-triggered repetition-rate switch.

A voltage-division-type (V/N) low-jitter self-triggered multi-stage switch is put forward. It comprises of a triggered corona gap, several quasi-uniform-field gaps, and an inversion inductor. When the corona gap is in the stage of self-breakdown, the multi-stage gaps are triggered and the switch is closed via an over-voltage. This type of V/N switch has the advantage of compact structure since the auxiliary components like the gas-blowing system and the triggered system are eliminated from the whole system. It also has advantages such as low breakdown jitter and high energy efficiency. The dependence of the self-triggered voltage on the over-voltage factor and the switch operating voltage is deduced. A switch of this type is designed and fabricated and experiments to research its characteristics are conducted. The results show that this switch can operate on a voltage of 1 MV at 50 Hz and can generate 1000 successive pulses with a jitter as low as 3% and an energy efficiency as high as 90%. This V/N switch can work under a high repetition rate with a long lifetime.

A multi-functional high voltage experiment apparatus for vacuum surface flashover switch research.

A multifunctional high voltage apparatus for experimental researches on surface flashover switch and high voltage insulation in vacuum has been developed. The apparatus is composed of five parts: pulse generating unit, axial field unit, radial field unit, and two switch units. Microsecond damped ringing pulse with peak-to-peak voltage 800 kV or unipolar pulse with maximum voltage 830 kV is generated, forming transient axial or radial electrical field. Different pulse waveforms and field distributions make up six experimental configurations in all. Based on this apparatus, preliminary experiments on vacuum surface flashover switch with different flashover dielectric materials have been conducted in the axial field unit, and nanosecond pulse is generated in the radial field unit which makes a pulse transmission line in the experiment. Basic work parameters of this kind of switch such as lifetime, breakdown voltage are obtained.

A large-dynamic-range current probe for microsecond pulsed vacuum breakdown research.

A large-dynamic-range current probe for microsecond pulsed vacuum breakdown research is fabricated. The basic principle of this probe is to turn the current signal to a voltage one via a load of fixed impedance and to test the voltage signal via a voltage divider of adjustable voltage ratio. With a segment of 40-Ω coaxial line, which is connected to the experimental chamber, and a self-fabricated two-stage resistor-capacitor voltage divider, the current probe is realized and is applied to test the vacuum breakdown current for 3-cm parallel-plate electrodes under microsecond pulses. The results show that the current probe is capable of responding to current signals with an amplitude of 10(-2)-10(3) A and a duration of 10(-2)-10(1) µs. Based on the current probe, the characteristics of the vacuum breakdown current under 30-µs quasi-sinusoidal pulses are summarized. The potential mechanisms for each type of current are also discussed in this paper.

A Tesla-type repetitive nanosecond pulse generator for solid dielectric breakdown research.

A Tesla-type repetitive nanosecond pulse generator including a pair of electrode and a matched absorption resistor is established for the application of solid dielectric breakdown research. As major components, a built-in Tesla transformer and a gas-gap switch are designed to boost and shape the output pulse, respectively; the electrode is to form the anticipated electric field; the resistor is parallel to the electrode to absorb the reflected energy from the test sample. The parameters of the generator are a pulse width of 10 ns, a rise and fall time of 3 ns, and a maximum amplitude of 300 kV. By modifying the primary circuit of the Tesla transformer, the generator can produce both positive and negative pulses at a repetition rate of 1-50 Hz. In addition, a real-time measurement and control system is established based on the solid dielectric breakdown requirements for this generator. With this system, experiments on test samples made of common insulation materials in pulsed power systems are conducted. The preliminary experimental results show that the constructed generator is capable to research the solid dielectric breakdown phenomenon on a nanosecond time scale.