US2085758A - Process and means for production of surface ionization in insulator bodies - Google Patents

Description

y .1937- A. J.AKRUTZSC'H 2,085,758

PROCESS AND MEANS FOR PRODUCTION OF SURFACE IONIZATION IN INEULATOR BODIES Filed Junef'7, 19:52

BY Q0 ATTdRA/Z'YS Patented July 1937 UNITED STATES" "PAT NT, OFFICE PROCESS AND MEANS FOR PRODUCTI ON OF SURFACE IONIZATION INSULATOR BODIES Arthur Johannes Krutzsch, Munich, Germany, assignor. to International Precipitation 60., Los Angeles, Calif a corporation of California Application June 7, 1932, Serial No. 615,942

9 Claims.

This invention relates to a new process and new means for producing ionization parallel with the surface of insulating materials. V

This ionization, which is manifested in the 5 form of creeping sparks, polar brush discharges and the like, is hereinafter termed surface ionization. Surface ionization of this kind comes into 20 tween the layers on the surface of the body of insulating material and the surrounding gases under the actionof electrical discharges or chemical decompositions within the gases or a mixture of gases. The discharges mayalso serve to clean insulation surfaces such for example as the surfaces of insulators.

Ionizing fields have been produced heretofore in systems provided with electrodesseparated by an insulating layer. For instance, at the n boundary of such a layer of insulatingmaterial a superficial ionization area is produced by supplyingan alternating voltage to electrodes separated by an insulating layer, whereby electric fields are produced which partly pass in the di- 5 electric and which partly pass on the surface of the insulating layer. By the employment of suitable voltages, so-called polar brushes or jumpover sparks are produced that alternately charge and discharge the sides of the insulator, that is,

40 the insulating layer separating the electrodes.

In this manner, the surface of the insulating layer is coated with an intense and uniform ionization layer. It has been shown that ionizers of this kind have an excellent ionization efiect.

This effect, however, is injured if the surface of the ionizer becomes coated with a layer 911 dust, moisture or like electrically conducting substances, since, in such an event, the electricity that would charge the sides of the insulating layer no longer passes as an ionizing current upon the insulating layer but as a simplecon ducted current within the layer ofdust or the 7 like. Externally, this difference becomes ap-' 55 parent in that the surface of the ionizer no In German-y June 13, 1931 longer shows the presence of a luminous area indicating the presence of the ionizing current.

Now, when the ionizer becomes coated with dust and like conducting material, the situation is such that-the ionizer. includes two elements connected in series: v

' 1. A resistance conductive dust layer formed.

upon the layer of insulating material.

2. A condenser-like system (the insulating layer between the conducting elements). 10

Thus, the entire voltage between the ionizerelectrodes is, in accordance with well known formulas, composed of the voltage along the resistance and of the voltage of the condenser.

Sincethe voltage of a condenser is proportional to the quantity of electricity present thereon, and'the quantity of electricity is equal to the product of the strength of the current and the time, this leads to the conclusion that agreat strength of field will arise in the aforementioned resistance (even if it be of great conductivity) where the voltage between the ionizing electrode increases very quickly for, in such an event, the

quantity of electricity present on the condenser and at the same time the voltage of the condenser are so small that practically the entire voltage. is present on the resistance.

Of course, this happens for only a short period of time, that is, only during the phase where the voltage rises steeply. If, therefore, the ionizer be fed with a voltage of rectangular shape for instance, a high field strength will develop on the ionizer surface for a short period of time, notwithstanding its conductivity. Thefieldso produced, however, is suflicient for the production of ionization and in the operation of the system, in accordance with this invention, the dust covered surfacesagain become luminous, showing the presence of a high ionization current.

To produce such steep fronts of the voltage 40 waves means which are known per se may'be employed.

In order to clearly describe the invention, reference is to be made to the following description and accompanying drawing in which:

Figs. 1, 2, and 3 show three'wave forms of voltages considered in the invention for producing ionization.

current or a pulsating continuous current of rec-- form or stepped form (see Fig. 2 for example) which are produced by well known means, say in machines of a suitable type of construction or in 5 suitably controlled discharge tubes.

Particularly suitable as ionizing voltages, according to this invention, are those proceeding along a conductor with a steep front to the waves, that is, these waves termed travelling waves.

These travelling waves (like that shown in Fig.

3 for example) may be produced by impulses in switching, it being possible, by suitable arrangement and dimensioning of the electrical magnitudes of the circuit, the resistances, the condensers, the self-induction of the windings or .by supplementary apparatus, to determine the size and shape of the front of the wave, in accordance with the conditions, particularly the conductivity and kind of coatings or dusts whichare to be controlled.

illustrated in Fig. 4 of. the drawing, which shows A an ionizer for an. electrical gas purifying plant, in which the strength of the field necessary for ionization is produced in a section of space 1ying at the side of the charging area by means of a voltage and the charge carriers so formed conveyed by another voltage into the space charging area, the ionizing area being produced in particular superficially at the boundary of a layer of insulating material which separates the ionizing electrodes of the different polarities from each other.

The ionizer is denoted by II. It consistsin the example illustrated of a plate or insulating body |2 of insulating material, on both of the sides of which is arranged on the surface thereofor in the vicinity of. the surface thereof, a series of ionizing electrodes l3, H, which consist of red or strip shaped conductors of any kind of conducting material connected up in parallel with each other. In this example the two series are connected up in parallel with each other and form one set of electrodes of the ionizer,

while the opposite electrode is formed by a plate |5 of metal embedded in the plate of insulating material. An alternating voltage from the transformer I8 is supplied to the ionizer. charge carriers produced by the ionizer are conveyed by means of a further voltage into the space charging area which lies at the side of the ionizer, charge the particles of dust held in suspension therev and are conveyed by means of the same voltage to the precipitating electrodes 20, 2|. This voltage which serves to convey the charged particles to the precipitating electrodes is sent over the conductors 24, 25 to the precipitating electrodes connected up in parallel therewith on the one hand' and to the ionizer II on the other hand, and, in the example shown, as a continuous current, which is rectified out of the transformer by means of the'rectifying tube 26. The condenser 30 which is connected up in parallel with the electrodes of the continuous current, serves to smooth out the continuous current.

The ionizer II is constituted as a condenserlike system consisting of the insulating body The- tangular form (see Fig. 1 for example), trapeze plate l2 any conducting coatings and conductors l3, ll, l5. An alternating voltage is supplied to the ionizer from the transformer l8 over the circuit I8, 36, 25, |4 (|3), I5, 32, 31, I8. Separating plates or depositing electrodes, 20, 2|, at which the dust or other matter in the gas to be purified, collects are fed by a different circuit 25, ll (13), 2| (20), 24, 26 and is not influenced by the ionizers operation. If dusts which conduct electricity or even those which conduct it only slightly are present in the separating area, that is, the area between the ionizer and the separating plates, say soot for example, metal dust or even moist gases or gases which would otherwise affect the surfaces and make them conductors, the surface of the plate |2 becomes coated with a layer thereof which conducts electricity more or less well. The voltage of the ionizer is then composed of the voltage along the resistance formed by the conducting layer ofthe dust and the like and the voltage of the condenser-like system. Now thevoltage of a condenser is proportional to the quantity of electricity which is present thereon, and this is equal to the product of. the strength of the current and the time. If the voltage supplied to the ionizer say'by the spark gap 32 interpolated in the circuit for example, be selected in such a way that it rises rapidly with a steep front to the wave,-

there will be produced in view of the short time, a low voltage at the condenser, so that practically the total voltage falls on the resistance formed by the coating.

If therefore the alternating voltage, alternating current or pulsating continuous current supplied to the ionizershows a steep front, there will be ,formed during the rapid variation in the voltage on thesurface of the dust or other conducting layer, notwithstanding its comparatively high conductivity, for a short time, a very strong electric field which will sufiice to ionize the vicinity of the ionizer. Under the influence of the continuous voltage which prevails between the ionizer and the precipitating electrodes, charge carriers are withdrawn from the ionizing area,

the particles of dust or other particles held in precipitating electrodes .20 and 2|.

An ionizing voltage with as steep a rise and fall of the voltage as possible will therefore be employed, which can be produced in any desired manner. If suitably built generators or tube rectifiers or even mechanical transformers like pendulum transformers for example, be used for the generation of the voltage with a steep front to the wave, the circumstance must be taken into account that a flattening of the front of the wave is produced by, the self induction of the transformer, by means of which the voltageis supplied as a rule to the ionizing circuit.

.This flattening is avoided if the steep voltage front be produced directly in the ionizing circuit, which is possible by means of spark gaps for example. By means of the spark gaps those trav-..

elling waves will be generated and utilized which in general it is endeavoured to avoid in electric circuits. .The sensitive parts such as transformers and the like can be protected "against the ac-' tion of the travelling waves in the usual way by protecting resistances 36, 31, 38. As the spark gap. when suitably constructed only responds when the voltage at it has risen to a certain value. it acts in a manner of speaking as an automatic switch. As soon as the spark passes the resistance of the spark channel falls in a very short time, about 10- seconds, to a low-value. In accordance herewith the voltage in the ionizer varies in jerks,.the jump in the voltage being more or less steep according to the conditions. By

suitably equalizing the capacity of the ionizer, theof the condenser 40 islarge as compared with the capacity of the ionizer.

The spark gap will therefore be so constructed that its capacity is small. If, however, the capacity of the ionizer is exceptionally small, it will be of advantage to even connect, in addition and parallel to the spark gap, a small capacity, as the final resistance of the spark is, as is well known,

. inversely proportional to the quantity of the electricity which passes through it. I

In order to obtain a rapid collapse of the resistance of the spark and to prevent a current from flowing between the spark gap electrodes before the spark proper passes, the arrangement will be so devised that the spark passes directly I from the so-called initial'voltage and that no glow, brush discharge or the liketakes place before the spark. Only a comparatively slight curvature is therefore given to' the electrodes of the spark gap. Care is also taken that the sparks which follow each other in accordance with the change in the voltage of the ionizer shall not meet many ions in the spark gap from the sparks which precede in each case and consequently pass even at slight amplitudes of the voltage or under some circumstances persist even as arcs or are discharges or the like. For this purpose the elec-. trodes of the spark gap may be specially constructed for example with cooling ribs or may be made of a special material of high thermal conductivity for example. The electrodes may also be cooled or the spark allowed to pass in a special or the electrodes may be'subjected to a blast. .A

favourable efiect is produced if the axis of the spark gap be horizontal as by this means the upward thrust of the heated air produced at the spark gap acts of itself to regenerate the spark gap. It is particularly favourable for this purpose to give the electrodes a considerable amount of curvature, but such curvature must not be so I great that glowing or discharges are formed before the spark passes.

A valuable constructional form of the idea on which this invention is based results if one or both of the electrodes of the spark gap be made hollow and the surface provided with one or more openings at the place where the spark is produced, see 45, Fig. 5. By means of a-suitable apparatus such as a motor 46 for example a pump 41, pipes 48a'fluid medium either liquid or gaseous under a head of pressure is then supplied to the spark gap or compressed air for example or an inert gas under pressure, such as nitrogen for example, is supplied or the medium may be withthe spark gap through the opening 45, the pipes 48 or pumping apparatus 46, 41.

Instead of one spark gap a number of spark gaps may be connected up in series in a suitable form in order to obtain great steepness in thejump in'the voltage. In like manner and for the same purpose-the conductors of the ionizer may be composed of pieces of conductors withdifferent travelling wave resistances. The voltage may also be intensified by the reflection of the travelling waves at the ionizer and particularly when a long conductor or a number of sections of conductors of definitely graduated wave resistances are interposed between spark gaps.

As the condenser means a high. capacitative drawn by the creation of a vacuum away from load on the transformer I 8 and the plant it is possible in order to reduce the loading current and to equalize the capacitative lead of the plant to use a self-induction coil 50 (see Fig. 6) which may be interposed at a suitable point for example in parallel with the secondary winding of the transformer l8. The magnitude of the selfinduction may conveniently be such that together with the total capacity of the loading circuit resonance for the primary or basic wave of the primary alternating current is produced.

In the present invention the spark gap doesthe spark gaps is of no consequence as far as this invention is concerned as the important point is the action of the special form of voltage. Since furthermore the self-induction of the ionizing circuit is kept as'small as possible so as not.

to flatten the rise in the voltage, the high frequency oscillation which will be produced in any case will be of, a magnitude which may be neglected.

It will be understood that the invention is not trated by way of example and that various structural changes and modifications may be made without departing fromthe spirit of my invention, and I desire therefore thatfthe appended claims should be construed in the light of prior knowledge.

It will be understood that the term alternating voltage with a steep rise and fall of the voltage" includes alternating voltages having steep fronts to the wave as for instance the rectangular, stepped and trapeze forms illustrated in Figs. 1, 2 and 3 rather than the usual sinuous form of alternating current wave.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:-

1. An ionizing device ccmprising spaced ionizing electrode members, a body of insulating material separating said members; a source of high voltage current, and means connecting said source with said ionizing'electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage front.

in short impulses 'of steep wave limited to the embodiments described and illus- Y 2. An ionizing device comprising a body of insulating material, an ionizing electrode member positioned at the surface of said body and a said first ionizing electrode member and separated therefrom by said body, a source of high voltage current, and means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage in short impulses of steep wave front.

3. An ionizing device comprising a body of insulating material, .an ionizing electrode member positioned at the surface of said body and a further ionizing electrode member in contact with said body and separated thereby from the first ionizing electrode member, a source of high voltage current, and means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage in short impulses of steepwave front.

4. An ionizing device comprising a body of insulating material, an ionizing electrode member positioned at the surface of said body anda further ionizing electrode member embedded in said body and separated thereby from the first ionizing electrode member, a source of high voltage current, and means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage in short impulses of steep wave front.

5. An ionizing device comprising spaced ionizing electrode members, a body of insulating material separating said members, a source of high voltage current, and means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including a spark gap for supplying said voltage in short impulses of steep wave front.

6. In an electrical precipitator, an ionizing de- '-vice comprising spaced ionizing electrode members, a body of insulating material separating said members, a source of high voltage current, means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage in short im-.

pulses of steep wave front, a collecting electrode izing device and the collecting electrode member, and means for passing a fiuid between at least one of said ionizing electrode members and the collecting electrode member.

7. In an electricalprecipitator, an ionizing device comprising a body of insulating material, an ionizingelectrode member positioned at the sur face of said body and a further ionizing electrode member spaced from said first ionizing electrode member and separated therefrom by said body, a source of high voltage current, means connecting said source with said ionizing electrode members to produce a high potential therebetween, said connecting means including means for supplying said voltage in short impulses of. steep wave front, a collecting electrode member spaced from said ionizing device, means for producing a high potential between said ionizing device and the collecting electrode member, and

means for passing a fluid between at least one of said ionizing electrode members and the collect ing electrode member.

8. Method of producing ionization at the surface of a body of insulating material in contact with spaced electrode members which comprises providing a high potential electric field between said spaced electrode members and maintaining a relatively high drop in voltage along the surface of said body by impressing short impulsesof steep wave front across said spaced electrode members.

9. Method of electrically precipitating suspended material from fluids which comprises passing a stream of fluid between a collecting electrode and a body of insulating material in contact with spaced electrode members, producing ionization at the surface of the body of insulating material by providing a high potential electrical field between saidspacedelectrodemembers, maintaining a relatively high drop in volt-

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