CA1050099A - High frequency power supply for corona generator - Google Patents
High frequency power supply for corona generatorInfo
- Publication number
- CA1050099A CA1050099A CA220,736A CA220736A CA1050099A CA 1050099 A CA1050099 A CA 1050099A CA 220736 A CA220736 A CA 220736A CA 1050099 A CA1050099 A CA 1050099A
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- Prior art keywords
- scr
- corona
- voltage
- power
- circuit
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/097—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser
- H01S3/0975—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser using inductive or capacitive excitation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/0915—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light
- H01S3/092—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of flash lamp
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/505—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/515—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/523—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with LC-resonance circuit in the main circuit
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optics & Photonics (AREA)
- Power Engineering (AREA)
- Oxygen, Ozone, And Oxides In General (AREA)
- Generation Of Surge Voltage And Current (AREA)
- Ac-Ac Conversion (AREA)
Abstract
HIGH FREQUENCY POWER SUPPLY FOR CORONA GENERATOR
Abstract of the Disclosure A corona generator having a high voltage, high frequency power supply wherein a plurality of silicon controlled rectifiers (SCR's) are driven in series.
The use of series connected SCR's without associated voltage equalization networks increases the turn-off time and hence, permits higher switching frequency.
The high frequency power output increases the capacity of the interconnected corona generator.
Abstract of the Disclosure A corona generator having a high voltage, high frequency power supply wherein a plurality of silicon controlled rectifiers (SCR's) are driven in series.
The use of series connected SCR's without associated voltage equalization networks increases the turn-off time and hence, permits higher switching frequency.
The high frequency power output increases the capacity of the interconnected corona generator.
Description
lOS~O99 The present invention relates to corona ~eneration devices, and more specifically to an i~proved power supply circuit and associated corona generator which operate at high frequency and efficiency~
It is generally known that the capacity of a corona generator is dependent in part on the frequency of the power supplies across the plates thereof. Traditionally, high voltage power is supplied to a corona generator at the frequency of the primary source, i.e., the line frequency. To increase the frequency of power applied to corona generators, it has been suggested that mechanically driven (motor generator) frequency converters be used. It also has been suggested that electronic circuits which include vacuum tubes or solid state devices may also be used to increase frequency.
It has generally been found that motor generator frequency converters are expensive and not particularly durable. Furthermore, frequency converters which utilize vacuum tubes or solid state circuits are often restricted with respect to efficiency.
Accordingly, it is an object of the present invention to provide an improved corona generator device which operates at high frequency and efficiency.
It is a further object to provide an improved high frequency power supply circuit which is particularly suited for operation with corona generators.
It is still a further object to provide an inexpensive high frequency power supply for corona generators which is constructed from durable, readily available solid state components.
~ -2-I:~
Thus, in accordance with the present teachings, a corona generating system is provided for supplying at least about 40,000 watts average power to a corona cell.
The system comprises a source of DC power, a transformer having a low voltage primary winding and a high voltage secondary winding with a turns ratio which is adapted to provide a high voltage power pulse across the secondary winding from a relatively low voltage impressed across the primary winding of between about 150 to 600 volts DC. At least two SCR's are connected in a series circuit relationship with the scource of DC power and the low voltage primary winding. Each of the SCR's are unequal to each other with respect to their forward voltage drop characteristic.
Means are provided for pulsing the gates of the SCR's at a desired frequency. The corona cell has spaced electrodes with a surface area large enough to generate a corona discharge of at least the 40,000 watts of average power and for generating a reverse commutating voltage of sufficient duration for turning off at least one of the SCR's within each pulse period with the corona cell representing the only commutating means for the SCR's in the system.
These objects and others will become readily apparent to one skilled in the art from the following - 2a ~
'~2 "~
,'~
105005~9 detailed description and drawings wherein;
Figure 1 is a diagram of the circuit used to supply high voltage, high frequency power to a corona generator which is also shown schematically therein;
Figures 2, 3 and 4 show various configurations of corona generators (with parts broken away) which may be used in conjunction with the power supply circuit of the present invention;
Figure 5 is a graphic representation of data obtained from a prior art circuit wherein voltage is plotted on the vertical axis and time on the longitudinal axis and Figure 6 shows comparison data obtained from the circuit of the present invention (dotted line).
Figures 7 and 8 show preferred voltage unequalization networks which may be used in the circuit of Figure 1.
Broadly, my invention involves a corona generator and associated high voltage frequency power supply which includes a plurality of silicon controlled rectifiers (here-inafter referred to as SCR's) which are electrically connectedin series with a source of DC potential and the low voltage winding of a high voltage transformer, the high voltage winding of which is connected to the plates of a corona generator.
More specifically, I have found that the circuit turn-off time of SCR's used as high power, high frequency electrical switches in a power supply may be reliably increased by driving two or more SCR's in series.
A more clearly detailed understanding of my invention may be obtained by reference to Figure 1 of the drawing wherein the circuit generally outlined by broken line 10 is a conventional rectifier circuit which supplies pulsed DC voltage. Rectifier circuit 10 includes a rectifier diode 11 interconnected with capacitor 12 and a source of 60 lHS00~9 cycle 220 volt AC current indicated as 13~ While the drawing shows the use of a single rectifier circuit suitable for operation on single phase current, it is contemplated that three-phase bridge type rectifier circuits are particularly suited for commercial application of the invention.
~ lso shown in Figure 1 is a conventional pulse generator circuit, the components of which are included within the confines of broken line generally 20. The pulse generator circuit includes a transformer 21 and a unijunction transistor 22. One winding of the transformer 21 is connected in series with a source of 60 cycle 110 volt AC
potential shown as 23. The other winding of the transformer 21 is connected to diode 24, and to a common collector conductor for several other circuit components including one side of capacitors 25 and 26.
Also included in pulse generator circuit 20 is a variable resistor 27 and a fixed resistor 28. The variable resistor 27 and the fixed resistor 28 are also connected to the unijunction transistor 22. One lead from the unijunction transistor 22 interconnects with fixed resistances 29 and 19.
It is to be understood that a wide variety of commercially available pulse generators are suitable for use in the present invention.
Figure 1 also includes an inverter circuit generally outlined by broken line 30. The inverter circuit 30 includes two SCR's 31 and 32 connected in series. The SCR 31 has a gate lead 35 and the SCR 32 has a gate lead 36.
Also included in the inverter circuit is a transformer 37 which possesses two secondary windings which are inter-connected with the gates 35 and 36 of the series connected SCR's 31 and 32.
The inverter circuit 30 includes a high voltage transformer 38 and a corona generator generally 40. The corona generator 40 is schematically shown and includes an upper electrode 41 and a lower electrode 42. The upper electrode 41 has a dielectric layer 43 and the lower electrode 42 has a dielectric layer 44. Between the electrodes 41 and 42, a corona gap 45 is defined.
The corona generator generally 40 is connected to the high voltage side of transformer 38 by means of conductors 46 and 47.
Figures 2, 3 and 4 of the drawing disclose in greater detail a variety of typical configurations of corona generators which may be utilized in the circuit generally shown in Figure 1. The corona generator 40, as shown in Figure 1, may comprise the structure shown in Figure 2 wherein a reaction chamber 50 is equipped with a gas conduit inlet 51 and a gas conduit outlet 52. Within the container 50, an upper electrode 53 is mounted along with lower electrode 54.
Electrodes 53 and 54 are provided with a dielectric layer 55 and 56 respectively. The electrodes 53 and 54 are connected with conductors 57 and 58 which in turn are connected with a source of high voltage, high frequency potential such as is produced in the circuit shown in Figure 1. Between the electrodes 53 and 54 a corona gap 59 is defined.
In Figure 3 an alternative corona generator structure is shown wherein electrodes 60 and 61 are separated by a single dielectric plate 62. The corona generator of Figure 3 possesses two corona gaps, 63 and 64.
Figure 4 shows still another suitable corona generator configuration for use in the present invention wherein electrode plates 70 and 71 are separated by means of lOSOO99 a single dielect~ic plate 72 which is affixed to the uppermost electrode plate 70. The corona ~enerator configuration of Figure 4 possesses a single corona gap 73. While Figures 2, 3 and 4 show typical plate type corona generators, it is to be understood that other well known corona generator configurations such as the well known tube type generator may be used.
In operation of the circuit shown in Figure 1, it is seen that the rectifier/capacitor combination 10 produces a steady DC potential at typically 311 volts ( ~ x 220 volts). This potential from the rectifier circuit 10 is supplied to the inverter circuit 30 through one side of the high voltage transformer 38, which is connected in series to the power supply circuit 10 through the series connected SCR's 31 and 32. The pulse generator circuit 20 is adjusted to produce the desired frequency of triggering pulses which range from about l/3 to 20,000 cycles per second. The trigger pulses from the pulse circuit 20 are fed through pulse _ _ transformer 37, the output of which appears in the two secondary windings thereof at the gates 35 and 36 of the SCR's 31 and 32. As is generally known in the art, the trigger pulses from the pulse circuit 20 will cause the SCR's to conduct (fire). Upon firing a current is passed through one side (low voltage winding) of the high voltage transformer 38.
At the high voltage winding of the transformer 38 a high voltage power pulse appears which will have a voltage from about 2.0 to 20.0 KV. The high voltage pulse from the transformer 38 then appears between plates 41 and 42 of the corona generator 40. This high voltage pulse creates a corona within the corona gap 45. A gas which is contained within the gap 45 is subjected to the high voltage corona, and in the case wherein the gas is or includes oxygen, ozone is 1050~99 produced.
Once the SCR's 31 and 32 are in a conducting mode, it is seen that they must be switched to a non~conducting mode in order to produce the high frequency pulses of current through the high voltage transformer 38. In the operation of the present circuit the SCR's connected in series 31 and 32 are switched to a non-conducting mode as follows:
When the above described power pulse is applied to the corona cell 40, the following sequence occurs:
The high voltage burst produces an electrical discharge at the instant the voltage exceeds the gas sparking potential in gap 45. The electrons produced are attracted towards the positive electrode. This electron flow constitutes the current flow giving rise to the corona power dissipation at that particular voltage. The electrons cannot pass the dielectric barrier and hence accumulate on the dielectric as in a capacitor. Hence, the current flow ceases.
Further corona action stops until another power pulse is applied. The abrupt current stoppage induces a reverse voltage pulse in the secondary of transformer 38 by Lenz's Law. This reverse voltage pulse is transformed to the primary and hence supplies the reverse voltage needed to turn-off (commutate) the SCR's 31 and 32.
The benefit of the two series SCR's shown in Figure 1 will now be explained. First, the present application taxes the capabilities of any SCR when large average powers are called for. Large here means about 40,000 watts average corresponding to 300 pounds per day of ozone. The limiting SCR parameters are turn-off time and frequency at the peak currents required. Figure 5 below shows the typical SCR
voltage history for a circuit in which a single SCR is used.
The first firing is at Tl, the SCR voltage drops (switches) from Vmax to a ~uch lower value Vmin~ The SCR conducts from Tl to T2 ttypically 100 microseconds). At T2, the reverse (commutating) pulse appears~ At T3 turn~off occurs, at T4 the reverse pulse net effect is zero and the SCR voltage climbs back to Vmax ready for the next firing. The best available SCR's require at least 10-15 microseconds turn-off at the high power levels of interest. That is T2 to T3 must be at least 10-15 microseconds. If, for examplel the voltage goes positive (at T4) less than 10-15 microseconds after T2, then the SCR
will not turn-off, and will immediately either destroy itself or blow any protective fuses present.
Figure 6 shows the benefit of reducing the SCR
voltage by using the series connected SCR's of the present invention. In the circuit of Figure 1, the duration of the actual reverse voltage is increased by the increment shown as T4-T4' in Figure 6. Hence, if two SCR's are in electrical series, and if they are perfectly matched, the turn-off situation is improved by may~e 30-50%. If the SCR's are unbalanced, that is if the two (or more) SCR's are unequal 2Q with respect to forward voltage drop characteristics, one SCR
may be improved by as much as 100-200% while the other is improved only slightly. However~ both SCR's must "latch-up"
before damage occurs since they are in series. Hence, the one SCR may latch-up frequently but the other never. This un-balance is in opposition to the normal use of series SCR's.
Normally, SCR's, as any rectifier, are limited in reverse voltage capability, say 1000 volts. If 3000 volt service is required, then three series units will do the job if they are perfectly matched. If not, the weakest one (say 900 volt) will break down, the rest will follow like a line of dominoes.
In essence, the above preferred unbalanced series SCR arrangement allows faster (shorter turn-off time) ~osoo99 operation than with a single SCR. It is obvious that further improvement can be achieved with three or more SCR's in series~
The unbalanced forward voltage charge characteristic of the multiple SCR's may be an inherent electrical characteristic of the SCR's which is produced by manufacturing techniques. The unbalance may also be produced by placing unbalanced shunt connected resistance elements with the SCR's. Such an arrangement is shown in Figure 7 which shows the series connected SCR's 31 and 32 of Figure l to which have been added unequalizing network shunt resistors 80 and 810 The resistors 80 and 81 preferably have a difference in value of at least about +lO~. Therefore if resistor 80 has a value of 5 ohms, resistor 81 will have a value of about 4.5 or 5.5 ohms.
In Figure 8 a more preferred unequalizing network is shown which includes capacitors 87 and 88 as well as the unequal resistors 80 and 81 of Figure 7. Capacitors 87 and 88 serve to protect the SCR's 31 and 32 from unwanted high voltage transits, and accordingly serve the well known "snubber" function. The value of the capacitors 85 and 86 is on the order of 0.2 microfarad +10~.
The circuit set forth in Figure 1 is constructed of conventional components which are readily available from commercial sources. In one preferred embodiment of the present invention the circuit component shown in Figure 1 may fall within the definitions set forth in the tables below.
TABLE I Rectifier Circuit 10 .
Reference # Component Rated Value ll Rectifier diode lO00 volt-lO00 amp 12 Capacitor 10-300 microfarad 13 Power Supply 220 volts AC
105~099 TABLE II Pulse Generator Circuit 20 Reference # Compone - ~-R-~ted Value . _ _ 21 Transformer 1 amp 25 volt 22 Unijunction transistor U2T
23 Power supply 110 volt AC
24 Diode 1 amp - 100 volt Capacitor 2000 microfarad -50 volt 26 Capacitor 0.2 microfarad -50 volt 27 Variable Resistor 10,000 ohms - 1 watt 28 Resistor 1/4 watt 29 Resistor 1/4 watt Resistor 1/4 watt TABLE III Inverter Circuit _ Reference # Component Rated Value 31 & 32 SCR General Electric Corporation type 394-1000 amps peak at 2000 Hart 3, 600 volts 10 to 15m sec. turn-off. Or GE type 609 3000 amps peak at 2000 Hart 3, 1200 volts 35 m. sec.
turn-off 37 Pulse Transformer Pulse Engineering Type 5258 38 Transformer Ratio of windings 9 to 1 As shown in Figure 1, the present circuit includes a corona generator which is generally shown to be of the opposed plate type. Various construction of corona generators are described in my previously filed application, Serial No. 830,248 now U.S. Patent No. 3,798,457, filed June 4, 1969. As shown in this patent the corona generators contain electrode plates which are preferably coated with porcelain enamel dielectrics~ having a thickness on the order of from about 0.10 to 0.5 millimeters. The corona gap defined by the opposed plates is preferably on the order of 0.75 to 2.0 millimeters. These corona generators preferably operate at high voltages on the order of 2.0 to 30.0 KV at a frequency ranging from about 1/3 to 20,000 Hz.
In one preferred operation of a corona generator, oxygen or an oxygen containing gas such as air is converted to ozone. It is found that the capacity of a given corona generator to produce ozone from oxygen is to some extent dependent upon the frequency of the power impressed across the electrode plates thereof. In the practice of the present invention the frequency which is produced by the power supply set forth in Figure 1 may range from about 2000 to 3000 Hz.
Compared to prior art power supplies which normally produce a frequency on the order of 50 to 60 Hz it is seen the power supply of the present invention is capable of producing a superior result in terms of enhancing the capacity and efficiency of a corona generator.
To specifically illustrate the operation of the device, the following example is given.
EXAMPLE
The power supply circuit generally shown in Figure 1 is connected to the leads of a corona generator of the type shown in Figure 2 and operated at a frequency of 2000 Hz. The area of each electrode plate is 322 cm2, the electrode gap is 1.1 mm and the thickness of a porcelain dielectric coating on the plates is on the order of 0.2 mm.
The corona generator was then ~onnected to a conventional source of 60 Hz pulsed potential. It was found that in the first instance, using the 2000 Hz frequency, the device was capable of producing 4500 grams per hour o~ ozone using an oxygen feed of 400,000 grams per hour. Using the 60 Hz power supply, it was found that the generator was capable of producing 7000 grams of ozone per hour using the same feed.
While the above description and specific example disclose the use of the present high voltage, high frequency power supply in conjunction with a corona generator, the present circuit may be used to provide power for devices which have similar load characteristics. Thus, in Figure 1 the corona generator 40 may be replaced by a plasma generating or laser powering device.
It is generally known that the capacity of a corona generator is dependent in part on the frequency of the power supplies across the plates thereof. Traditionally, high voltage power is supplied to a corona generator at the frequency of the primary source, i.e., the line frequency. To increase the frequency of power applied to corona generators, it has been suggested that mechanically driven (motor generator) frequency converters be used. It also has been suggested that electronic circuits which include vacuum tubes or solid state devices may also be used to increase frequency.
It has generally been found that motor generator frequency converters are expensive and not particularly durable. Furthermore, frequency converters which utilize vacuum tubes or solid state circuits are often restricted with respect to efficiency.
Accordingly, it is an object of the present invention to provide an improved corona generator device which operates at high frequency and efficiency.
It is a further object to provide an improved high frequency power supply circuit which is particularly suited for operation with corona generators.
It is still a further object to provide an inexpensive high frequency power supply for corona generators which is constructed from durable, readily available solid state components.
~ -2-I:~
Thus, in accordance with the present teachings, a corona generating system is provided for supplying at least about 40,000 watts average power to a corona cell.
The system comprises a source of DC power, a transformer having a low voltage primary winding and a high voltage secondary winding with a turns ratio which is adapted to provide a high voltage power pulse across the secondary winding from a relatively low voltage impressed across the primary winding of between about 150 to 600 volts DC. At least two SCR's are connected in a series circuit relationship with the scource of DC power and the low voltage primary winding. Each of the SCR's are unequal to each other with respect to their forward voltage drop characteristic.
Means are provided for pulsing the gates of the SCR's at a desired frequency. The corona cell has spaced electrodes with a surface area large enough to generate a corona discharge of at least the 40,000 watts of average power and for generating a reverse commutating voltage of sufficient duration for turning off at least one of the SCR's within each pulse period with the corona cell representing the only commutating means for the SCR's in the system.
These objects and others will become readily apparent to one skilled in the art from the following - 2a ~
'~2 "~
,'~
105005~9 detailed description and drawings wherein;
Figure 1 is a diagram of the circuit used to supply high voltage, high frequency power to a corona generator which is also shown schematically therein;
Figures 2, 3 and 4 show various configurations of corona generators (with parts broken away) which may be used in conjunction with the power supply circuit of the present invention;
Figure 5 is a graphic representation of data obtained from a prior art circuit wherein voltage is plotted on the vertical axis and time on the longitudinal axis and Figure 6 shows comparison data obtained from the circuit of the present invention (dotted line).
Figures 7 and 8 show preferred voltage unequalization networks which may be used in the circuit of Figure 1.
Broadly, my invention involves a corona generator and associated high voltage frequency power supply which includes a plurality of silicon controlled rectifiers (here-inafter referred to as SCR's) which are electrically connectedin series with a source of DC potential and the low voltage winding of a high voltage transformer, the high voltage winding of which is connected to the plates of a corona generator.
More specifically, I have found that the circuit turn-off time of SCR's used as high power, high frequency electrical switches in a power supply may be reliably increased by driving two or more SCR's in series.
A more clearly detailed understanding of my invention may be obtained by reference to Figure 1 of the drawing wherein the circuit generally outlined by broken line 10 is a conventional rectifier circuit which supplies pulsed DC voltage. Rectifier circuit 10 includes a rectifier diode 11 interconnected with capacitor 12 and a source of 60 lHS00~9 cycle 220 volt AC current indicated as 13~ While the drawing shows the use of a single rectifier circuit suitable for operation on single phase current, it is contemplated that three-phase bridge type rectifier circuits are particularly suited for commercial application of the invention.
~ lso shown in Figure 1 is a conventional pulse generator circuit, the components of which are included within the confines of broken line generally 20. The pulse generator circuit includes a transformer 21 and a unijunction transistor 22. One winding of the transformer 21 is connected in series with a source of 60 cycle 110 volt AC
potential shown as 23. The other winding of the transformer 21 is connected to diode 24, and to a common collector conductor for several other circuit components including one side of capacitors 25 and 26.
Also included in pulse generator circuit 20 is a variable resistor 27 and a fixed resistor 28. The variable resistor 27 and the fixed resistor 28 are also connected to the unijunction transistor 22. One lead from the unijunction transistor 22 interconnects with fixed resistances 29 and 19.
It is to be understood that a wide variety of commercially available pulse generators are suitable for use in the present invention.
Figure 1 also includes an inverter circuit generally outlined by broken line 30. The inverter circuit 30 includes two SCR's 31 and 32 connected in series. The SCR 31 has a gate lead 35 and the SCR 32 has a gate lead 36.
Also included in the inverter circuit is a transformer 37 which possesses two secondary windings which are inter-connected with the gates 35 and 36 of the series connected SCR's 31 and 32.
The inverter circuit 30 includes a high voltage transformer 38 and a corona generator generally 40. The corona generator 40 is schematically shown and includes an upper electrode 41 and a lower electrode 42. The upper electrode 41 has a dielectric layer 43 and the lower electrode 42 has a dielectric layer 44. Between the electrodes 41 and 42, a corona gap 45 is defined.
The corona generator generally 40 is connected to the high voltage side of transformer 38 by means of conductors 46 and 47.
Figures 2, 3 and 4 of the drawing disclose in greater detail a variety of typical configurations of corona generators which may be utilized in the circuit generally shown in Figure 1. The corona generator 40, as shown in Figure 1, may comprise the structure shown in Figure 2 wherein a reaction chamber 50 is equipped with a gas conduit inlet 51 and a gas conduit outlet 52. Within the container 50, an upper electrode 53 is mounted along with lower electrode 54.
Electrodes 53 and 54 are provided with a dielectric layer 55 and 56 respectively. The electrodes 53 and 54 are connected with conductors 57 and 58 which in turn are connected with a source of high voltage, high frequency potential such as is produced in the circuit shown in Figure 1. Between the electrodes 53 and 54 a corona gap 59 is defined.
In Figure 3 an alternative corona generator structure is shown wherein electrodes 60 and 61 are separated by a single dielectric plate 62. The corona generator of Figure 3 possesses two corona gaps, 63 and 64.
Figure 4 shows still another suitable corona generator configuration for use in the present invention wherein electrode plates 70 and 71 are separated by means of lOSOO99 a single dielect~ic plate 72 which is affixed to the uppermost electrode plate 70. The corona ~enerator configuration of Figure 4 possesses a single corona gap 73. While Figures 2, 3 and 4 show typical plate type corona generators, it is to be understood that other well known corona generator configurations such as the well known tube type generator may be used.
In operation of the circuit shown in Figure 1, it is seen that the rectifier/capacitor combination 10 produces a steady DC potential at typically 311 volts ( ~ x 220 volts). This potential from the rectifier circuit 10 is supplied to the inverter circuit 30 through one side of the high voltage transformer 38, which is connected in series to the power supply circuit 10 through the series connected SCR's 31 and 32. The pulse generator circuit 20 is adjusted to produce the desired frequency of triggering pulses which range from about l/3 to 20,000 cycles per second. The trigger pulses from the pulse circuit 20 are fed through pulse _ _ transformer 37, the output of which appears in the two secondary windings thereof at the gates 35 and 36 of the SCR's 31 and 32. As is generally known in the art, the trigger pulses from the pulse circuit 20 will cause the SCR's to conduct (fire). Upon firing a current is passed through one side (low voltage winding) of the high voltage transformer 38.
At the high voltage winding of the transformer 38 a high voltage power pulse appears which will have a voltage from about 2.0 to 20.0 KV. The high voltage pulse from the transformer 38 then appears between plates 41 and 42 of the corona generator 40. This high voltage pulse creates a corona within the corona gap 45. A gas which is contained within the gap 45 is subjected to the high voltage corona, and in the case wherein the gas is or includes oxygen, ozone is 1050~99 produced.
Once the SCR's 31 and 32 are in a conducting mode, it is seen that they must be switched to a non~conducting mode in order to produce the high frequency pulses of current through the high voltage transformer 38. In the operation of the present circuit the SCR's connected in series 31 and 32 are switched to a non-conducting mode as follows:
When the above described power pulse is applied to the corona cell 40, the following sequence occurs:
The high voltage burst produces an electrical discharge at the instant the voltage exceeds the gas sparking potential in gap 45. The electrons produced are attracted towards the positive electrode. This electron flow constitutes the current flow giving rise to the corona power dissipation at that particular voltage. The electrons cannot pass the dielectric barrier and hence accumulate on the dielectric as in a capacitor. Hence, the current flow ceases.
Further corona action stops until another power pulse is applied. The abrupt current stoppage induces a reverse voltage pulse in the secondary of transformer 38 by Lenz's Law. This reverse voltage pulse is transformed to the primary and hence supplies the reverse voltage needed to turn-off (commutate) the SCR's 31 and 32.
The benefit of the two series SCR's shown in Figure 1 will now be explained. First, the present application taxes the capabilities of any SCR when large average powers are called for. Large here means about 40,000 watts average corresponding to 300 pounds per day of ozone. The limiting SCR parameters are turn-off time and frequency at the peak currents required. Figure 5 below shows the typical SCR
voltage history for a circuit in which a single SCR is used.
The first firing is at Tl, the SCR voltage drops (switches) from Vmax to a ~uch lower value Vmin~ The SCR conducts from Tl to T2 ttypically 100 microseconds). At T2, the reverse (commutating) pulse appears~ At T3 turn~off occurs, at T4 the reverse pulse net effect is zero and the SCR voltage climbs back to Vmax ready for the next firing. The best available SCR's require at least 10-15 microseconds turn-off at the high power levels of interest. That is T2 to T3 must be at least 10-15 microseconds. If, for examplel the voltage goes positive (at T4) less than 10-15 microseconds after T2, then the SCR
will not turn-off, and will immediately either destroy itself or blow any protective fuses present.
Figure 6 shows the benefit of reducing the SCR
voltage by using the series connected SCR's of the present invention. In the circuit of Figure 1, the duration of the actual reverse voltage is increased by the increment shown as T4-T4' in Figure 6. Hence, if two SCR's are in electrical series, and if they are perfectly matched, the turn-off situation is improved by may~e 30-50%. If the SCR's are unbalanced, that is if the two (or more) SCR's are unequal 2Q with respect to forward voltage drop characteristics, one SCR
may be improved by as much as 100-200% while the other is improved only slightly. However~ both SCR's must "latch-up"
before damage occurs since they are in series. Hence, the one SCR may latch-up frequently but the other never. This un-balance is in opposition to the normal use of series SCR's.
Normally, SCR's, as any rectifier, are limited in reverse voltage capability, say 1000 volts. If 3000 volt service is required, then three series units will do the job if they are perfectly matched. If not, the weakest one (say 900 volt) will break down, the rest will follow like a line of dominoes.
In essence, the above preferred unbalanced series SCR arrangement allows faster (shorter turn-off time) ~osoo99 operation than with a single SCR. It is obvious that further improvement can be achieved with three or more SCR's in series~
The unbalanced forward voltage charge characteristic of the multiple SCR's may be an inherent electrical characteristic of the SCR's which is produced by manufacturing techniques. The unbalance may also be produced by placing unbalanced shunt connected resistance elements with the SCR's. Such an arrangement is shown in Figure 7 which shows the series connected SCR's 31 and 32 of Figure l to which have been added unequalizing network shunt resistors 80 and 810 The resistors 80 and 81 preferably have a difference in value of at least about +lO~. Therefore if resistor 80 has a value of 5 ohms, resistor 81 will have a value of about 4.5 or 5.5 ohms.
In Figure 8 a more preferred unequalizing network is shown which includes capacitors 87 and 88 as well as the unequal resistors 80 and 81 of Figure 7. Capacitors 87 and 88 serve to protect the SCR's 31 and 32 from unwanted high voltage transits, and accordingly serve the well known "snubber" function. The value of the capacitors 85 and 86 is on the order of 0.2 microfarad +10~.
The circuit set forth in Figure 1 is constructed of conventional components which are readily available from commercial sources. In one preferred embodiment of the present invention the circuit component shown in Figure 1 may fall within the definitions set forth in the tables below.
TABLE I Rectifier Circuit 10 .
Reference # Component Rated Value ll Rectifier diode lO00 volt-lO00 amp 12 Capacitor 10-300 microfarad 13 Power Supply 220 volts AC
105~099 TABLE II Pulse Generator Circuit 20 Reference # Compone - ~-R-~ted Value . _ _ 21 Transformer 1 amp 25 volt 22 Unijunction transistor U2T
23 Power supply 110 volt AC
24 Diode 1 amp - 100 volt Capacitor 2000 microfarad -50 volt 26 Capacitor 0.2 microfarad -50 volt 27 Variable Resistor 10,000 ohms - 1 watt 28 Resistor 1/4 watt 29 Resistor 1/4 watt Resistor 1/4 watt TABLE III Inverter Circuit _ Reference # Component Rated Value 31 & 32 SCR General Electric Corporation type 394-1000 amps peak at 2000 Hart 3, 600 volts 10 to 15m sec. turn-off. Or GE type 609 3000 amps peak at 2000 Hart 3, 1200 volts 35 m. sec.
turn-off 37 Pulse Transformer Pulse Engineering Type 5258 38 Transformer Ratio of windings 9 to 1 As shown in Figure 1, the present circuit includes a corona generator which is generally shown to be of the opposed plate type. Various construction of corona generators are described in my previously filed application, Serial No. 830,248 now U.S. Patent No. 3,798,457, filed June 4, 1969. As shown in this patent the corona generators contain electrode plates which are preferably coated with porcelain enamel dielectrics~ having a thickness on the order of from about 0.10 to 0.5 millimeters. The corona gap defined by the opposed plates is preferably on the order of 0.75 to 2.0 millimeters. These corona generators preferably operate at high voltages on the order of 2.0 to 30.0 KV at a frequency ranging from about 1/3 to 20,000 Hz.
In one preferred operation of a corona generator, oxygen or an oxygen containing gas such as air is converted to ozone. It is found that the capacity of a given corona generator to produce ozone from oxygen is to some extent dependent upon the frequency of the power impressed across the electrode plates thereof. In the practice of the present invention the frequency which is produced by the power supply set forth in Figure 1 may range from about 2000 to 3000 Hz.
Compared to prior art power supplies which normally produce a frequency on the order of 50 to 60 Hz it is seen the power supply of the present invention is capable of producing a superior result in terms of enhancing the capacity and efficiency of a corona generator.
To specifically illustrate the operation of the device, the following example is given.
EXAMPLE
The power supply circuit generally shown in Figure 1 is connected to the leads of a corona generator of the type shown in Figure 2 and operated at a frequency of 2000 Hz. The area of each electrode plate is 322 cm2, the electrode gap is 1.1 mm and the thickness of a porcelain dielectric coating on the plates is on the order of 0.2 mm.
The corona generator was then ~onnected to a conventional source of 60 Hz pulsed potential. It was found that in the first instance, using the 2000 Hz frequency, the device was capable of producing 4500 grams per hour o~ ozone using an oxygen feed of 400,000 grams per hour. Using the 60 Hz power supply, it was found that the generator was capable of producing 7000 grams of ozone per hour using the same feed.
While the above description and specific example disclose the use of the present high voltage, high frequency power supply in conjunction with a corona generator, the present circuit may be used to provide power for devices which have similar load characteristics. Thus, in Figure 1 the corona generator 40 may be replaced by a plasma generating or laser powering device.
Claims (4)
1. A corona generator system for supplying at least about 40,000 watts average power to a corona cell which comprises.
a. a source of DC power.
b. a transformer having a low voltage primary winding and a high voltage secondary winding with a turns ratio adapted to provide a high voltage power pulse across said secondary winding from a relatively low voltage impressed across said primary winding of between about 150 to 600 volts DC;
c. at least two SCR's connected in a series circuit relationship with said source of DC power and said low voltage primary winding, each of said SCR's being unequal to each other with respect to their forward voltage drop character-istic;
d. means for pulsing the gates of said SCR's at a desired frequency;
e. said corona cell having spaced electrodes with a surface area large enough to generate a corona discharge of at least said 40,000 watts of average power and for generating a reverse commutating voltage of sufficient duration for turning off at least one of said SCR's within each pulse period;
said corona cell representing the only commutating means for said SCR's in said system.
a. a source of DC power.
b. a transformer having a low voltage primary winding and a high voltage secondary winding with a turns ratio adapted to provide a high voltage power pulse across said secondary winding from a relatively low voltage impressed across said primary winding of between about 150 to 600 volts DC;
c. at least two SCR's connected in a series circuit relationship with said source of DC power and said low voltage primary winding, each of said SCR's being unequal to each other with respect to their forward voltage drop character-istic;
d. means for pulsing the gates of said SCR's at a desired frequency;
e. said corona cell having spaced electrodes with a surface area large enough to generate a corona discharge of at least said 40,000 watts of average power and for generating a reverse commutating voltage of sufficient duration for turning off at least one of said SCR's within each pulse period;
said corona cell representing the only commutating means for said SCR's in said system.
2. The corona system as defined in claim 1 further comprising a forward voltage unequalization network connected across each SCR.
3. The corona system as defined in claim 2 wherein each of said unequalization networks comprise an impedance of unequal magnitude.
4. The corona system as defined in claim 3 wherein each of said unequalization networks comprise a combination of resistance and capacitance.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US45639674A | 1974-03-29 | 1974-03-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1050099A true CA1050099A (en) | 1979-03-06 |
Family
ID=23812588
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA220,736A Expired CA1050099A (en) | 1974-03-29 | 1975-02-25 | High frequency power supply for corona generator |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS50133426A (en) |
| CA (1) | CA1050099A (en) |
| DE (1) | DE2513026A1 (en) |
| FI (1) | FI62916C (en) |
| FR (1) | FR2266360B1 (en) |
| GB (1) | GB1500773A (en) |
| IT (1) | IT1034658B (en) |
| NO (1) | NO751082L (en) |
| SE (1) | SE404472B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5443800A (en) * | 1993-06-01 | 1995-08-22 | Liftech Corporation | Pulse train generating circuit for control of an ozone generating means |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4330762A (en) * | 1979-03-21 | 1982-05-18 | United Kingdom Atomic Energy Authority | Circuit for stabilizing an electrical discharge within a glow discharge gas laser |
| US4451766A (en) * | 1982-05-03 | 1984-05-29 | Hughes Aircraft Company | Radio frequency laser pumping system |
-
1975
- 1975-02-25 CA CA220,736A patent/CA1050099A/en not_active Expired
- 1975-03-25 DE DE19752513026 patent/DE2513026A1/en not_active Withdrawn
- 1975-03-26 NO NO751082A patent/NO751082L/no unknown
- 1975-03-27 JP JP50036148A patent/JPS50133426A/ja active Pending
- 1975-03-27 FI FI750954A patent/FI62916C/en not_active IP Right Cessation
- 1975-03-27 SE SE7503623A patent/SE404472B/en unknown
- 1975-03-27 IT IT21759/75A patent/IT1034658B/en active
- 1975-03-27 GB GB13023/75A patent/GB1500773A/en not_active Expired
- 1975-03-27 FR FR7509772A patent/FR2266360B1/fr not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5443800A (en) * | 1993-06-01 | 1995-08-22 | Liftech Corporation | Pulse train generating circuit for control of an ozone generating means |
| WO1996039355A1 (en) * | 1993-06-01 | 1996-12-12 | Lifetech Corporation | Pulse train generating circuit for control of an ozone generating means |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2266360B1 (en) | 1981-08-07 |
| DE2513026A1 (en) | 1975-10-02 |
| FI750954A (en) | 1975-09-30 |
| FI62916C (en) | 1983-03-10 |
| FI62916B (en) | 1982-11-30 |
| SE7503623L (en) | 1975-09-30 |
| AU7964675A (en) | 1976-09-30 |
| FR2266360A1 (en) | 1975-10-24 |
| GB1500773A (en) | 1978-02-08 |
| JPS50133426A (en) | 1975-10-22 |
| IT1034658B (en) | 1979-10-10 |
| SE404472B (en) | 1978-10-02 |
| NO751082L (en) | 1975-09-30 |
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