RU2660157C1 - Method of automatic forced voltage recovery after various character of arc-throughs in the electrostatic precipitator - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention refers to electrical gas cleaning and can be used in the automatic control systems for high voltage rectifier power supply units of electrostatic precipitators. Method includes automatic adjustment of the voltage of the electrostatic precipitator by means of changing the angle of adjustment of the thyristor or of the triac key in the power supply circuit of the electrostatic precipitator. In this case, the average value of the current through the electrostatic precipitator is measured prior to the arc-through of the interelectrode space and the nature of the breakdown is determined – arc, spark or arc-throgh during the inter-current pause. At the same time, the dampening pause time T_dampening on the electrostatic precipitator, which depends on the absolute value of the average current of the electrostatic precipitator just before the arc-through, and the larger value of the current corresponds to the longer damping pause time, to the smaller value – the shorter pause duration, is established only after arc-through. Working angle is set automatically to the next half-cycle after the arc-through, at which the voltage recovery at the electrostatic precipitator is provided during one half-period up to the value below the arc-through voltage level in accordance with the mathematical expression taking into account the minimum and maximum values of the voltage on the electrodes prior to arc-through and the voltage after the arc-through is completed.

EFFECT: degree of gas purification is increased due to the increase in the average voltage at the electrostatic precipitator in the mode of spark- and arc-throughs.

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Description

The invention relates to the field of electric cleaning of gases from dust and mists in various industries and agriculture and can be used in automatic control systems for high-voltage converting power units of electrostatic precipitators. Known methods for automatically controlling the maximum average value of the operating voltage on the electrostatic precipitator, at which the angle of regulation of the thyristor switch increases to achieve a natural maximum average value of the operating voltage, limited either by the nominal parameters of the converter unit or the current-voltage characteristic of the electrostatic precipitator (the presence of a “reverse corona”, spark arc breakdowns of the precipitation space, etc.). There are also known methods that are technically close to the present invention — methods for automatically controlling the voltage of an electrostatic precipitator by changing the angle of regulation of the thyristor switch depending on the magnitude of the operating voltage on the electrostatic precipitator, in which, in order to prevent prolonged breakdowns, they suppress electric breakdowns and relieve tension from the electrostatic precipitator after each breakdown by locking the thyristor key (see ed. certificate of the USSR No. 355606, publ. 30.09.72, No. 1798004, publ. 28.04.93 and RF patent No. 2147469, op Bl. 04/20/2000), as well as patent No. 2147468 from 10.16.1998, which establishes the relationship between the voltage before the breakdown of the interelectrode space and the initial angle of regulation (recovery angle), formed during the first half-period after the breakdown, and then manually set the angle of regulation, not changing during the entire period of regulation.

The closest in technical essence to the present invention is a method for automatically controlling the voltage of the electrostatic precipitator by breakdowns by changing the angle of regulation of the thyristor (triac) key in the power supply circuit of the electrostatic precipitator, in which the average value of the current through the electrostatic precipitator is measured before the breakdown of the interelectrode space and the damping time is set in electrostatic precipitator, depending on this value, as well as during the time interval “T” from the moment of occurrence breakdown before the end of the current of the electrostatic precipitator of the current half-cycle, measure the current and voltage of the electrostatic precipitator and, if the current value is greater than zero and the voltage is zero (arc breakdown), set the duration of the damping pause by turning off the power thyristors of the unit in the next half-cycle for the time Tgash, if during the “T” interval, the current and voltage values are greater than zero (spark breakdown), the damping pause time “Tgash” is set to zero, during breakdowns in the inter-current pause, when the current and voltage tra zero, set the pause quenching "Tgash" equal to zero (RF Patent №2455075, publ. 07/10/2012).

A significant drawback of these methods is that when the electrostatic precipitators are supplied with pulsed current, which is typical for power supply from single-phase converting units with one- and two-half-wave rectification schemes, as well as when powered from special pulse sources, the time for suppressing electrical breakdowns (voltage removal from the electrostatic precipitator) taking into account the nature breakdown (“arc”, “spark”, “inter-pause pause”) - “Tgash” is set automatically, and the working angle of the adjustable voltage recovery to a level below the breakdown voltage tanavlivayut manually.

This leads to an unjustified decrease in the average value of the voltage on the electrostatic precipitator and, as a result, to a deterioration in the degree of gas purification.

The aim of the present invention is to increase the degree of purification of gases by increasing the average voltage on the electrostatic precipitator in the mode of spark and arc breakdowns.

This goal is achieved by the fact that in the known method of automatic voltage regulation, which consists in changing the angle of regulation of the thyristor switch of the high-voltage converter power supply unit of the electrostatic precipitator, in order to maintain the average value of the voltage on the electrostatic precipitator at the highest possible level, the system automatically determines the nature of the breakdown (arc breakdown, spark breakdown or inter-current pause) and automatically sets the working angle of voltage recovery during the next half-periods Nia on electrostatic a value at which its value is below the voltage before breakdown.

The difference of the proposed method of regulation is that during the time interval “t” from the moment of breakdown to the end of the current of the electrostatic precipitator of the current half-period, the value of the current and voltage of the electrostatic precipitator is measured and the nature of the breakdown (breakdown of an arc, spark, or breakdown in the inter-arc pause) is determined to form the necessary the duration of the pause "Tgash" in the case of an arc breakdown. The value of the maximum and minimum values of the voltage of the electrostatic precipitator is also continuously measured and these values are recorded until the moment of breakdown. After the breakdown, the working angle is automatically set, which ensures the restoration of the voltage on the electrostatic precipitator during one half-cycle to a value below the voltage level at which the breakdown occurred, then the control angle gradually increases until the next breakdown.

The voltage on the electrostatic precipitator during the transition period from the moment of breakdown to the time interval for applying a pulse to restore the voltage on the electrostatic precipitator is generally described by the expression

where U _max is the maximum voltage value before breakdown;

U _rev - voltage on the filter after the end of the transient current;

U _nk - voltage of the beginning of corona

t is the end time of the breakdown current;

t ₁ is the end time of the transition process;

ωL is the inductive reactance of the reactor unit;

C is the geometric capacity of the electrostatic precipitator;

R is the active resistance (load) of the electrostatic precipitator.

Imagine this expression differently:

wherein the on-time t _VC (φ _VC - switching angle) power thyristors is calculated by the following formula:

where ϕ _p is the value of the operating angle of the inclusion of power thyristors before breakdown.

After restoration, the voltage should be less than the voltage before spark breakdown, i.e. be about 0.8 of U _max .

From the above description it follows that the differences of the proposed method of automatic forced voltage recovery after the various types of breakdowns in the electrostatic precipitator are significant and, therefore, satisfy the criteria of an inventive step.

In FIG. 1 presents a possible variant of a block diagram of a device for implementing the inventive method.

The block diagram contains a thyristor switch 1, a current-limiting inductor 2, a high-voltage converter 3, an electrostatic precipitator 4, an electrostatic precipitator voltage sensor 5, an electrostatic precipitator current sensor 6, a shaper 7 of the maximum, average, minimum and threshold (U = 0) values of the voltage of the electrostatic precipitator, shaper 8 maximum, average and threshold (I = 0) values of the current of the electrostatic precipitator, a selector of 9 breakdowns in the electrostatic precipitator, a detector 10 of the nature of breakdowns in the electrostatic precipitator (arc, spark breakdown, inter-pause pause), processor 11 - form Vatel signal management control algorithms, an equalizer 12, a voltage level after breakdown in an electrostatic precipitator, the pulse generator 13, the sampling and synchronization to the mains, a pulse-width modulator 14 (phase shifter), the key generator 15, a thyristor control pulses 1.

The scheme works as follows.

When applied to the converter unit and the voltage regulator of the supply network and performing the “Start” operation on the thyristor key 1, control pulses appear from the driver 15, the phase position of which is set by the pulse-width modulator 14 (phase-shifting device). The starting angle of regulation has a maximum value. Thyristor key 1 opens. Voltage appears on the electrostatic precipitator 4.

As the voltage at the output 16 of the shaper 7 and the input 17 of the pulse-width modulator 14 increases, the angle of regulation decreases, therefore, the voltage on the electrostatic precipitator increases.

The process of accelerating the aggregate - electrostatic precipitator system occurs at a speed determined by the state of the processor 11, and continues until one of the following situations occurs:

1. The angle of regulation will reach its minimum value. The voltage on the electrostatic precipitator in this case will be the greatest. The acceleration process will stop;

2. The value of the current of the electrostatic precipitator will reach the nominal current value of the converter unit or the set current limit setting;

3. In the electrostatic precipitator, at a certain voltage level, breakdowns of the precipitation space will occur.

In the event of breakdowns in the filter, voltage pulses appear at the output of the selector 9, which are fed to the input 18 of the breakdown character detector 10. At the same time, signals from the voltage shaper 7 and current shaper 8, which determines the type of breakdown - arc, are applied to the inputs 19 and 20 of the breakdown character detector 10 spark or breakdown in interflood pause. Depending on the type of breakdown, the signal from the detector 10 is supplied respectively to the input of either 21, 22, or 23 of the processor 11. Simultaneously, the signals 24, 25, 26, 27 of the processor 11 are supplied with signals from the shapers 7, 8 of the corrector 12 of the voltage recovery level and the shaper 13 pulses of sampling and synchronization. Depending on the combination of signals, the processor implements the necessary control algorithm. There are three types of breakdown of the interelectrode space, in which various parameters of the voltage at the electrodes after the end of the breakdown. In the case of arc breakdown and spark breakdown in the inter-pause pause after the end of the breakdown, there is no voltage, and in the case of spark breakdown occurring at the maximum voltage on the electrodes, residual voltage arises after the end of the transient mode. Therefore, the processing of these breakdowns has various control algorithms.

In an arc breakdown from the processor 11, a signal determining the duration of the damping pause Tgash is supplied to the input 28 of the pulse-width modulator 14, and an input determining the angle of the voltage recovery across the filter in the next half-cycle after the damping pause is fed to input 29 (equation (3).

In the case of spark breakdown, suppression is not performed (therefore, Tmash = 0), a signal is determined from the processor 11 to the input 30 of the pulse-width modulator 14, which determines the magnitude of the voltage recovery angle at the filter in the next half-cycle - equation (3).

During breakdown in the inter-current pause, suppression is not performed (therefore, Tgash = 0), from the processor 11 to the input 29 of the pulse-width modulator 14, a signal is determined that determines the angle of voltage recovery on the filter in the next half-cycle - equation (3).

The difference in calculating the recovery angle in the last two algorithms is that (according to equation 3) in the first case, the voltage after breakdown is present and the switching angle will increase in proportion to the value of this voltage. The control signals are supplied to the inputs 31 and 32 of the shaper 15 from the pulse-width modulator 14 and the shaper 13, and from the output to the thyristor switch 1. The processes of damping and voltage recovery or only voltage recovery are implemented depending on the nature of the breakdown in the electrostatic precipitator.

By way of illustration in FIG. Figures 2, 3, 4, 5, 6, 7 show the oscillograms obtained during the implementation of the main elements of the method on the model of the control system “converter unit - electrostatic precipitator”.

The oscillograms 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 28, 29, 30 correspond to the signals at the inputs (outputs) of the same name of the block diagram of FIG. one.

Oscillograms 16, 17, 19, 20, 24, 25 in FIG. 2, 3 and 4, 5 are given at t _p = t _in = 2 ms and 5 ms, respectively, in order to show that in this case, when the restoration starts at zero voltage on the electrostatic precipitator (after arc breakdown and breakdown in the inter-arc pause), U _max and I _max significantly exceed the corresponding values preceding the breakdown. And in the case of spark breakdown (Fig. 4), the residual voltage on the electrostatic precipitator is not equal to zero, and the larger it is, the lower the levels of U _max and I _max differ from the previous breakdowns. This confirms that the voltage recovery on the electrostatic precipitator should be carried out in different ways and the recovery angle should be greater than the working angle preceding the breakdown - t _bk > t _p (ϕ _bk > ϕ _p ).

Oscillograms 16, 17, 19, 20, 24, 25 in FIG. 6, 7 are given for t _vk > t _p , and the values of t _{vk are} calculated in accordance with equation (3).

In this case, the maximum values of the recovery voltage after the arc breakdown (Fig. 6) and breakdown in the inter-arc pause (Fig. 7) make up 90% of the breakdown level, which satisfies the given conditions.

Claims (5)

A method of automatically adjusting the voltage of an electrostatic precipitator by changing the angle of regulation of a thyristor (triac) key in a power supply circuit of an electrostatic precipitator, measuring the average value of the current through an electrostatic precipitator before the breakdown of the interelectrode space and establishing the nature of the breakdown — arc, spark, or interstitial breakdown, while pause blanking T _gash on electrostatic, depending on the absolute value of the precipitator mean current immediately before breakdown, - largely The current value corresponds to a longer blanking dwell time, a smaller value - a shorter dwell time - is set only after an arc breakdown, characterized in that the working angle is automatically set to the next half period after the breakdown, at which the voltage on the electrostatic precipitator is restored within one half period to the value below the breakdown voltage according to the following expression:

where ϕ _p - the magnitude of the working angle of regulation to the breakdown of the interelectrode space; U _min and U _max - the minimum and maximum voltage values on the filter electrodes before the breakdown of the interelectrode space; U _rev - voltage on the electrodes of the filter after the breakdown of the interelectrode space.

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