SU1733102A1 - Device for feeding scrubbing electrofilter with pulse sign- variable voltage - Google Patents

Abstract

The invention relates to electrostatic methods of separation of materials, it can be mainly used to power the electrostatic precipitators of gas cleaning and allows to increase the reliability of the power sources of electrostatic precipitators. The device for supplying the gas cleaning electrofilter with a pulse alternating voltage contains a single-phase step-up transformer 2. The primary winding of which is connected to the supply mains through a low-voltage switch 4 and the secondary 7 is connected to the doubler input

Description

(L

WITH

 with so

about

go

fig-1

voltages on two rectifying diodes 8, 9 and two capacitors 10.11, the output of which is connected to the cathode and anode of the first 17 and second 18 thyristor switches shunted by the first 24 and second 25 reverse diodes, respectively, and the anode of the first torque switch 17 through the choke 20 designed to connect to the corona electrode of the electrostatic precipitator 1 gas cleaning, an additional

The invention relates to electrostatic methods of separation of materials and can be used in heat and power engineering, metallurgy, the building materials industry and other areas as a power source for an electro-filter for gas cleaning.

A device is known that implements a method of controlling the operation of an electrostatic precipitator (ESP) and which generates a cyclically varying pulsating voltage in the ESP in the positive and negative parts of the cycle.

The disadvantage of this device is the presence of an additional switch, designed for triple voltage of the power source, which complicates the circuit of the device and reduces the reliability of its operation.

The closest to the present invention is a device for powering an electrostatic precipitator, which possesses wide functional capabilities, including, for example, forming an alternating alternating voltage on an EF and containing a single-phase step-up transformer, the primary winding of which through a low-voltage switch controlled by a control unit control, is connected to the mains, and the secondary winding is connected to the input of the voltage doubler on two rectifying diodes and two capacitors, the output of which is connected ene to the cathode and anode of the first thyristor and the second key, actuated by the pulse shaper shunted by first and second freewheeling diodes, respectively, the anode of the first thyristor Nogo key through the throttle is designed for connection to the discharge electrode FE gas purification.

However, the inductance of the oscillating circuit, which forms an impulse voltage of the required form on the ESP, is included in the diagonal of the half-bridge inverter, shoulders

the choke 21 and two damping R-chains 12,14 and 13,15 connected in parallel to the capacitors 10 and 11 of the voltage doubler in the non-conductive direction for the supply voltage, while the additional choke 21 is connected to the cathode of the second thyristor / o key 18, and its other output is intended for connection to the corona electrode of the electrostatic precipitator 1 gas cleaning. 3 il.

which are formed by two storage capacitors and two thyristor switches.

As a result, the short-circuit current through the thyristors of the keys during the emergency tipping of the half-bridge inverter (the simultaneous activation of both thyristor keys due to failures in the control system) is unlimited and can

to reach large values, which can lead to a massive failure of thyristors of keys.

In addition, when the working switches of the thyristor switches, the thyristors of the idle arm are affected by high voltage rise rates (dU / dt).

This requires the use of unreasonably powerful thyristors in the implementation of this device, which leads to a sharp increase in the cost of the device, since the main cost in the power source is the cost of the high-voltage switches thyristors,

The reliability of the device is reduced due to the specified critical effects on the thyristors of the current amplitudes when the inverter overturns and high values of dU / dt at the operating switches.

The aim of the invention is to increase the reliability of its work.

This goal is achieved by the fact that the device for powering the gas cleaning EFF with pulsed alternating voltage,

containing a single-phase step-up transformer, the primary winding of the generator through a low-voltage switch controlled by the control unit, and control, is connected to the mains supply, and the secondary is connected to the input of the voltage doubler on two rectifying diodes and two capacitors, the output of which is connected to the cathode and the anode of the first and second pulse-controlled thyristor switches, shunted by the first and second reverse diodes, respectively, and the anode of the first thyristor switch through the choke assigned to be connected to the corona-forming electrode of the EFFU of gas cleaning, equipped with an additional choke, and the voltage doubler is supplied with two damping RD-chains connected parallel to the capacitors of the voltage doubler and non-conducting for the supply voltage and an additional choke is connected by one output to the cathode of the second thyristor the other, to the corona electrode of the gas purification ESP.

It is known to switch on drossels in series with thyristors to limit the short-circuit current and dU / dt, with the dU / dt being reduced by the combined operation of drossel and thyristor RC protective circuits. However, the introduction of chokes into the circuit leads to a significant increase in operating voltages on the non-switched thyristor switch of the circuit (up to three times the value with respect to the source voltage). Overvoltage can be reduced to twice the value, if during the formation of the voltage of one of the polarities the capacitor of the forming polarity of the other polarity is not charged, which is achieved by applying from the network through the switch only one half-wave of the doubler circuit and then polarity to reset the voltage on a charged capacitor by forcibly tipping the half-bridge inverter (simultaneous activation of both thyristor switches). However, due to the presence of non-return valves connected in parallel to the thyristor switches and the high quality of the circuit, the objective of zeroing voltage cannot be achieved: by the end of the oscillatory process in the tilting circuit, the values of the voltage doubler capacitors return to their original state. as the losses in the oscillatory circuit do not exceed 5-7% of the energy stored in the capacitor. Therefore, to zero the voltage on a capacitor, a time equal to several tens of power supply frequency periods is required. This leads to a decrease in the degree of gas purification at this time, which is unacceptable.

Therefore, to dramatically reduce the time to zero the voltage on a charged capacitor, the voltage doubler before switching the polarity

ten

15

20

25

thirty

35

40

45

50

55

Voltage EMFs parallel to the capacitors of the voltage doubler are fitted with damping RD-circuits that absorb the energy stored in the oscillating circuit.

In addition, the introduction of damping RD circuits into the circuit reduces the short-circuit current in the tilting circuit of the half-bridge inverter by more than two times.

FIG. 1 shows the principal functional-electrical circuit of the proposed device; in fig. 2 diagrams illustrating the operation of the device during the formation of a pulsed positive and negative voltage on the ESP in FIG. 3 are diagrams explaining the process of switching the polarity of the supplying ESP voltage.

The device for supplying the gas purification filter unit EF 1 with a pulsed alternating voltage contains a single-phase step-up transformer 2, the primary winding 3 of which is connected to the mains supply and a low-voltage switch 4, which can be made of two control switches, which are sharply activated, 5 and 6, and the secondary winding 7 is connected to the input of the voltage doubler, made on the rectifying diodes 8 and 9 and the capacitors 10 and 11, shunted by the RD-circuits of the gz diodes 12 and 13 and the resistors 14 and 15 in the net po- for the supply voltage O The common point of the capacitors of the doubler voltage of the damping RD-circuits through shunt 16 is connected to the common bus of the device to which one of the terminals of the secondary winding 7 of the transformer 2 is also connected. The capacitors 10 and 11 of the voltage doubler and thyristor switches (TC) 17 and 18 are controlled shaper 19 pulses, with series-connected throttles 20 and 21 in their chains and non-return valves 22 and 23, which can be made of series-connected diodes 24 and 25 and protective chokes 26 and 27 in the circuit of these diodes and connected in parallel The keys 17 and 18 form a half-bridge inverter, in the diagonal of which the EF 1 is included. The corona electrode EF 1 is connected to the common point of the chokes 20 and 21, and the precipitation electrode is connected to the common point of the device busbars. Parallel to the ESP 1, a voltage divider 28 is installed, the output of which is connected to the first information input of the control and control unit 29 by the low-voltage switch 4, the second information input of which receives a signal from the shunt 16.

The pulse former 19 generates narrow (up to 30 µs) control pulses with the required repetition rate (25–200 Hz) and can be performed, for example, according to.

The control and regulation unit 29 performs the phase-pulse control of the thyristors of the low-voltage switch A and regulates the current of the EF during sparks and short-circuits. in EF and can be performed, for example, according to.

The device works as follows.

To form a positive polarity voltage across the EF, the valve 5 of the switch 4 is turned on and through the transformer 2 a positive half-wave of the supply voltage is transmitted, charging through the diode a capacitor 10 of the voltage doubler. The voltage to which the capacitor is charged is set by the control unit 29, which produces an appropriate control angle to the valve 5. Then, from the driver 19, a control pulse is outputted to the TC 17, after switching on the oscillator discharge of the capacitor 10 through the choke 20 to the capacitor EF 1, charge it before the voltage

Uoo 2E - UEFO,

where UEF is the voltage amplitude at EF; E is the voltage across the capacitor 10; iffo is the initial voltage at EF. In the discharge circuit, the current is sinusoidal. At the moment of changing the sign of the current through TC 17, it turns off, which causes the current to switch from TC 17 to check valve 22 and the reverse half-wave of the current flows in the circuit, which indicates the oscillating discharge of the EF capacitance to the capacitance of the source - capacitor 10, returning the accumulated energy to the source. After the reverse half-wave of the current passes through zero, the valve 22 is turned off. The reverse current flowing through the inductor 26 of the valve 22 creates a reverse voltage on the TC 17, which is necessary to restore the thyristor control capacitance TC 17. The application time of the reverse voltage must exceed the recovery time of the thyristor control capacitance TC 17. This time is equal to the duration of the reverse half-current and it is determined by the total inductance of the chokes 20, 26 and the capacity of the ESP 1. After turning off the valve 22, the oscillatory process is completed and the capacity of the ESP 1 is discharged by the corona current exponentially to voltage is not lower than the voltage of the beginning of the crown. Since the energy of the source - capacitor 10 is spent in the ESP on the ionization of dust and gas

flow, charge of dust particles and their deposition on the precipitation electrode ESP. a periodic charge of the capacitor 10 is required. Which is accomplished by turning on the valve 5 of the switch 4.

Next, the process of forming a positive polarity pulse voltage is repeated. Thus, the EF is affected by a constant voltage component at a level not lower than the voltage of the beginning of the crown, on which voltage pulses are applied, having a specified amplitude and following with a given frequency.

The formation of a pulsed negative voltage voltage is carried out similarly to the formation of a pulsed positive voltage, with the switch 6 valve 4 and the corresponding channels of the voltage doubler (diode 9 and capacitor 11) and half bridge inverter (capacitor 11, TC 18, choke 21 and reverse valve 23).

The duration of each polarity and the frequency of the pulse voltage on the ESP is determined by the peculiarities of the dust collection process and is set by the former 19.

Let us consider the process of transition from one polarity of the supplying EF voltage to another. Suppose that an impulse positive voltage was formed on the ESP, i.e. the capacitor 10 is charged through the transformer 2 and the valve 8 to the power supply voltage by turning on the valve 5 of the switch 4 and the capacitor 11 is discharged. The polarity of the voltage on the capacitor 10 is indicated in FIG. one.

 To zero the voltage on the capacitor 10 from block 19, control pulses are output to TC 17 and 18 (Fig. 3), after switching on which the oscillating discharge of capacitor 11 along the circuit begins: (+) - TC 17 - chokes 20 and 21 - TC 18 - resistor 15 - valve 13 - (-). The current in the circuit is limited by droplets 20, 21. This mode is similar to the emergency mode of the inverter overturning when the two TCs spontaneously turn on. When the voltage sign on the capacitor 10 changes, the current from it commutes to the circuit: resistor 14 to valve 12, then the current stored in the droplets x 20 and 21 begins to decrease exponentially with the time constant determined by the ratio of the active resistance of the circuit and inductance chokes 20 and 21. After the current in the circuit drops to a value below the holding current of the thyristors TC 17 and 18, they are turned off and the zeroing process is completed. Ask the value of the resistors 14

and 15, the end time of the transient process can be adjusted within the required limits. i.e., the time of preparing the circuit for switching the polarity of the supplying EF voltage. By the time the voltage is zeroed on the capacitor 10, the EF capacity is also discharged to zero. the switch 6 of the switch 4 and the capacitor 11 is charged through the transformer 2 and the diode 9 to the required voltage. Then the circuit 19 of the TC 18 is turned on and an impulse voltage of negative polarity is generated on the ESP.

The transition from the negative polarity of the ESP to the positive supply is made in a similar way. Diagrams explaining the process of switching the polarity of the supplying ESP voltage are shown in FIG.

Such a sequence of operation of the elements of the device circuit in the mode of generating a pulse voltage of one polarity or another reduces the voltage level on an unencrypted thyristor switch from three times the value to two times relative to the supply voltage, i.e. the voltage on the capacitors 10 and 11, which increases the reliability of the device.

Due to the fact that switching from polarity to polarity occurs at zero voltage on the ESP, there is no overvoltage either on the EF itself or on the thyristor switches, which further increases the reliability of the device.

Thus, due to the introduction of chokes in series with high-voltage thyristor switches, the short-circuit current value decreases sharply. with the simultaneous switching on of both keys and the rate of increase of the direct voltage on the thyristors of the non-working key, and by installing RD circuits parallel to the capacitors

Claims (1)

Voltage amplifier reduces the time of switching the supply voltage from one to another polarity to one half period of the mains frequency. The invention The device for powering the gas cleaning electrostatic precipitator by pulsed alternating voltage, contains a single-phase step-up transformer, the primary winding of which is connected to the power supply through a low-voltage switch, and its secondary winding is connected to the input of two voltage switches, which are provided with two non-triggers, and you can use the same power supply circuit, which is provided with two non-triggered diodes, and you can use the same power supply circuit, which is provided with two non-triggered diodes, and you can use the same power supply circuit, which is provided with two non-triggered diodes, and you can use the same power supply circuit, which is provided with two non-triggered diodes, and you can use the same power supply circuit, which is provided with two non-triggered diodes, and you can use the same power supply circuit, which is provided with two non-triggered diodes, which are connected to two voltage switches, which are made on two non-triggered diodes, and you can use the same power supply voltage signals, which are provided with two voltage switches, which are connected to two power supply diodes that are connected to the power supply and are connected to the power supply. the outputs of which are connected to the cathode and the anode of the first and second thyristor switches, shunted respectively by the first and second check valves, form pulse generator, its outputs connected to the control inputs of the thyristor switches, control and regulation unit, its outputs connected to the control inputs of the low-voltage switch, and the first choke, one output of which is connected to the anode of the first thyristor switch, and the second is the output of the device intended for connection to the discharge electrode of the electrostatic precipitator, characterized in that, in order to increase the reliability of the device, it additionally contains a second choke, and a voltage doubler - two demos RD circuits, while RD circuits are connected in parallel to the voltage doubler capacitors in the non-conductive direction for the supply voltage, one output of the second throttle is connected to the cathode of the second thyristor switch, and its second output is the output of the device for connection to an electrostatic precipitator corona electrode. Ts18 ff6 fig.Z t