RU2111605C1 - Method and device for rectifying ac current - Google Patents

Abstract

FIELD: gaseous-discharge engineering; plasma valves. SUBSTANCE: method involves use of thermionic valve for rectifying ac current; interelectrode gap is filled with alkali metal vapors at pressure not over 300 Pa, AC voltage is applied, non-self-sustained arc discharge is fired at positive potential across anode and glow discharge is fired at negative potential across anode. Anode temperature is maintained 10 to 20 K higher than alkali metal vapor temperature; this temperature and interelectrode gap are found from definite analytical expressions. Thermionic valve has heat-insulating vessel holding alkali metal, casing provided with heater that has anode and cathode, variable-conductance heat pipe with heat-insulated gas-accumulating space and self-contained heater, anode temperature sensor, and controller whose input communicates with sensor and outputs, with heater. EFFECT: enlarged range of rectified voltages and reduced power loss during ac voltage rectification. 2 cl, 3 dwg

Description

 The invention relates to gas-discharge equipment, and more particularly to gas-discharge devices of power electronics.

 In practice, a method of rectifying alternating current using a gas discharge device containing an anode and a cathode separated by an interelectrode gap filled with a working fluid (gas or mercury vapor), which consists in applying an alternating voltage between the anode and cathode and igniting an arc discharge in the gap, is quite widely known and applied. with a positive potential of the anode and smoldering with a negative potential of the anode, for example, mercury valves for rectifying the current [1].

 The disadvantages of this method are the increased cost of energy (power) and a decrease in reliability due to the significant difference between the ignition voltages of the discharge (hundreds of volts) and its burning (several volts - tens of volts), which requires the use of special measures and schemes to reduce peak loads at the time of ignition of the discharge . All this limits the possibilities of plasma valves, especially in the range of increased power and voltage when working at load. The use of mercury vapor for rectification of alternating current requires forced cooling of the valves in order to stabilize the pressure and reduce the likelihood of reverse ignitions, which also leads to additional energy costs.

 The disadvantage of devices in which this method is implemented is that to maintain a discharge at the moment of voltage polarity reversal, an igniter circuit is used, which feeds the auxiliary arc discharge in the gap and requires additional costs of electric power, reducing the overall efficiency of the method and devices in which it is being implemented.

 Closest to the claimed one is a method of rectifying current using a thermionic valve containing an anode and a heated thermal cathode located in the housing and separated by an interelectrode gap, including filling the interelectrode gap with alkali metal vapors, heating the thermal cathode and cooling the anode, applying alternating voltage between the anode and the thermal cathode with ignition non-self-sustaining arc discharge in the gap with a positive anode potential and smoldering with a negative anode potential [2].

 This method is implemented in a thermionic valve containing a thermally insulated alkali metal tank equipped with a heater, a housing, an anode and a thermal cathode installed in it, separated by a gap filled with alkali metal vapors and connected with the tank cavity [3].

 The disadvantage of this method and device is the low value of the rectified voltage (units of volts - tens of volts), which is due to the low electric strength to reverse arc breakdown of the vapor of the working fluid in the interelectrode gap and the high probability of ignition of surface discharges on an electrician.

 The technical result of the invention is to increase reliability, increase the efficiency of the method of rectifying current and expanding the range of operating voltages.

где
ε₀ - диэлектрическая постоянная; e - заряд электрона; m_а - масса атома; P_рт - давление паров щелочного металла в зазоре; κ_a - теплопроводность паров; U_p - величина приложенного переменного напряжения, давление паров щелочного металла поддерживают не выше 300 Па, температуру анода поддерживают выше температуры паров щелочного металла в зазоре на 10 ... 20, при этом величину межэлектродного зазора Δ_МЭЗ вентиля устанавливают исходя из выражения
(5...10)l_ia≤ Δ_МЭЗ≤(1...3)l_ea,
где
l_ea = 1/(n_aQ_ea) - длина ионизации электронным ударом; l_ia = 1/(n_aQ_ia) - длина перезарядки иона; n_а - концентрация атомов пара в зазоре; Q_ea - сечение ионизации электронным ударом; Q_ia - сечение перезарядки.The specified technical result is achieved by the fact that according to the method of rectifying the current using a thermionic valve containing an anode and a heated thermal cathode, located in the housing and separated by an interelectrode gap, including filling the interelectrode gap with alkali metal vapors, heating the thermocathode and cooling the anode, applying alternating voltage between the anode and a thermal cathode with ignition of a non-self-sustaining arc discharge in the gap with a positive potential of the anode and smoldering with a negative potential node, T _pm alkali metal vapor temperature is maintained in the nip, based on the ratio

Where
ε ₀ is the dielectric constant; e is the electron charge; m _a is the mass of the atom; P _RT - vapor pressure of an alkali metal in the gap; κ _a is the thermal conductivity of the vapor; U _p is the value of the applied alternating voltage, the vapor pressure of the alkali metal is maintained not higher than 300 Pa, the temperature of the anode is maintained above the temperature of the vapor of the alkali metal in the gap by 10 ... 20, while the value of the interelectrode gap Δ of the valve’s _{MEZ is} set based on the expression
(5 ... 10) l _ia ≤ Δ _MEZ ≤ (1 ... 3) l _ea ,
Where
l _ea = 1 / (n _a Q _ea ) is the length of ionization by electron impact; l _ia = 1 / (n _a Q _ia ) is the ion recharge length; n _a is the concentration of vapor atoms in the gap; Q _ea is the cross section for ionization by electron impact; Q _ia is the recharge cross section.

 In addition, the achievement of the technical result is ensured by the fact that the thermionic valve comprising a thermally insulated alkali metal tank equipped with a heater, a housing, an anode and a thermal cathode installed in it, separated by a gap filled with alkali metal vapors and connected with the tank cavity, is equipped with a variable conductivity heat pipe, having an evaporation, condensation sections and a thermally insulated gas storage volume, equipped with an autonomous heater, a temperature sensor, installed on the working surface of the anode facing the gap, and a regulator having an input and two outputs, its input connected to a temperature sensor, and the outputs, respectively, to heaters of the tank and gas storage volume of the pipe, the evaporation section of which contacts the outer surface of the anode, and the condensation the site is located outside the valve body.

 Since the proposed method can only be implemented in the proposed device, characterized by certain design features claimed in the FI, therefore, both objects are combined into a group of inventions, which makes it possible to achieve the specified technical result during implementation.

где
ε₀ - диэлектрическая постоянная; e - заряд электрона; m_а - масса атома; P_рт - давление паров щелочного металла в зазоре; κ_a - теплопроводность паров; U_p - величина приложенного переменного напряжения,
давление паров щелочного металла поддерживают не выше 300 Па,
температуру анода поддерживают выше температуры паров щелочного металла в зазоре на 10 ... 20 К,
при этом величину межэлектродного зазора Δ_МЭЗ вентиля устанавливают, исходя из выражения
(5...10)l_ia≤ Δ_МЭЗ≤(1...3)l_ea,
где
l_ea = 1/(n_aQ_ia) - длина ионизации электронным ударом; l_ia = 1/(n_aQ_ia) - длина перезарядки иона; n_а - концентрация атомов пара в зазоре; Q_ea - сечение ионизации электронным ударом; Q_ia - сечение перезарядки.The claimed technical solution meets the criterion of "novelty." It contains a new set of essential features in the distinguishing part of the patent formula:
the temperature T _RT of alkali metal vapors in the gap is maintained based on the ratio

Where
ε ₀ is the dielectric constant; e is the electron charge; m _a is the mass of the atom; P _RT - vapor pressure of an alkali metal in the gap; κ _a is the thermal conductivity of the vapor; U _p - the value of the applied alternating voltage,
the alkali metal vapor pressure is maintained not higher than 300 Pa,
the anode temperature is maintained above the alkali metal vapor temperature in the gap by 10 ... 20 K,
the magnitude of the interelectrode gap Δ of the _MEZ valve is set based on the expression
(5 ... 10) l _ia ≤ Δ _MEZ ≤ (1 ... 3) l _ea ,
Where
l _ea = 1 / (n _a Q _ia ) is the length of ionization by electron impact; l _ia = 1 / (n _a Q _ia ) is the ion recharge length; n _a is the concentration of vapor atoms in the gap; Q _ea is the cross section for ionization by electron impact; Q _ia is the recharge cross section.

 Moreover, a new set of features in the claimed device is expressed in the fact that it is equipped with a heat pipe of variable conductivity, having an evaporation, condensation sections and a thermally insulated gas storage volume, equipped with an autonomous heater, a temperature sensor mounted on the working surface of the anode facing the gap, and a regulator, having an input and two outputs, its input connected to a temperature sensor, and the outputs, respectively, to the heaters of the tank and the gas storage volume of the pipe, evaporate Yelnia portion which contacts the outer surface of the anode and the condensing section is located outside the valve body.

 The claimed technical solution meets the criterion of "inventive step".

Sign: the temperature T _RT of alkali metal vapor in the gap is maintained based on the ratio

Where
ε ₀ is the dielectric constant; e is the electron charge; m _a is the mass of the atom; P _RT - vapor pressure of an alkali metal in the gap; κ _a is the thermal conductivity of the vapor; U _p - the value of the applied alternating voltage, can significantly increase the electrical strength characteristics of the vapors with respect to the reverse arc breakdown (the value of the breakdown voltage is hundreds to thousands of volts 500 ... 3000 V), that is, it ensures the achievement of the purpose of the invention.

 Sign: the vapor pressure of the alkali metal is maintained not higher than 300 Pa, which allows to reduce the voltage loss on the valve in the conducting state, that is, it helps to achieve the goal in terms of increasing the efficiency of the method.

 Symptom: the anode temperature is maintained above the alkali metal vapor temperature in the gap by 10 ... 20 K to achieve the goal: increasing the reliability of the method — the probability of reverse ignitions is reduced due to a decrease in the emissivity of the anode (for the mode of reverse polarity of the electrodes).

Sign: while the magnitude of the interelectrode gap Δ of the _MEZ valve is set based on the expression
(5 ... 10) l _ia ≤ Δ _MEZ ≤ (1 ... 3) l _ea ,
Where
l _ea = 1 / (n _a Q _ia ) is the length of ionization by electron impact; l _ia = 1 / (n _a Q _ia ) is the ion recharge length; n _a is the concentration of vapor atoms in the gap; Q _ea is the cross section for ionization by electron impact; Q _ia is the cross-section of recharge, leading to the achievement of the purpose of the invention is to increase its efficiency. The choice of the interelectrode gap in the specified limits allows to prevent breakdown in the reverse current mode by reducing the probability of ionization by direct electron impact and at the same time to minimize voltage losses in the conductive state of the valve: ΔU _p (Δ _MEZ ) = ΔU _{P min} , where ΔU _p - voltage drop on a non-self-sustaining arc discharge.

 Symptom: it is equipped with a heat pipe of variable conductivity, which has an evaporation, condensation sections and a heat-insulated gas storage volume, equipped with an autonomous heater, a temperature sensor mounted on the working surface of the anode facing the gap, and a regulator having an input and two outputs, and its input is connected to temperature sensor, and the outputs, respectively, with heaters of the tank and the gas storage volume of the pipe, the evaporation section of which is in contact with the outer surface of the anode, and The separation section is located outside the valve body, which allows to achieve the goal of the invention - significantly expand the range of valve operating voltages and at the same time increases efficiency by creating an autonomous valve cooling system and maintaining its operating temperature.

 The proposed technical solution meets the criterion of "industrial applicability". This method can be used in gas discharge technology in the development of powerful (power) valves, in automation elements (transforming a sensor signal into an electric one for additional organs), etc., is especially effective in stand-alone devices.

 The application materials contain a sufficient and necessary amount of information that fully disclose the possibility of implementing the invention.

 Currently, a design of a sample of a plasma high-temperature diode (VPTD) has been developed and tested, which experimentally confirmed the efficiency of AC rectification.

 Figure 1 shows the distribution of potential, the temperature of the atoms of the working fluid in the interelectrode gap for the glow discharge state, explaining the physical essence of the valve effect of the ion layer at the anode (reverse voltage period). Figure 2 shows a diagram of the interelectrode gap VPTD. In FIG. 3 shows the test results.

или

которые преобразуются с учетом уравнения Пуассона к виду

или

С учетом (5^*) оно принимает вид

Решение уравнения имеет следующий вид:

где
E_k - напряженность поля на отрицательном электроде; d_k - протяженность ионного слоя; T_а - температура атомов, T_рт = T_а. Вид распределения дан на фиг.1.The physical nature of the proposed technical solution, namely increasing the value of the rectified AC voltage, is as follows. The ionic layer at the negative electrode in a glow discharge (the period of the reverse voltage is the negative potential at the anode) has a fairly high resistance - up to 10 ⁵ ... 10 ⁶ Ohms, that is, the layer can be considered as a dielectric in a strong electric field in the drift approximation and described the following equations:

or

which are transformed taking into account the Poisson equation to the form

or

Given (5 ^* ), it takes the form

The solution to the equation is as follows:

Where
E _k is the field strength at the negative electrode; d _k is the length of the ion layer; T _a is the temperature of atoms, T _rt = T _a . The type of distribution is given in figure 1.

где
T_аk - температура пара у поверхности анода в режиме тлеющего разряда (граница "астонова" свечения и темного пространства).It is characteristic that the entire change in the field and potential falls on a narrow region of the ionic layer with a length of (5... 7) l _ia , where the "aston glow" is concentrated. In it there is an increase in the temperature of the working fluid due to

Where
T _ak is the temperature of the vapor near the surface of the anode in the glow discharge mode (the boundary of the "Aston" glow and dark space).

где
κ_aреак - реактивная теплопроводность возбужденных атомов; T T $\genfrac{}{}{0ex}{}{\text{*}}{\text{a}}$ - критическая величина температуры атомов в "астоновом свечении", с которой начинается переход в самостоятельный дуговой разряд.Thus, the balance of the thermal state of the working fluid in the "glow" determines the stability of the glow discharge and its valve properties: by adjusting the temperature of the vapor in the interelectrode gap and its thermophysical characteristics, the value of the voltage of the reverse arc breakdown can be adjusted:

Where
κ _areak - reactive thermal conductivity of excited atoms; TT $\genfrac{}{}{0ex}{}{\text{*}}{\text{a}}$ is the critical value of the temperature of atoms in the "aston glow", with which the transition to an independent arc discharge begins.

с учетом U_p < U_проб можно осуществлять выпрямление переменного тока предлагаемым способом.Choosing the value of steam temperature from the dependence

taking into account U _p <U _samples, it is possible to rectify the alternating current by the proposed method.

 The implementation of the proposed method and the operation of the device are as follows.

The valve is heated to operating temperature by heaters, FIG. 2. The cathode 1 is heated from the helix 4, the anode 2 is heated by radiation from the cathode, the housing 3 is heated by radiation and thermal conductivity, then the alkaline metal tank (cesium or barium) 5 is heated from the heater 6, placed in a screen-type heat insulator 7. Interelectrode gap the valve is filled with alkali metal vapor using a tube. The vapor temperature in the gap at its pressure is selected from the relation (*) taking into account the operating voltage U _p . When an alternating voltage is applied to the valve, it rectifies; the essence of the valve effect is described above. In the forward current mode (minus at the cathode, plus at the anode), a non-self-sustaining arc discharge in alkali metal vapors burns in the gap, which goes out when the polarity of the electrodes changes. In reverse current mode, a dense glow discharge is lit in the gap, which determines the locked state of the valve. Regulation of the thermal state of the anode 2 is carried out using an adjustable heat pipe 8 (variable conductivity), which allows you to maintain its temperature in the nominal operating mode and change it when the operating voltage deviates from the nominal value. This is ensured by the presence of feedback, including a temperature sensor 11, a regulator of heaters 10, and a heat-insulated gas storage volume 9 of the heat pipe 8, equipped with a heat-insulating screen 12 and an autonomous heater 13. With an increase in the operating voltage, the heat flux to the anode 2 increases, its temperature increases, the sensor signal 11 enters the regulator 10, as a result, the current of the heaters 6 and 13 decreases, which leads to a decrease in the temperature of the tank 5 and the gas storage volume 9. The vapor pressure in the gap decreases, which prevents reverse breakdown, and also increases the length of the condensation section of the heat pipe 8, from which there is a discharge of heat removed from the valve (anode).

With a decrease in U _p, the regulation process occurs in the opposite way.

 This method of rectifying the current was tested experimentally on a steam-filled device (with cesium and barium filling). The test results are shown in figure 3.

 The waveform of the rectified voltage indicates the operability of the proposed device and the possibility of implementing a method of rectifying current.

 These method and device significantly expand the capabilities of plasma devices.

Claims (2)

1. A method of rectifying current using a thermionic valve containing an anode and a heated thermal cathode located in the housing and separated by an interelectrode gap, including filling the interelectrode gap with alkali metal vapors, heating the thermal cathode and cooling the anode, applying an alternating voltage between the anode and the thermal cathode with igniting a non-self-sustaining arc discharge in the gap with a positive potential of the anode and smoldering - with a negative potential of the anode, characterized in that the temperature T _{p t} alkali vapor metal in the gap support based on the ratio

where ε ₀ is the dielectric constant;
e is the electron charge;
m _a is the mass of the atom;
P _{r t the} pressure of the alkali metal in the gap,
κ _a - - thermal conductivity of the vapor;
U _p - the value of the applied alternating voltage,
the alkali metal vapor pressure is maintained not higher than 300 Pa, the anode temperature is maintained above the alkali metal vapor temperature in the gap by 10 - 20 K, and the interelectrode gap Δ _{me.s of the} valve is determined from the expression
(5 - 10) l _ia ≤ Δ _{mes s} ≤ (1 ... 3) l _ea ,
where l _{e a} = 1 / (n _a • Q _{e a} ) is the length of electron impact ionization:
l _{i a} = 1 / (n _a • Q _{i a} ) - ion recharge length;
n _a is the concentration of vapor atoms in the gap;
Q _{e a} is the cross section for ionization by electron impact;
Q _{i a} is the charge exchange cross section.  2. Thermal emission valve comprising a thermally insulated alkali metal tank, a heater equipped with a housing, an anode and a thermal cathode installed therein, separated by a gap filled with alkali metal vapors and connected to the tank cavity, characterized in that it is equipped with a variable conductivity heat pipe having an evaporative, condensation sections and a heat-insulated gas storage volume, equipped with an autonomous heater, a temperature sensor mounted on the working surface of the anode facing a gap, and a controller having an input and two outputs, its input connected to a temperature sensor, and the outputs to heaters of the tank and the gas storage volume of the pipe, respectively, the evaporation section of which contacts the outer surface of the anode, and the condensation section is located outside the valve body.

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