The present invention relates to electrostatic filters in general, and more particularly to improvements in so-called high tension (ionic bombardment) filters. Still more particularly, the invention relates to improvements in a method and apparatus for automatically regulating the operation of high tension filters by regulating the potential which is applied to such filters.
In presently known high tension filters, the potential which is applied thereto is increased to reach the breakdown value and is thereupon reduced to a variable extent and for a variable interval of time to a value below the preceding breakdown value. Such operation is followed by a renewed increase of potential to the breakdown value. This is deemed to be advisable and advantageous because the electrical filter output can be regulated in a more satisfactory way to follow the varying breakdown resistance of the gaseous carrier medium for solid impurities which require segregation from the carrier medium.
The operating potential of a high tension filter is invariably limited by spark discharge between the corona discharge electrode and the collecting electrode of the filter. As a rule, the filter potential is selected in such a way that some arcing in the filter will take place because the rate of separation (i.e., the separation efficiency) is then at a maximum value. On the other hand, the frequency of arcing should not be too high.
The aforediscussed prior filtering methods and apparatus exhibit the drawback that each arcing leads to a total collapse of the electric field and, by using modern operational switches (thyristors), each arcing is followed by a complete shutdown of the supply of potential for a period of a few half waves in order to avoid the initiation of an immediately ensuing follow-up arcing. This entails the development of breakdown times during which the charging does not take place in an optimum way and to an interruption of field forces which are required for separation.