ABSTRACT
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.
ABSTRACT
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%.
ABSTRACT
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.
