FI62916B - KORONAGENERATORANORDNING - Google Patents

Description

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USA (US) U56396 (71) Union Carbide Corporation, 270 Park Avenue, New York, N.Y. 10017, USA (72) Frank Eugene Lovther, Severna Park, Maryland, USA (7h) Berggren Oy Ab (5U) Corona Generator System - Koronageneratoranordning a primary winding and a high voltage secondary winding connected to said corona cell, the speed ratio of the transformer being adjusted so as to provide a high voltage pulse to the secondary winding when a relatively low voltage is applied to the primary. The system further comprises at least two thyristors connected in series with each other and with a low voltage primary winding of said DC voltage source and transformer, and pulse means for controlling the gates of said thyristors at a desired frequency, the thyristors commutating There are no other means in the system for commutating thyristors.

It is well known that the capacity of a corona generator depends in part on the frequency of the power supplies across its plates. Traditionally, high voltage power is supplied to a corona generator at a frequency of 2 62916 primary sources, i. the network frequency. In order to increase the frequency of the power supplied to the corona generators, it has been proposed to use mechanically operated (motor generator) frequency converters. It has also been suggested that electronic circuits containing electron tubes or solid state devices can be used to increase the frequency.

It has generally been found that frequency converters formed by a motor generator are expensive and not particularly durable. In addition, known frequency converters using electron tubes or solid state circuits are often limited in terms of efficiency.

The series-connected thyristors used in high-frequency generators are known e.g. U.S. Patent Nos. 3,579,111, 3,351,779, and 3,784,838. However, these publications teach that when multiple series-connected thyristors are used, the voltage is evenly distributed over all of them.

The object of the invention is to provide an improved high-frequency power supply circuit which is particularly suitable for use in connection with interest generators. Essential to the invention is the abandonment of the conventional attempt to make the impedances and voltages of thyristor circuits the same and to intentionally obtain different impedance values, either with different thyristors or with different additional components.

The main features of the invention will become apparent from the appended claims.

The main requirement states that the difference in impedances is at least 10% in order to show that this is not a random difference caused by ordinary manufacturing tolerances, but a difference obtained and verified by component selection. This can, of course, be achieved by selecting sufficiently different thyristors, or alternatively by connecting suitable, different additional components, such as resistors and capacitors, to the circuit.

3,62916

In order that the present invention may be more readily understood, the following description is given by way of example only with reference to the accompanying drawings, in which:

Fig. 1 is a circuit diagram showing a high voltage high frequency voltage supply circuit to a corona generator;

Figures 2, 3 and 4 show various shapes of corona generators (parts of which have been cleaved off) which can be used in connection with the voltage supply circuit of Figure 1;

Figure 5 is a graphical representation of the results obtained from the circuit using a single controlled rectifier, i.e. a thyristor, with the voltage plotted on the vertical axis and time on the horizontal axis;

Fig. 6 is another curve drawn in the same manner as Fig. 5, but further showing as a dashed line the reference values obtained from the scope of the present invention; and

Figures 7 and 8 show preferred voltage impedance control networks that can be used in the circuit of Figure 1.

The circuit, generally outlined by dashed line 10 in Figure 1, is a conventional filtered half-wave rectifier circuit for supplying pulsed direct current, known from U.S. Pat. No. 3,784,838, and comprises a rectifier diode 11 connected to a capacitor 12 and a source 13 supplying 60 volt 220 cycles. alternating current. Although the drawing shows the use of only one half-wave rectifier circuit suitable for operation with a single-phase current, it has been studied that three-phase bridge-type rectifier circuits are particularly suitable for commercial use of the invention and that full-wave rectifier can be used instead of half-wave.

A conventional pulse generator circuit included in the space delimited by the dashed line 20 comprises a transformer 21 and a bipolar transistor 22. The second winding of the transformer is connected in series with a 60-cycle 110 volt AC power supply 23, while the second winding is connected to a diode 24 and a common conductor. , which include the other side of capacitors 25 and 26. The pulse generator circuit 20 also comprises a control resistor 27 and a fixed resistor 28, which are also connected to a dual transistor transistor 22. One wire from the double base transistor 22 communicates with fixed resistors 29 and 29a. It is to be understood that a variety of commercially available pulse generators are suitable for use in this invention.

Figure 1 also includes a solid state DC-DC converter circuit, generally outlined by dashed line 30, comprising two thyristors 31 and 32 connected in series. Thyristor 31 has an input line 35 and thyristor 32 has an input line 36. The DC-DC converter circuit also includes a transformer 37 with two secondary windings connected in series j | connected to inputs 35 and 36 of thyristors 31 and 32.

The DC-DC converter circuit 30 further includes a high-voltage converter! 38 and a corona generator 40. The corona generator 40 is shown schematically and comprises an upper electrode 41 and a lower electrode 42 and an electrically insulating layer 43 on the surface of the upper electrode 4l. and on the surface of the lower electrode 42 of the electrically insulating layer 44, the corona gap is bounded between the electrodes 41 and 42.

Generally, the corona generator shown at 40 is connected to the high voltage winding of the transformer 38 by means of conductors 46 and 47.

Figures 2, 3 and 4 of the drawing reveal in more detail the shapes of a number of corona generators that can be used in the circuit of Figure 1.

The corona generator shown in Fig. 1 may be as shown in Fig. 2, wherein the reaction chamber 50 is provided with a gas inlet pipe 51 and a gas outlet pipe 52. Inside the chamber 50 there are an upper electrode 53 and a lower electrode 54 bounded by a corona gap 59 and provided with electrically insulating means. with porcelain layers 55 and 56, respectively. The electrodes 53 and 54 are connected to leads 57 and 58, which in turn are connected to a high-voltage, high-frequency voltage source, such voltage being produced in the circuit shown in Figure 1.

Figure 3 shows an alternative corona generator structure in which the electrodes 60 and 6l are separated by a single glass electrically insulating plate 62 defining two corona gaps 63 and 64.

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Figure 4 shows another suitable form of corona generator for use in the present invention, in which form the electrode plates 70 and 71 are separated by a single electrically insulating plate 72, in this case porcelain attached to the upper electrode plate 70, leaving one corona gap 73 for the lower electrode plate 71. and an electrically insulating plate 72. Although Figures 2, 3 and 4 show typical plate-type corona generators, it is to be understood that other well-known forms of Korona generators, such as a tube-type generator, may be used.

It is found that when the circuit shown in Figure 1 is operating, the rectifier / capacitor combination of the power supply circuit 10 supplies a constant DC voltage, typically 311 volts (VT x 220 V), to the DC converter circuit 30 via a low voltage winding of the high voltage transformer 38 via two thyristors 31 and 32 connected in series. The pulse generator circuit 20 is adjusted to produce a desired pulse repetition frequency of tripping pulses ranging from about 1/3 to 20,000 Hz via a pulse transformer 37 whose output occurs in two secondary windings at the inputs 35 and 36 of the thyristors 31 and 32. The trip pulses from the pulse circuit 20 glow) resulting in current high-voltage transformer 38 of the other side (ie. the low-voltage winding) therethrough. The high voltage winding of the transformer 38 has a high voltage power pulse of about 2.0 to 20.0 kV, which then appears between the plates 41 and 42 of the corona generator 40, ionizing the gas in the corona gap 45. The gas contained in gap 45 is exposed to this high voltage corona; in the case where the gas is or contains oxygen, ozone is formed.

If the thyristors 31 and 32 are in the conductive position, they must be connected to the non-conductive position to generate high frequency pulses of current through the high voltage transformer 38. Ko. in the circuit where the thyristors are connected in series, the commutation to the non-conductive position takes place as follows:

When the power pulse described above is directed to the corona generator 40, the following sequence occurs: 6 62916 (a) A high voltage discharge causes an electrical discharge at the moment when the voltage exceeds the spark voltage of the gas across the gap 45. The electrons formed are drawn towards the electrode 41 and 44 which is positive. This electron current generates a current flow that causes the corona power to dissipate at this particular voltage. The electrons are unable to pass through the insulating layer and as a result they accumulate in the insulator as in a capacitor. As a result, (b) the current flow on the secondary side of the transformer 38 ceases and more corona operation ceases until the next power pulse is driven in. However, a sudden power failure causes (c) an opposite voltage pulse on the 30 second side of the transformer according to Lenz’s law. This opposite voltage pulse shifts to the primary side and thus supplies the opposite voltage required (d) to turn off (commutate) the thyristors 31 and 32. If the input terminals 35 and 36 of the thyristors 35 and 36 are now discharged of energy, there will be a delay until the next trip pulse and during this delay the voltage across the thyristors will increase.

The advantage of using the two thyristors shown in Figure 1 connected in series is that this application strains the capacity of any single thyristor when high average powers are required. High in this context means an average of about 40,000 W, which corresponds to just over 135 kg / day of ozone. Limiting thyristor parameters are "off" time and frequency at the required peak currents.

Figure 5 below shows a typical thyristor voltage program for a circuit using a single thyristor. The first glow occurs at T ^. The thyristor voltage then drops (switches on) from Vmax to a much lower value when the thyristor

lights up and the thyristor then leads from moment T to moment (typically 100 microseconds) „At the moment, the opposite (commutative) pulse appears as a result of the increase in charge in generator 40. At time T ^ the switch-off takes place when the voltage becomes negative, at time T ^ the total effect of the opposite pulse is zero and the thyristor voltage pains back to V_QV

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ready for the next ignition.

7 62916

The best available thyristors must be exposed to opposite or zero voltage for at least 10 to 15 microseconds at interesting high power levels. This means that the time interval T2-T4 must be at least 10-15 microseconds. For example, if the voltage becomes positive (at time T 1) after a moment T 1 in a shorter time than the required delay (10-15 microseconds), the thyristor will not be completely turned off and will immediately either destroy itself or blow any protective fuses present.

Figure 6 shows how, by using thyristors connected in series with the present invention, reducing the peak voltage across each thyristor can extend the time period during which the thyristors are off. In the circuit of Figure 1, the actual duration of the opposite voltage increases with the increase shown by T ^ -T ^ 1 in Figure 6. Therefore, if the two thyristors are electrically in series, and if they are perfectly matched, the switch-off time increases by up to 30-50%. If the thyristors are different in impedance, i.e. if the two (or more) thyristors are different in terms of the propagating voltage-drop feature, one thyristor can remain off for up to 100-200% longer than it would be when used alone, while the other detects only a relatively small improvement. However, because the thyristors are in series, they must both “block” (i.e., remain conductive) before damage occurs, so a 100-200% improvement in one thyristor represents a total improvement in the same order, as the other thyristor may “block” repeatedly. , but another never.

This imbalance is the complete opposite of normal operation of series-connected thyristors. Normally, thyristors, like all other forms of rectifier, are limited in their opposite voltage capacity to approximately 1000 volts. If the use of 3000 volts is required, the three units connected in series will perform the task if they are perfectly matched. If not, the weakest of them (e.g. 900 volts) will be damaged, leaving the rest to follow like a string of falling dominoes or playing cards.

Essentially, the above recommended unbalanced series-connected thyristor arrangement allows faster operation of 8,62916 (shorter time interval T ^ -T ^ during the shutdown operation) than with a single thyristor or even a balanced pair of thyristors, which in itself provides a significant technical advantage over the use of a single thyristor. It is obvious that further improvement can be achieved with three or more thyristors connected in series.

The unbalanced forward voltage-charge characteristic of these many thyristors may be an inherent electrical characteristic of the thyristors provided by the fabrication technique. The difference can also be achieved by placing corrective impedance elements connected in parallel in connection with thyristors. Such an arrangement is shown in Fig. 7, which shows the thyristors 31 and 32 connected in series in Fig. 1, to which unbalanced network impedances connected in parallel in the form of resistors 80 and 8l have been added. The difference between the values of resistors 80 and 81 is at least 10%. Thus, i; if the value of resistor 80 is 5 ohms, the value of resistor 8l is either n.

i 4.5 or 5.5 ohms.

Figure 8 shows a more preferred unbalanced network in which the impedances connected in parallel contain reactive components, in this case capacitors 85 and 86 together with different resistors 80 and 81 used alone in Figure I 7. Capacitors 85 and 86 operate to protect thyristors 31 and I 32 from unwanted transient high voltages and thus operate in the well-known "shock absorber" function. The values of capacitors 85 and 86 can be of the order of 0.2 micro-farads.

The circuit shown in Figure 1 is constructed of conventional components readily available from commercial sources. In a preferred embodiment of the present invention, the various circuit components shown in Figure 1 may fall within the definitions set forth in the table below.

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Table I Rectifier circuit 10

Reference number Component Nominal value

11 Rectifier diode 1000 V - 1000 A

12 Capacitor 10-300 microfarads 13 Voltage source 220 V AC

Table II Pulse Generator Circuit 20

Reference number Component Nominal value

21 Transformer 1 A 25 V

22 Double-ended transistor U 2 T

23 Power supply 110 V AC

24 Diodes 1 A - 100 V

25 Capacitor 2000 microfaradia -50V

26 Capacitor 0.2 microfarads - 50V

27 Control resistor 10,000 ohms - 1W

28 Answer 1/4 W

29 Answer 1/4 W

30 Answer 1/4 w

Table III DC-AC converter circuit 30

Reference number Component Nominal values 31 and 32 Thyristor GE type 394-1000 A peak at 2000 V Hz 600 V 10-15

mikrosek. shutdown or GE type 609-3000 A peak at 2000 V

Hz 1200 V, 35 microns. switch-off 37 Pulse transformer Pulse Engineering Type 5258 38 Transformer Winding ratio 9: 1

As seen in Figure 1, this circuit includes a corona generator, which is generally shown to be of the opposite plate type. Various structures of Corona generator types are described in U.S. Patent No. 3,798,457, previously filed. As disclosed in this patent, the corona generators comprise electrode plates, preferably coated with porcelain enamelers having a thickness of the order of about 0.10 to 0.5 mm. The corona gap bounded by the opposing plates is of the order of 0.75-2.0 mm. These corona generators prefer to operate at higher voltages in the order of 2.0-30.0 kV, 10 6291 6 at a frequency ranging from about 1/3 to 20,000 Hz.

In one preferred operation of the corona generator, oxygen or an oxygen-containing gas such as air or oxygen-enriched air is converted to ozone. It is found that the ability of a particular corona generator to produce ozone from oxygen depends to some extent on the frequency of the power supplied across its electrode plates. In the practice of this invention, the frequency produced by the power supply circuit of Figure 1 may range from about 2000-3000 Hz. It is found that, compared to prior art power supplies that normally produce frequencies in the order of 50-60 Hz, the power supply of the present invention is thus capable of producing much better results in terms of the capacity and efficiency of corona generators.

The following example is given to illustrate the operation of the device in detail.

Example

The power supply circuit generally shown in Fig. 1 is connected to the conductors of a corona generator of the type shown in Fig. 2, and the pulse generator 20 of Fig. 1 is set to operate at a frequency of 2000 Hz. Both 2. .

the electrode plate has an area of 322 cm, an electrode gap of 1.1 mm and an electrically insulating porcelain coating on the plates of the order of 0.2 mm.

For comparison, a corona generator was later connected to a conventional 60 Hz pulse voltage source.

It was found that in the first case, using a frequency of 2000 Hz, the device was able to produce 4500 g / h of ozone using a 400,000 g / h oxygen supply. However, using a 60 Hz power supply, the generator was able to produce 135 g of ozone per hour using the same feed.

Although the above description and special example reveal the use of such a high voltage high frequency power supply in connection with a corona generator, this circuit can be used to provide power for other devices with similar load characteristics. Thus, in Figure 1, the corona generator 40 may be replaced by a plasma generating or laser drive.

Claims (3)

6291 6 11 A corona generator system comprising a corona cell, a DC voltage source (10), a transformer (38) having a low voltage primary winding and a high voltage secondary winding connected to said corona cell, the low voltage ratio of the transformer being adjusted so as to provide a high voltage to the secondary winding at least two thyristors (31, 32) connected in series with each other and with said low voltage primary winding (10) and transformer, and pulse means (20, 37) for controlling the gates (35, 36) of said thyristors (31, 32) at a desired frequency , wherein the thyristors commutate the low-voltage primary winding under the effect of an inverted voltage induced by the charge on the corona cell electrodes, and there are no other means in the system for commutating the thyristors, characterized in that the first part (31; 32, 13, 11, 38) , 80; 31, 80 , 83) containing said first thyristor (31), the impedance differs by at least 10% in the second part (32; 32, 8l; 32, 8l, 86) containing said second thyristor (32). Corona system according to claim 1, characterized in that the impedance of the first thyristor (31) differs by at least 10% from the impedance (32) of the second thyristor (32). Corona system according to claim 1, characterized in that the difference between the impedances of the first and second parts of the series connection (31, 32, 13, 11, 38) is provided by two resistors (80) with resistances of at least 10% and each of which is connected across its own thyristor (31; 32). A corona system according to claim 1, characterized in that the first part (31, 80, 85) of said series connection (31, 32, 13, 11, 38) comprises a pair connected in series comprising a first resistor (80) and a first capacitor ( 85), and connected across the first thyristor (31), that the second series connection portion (32, 8l, 86) comprises a series-connected pair comprising a second resistor (8l) and a second capacitor (86) and connected to the second thyristor (31). 32), wherein the total impedance of the first pair (81, 85) differs from the total impedance of the second pair (8l, 86) by at least 10%. 12 6291 6