RU2144257C1 - High-voltage generator of short pulses - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: high-voltage generator of short pulses can be used for initiation of pulse-periodical electric discharge such as pulse corona discharge or pulse barrier discharge. Technical result consists in generation of high-voltage pulses with maximally shortened front of growth up to 5-10 ns with high pulse repetition rate of about 2000 Hz with maximum energy efficiency of generator at level of 90%. To achieve mentioned result there is proposed device incorporating high-voltage source, working capacitor, high-voltage switch connecting working capacitor to load. High- voltage source is made of network rectifier, semiconductor converter, one or several pulse high-voltage transformers providing for charge of working capacitor in small portions formed by each operation of converter so that frequency of charging pulses is at least 3 times higher than frequency of operation of high-voltage switch. Pulse switch presents uncontrolled self-punctured arrester, one or several pins, filaments, needles, blades or other parts with sharp edges on which corona discharge can be initiated with supply of voltage which value is below puncture level to electrodes of arrester. EFFECT: generation of high voltage pulses with maximally shortened front of growth. 2 cl, 2 dwg

Description

 Devices for generating short high-voltage pulses can be used in various fields of modern industry and science, including the generation of pulsed (pulse-periodic) electric discharges [1]. Systems based on pulsed corona discharge are now one of the most promising and rapidly developing areas in environmental engineering and technology. These include installations for the purification of water, air, furnace, fuel and ventilation gases, pulse-type electrostatic precipitators, as well as systems for the production of ozone. However, the real development of these extremely important systems is hampered by the lack of cheap and durable power sources that generate short high voltage pulses and have the characteristics necessary for industrial applications.

 To generate short high-voltage pulses for igniting a pulsed corona discharge, currently mainly used circuits based on thyratrons or controlled arresters (with a third electrode). However, both schemes have certain disadvantages. Both industrial thyratrons and controlled arrester are quite expensive and have short service life in the mode of generation of short pulses. In addition, the use of thyratrons and controlled arresters involves additional energy costs for heating (heating) the cathode and for the formation of control pulses (start), which naturally reduces the energy efficiency of the pulse generator as a whole.

 The use of uncontrolled self-breakdown arresters (which have the best time characteristics in the single pulse mode) in a standard circuit with ballast resistance leads to a very large energy loss when charging the working capacitance (ohmic resistance losses can be about 50%). In addition, an uncontrolled discharger of a conventional type cannot provide a response frequency (switching) of 1000 Hz or higher, which is usually necessary in practical applications of pulsed corona discharges in gas purification or for the generation of ozone.

 The prototype of our invention is a device for creating short high voltage pulses, described in [2], which shows a number of circuits using various types of controlled dischargers (dischargers with an external ignition pulse, dischargers with rotating electrodes) for igniting a pulsed corona discharge. However, the arrester proposed there with an external ignition pulse is quite technically complicated, since synchronization of the operation of its channels requires continuous alignment of all discharge gaps with sufficiently high accuracy. In addition, the use of an external ignition pulse supplied to the main electrodes of the arrester implies significant control energy losses that reduce the efficiency of the system.

 Dischargers with rotating electrodes, offered there, are also technically too complicated, which sharply limits the range of their practical application. In addition, both dischargers with rotating electrodes and dischargers with an external ignition pulse cannot provide switching times (rise front of the current pulse) of the order of 10 ns, which are necessary for some practical applications.

 The aim of our invention is to create a simple, cheap, easy-to-use and easily scalable generator of high voltage short pulses, providing the minimum possible switching time (about 10 ns), high energy efficiency and a sufficient pulse repetition rate.

 For this, we proposed a high-voltage pulse generator containing a network rectifier, a semiconductor converter, one or more high-voltage pulse transformers, a high-voltage rectifier, a pulse capacitor (this can be the output capacitance of a high-voltage rectifier), an uncontrolled self-breakdown spark gap of a special design connected to a discharge chamber of a pulse corona discharge. A pulse capacitor, an uncontrolled arrester, and a discharge chamber are connected in series, as shown in FIG. 1.

 The circuit of a device generating high voltage pulses for maintaining a corona discharge is similar to that of a relaxation generator, but has some significant differences. The working capacitance is charged in small portions (steps) formed during each operation of the semiconductor converter, as shown in FIG. 2. In this case, the charging of the capacitance occurs in the same way as a conventional rectifier with ballast current-limiting resistance, but in this case, the charging current is not limited by the resistance, but by the charging circuit itself, which gives out a charge to the working capacity in portions following each other with each pulse of the converter. In this case, energy loss during charging of the tank practically does not occur.

 Upon reaching a certain voltage at the working capacitance, the voltage at the arrester reaches the breakdown value, and the arrester closes the working capacitance to the discharge chamber. The discharge chamber is charged to a certain voltage and after ignition of the corona discharge (in the chamber) it is quickly discharged by a discharge current together with the working capacity. After the voltage on the chamber and the working capacitance drops below the corona discharge threshold, the arrester goes out and the process of charging the capacitance (5) (Fig. 1) starts again.

 There is a dependence of the stability and efficiency of the system on the magnitude of the charge of the working capacity at each pulse of the Converter. Each pulse of the converter charges the working capacitance (5) by a certain value ΔU. Obviously, the smaller ΔU, the better, since it is possible to more accurately adjust the voltage of the working capacitance and achieve a larger corona discharge current, preventing its transformation into a spark discharge. For stable operation of the system, it is necessary that the frequency of operation of the pulse transformer be at least 3 times higher than the frequency of operation of the spark gap.

 For stable operation of an uncontrolled self-breakdown arrester in the mode of shortest opening times and maximum switching frequency (which is especially important for closing the arrester in modes with incomplete discharge of the working capacity), it is necessary that the arrester design provides some leakage of current through it even when the arrester is closed . This is achieved by the fact that one or both electrodes of an uncontrolled self-breakdown spark gap are made in the form of one or more pins, threads, needles, blades or other parts with sharp edges that can corona at a voltage below the breakdown. The resulting "dark" current (with a closed arrester) allows you to maintain a certain stationary concentration of electronically excited gas molecules, which accelerates the development of breakdown in the arrester and thereby reduces the switching time. In addition, the "dark" current through the spark gap in the closed state, supported by a weak corona discharge from the spark gap electrodes, has a stabilizing effect on the quenching of the spark gap in the mode of incomplete discharge of the working capacitance, since this leakage compensates for the residual corona current through the pulsed corona discharge chamber.

 In some cases, the discharge chamber of a pulsed corona discharge (or an uncontrolled self-breakdown spark gap) can be connected in parallel (shorted) by a large resistance to bias the DC component of the voltage on the discharge chamber. This connection method can be important for practical applications such as flash-type electrostatic precipitators or ozone generators (that is, where the constant voltage component plays a large role). In some cases, such resistance has a stabilizing effect on the operation of the system at the time of start-up. The resistance value is chosen so (not too small) so as to practically not worsen the energy efficiency of the voltage pulse generation system as a whole.

Execution examples
Example 1. In the first case, in the circuit shown in FIG. 1, a spark gap of the following design was used - the anode was a system of rods with a diameter of 2 mm stainless steel; the cathode is a cylindrical shape with an end (working) plane parallel to the plane passing through the ends of the anode rods. Air was blown through the arrester with a flow rate of 1 to 100 l / h at a pressure of 2 atm abs. pressure. A discharge chamber of a pulsed corona discharge acted as a load.

 The ends of all the arrester rods were stably corona when a voltage below the breakdown voltage was applied to the electrodes of the arrester.

 The described arrester provided switching with a frequency of up to 2000 Hz and a current rise time of about 8 ns.

 Example 2. In the second case, in the circuit shown in FIG. 1, a spark gap of a different design was used: the anode was a system of radially diverging rods with a diameter of 3 mm. The cathode was an external cylinder covering the rods of the anode. Air was blown through the arrester at a flow rate of 1-100 l / h at atmospheric pressure. A discharge chamber of a pulsed corona discharge acted as a load.

 The ends of all the arrester rods were stably corona when a voltage below the breakdown voltage was applied to the electrodes of the arrester.

 The described arrester provided switching with a frequency of up to 2000 Hz and a current rise time of about 8 ns.

 Example 3. In the third case, in the circuit shown in FIG. 1, a spark gap of a design similar to example 1 was used.

 Air was blown through the arrester at a flow rate of 1-100 l / h at atmospheric pressure. The load was the discharge chamber of a pulsed barrier discharge shorted by a resistance of 1000 Ohms.

 The ends of all the arrester rods were stably corona when a voltage below the breakdown voltage was applied to the electrodes of the arrester.

 The described arrester provided switching with a frequency of up to 2000 Hz and a current rise time of about 8 ns.

Literature:
1. Proceedings of XVII th International Symposium on Discharges and Electrical Insulation, Berkeley, California, 1996.

 2. US patent N 4541848, B 03 C 3/66, 09.17.85.

Claims (3)

 1. A high voltage pulse generator, consisting of a high voltage source, a high voltage rectifier, a working capacitance and a high voltage switch, closing the working capacitance to a load, characterized in that said high voltage source supplying a high voltage rectifier consists of a network rectifier, a semiconductor converter, one or several pulsed high-voltage transformers, providing charging of the working capacity in small portions, formed at each actuation and transmitter, so that the frequency of the charging pulses working capacity of at least 3 times higher than the frequency of the high-voltage switch actuation.  2. The device according to claim 1, characterized in that the aforementioned high-voltage switch is an uncontrolled self-breakdown spark gap, one or both of which electrodes are made in the form of one or more pins, threads, needles, blades or other parts with sharp edges on which ignition is possible corona discharge when a voltage arrester is applied to the electrodes, the value of which is lower than the breakdown voltage.  3. The device according to claim 1, characterized in that the said working capacity is the output capacity of the high voltage rectifier.

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