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The principle of coaxial transmission line pulse transformer and square-wave response of it
Review of Scientific Instruments
Abstract
Transmission line pulse transformers have been widely used in pulsed power technology. Traditional transmission line pulse transformers often use separate structures, which always introduces larger spurious parameters, and have lower voltage levels. In order to solve these problems, this note proposes a coaxial transmission line pulse transformer. A circular symmetric structure is used in the input and output ports of the coaxial transmission line pulse transformer, and there are no spurious parameters theoretically. Furthermore, this structure is suitable for hundreds of kilovolts high voltage applications. The structure and working principle of the coaxial transmission line pulse transformer are introduced in this note, and the circuit simulation research is conducted. The factors that affect the pulse transformation are analyzed. Furthermore, experimental studies of the square wave impulse response are conducted on an actual device. The result shows that the proposed coaxial transmission line pulse transformer can achieve the purpose of increasing the voltage amplitude while keeping the pulse waveform undistorted.
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A novel structure of transmission line transformer (TLT) with mutually coupled windings is described in this paper. All transmission lines except the first stage of the transformer are wound on a common ferrite core for the TLT with this structure. A referral method was introduced to analyze the TLT with this structure, and an analytic expression of the step response was derived. It is shown that a TLT with this structure has a significantly slower droop rate than a TLT with other winding structures and the number of ferrite cores needed is largely reduced. A four-stage TLT with this structure was developed, whose input and output impedance were 4.2 Ω and 67.7 Ω, respectively. A frequency response test of the TLT was carried out. The test results showed that pulse response time of the TLT is several nanoseconds. The TLT described in this paper has the potential to be used as a rectangle pulse transformer with very fast response time.
This paper discusses a high-voltage pulse generator for producing
corona plasma. The generator consists of three resonant charging
circuits, a transmission line transformer, and a triggered spark-gap
switch. Voltage pulses in the order of 30-100 kV with a rise time of
10-20 ns, a pulse duration of 100-200 ns, a pulse repetition rate of
1-900 pps, an energy per pulse of 0.5-12 J, and the average power of up
to 10 kW have been achieved with total energy conversion efficiency of
80%-90%. Moreover, the system has been used in four industrial
demonstrations on volatile organic compounds removal, odor emission
control, and biogas conditioning
A high-voltage transmission-line pulse transformer has been constructed based on modern cable technology. The transformer has been successfully tested for output powers of 0.5 GW. The high-voltage cable is equipped with a resistive layer (semicon) on the inner conductor and on the inside of the outer conductor. Semicon cables are commonly used in high-voltage transmission of electrical power. The pulse transformer was built using a coaxial semicon cable, with the inner conductor used as secondary winding and the screen as primary winding. Such a transmission-line transformer works in the same way as an ordinary transformer. The input is transformed to the desired output using a step-up or a step-down configuration. An output voltage of 85 kV with 1-μs duration was achieved into a 15 Ω load. Because the windings are coaxial the magnetic leakage is kept low and, therefore, the coupling coefficient is high. This type of transformer is useful in applications where weight is an important factor. Another advantage is the simple design and that it can be manufactured at a low cost.
Using a referral method, a multistage transmission line pulse transformer (TLT) was simplified, and a simple circuit of the TLT frequency response was also established. On this basis, a frequency response equation of the TLT was deduced from a two-port network model of the transmission line. According to the equation, TLT frequency response curves were calculated. Numerical simulations of the frequency response were conducted in terms of the simplified circuit, and the result of the numerical analysis agreed with that of theoretical calculations well. Both of these two results indicated that the TLT has an outstanding performance in frequency response if the secondary line inductance and stray capacitance are suitable. Particularly, the range of frequency response can be 30 kHz~1 GHz when the secondary line inductance is 6 mH and the stray capacitance is 8 pF.
A four-stage high-voltage transmission line pulse transformer with a voltage gain of approximately 4 is developed for transforming a high-voltage quasi-rectangular pulse with a pulse duration of several hundred nanoseconds. A method for enhancing the inductive isolation of secondary lines is employed to suppress the pulse droop through winding the coaxial cables onto the magnetic rings. An optimization of the distribution of inductive isolation (i.e., the magnetic rings) is explored for saving the magnetic rings, thus reducing the volume and weight of the transformer. The experimental results indicate that this transformer is capable of transforming the pulse voltage from 25 kV into about 100 kV, simultaneously keeping the pulse waveform almost unchanged. In the circuit simulation with PSpice for this transformer, we obtain a quasi-rectangular pulse of 100 kV when inputting a 25-kV pulse, which is in good agreement with that of the experiment. The result of frequency response indicates that this transformer has the potential to be normally applied in a broad bandwidth of 1 kHz-10 MHz.
The design, construction, and operational characteristics of a 200 kV transmission line pulse transformer is described. The transformer is wound using a new winding method that enhances the isolation of the output of the transformer from the input. As a result, pulse droop is substantially reduced, minimizing pulse distortion in the transformer. The ways in which both pulse rise time and droop can be further improved are investigated using a simple model for the transformer. The frequency response performance of the transformer is also described and modeled. As a result, it is shown that this type of transformer has the potential to be used as a high‐frequency, continuously excited power transformer. © 1996 American Institute of Physics.
Transmission line transformers (TLT's) as pulse transformers have received increasingly more attention due to their excellent frequency response characteristics over conventional wound transformers. This transformer basically consists of equal lengths of transmission line (normally coaxial cables are used) connected in parallel at the input side of the transformer, and in series at the output side so that the output voltage can be boosted in proportion. Because the reactance of the outer conductor increases with the rise of the frequency of the input voltage, the output voltage of each transmission line can be isolated mutually when the frequency is high enough. Then, the output voltage will be amplified through the voltage superposition. To minimize the substantial loss of voltage gain and obtain a low pulse droop rate, one stage transformer is entwined together as a unit, the number of stages of the transformer can increase easily by piling units one by one. This spiral construction makes the transmission line transformers much more compact. On the other hand, with the development of modern semiconductor technology, high voltage, fast rise time power semiconductor devices have been produced, the collector emitter breakdown voltage of one IGBT is to 1.7 kV and the rise time is 100 ns. This paper describes a kind of compact pulse power supply constructed by combining transmission line transformer and modern power semiconductor devices-IGBTs. High voltage IGBTs (VCES=1.7 kV) have been used as charge switches, short pulses can be obtained at the input port of the transformer, then the output pulse amplitude is 10 kV through a 10-stage transmission line transformer. Finally, the output voltage pulse waveforms are given in the paper.
A new type of fast-rise-time pulse transformer based on transmission-line transformer (TLT) techniques is described. The transformer is wound using loosely coupled wire pairs or a two-wire twin cable rather than transmission lines in order to avoid high-voltage (HV) cable-failure problems, which are experienced with commercial coaxial transmission lines commonly used in TLTs. Although the high-frequency response associated with conventional TLTs is not quite as good, when using wire pairs, it is still quite possible to design high-turns-ratio transformers with rise times of below 100 ns. However, pulse rise times can be a little longer than this due to the switching-speed limitations of the switches used in the pulse generators that drive the transformers. The frequency response of the transformer can be predicted by a relatively simple transformer model, which can also be used to predict the rise-time performance with a variety of loads. The model can be further used to determine how much inductance is required at each stage of the transformer to achieve the specified low-frequency performance. It also shows that mutual coupling of windings within the transformers can significantly improve their low-frequency response and pulse droop. The results are presented on both low-voltage test transformers and medium-scale HV pulse transformers driven by an insulated-gate-bipolar-transistor switched-pulse generator
The advent of fast rise-time pulse techniques and their increasing importance brought on by high-speed microminiature circuits and the computer industry has resulted in an increased demand for pulse transformers of various types. The basic idea of constructing transmission line type transformers has been known and used for a number of years. However, such devices have not gained widespread usage, partly because their existence is not well known, but largely because of a lack of basic understanding of their operating principles in terms of elementary fundamentals as well as their capabilities and limitations. The purpose of this paper is twofold. One aim is to develop in step-by-step fashion the basic ideas of transmission line transformers from ordinary transmission line theory. The subject will be approached from the point of view of pulse response rather than ac excitation as is usually the case. Both impedance transformers and balanced-to-unbalanced (balun) transformers, including inverters, will be considered with physical insights into their operation. Several fundamental concepts will be developed and explored in detail (without mathematics), since they have a strong bearing on practical applications. The second purpose is to present new information and pulse measurements which will be useful in the design and applications of such devices, showing their capabilities and hitherto unexplored limitations, as derived from the fundamental concepts. Thus, this paper is partly supplementary to other published work and partly new work with the goal of providing a convenient fundamental understanding of these devices and their inherent potential and shortcomings. Although the intention is not to give a detailed design procedure, some approximate calculations and discussion of significant design criteria are included.
Transmission line transformers for high voltage pulsed power generation
- P W Smith
- C R Wilson