Pulse generator with transformer output. DIY pulse generator

The generator, depending on the voltage of the power source, generates high-voltage pulses with an amplitude of up to 25 kV. It can be powered by a 6V galvanic battery (four "A" cells), battery 6 ... 12V, vehicle on-board network, laboratory power supply up to 15V. The range of application is wide enough: electric fences on a farm for animals, a gas lighter, an electroshock protection device, etc. In the manufacture of such devices, the greatest difficulties are caused by a high-voltage transformer.

Even with a successful manufacture, it does not differ in reliability and often fails from dampness or due to insulation breakdown between the coils. An attempt to make a high-voltage generator based on a diode voltage multiplier also does not always give a positive result.

The easiest way is to use a ready-made high-voltage transformer - an automobile ignition coil from a car with a classic ignition system. This transformer is highly reliable and can operate even in the most unfavorable field conditions. The ignition coil is designed for tough operation in all weather conditions.

The schematic diagram of the generator is shown in the figure. An asymmetrical multivibrator is made on transistors VT1 and VT2, it produces pulses with a frequency of about 500 Hz. These pulses flow through the collector load of the transistor VT2 - the primary winding of the ignition coil. As a result, an alternating pulsed high-voltage voltage is induced in its secondary winding, which has a significantly larger number of turns.

This voltage is applied to the arrester, if it is a self-protection device or a gas lighter, or to an electric fence. In this case, voltage is supplied to the fence from the central terminal of the ignition coil (from the terminal from which the voltage is supplied to the distributor and candles), and the common plus of the circuit must be grounded.

If the generator will be used as a means of self-defense, it is most convenient to make it in the form of a stick. Take a plastic or metal tube of such a diameter that the ignition coil is tightly inserted into it with its metal body. Place batteries and transistors in the rest of the pipe space. S1 in this case is an instrument button. The upper part of the coil body will have to be redone.

The most convenient way is to take an old-style plug for a 220V network, with screw-out contacts. The hole for the wire in it must be drilled so that part of the ignition coil with a high-voltage contact fits tightly into it. Then you need to remove the installation wires from this contact and from the general plus of the circuit and, along the very edges of the plug, bring them to the pin contacts of the plug.

Then this plug must be coated with epoxy glue in the drilled hole for the wire and tightly fit onto the plastic housing of the high-voltage contact of the coil. Screw the discharge tabs under the pins of the plug, the distance between which should be about 15 mm.

The ignition coil can be any from a contact ignition system (from an electronic one is not suitable), preferably imported - it is smaller in size and summer.

The adjustment consists in selecting the R1 rating so that there is a reliable electric discharge between the discharge lobes.

A pulse current generator (PCG) is designed for the primary conversion of electrical energy. Includes an alternating current electrical network with a frequency of 50 Hz, a high-voltage transformer, a rectifier, a current-limiting device, and protection equipment. In the GIT, the charging and discharge circuits are distinguished, which are interconnected by a capacitor bank. The PCG, which is a power source, is connected to the technological unit through a discharge circuit.

Pulse generators are characterized by the following main parameters: voltage across the capacitor bank U,the electric capacity of the battery C, the energy stored in the capacitors W n,pulse energy W 0 pulse repetition rate υ.

The purpose of the charging circuit is to charge the capacitor bank to a given voltage. The circuit includes a current-limiting device, a step-up transformer and a high-voltage rectifier. Selenium or silicon columns are used to rectify the charging current. The high-voltage transformer increases the initial voltage of the supply network 380/220 V to (2-70) 10 3 V.

In the scheme L - C - Dwe have ή 3\u003e 50%.

When using generators of pulse currents, significant energy losses at the stage of discharge formation. This disadvantage is deprived of the widespread system in which generators of pulse currents and voltage are combined (Fig. 30). In this system, the breakdown of the forming gap is performed due to the energy of the capacitor bank of the voltage generator, which creates a conductive channel in the main working gap and provides the main discharge energy in the discharge gap of the pulse current generator.

The ratio of electric voltages and capacities characteristic of such a system is: »at where index 1 corresponds to a voltage generator, and index 2 - to a current generator. So, for example

Energy and weight and dimensions of the generator significantly depend on the high-voltage transformer and rectifier. The efficiency of the charging and rectifier device is increased by using high-voltage silicon poles. Rectifiers have high characteristic values \u200b\u200b- specific

volume from 0.03 to 0.28 m 3 / kW and specific gravity 25-151 kg / kW.

In electric pulse installations, single units are also used, including a transformer and a rectifier, which reduces the main dimensions and simplifies the switching network.

Pulse capacitors are designed to store electrical energy. High-voltage pulse capacitors should have an increased specific energy capacity, low internal inductance and low resistance at high discharge currents, and the ability to withstand multiple charge-discharge cycles. The main technical data of the pulse capacitors are shown below.

Voltage (nominal), kV ................................... 5-50

Capacity (nominal), μF. ... ................................... 0,5-800

Discharge frequency, number of pulses / min ....................... 1-780

Discharge current, kA .............................................. ................. 0.5-300

Energy consumption, J / kg ............................................. ....... 4,3-30

Resource, number of pulses .............................................. .10 e - 3 10 7

One of the main characteristics of pulse capacitors, which affects the dimensions of the battery and the electric pulse installation as a whole, is the indicator of the specific volumetric energy capacity

(3.23)

where E n- accumulated energy; V to- condenser volume.

For existing capacitors ω with\u003d 20 -g 70 kJ / m 3, which determines the increased size of the storage. So the volume of the battery for E n\u003d 100 kJ is 1.5-5.0 m 3. In storage units, capacitors are connected into batteries, which ensures the summation of their electrical capacity, which is equal to 100-8000 μF.

High-voltage switches are used for instantaneous release of electrical energy stored in a capacitor bank in a technological unit. High-voltage switches (arresters) "perform two functions: disconnect the discharge circuit

from the drive when charging it; instantly include the drive in the load circuit.

Various design schemes of arresters and the types of switches corresponding to these schemes are possible: air, vacuum, gas-filled, contact poppet, ignitron and trigatron, with a solid dielectric.

The main requirements for switches are as follows - to withstand high-voltage operating voltage without breakdown, to have low inductance and low resistance, to provide a given current pulse repetition rate.

In laboratory electric pulse installations, mainly air-type arresters are used, which provide switching of high energies with a long service life and have a relatively simple design scheme (Fig. 31).

Arresters of this type have a number of significant disadvantages limiting their use: the effect of the surface condition and the state of atmospheric air (dustiness, humidity, pressure) on the stability of the reproduced pulse; nitrogen oxides are formed, which have an effect on humans; a powerful high-frequency sound pressure is generated.

In industrial mobile installations, mechanical poppet switches have become widespread (see Fig. 31, and).Arresters of this type are simple in terms of electrical circuit and design, reliable during transportation and work in areas with rugged relief, but they require regular cleaning of the surface of the disc elements. I

The electric pulse installation also includes control units for the pulse generator and the technological process, protection and interlocking systems, auxiliary systems that provide mechanization and automation of processes in the technological unit.

The control unit includes electrical circuits for starting, blocking and a synchronization pulse shaping circuit.

The interlocking system is used to “instantly cut off the high voltage. The control system consists of a voltmeter and a kipovoltmeter indicating the mains voltage and on the capacitor bank, respectively, of indicator lamps, sound signals, and a frequency meter.

Technological unit

The technological unit is designed to convert electrical energy into other types of energy and to transfer the converted energy to the processing object.

With regard to the specifics of the discharge-pulse technology of rock destruction, the technological unit includes: a working discharge chamber, a working body in the form of an electrode system or an electrohydraulic fuse, a device for inlet and outlet of a working fluid, and a device for moving electrodes or an exploding conductor (Fig. 32). The working discharge chamber is filled with a working liquid or a special dielectric composition.

Discharge (working) chambers are divided into open and closed, buried and surface, stationary, mixing and remote. Cameras can be disposable and reusable; vertical, horizontal and inclined. The type and shape of the working chamber must ensure the maximum release of accumulated electrical energy, maximum l.p. converting this energy into mechanical, transferring this energy to the object of processing or to its specified area.

The working technological body is designed to directly convert electrical energy into mechanical energy and to enter this energy into the working environment, and through it - to the processing object. The type of the working body depends on the type of electric discharge in the liquid used in this technological process - with the free formation of the discharge, electrode systems are rational (Fig. 33, and);with an initiated discharge - an electro-hydraulic fuse with an exploding conductor (Fig. 33.6).

The working body experiences dynamic loads, the action of an electromagnetic field and ultraviolet radiation, as well as the influence of the working fluid.

The electrode system is used with free discharge formation. Based on the design factor, rod linear and coaxial systems are distinguished. The simplest in execution are linear (opposing or parallel) systems with combinations of tip-tip and tip-plane electrode shapes. The disadvantages of linear systems are their significant inductance (1-10 μH) and non-directional action.

Coaxial systems with low self-inductance and high efficiency are more perfect. converting accumulated electrical energy into plasma energy. The disadvantage of coaxial systems is their low reliability and fragility. The electrode system is technologically advanced and efficient due to high frequency the process of creating mechanical loading forces.

By the number of repeated discharges, one-time and multiple-action systems are distinguished. Reusable systems are more economical and productive. The amount of energy converted by the electrode system also influences design and durability.

In the mining industry, electrode systems designed for a pulse repetition rate of 1-12 per minute are more widely used. With an electric discharge due to thermal processes, erosion of the electrodes occurs, the intensity of which depends on the material of the electrodes and the working fluid, as well as on the amount of energy released in

discharge channel. The working part of the electrodes is made of steel St3 or St45; the diameter of the protruding part must be more than 8 mm with a length of at least 12 mm. In the electrode zone, the melting point of iron is reached in 10 -6 s, and the boiling point in 5 10 -6 s.

The resulting intense destruction of the electrode is accompanied by the formation of plasma jets (vapors and liquid drops of metal). The weakened area of \u200b\u200bthe electrode is the insulating layer at the border of the rod exit - current lead and water.

The main requirements for the electrode system are: high coefficient of conversion of electrical energy, high

operational and technological indicators, economically feasible durability. Electrodes made of copper alloy, tungsten carbide and nickel have the highest erosion resistance.

The cathode surface area should exceed the anode area by 60-100 times, which, in combination with the application of a positive voltage pulse to the anode, will provide a decrease in energy losses at the stage of discharge formation and increase the efficiency. systems. Rational insulation material - fiberglass, vacuum rubber, polyethylene.

An electro-hydraulic fuse is used for an initiated discharge, it perceives dynamic loads, the effect of high-current fields and working fluid, which leads to the destruction of the housing, insulation and electrode.

In an electro-hydraulic fuse, the positive electrode is insulated from the body; the exploding conductor is installed between the electrode and the grounded housing, which acts as a negative electrode.

Depending on the technological problems to be solved, conductors of copper, aluminum, tungsten are used; conductor dimensions within the range of 0.25-2 mm diameter, 60-300 mm length. The design of an electro-hydraulic fuse should ensure the concentration of energy in the required direction and the formation of a cylindrical shock wave front, as well as the manufacturability of operations for installing and replacing an exploding conductor.

To fulfill some of these requirements, it is necessary that the body of the electro-hydraulic fuse serves as a rigid barrier for the propagating wave front.

This is ensured by the use of special cumulative notches in the fuse body and a certain combination of the linear dimensions of the body and conductor. So, the diameter of the fuse body should be 60 times or more larger than the diameter of the exploding conductor.

In recent years, new design schemes and special devices have been developed that increase the effectiveness of the action of the working bodies, ensuring the direction of the action on the object of processing the generated waves and hydraulic flow.

These devices include passive reflective surfaces, electrodes with complex geometry, and generators of diverging waves. There are also devices for pulling an exploding conductor, which complicates the design of the fuse, but increases the manufacturability of the process.

For direct conversion of the energy of an electric discharge into the energy of a compression pulse, special electro-explosive cartridges are used (Fig. 34).

The working fluid that fills the technological unit plays a very important role in the electrical discharge process. It is in the liquid that the discharge is reproduced with the direct transformation of electrical energy into mechanical energy.

Ionization is observed in the liquid, as well as the release of unreacted oxygen and hydrogen (up to 0.5 10 -6 m 3 / kJ), the liquid is drawn into motion by the propagating wave front, which forms a hydraulic flow in the technological unit capable of performing mechanical work.

Water (technical, marine, distilled) and aqueous electrolytes are used as a working fluid; hydrocarbon (kerosene, glycerin, transformer oil) and silicone (polymethylsiloxanes) liquids, as well as special dielectric, liquid and solid compounds. Industrial water is more widely used, the specific electrical conductivity of which is (1-10) S / m.

The electrical conductivity of a liquid significantly affects the amount of energy required to form a discharge, since it determines the value of the breakdown voltage and the speed of streamer movement. The minimum tension at which streamers arise is estimated at 3.6 10 3 V / mm.

The specific electrical conductivity (S / m) of some liquids used to fill the process unit are shown below.

Process water (tap) ............................................. ............ (1-10) 10 -2

Sea water................................................ ............................................. 1-10

Distilled water................................................ ............................ 4,3 -10 -4

Glycerol................................................. .................................................. ..6.4 10 -6

It is seen that dielectric liquids have low ionic conductivity. The specific electrical resistance of the liquid (r g) also determines the value of the electrical efficiency. and depends on the amount of energy introduced into a unit volume of the working fluid. So, for water, the pw parameter decreases with an increase to values \u200b\u200bof 500-1000 kJ /; with a further increase in W 0, the parameter p is stabilized within 10-25 Ohm-m.

The electric discharge in a liquid also depends on the density of the working liquid - with an increase in density, the peak of overvoltages and the steepness of the current decay decrease. To increase the voltage of the discharge circuit, and, accordingly, the magnitude of the breakdown voltage, working fluids with low specific conductivity should be used (for example, industrial water).

The use of liquids with a higher conductivity facilitates the formation of sliding discharges; increases energy losses at the stage of channel formation and decreases the shock wave amplitude.

Viscous compounds are also used as a working fluid (spindle oil - 70%, aluminum powder - 20%, chalk - 10%), which increases the shock wave amplitude by 20-25% and reduces energy losses.

Metallized dielectric filament and paper strips impregnated with electrolyte are also used as a dielectric. The introduction of a solid dielectric reduces the total energy consumption for breakdown (4-5 times), reduces the required number of streamers (4-6 times), reduces thermal radiation and ultraviolet radiation. The introduction of solid particles of conductive additives into the flow of the working fluid is used instead of exploding conductors.

The task of the calculation is to determine the structure of the electrical circuit, select the element base, and determine the parameters of the electrical circuit of the pulse generators.

Initial data:

· Type of technological process and its characteristics;

· Constructive use of the discharge circuit;

· Characteristics of supply voltage;

· parameters electrical impulse and etc.

Calculation sequence:

The sequence of the calculation depends on the structure of the electrical circuit of the generator, which consists in whole or in part of the following elements: a source of constant (alternating) voltage, an auto-generator, a rectifier, a discharge circuit, a high-voltage transformer, a load (Figure 2.14).

· Calculation of the voltage converter (Fig. 2.15, a);

· Calculation of the actual pulse generator (Fig. 2.16).

2.14. Complete block diagram of the pulse generator: 1 - voltage source; 2 - autogenerator; 3 - rectifier; 4 - smoothing filter; 5 - discharge circuit with a high-voltage transformer; 6 - load.

Calculation of the converter (Fig. 2.15 a). Supply voltage U n \u003d 12V DC. We select the output voltage of the converter U 0 \u003d 300V at a load current J 0 \u003d 0.001 A, output power P 0 \u003d 0.3 W, frequency f 0 \u003d 400Hz.

The output voltage of the converter is selected from the conditions for increasing the stability of the generator frequency and to obtain good linearity of the output voltage pulses, i.e. U n \u003e\u003e U on dash, usually U n \u003d 2U on dash.

The frequency of the output voltage is set on the basis of the conditions for optimum performance of the master oscillator of the voltage converter.

The values \u200b\u200bof P 0 and U 0 make it possible to use the KY102 series dinistor VS in the generator circuit.

As a transistor VT, we use MP26B, for which the limiting modes are as follows: U kbm \u003d 70V, I KM \u003d 0.4A, I bm \u003d 0.015A, U kbm \u003d 1V.

We offer the transformer core made of electrical steel. We accept B M \u003d 0.7T, η \u003d 0.75, 25s.

We check the suitability of the performed transformer for operation in the converter circuit under the conditions:

U cbm ≥2.5U n; I km ≥1.2I kn; I bm ≥1.2 I bn. (2.77)

Collector current of the transistor

Collector current maximum:

According to the output collector characteristics of the MP26B transistor for a given collector current β st \u003d 30, therefore the base saturation current

AND.

Base current:

I bm \u003d 1.2 · 0.003 \u003d 0.0036A.

Therefore, according to the condition (2.78), the MP26B transistor is suitable for the designed circuit.

Resistor resistance in the voltage divider circuit:

Ohm; (2.79)

Ohm.

We accept the nearest standard values \u200b\u200bof the resistances of the resistors R 1 \u003d 13000 Ohm, R 2 \u003d 110 Ohm.

Resistor R in the base circuit of the transistor regulates the output power of the generator, its resistance is 0.5 ... 1 kOhm.

Cross-section of the core of the transformer TV1:

Fig 2.15. Principled electrical circuit pulse generator: a - converter;

b - pulse generator

We choose a core Ш8 × 8, for which S c \u003d 0.52 · 10 -4 m2.

The number of turns in the windings of the transformer TV1:

Vit .; (2.81)

vit .; (2.82)

vit. (2.83)

Filter capacitor capacity VC1:

Diameter of wires of windings of transformer TV1:

We choose standard wire diameters d 1 \u003d 0.2 mm, d 2 \u003d mm, d 3 \u003d 0.12 mm.

Taking into account the thickness of the enamel insulation d 1 \u003d 0.23 mm, d 2 \u003d 0.08 mm, d 3 \u003d 0.145 mm.

Figure: 2.16. Calculation scheme of the pulse generator

Calculation of pulse generators (Fig.2.16)

We accept the voltage at the generator input equal to the voltage at the converter output U 0 \u003d 300 V. Pulse frequency f \u003d 1… 2 Hz. Pulse voltage amplitude is not more than 10 kV. The amount of electricity in a pulse is no more than 0.003 Cl. Pulse duration up to 0.1 s.

We choose a VD diode of type D226B (U arr \u003d 400 V, I pr \u003d 0.3 A, U pr \u003d 1 V) and a thyristor of type KN102I (U on \u003d 150 V, I pr \u003d 0.2 A, U pr \u003d 1 , 5 V, I on \u003d 0.005 A, I off \u003d 0.015 A, τ on \u003d 0.5 · 10 -6 s τ off \u003d 40 · 10 -6 s).

Direct resistance to direct current of the diode R dd \u003d 3.3 Ohm and thyristor R td \u003d 7.5 Ohm.

Pulse repetition period for a given frequency range:

. (2.86)

The resistance of the charging circuit R 3 must be such that

Ohm. (2.88)

Then R 3 \u003d R 1 + R d.pr \u003d 20 · 10 3 + 3.3 \u003d 20003.3 Ohm.

Charge current:

A. (2.89)

Resistor R 2 limits the discharge current to a safe value. Its resistance:

Ohm, (2.90)

where U p is the voltage across the charging capacitor VC2 at the beginning of the discharge, its value is equal to U off. In this case, the condition R 1 \u003e\u003e R 2 (20 · 10 3 \u003e\u003e 750) must be observed.

Discharge circuit resistance:

R p \u003d R 2 R t. Pr \u003d 750 + 7.5 \u003d 757.5 Ohm.

The conditions for stable inclusion (2.91, 2.92) are satisfied.

, , (2.91)

, . (2.92)

Capacitor VC2:

. (2.93)

Capacitance VC2 for frequency f \u003d 1 Hz:

F

And for a frequency of 2 Hz:

C 2 \u003d 36 · 10 -6 F.

Amplitude of the current in the charging circuit of the capacitor VC2

, (2.94)

Amplitude of the current in the charging circuit of the capacitor VC2:

, (2.95)

Pulse energy:

J. (2.96)

Maximum amount of electricity per pulse:

q m \u003d I p τ p \u003d I p R p C 2 \u003d 0.064 757.5 72 10 -6 \u003d 0.003 C (2.97)

does not exceed the specified value.

Let's calculate the parameters of the output transformer TV2.

Estimated transformer power:

Tue, (2.98)

where η t \u003d 0.7 ... 0.8 is the efficiency of a low-power transformer.

Cross-sectional area of \u200b\u200bthe transformer core:

The number of turns of each transformer winding per

vit / B. (2.100)

The number of turns in the windings of the TV2 transformer:

W 4 \u003d 150 N \u003d 150 16.7 \u003d 2505 vit .; (2.101)

W 5 \u003d 10000 16.7 \u003d 167 10 3 vit.

Diameter of wires in windings (2.85):

mm;

mm.

We select the standard diameters of wires with enameled insulation d 4 \u003d 0.2 mm, d 5 \u003d 0.04 mm.

Example.Determine the voltage and currents in the circuit fig. 2.16.

Given: U c \u003d 300 V AC 400 Hz, C \u003d 36 10 -6 F, R d.p \u003d 10 Ohm, R tp \u003d 2.3 Ohm, L w \u003d 50 mH, R 1 \u003d 20 kOhm , R 2 \u003d 750 Ohm.

Capacitor voltage at the time of charging:

, (2.102)

where τ st \u003d 2 · 10 4 · 36 · 10 -6 \u003d 0.72 s.

Impedance of the capacitance charge circuit VC2:

The charge current is:

AND.

Scheme and theories of action

As shown in fig. 3.2, a current-limited transformer T1 is connected to a bridge rectifier D1-D4 and charges an external storage capacitor C through an overvoltage protection resistor R18. An external storage capacitor is connected between the discharge ground and the electrode of the spark gap G1. The load in this project is not connected as standard, but between the discharge ground and the electrode of the spark gap G2. Please note that the load is complex, usually with high inductance (not in all cases) with a small active resistance from the Load inductance wire. The spark gap electrodes G1 and G2 are located at a distance 1.2-1.5 times greater than the breakdown distance at a given voltage.

The third trigger electrode TE1 is discharged by a short high-voltage pulse of low energy at G2, creating a voltage peak that ionizes

Figure: 3.2. Schematic diagram of a pulse generator

Note:

Special note regarding diodes D14, D15. The polarity can be reversed to obtain a large triggering effect at low impedance loads, as is the case with can deformation devices, wire explosions, plasma weapons, etc.

Attention! If the load impedance is too high, energy can be directed backwards through the diodes and transformer T2 and damage these components.

Note that circuit ground and common ground are isolated from each other.

Discharge ground is connected to chassis and ground through the green wire on the power cord.

For greater safety, it is recommended to use momentary pushbuttons as the S3 switch, which is turned on only when pressed.

If the device is located in a place where unauthorized personnel have access, it is recommended to use a switch with a lock as S4.

the gap between G1 and G2, which leads to the discharge of the energy stored in the external capacitive storage into a load with a complex resistance.

The charge voltage of the external capacitive storage is set by the resistive divider circuit R17, which also outputs a signal for the voltmeter Ml. The charge voltage is set by a control variable resistor R8 connected in series with R17. This control signal sets the off level of Comparator II, which sets the dc bias of Q1. In turn, Q1 controls the relay, which turns off the relay. The contacts of the de-energized relay RE1 remove the energy supply to the primary winding of T1. When R8 is set to a preset value, it automatically maintains a certain voltage level in external capacitive stores. The S3 safety button provides the ability to manually delay the charging of the external capacitor.

LA1 red LED lights up when power is turned on. The yellow LED LA2 lights up when the charge reaches the set value.

The triggering electrode circuit is a special capacitive discharge (CD) system, where the energy of the capacitor C6 is directed to the primary winding of the pulse transformer T2. On the secondary winding of T2, a sequence of positive high voltage pulses is generated, which is fed to capacitors C8 and C9 through decoupling diodes D14 and D15. These high voltage dc pulses cause ionization in the gaps by discharging through the TE1 trigger electrode. At the input of this circuit, there is a voltage doubler consisting of capacitors C4, C5 and diodes D8 and D9. Start switch S1 energizes the circuit causing the spark gap to operate immediately. The silicon triode SCR removes the charge from C6, the unlocking current to the SCR is supplied by the DIAC dynistor, the offset to which is set by the variable resistance R14 and the capacitor C7.

A 12 V voltage step-down transformer TK supplies the control circuit, which also includes the RE1 relay. If there is no 12 V voltage in the system, it can only be started by manually activating RE1. The rectifier on diodes D10-D13 rectifies an alternating voltage of 12 V, which is then filtered on a capacitive filter C1. Resistor R5 decouples the power supply for control through the Zener diode Z3, Z4, which is necessary for the stable operation of the comparator circuit. Power for energy storage is supplied from 115 VAC, with fuse F1 engaged and 115 VAC switched on by switch S4.

Comment

In our laboratory at Information Unlimited, the energy storage equipment includes 10 oil condenser racks. Each rack houses 50 4500 V, 32 μF capacitors, connected in parallel to achieve a total capacitance of 1600 μF, or about 13,000 J at 4000 V per rack. All 10 racks connected in parallel give 130,000 J. It is very important at these energy levels to correctly make connections and assemble the system, observing the required location and thickness of the wires to receive pulses with a power of hundreds of megawatts. Explosion shields are installed around the storage racks to protect personnel from hazardous voltages.

Charging time for one rack is about 10 minutes. With such a charge, the use of 10 racks would be impractical, since it would take almost 2 hours to charge them. We use a 10,000 V, 1 A charging system that allows all 10 oil capacitor racks to be charged to store 130,000 J of energy for 1 min. ... Such a high voltage charger can be purchased by special order.

The order of the preliminary assembly of the device

This section assumes that you are familiar with the basic tools and have ample build experience. The pulse generator is assembled on a metal chassis 25.4 x 43.2 x 3.8 cm, made of galvanized iron 1.54 mm thick (caliber 22). It uses a 6500V, 20mA current limited RMS transformer. It is necessary to follow the above drawing as closely as possible. You can use a more powerful transformer, then you will have to change the size of the device. We offer to connect in parallel up to 4 previously used transformers; to get a charging current of 80mA. A voltmeter and controls are installed on the front panel. It is recommended to replace S4 with a key switch if the device is located in an area where unauthorized personnel have access.

When assembling the device, observe the following sequence of steps:

1. If you purchased a kit, lay out and identify all components and structural parts.

2. Cut a 0.25 cm grid perforation board with a size of 15.9 x 10.8 cm (6.25 x 4.25 inches) from the workpiece.

Figure: 3.3. Pulse generator circuit board

Note:

The dotted line shows connections on the back of the board. Large black dots show holes in the board that are used to install components and connections between them.

3. Insert the elements as shown in fig. 3.3, and solder them to the terminals of the elements, to those contact pads, where necessary, as you move from the lower left edge to the right. The dotted line shows the wire connections on the back of the board according to the schematic diagram. Avoid wire bridges, potential short circuits, and cold soldering as these will inevitably cause problems. Solder joints should be shiny and smooth, but not spherical.

4. Connect the circuit board with wires to the following points (see Fig. 3.3):

- with the chassis ground with a # 18 vinyl-insulated wire 20 cm long;

- with TE1 high voltage wire 20 kV 10 cm long;

- with resistor R18, vinyl-insulated wire # 18 20 cm long;

- with anodes D3 and D4 with a # 18 vinyl-insulated wire 30 cm long (circuit ground);

- with TK (2) 12 V DC with vinyl-insulated wire # 22 20 cm long;

- with a voltmeter M1 (2) with a vinyl-insulated wire # 22 20 cm long. Check all connections, components, the location of all diodes, semiconductor elements, electrolytic capacitors CI, C2, C4, C5, C7. Check the quality of the solders, potential short circuits, the presence of cold soldering spots. Solder joints should be smooth and shiny, but not spherical. Check this carefully before turning on the device.

5. The spark gap is assembled as follows (Fig. 3.4):

- make the base BASE1 from a sheet of galvanized iron 1.4 mm thick (gauge 20) and dimensions 11.4 x 5 cm (4.75 x 2 inches);

- make two BRKT1 staples from 1.4 mm (20 gauge) galvanized iron sheet, each 6.4 x 3.2 cm (2.5 x 1.25 inches). Fold the edge in the form of a visor measuring 1.9 cm;

- make two BLK1 blocks of polyvinyl chloride (PVC) or similar material 1.9 cm thick and 2.5 x 3.2 cm (1 x 1.25 inches). They must have good insulating properties;

- make the BLK2 block from Teflon. It must withstand high voltage triggering impulse;

- gently solder the COL1 flanges to the BRK1 brackets. Adjust the armature to ensure accurate alignment of the tungsten electrodes after assembly. At this point, you will need to use a propane gas blowtorch, etc .;

- Grind off the sharp ends from the eight screws. This is to prevent breakage of the PVC material due to corona discharge generated at the sharp ends at high voltage;

- pre-assemble the parts, drill the necessary holes in them for assembly. Follow the illustration for correct placement;

Figure: 3.4. Spark gap and ignition device

Note:

The spark gap is the heart of the system, and it is there that the energy accumulated by the capacitors over the entire period of charge a is quickly transferred to the load in the form of a high-power pulse. It is very important that all connections are capable of withstanding high currents and high discharge voltages.

The device shown here is designed for the HEP90 and is capable of switching energies up to 3000 J (with a properly regulated pulse), which is usually sufficient for efficient experiments with mass transfer devices, can bending, wire blasting, magnetism and other similar projects.

A high energy switch capable of operating at 20,000 Joules can be supplied by special order. Both switches use a high voltage trigger pulse, which depends on the high impedance of the line load. This is usually not a problem for loads with moderate inductance, but can be a problem with low inductance. This problem can be solved by placing multiple ferrite or ring cores in these lines. The cores react very strongly to the triggering pulse, but at the main discharge they reach saturation.

The design of the spark gap must take into account the mechanical forces that arise from strong magnetic fields. This is very important when working with fdxhy energy and will require additional means to reduce inductance and resistance.

Attention! During experiments, a shield should be installed around the device to protect the operator from possible debris in the event of a device breakdown.

For reliable starting, the starting gap must be set depending on the charge voltage a. The gap should be at least 0.6 cm from the bracket. If the inclusion is unstable, you need to experiment with this value.

- attach the large block lugs LUG1 to each side of the BRKT1 brackets. The connection must be made carefully as the impulse current reaches the kiloampere value;

- temporarily set the main gap to 0.16 cm and the trigger gap to 0.32 cm.

Final Assembly Procedure

The following are the steps for final assembly:

1. Make the chassis and panel as shown in fig. 3.5. It is wise to make a square hole in the panel to accommodate the voltmeter prior to fabricating the panel. The voltmeter that is used requires a 10 cm square hole. Other, smaller holes can be identified from the drawing and drilled after connecting the chassis and panel.

Note:

Fabricate the front panel from 1.54 cm (22 gauge) galvanized iron sheet, 53.34 x 21.59 cm (21 x 8.5 inches). Bend 5 cm on each side to connect to the chassis as shown in the illustration. Punch holes for the voltmeter.

Make a 1.54 cm (22 gauge) galvanized iron chassis with dimensions 55.88 x 27.9 cm (22 x 15 inches). Fold 5cm on each side and make a 1.25cm visor. The overall size will be (25x43x5cm) with a 1.25cm visor at the bottom of the chassis.

Make smaller holes and holes for connections as you proceed.

The visor running on the supplied part of the chassis is not shown in the figure.

Figure: 3.5. Drawing for the manufacture of chassis

2. Try on the control panel and drill the necessary holes for controls, indicators, etc. Pay attention to the insulating material between the chassis and the parts of the device, see fig. 3.6 part of PLATE1. This can be achieved with a small amount of RTV silicone sealant at room temperature. Drill the appropriate holes as you go, checking for correct location and dimensions.

Figure: 3.6. General view of the assembled device

Note:

The wires are shown slightly elongated to provide clarity of images and connections.

Dotted lines show components and connections under the chassis.

3. Try on the rest of the parts (see Fig. 3.6) and drill all holes required for mounting and placement. Note the fuse holders FH1 / FS1 and the insulation of the BU2 input power cord. They are located on the underside of the chassis and are shown in dotted lines.

4. Provide sufficient space for the high voltage components: for the output terminals of the transformer, high voltage diodes and resistor R18. Please note that the high voltage diodes are mounted on the plastic board with double sided RTV tape.

5. Replace the control panel. Secure the circuit board with a few pieces of RTV adhesive tape when you are sure everything is fine.

6. Make all connections. Pay attention to the use of wire nuts when connecting terminals T1 and T2.

Electrical preliminary tests

Follow these steps to carry out preliminary electrical tests:

1. Short-circuit the output terminals of the transformer using the high-voltage wire with clamp.

2. Remove the fuse and install a 60 W barreter (vacuum current stabilizer) in its holder as a ballast during the test period.

3. Set the switch S4 (see Fig. 3.7) to the off state, turn the axis of the switch combined with the variable resistance R8 / S2 to the “off” position, set the variable resistances R14 and R19 to the middle position and connect the device to the 115 V AC network. by plugging the COl power cord into an outlet.

4. Rotate the axis of the combined switch with variable resistance R8 until closed and watch the lamps LA1 and LA2 light up.

5. Press the charge button S3 and make sure that the RE1 relay is switched on (a clicking sound is heard) and the LA2 lamp is off for a while while the S3 button is pressed.

6. Switch on S4 and press S3, notice that the barreter switched on in accordance with point 2 is on full heat.

7. Press the S1 Start button and observe the flash between the TE1 trigger electrode and the main discharge gap between G1 and G2. Pay

Figure: 3.7. Front panel and controls

attention that the axis of variable resistance is set to the average value, but by turning the axis clockwise, you can increase the discharge.

Basic tests

To carry out the tests, follow these steps:

1. Unplug the power cord and turn off S2 and S4.

2. Connect a 30 µF, 4 kV capacitor and a 5 kΩ, 50 W resistor as C and R as shown in fig. 3.6.

3. Remove the ballast lamp and insert a 2 A fuse.

4. Set the trigger gap to 0.32 cm and the main gap to 0.16 cm.

5. Connect a high-grade voltmeter through an external capacitor.

6. Switch on the device and switch on S2 and S4. Press button S3 and make sure the external capacitor is charged to 1 kV before disconnecting RE1. Note that in normal state, LA2 is on and off only for the duration of the charge cycle. When the preset charge is reached, the LA2 LED turns on again, indicating that the system is ready.

7. Rotate R8 / S2 30 ° clockwise and notice that the voltage gets higher before stopping charging.

8. Press the S1 button and observe an instant, powerful arc in the main gap that occurs when energy is directed into an external load.

9. Charge the device to 2500 V by measuring the voltage with an external voltmeter connected through a capacitor. Adjust R19 so that the front panel voltmeter reads 2.5 at full scale 5. Mark the front panel to know where the voltage is 2500 V. The front panel meter now reads the charge voltage with sufficient accuracy with sufficient external accuracy. voltmeter. Repeat step 8, observing an intense arc as you discharge. Repeat the charge and discharge cycles at different voltages to familiarize yourself with operating the instrument.

This completes the verification and calibration of the device. Further operations will require additional equipment, depending on the project in which you are experimenting.

Mathematical relationships useful for bottom equipment

System storage energy:

Ideal current rise is achieved in LC systems. Use a factor of 0.75 when using oil-immersed capacitors, and lower values \u200b\u200bfor photo and electrolytic capacitors. Time to reach peak current at 1 A cycle:

Magnetic flux

A \u003d coil edge area in m 2; Le \u003d distance between poles in m; M \u003d mass in kg. Power:

Acceleration: Speed:

where t is the time to reach the peak current.

The most common generators of rectangular and linearly varying (sawtooth) voltage pulses.

Pulse signal generators (pulse generators) can operate in one of three modes: self-oscillating, waiting and synchronization.

In the self-oscillating mode, the generators continuously generate pulse signals without external influence. In the standby mode, the generators generate a pulse signal only upon the arrival of an external (trigger) signal. In synchronization mode, the generators generate voltage pulses whose frequency is equal to or multiples of the frequency of the synchronizing signal.

Generators of rectangular pulses are divided into multivibrators and blocking generators. Both those and others can operate in both self-oscillating and standby modes.

Self-oscillating multivibrators can be built on discrete, logic gates or operational amplifiers. An op-amp-based self-oscillating multivibrator is shown in Fig. 11.12.

Figure: 11.12. OA-based self-oscillating multivibrator

In this circuit, using resistors R 1 and R 2, a positive feedback is introduced, which is a necessary condition for the occurrence of electrical oscillations. Depending on the output voltage (which can be equal to either + E supply or –E supply, where E supply is the supply voltage of the op-amp), either the voltage U +1 or the voltage U +2 is set at the non-inverting input of the op-amp. Capacitance C, entering the negative feedback circuit, is recharged with a time constant τ= RC... The pulse repetition period T is determined by the expression

.

Thus, this multivibrator generates rectangular voltage pulses.

Blocking generators are used to obtain powerful rectangular pulses of short duration (from fractions of a microsecond to fractions of a millisecond) and a duty cycle of up to several tens of thousands. The main element of such generators is a pulse transformer (Fig. 11.13).

Figure: 11.13. Self-oscillating blocking generator

The blocking generator can operate in self-oscillating, standby or synchronized modes. During a pause (there is no output voltage), the capacitor is recharged along the E – R – W 2 circuit with a time constant τ 1 \u003d RC... At the moment when the voltage across the capacitor C (and, therefore, at the base of the transistor) becomes equal to zero, the transistor starts to open (exit the cutoff mode), collector current begins to flow, which causes a positive feedback signal (through the winding of the transformer W 2) , under the influence of which the transistor abruptly goes into saturation mode. In this case, the capacitor C is recharged along the circuit W 2 –C– the input resistance of the transistor r in with time constant τ 2 = r in ·FROM... With an increase in the voltage across the capacitor C, the base current begins to decrease and at the end of the charge the transistor goes out of saturation and closes. After that, the energy stored in the inductor is discharged to the load. As r in << R, while the time of the transistor in the open state t u and, consequently, the pulse duration on the load is much less than the pulse repetition period.

Voltage ramp generator ... A linearly varying voltage (LIN) is a voltage that changes linearly over a period of time called a working stroke, and then returns to its original level during a period of time called a reverse stroke (Figure 11.14).

Figure: 11.14. Linear voltage

In fig. 11.14 the following designations are adopted: U 0 - initial level, U m - LIN amplitude, T p - working stroke time, T 0 - return stroke time.

Devices designed for the formation of LIN are called LIN generators (CLAY). LIN generators are often called sawtooth voltage generators.

The principle of constructing LIN generators is based on direct current charging of the capacitor. The basis of CLAY (Fig. 11.15) is a capacitance through which a direct current flows from a DC source IT, due to which, when the KU key device is open, the voltage across the capacitance is determined by the expression

, (for i from = I= const), i.e. changes linearly.

CLAY can work either in waiting (Fig. 11.15, and), or in a self-oscillating mode (Fig.11.15, b). CLAY in the self-oscillating mode forms the LIN regularly, and to obtain the LIN in the CLAY in the standby mode, an external voltage pulse U input is required.

Figure: 11.15. Linear voltage generators,

working in standby (a) and self-oscillating (b) modes

All CLAYS can be divided into three types:

a) with an integrating RC-chain (Fig. 11.16);

b) with a current-stabilizing two-pole (Figure 11.17);

c) with compensating feedback (OS) (Figure 11.18).

Figure: 11.16. CLAY based on transistor key

(with integrating RC circuit)

Until the moment in time t 1 the transistor switch is in saturation mode, i.e. voltage U ke , and hence the voltage U out are equal to zero. When served at a point in time t 1 of the blocking voltage pulse, the transistor enters the cut-off mode, and the capacitance C is charged from the source E to through the resistor R to, and the voltage across the capacitance tends to the level E to. At the time t 2 the transistor again enters the saturation mode, and the capacitance is discharged through the low resistance of the collector-emitter gap of the transistor.

Let us consider the principle of constructing a CLAY with a current-stabilizing two-terminal device, which ensures the flow of direct current through it, regardless of the applied voltage (Fig. 11.17). The simplest current-stabilizing element is a transistor. With a constant base current (for example, i bae), even with a significant decrease in voltage u eq between the emitter and the collector (for example, from U 2 to U 1), the collector current of the transistor decreases slightly.

Figure: 11.17. CLAY with a current-stabilizing two-pole

The disadvantage of this circuit is that when connected to the output (i.e., to capacitance C) of the load resistance, the linearity of the output voltage is distorted.

Consider a CLAY with a compensating feedback (based on an OA) (Fig. 11.18). At a moment in time t 1 key TOopens and carries out and carries out a direct stroke, and at the moment of time t 2 the key is closed, the capacity FROMdischarges and zero voltage is set at the output. Capacity FROMcharged with a constant current, which means that the voltage on it (like the voltage U out) changes linearly (Figure 11.18, b). Compensating voltage U to repeats the voltage across the tank U c when the key opens and the capacity is charged from the source U... Since the compensating voltage is switched on oppositely to the voltage across the capacitor, the voltage applied to the resistor R, all the time constant and equal U.

Figure: 11.18. CLAY with compensating feedback

Flowing through a resistor Rcurrent is determined by the expression

i R =(E- U in )/ R.

If the opamp is close to ideal, ( K → ∞,U in → 0 ,i – → 0 ), then i R = E/ R= const. Then the output voltage is determined by the expression

.