Patent Publication Number: US-2017354978-A1

Title: Electrostatic air filter

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrostatic air filters and associated systems for cleaning gas flows. More particularly, the invention is related to electrostatic air filters for use in highly contaminated atmospheres. 
     2. Description of the Related Technology 
     Electrostatic air purifiers and conditioners are known and may utilize parts referred to as “corona” wire or “corona electrode”, “collecting electrode”, and barriers between these electrodes. The collector electrodes and or corona electrodes may be mounted and one or more sets of electrodes may be removable to facilitate cleaning. One of the functions of the barriers is to impair spark-over or creeping (along the surface) discharge between the electrodes. 
     It is also known to arrange an ion collecting member (Collecting cartridge or collecting electrode) and an ion emitting member (Corona electrode or corona frame) to be supported on the floor of the housing. 
     Known designs provide for electrodes to be attached flush to the walls of the housing in order to prevent dirty air from bypassing between the electrodes and the walls. Electrostatic air filters include electrodes at greatly different electrical potentials. The difference in voltage often approaches or exceeds 10 kV. The electrodes are typically mounted on a non-conductive structures in order to maintain electrical isolation between structures having high differences in potential. 
     A disadvantage of such designs is that electrically conductive matter which may enter into the housing with the air may settle on the barriers, the floor of the housing and/or on the walls including on the non-conducting structures between the electrodes. This disadvantage is more pronounced in environments that are characterized by chemically aggressive or electrically conductive matter. 
     Such an aggressive or conductive matter may contaminate non-conducting structures including plastic barriers and walls and makes them electrically conductive. The contamination may be difficult or even impossible to remove. Chemically aggressive contaminates may penetrate into a plastic body and change the physical properties of non-conductive materials (like ABS) to be semi-conductive. The contamination of the barriers and walls shortens the effective distance between the electrodes and may provoke an electrical discharge (spark or creeping discharge) between a corona wire and a collecting electrode. 
     In a device having non-conductive structures between electrical components having a high differential potential between the corona frame and the collecting cartridge is such that electrical discharge like spark or arcing between the electrodes takes place while the corona discharge occurs and ions are emitted from the corona electrode to the collecting electrode. When the barriers between these electrodes become semi-conductive the ions emitted from the corona wire may travel through the barrier surface. This ion flow constitutes an ionic current flowing from the corona electrode to the barrier. The barrier then assumes the electrical potential that is close to the electrical potential of the corona wire effectively shortening the gap D. The same event happens when particles settle on the walls between components at high potential differences. 
     In this event an electrical discharge may occur from the barriers&#39; edges (or from the contaminated walls) to the collecting cartridge. This unfortunate event shortens the lifetime of electrostatic air conditioning systems when they are employed in certain geographical, industrial or climatic regions with chemically aggressive or electrically conductive contaminations present in the air. 
     Known corona frames may be made of electrically insulating material (plastic). Thin corona wires may be located on the frame. The wires are parallel to each other. The conductive wires meet and touch an electrically insulating material of the frame at the bottom and at the top of the corona frame. The electric field strength at the spot where two materials touch each other is substantially higher than in the middle part of the wires. Additional insulating barriers are installed on the frame to alleviate the electric field raise. These barriers are located at the side of the corona frame that is closest to the opposite electrodes. 
     The disadvantage of such design is the same as above, i.e., the dust, containing chemically aggressive or electrically conductive matter (vapor or particles), may enter into the air conditioner and settles on the corona frame barriers. 
     The ions emitted from the corona wire go to the edges of the corona frame barriers. When the barrier becomes semi-conductive, the barrier then assumes the electrical potential that is close to the electrical potential of the corona wire, effectively shortening the gap between the corona electrodes and the collector electrodes. 
     Therefore some “hissing” and even sparking may occur from the barrier edges (or from the contaminated walls) to the corona or collecting electrodes. Again, this unfortunate event shortens the lifetime of electrostatic air conditioning system that works in certain geographical, industrial or climatic regions where chemically aggressive or electrically conductive contaminations are common in the air. 
     Another drawback to existing corona frame designs is the wire vibration that occurs from time to time and which causes unpleasant noise, as well as may lead to the wire degradation and damage. 
     US Patent Publication No. 2014/0174294 shows an electrostatic air conditioner having at least one ion emitting member (i.e., corona frame) and at least one ion collecting member (i.e., collecting cartridge). The corona frame and collecting cartridge are configured to have active and passive areas and be removable from the housing within which they are positioned. The passive areas provide additional spacing between the active area and the side walls of the housing, and provide several advantages over existing electrostatic air conditioners, e.g., eliminates barriers between active corona wires and the housing walls, which prevents any settling of chemically active or electrically active matter (vapor or particles) on such barriers and/or housing walls (due to air flow). 
     Electrostatic air filters may have one or more stages. One-stage electrostatic air filters may contain a corona electrode and a collecting electrode. The collecting electrode may be flat or corrugated plates. When sufficient electrical potential difference on the order of kilovolts or tens of kilovolts is applied between the corona and collecting electrodes, a corona discharge may take place and ions are emitted from the corona electrodes. These ions travel with a stream of air toward the collecting electrodes. Dust particulates in the air become charged with the ions, and thus carry the electrical charge by themselves. When electrically charged particles reach the collecting electrodes, they settle there while clean air continues to pass further. 
     U.S. Pat. No. 2,526,402 shows an electrostatic air filter. The filter contains a plurality of collecting electrodes alternating with repelling electrodes. The collecting electrodes are assembled on a first set of conductive rods. The repelling electrodes are assembled and electrically connected to a second set of conductive rods attached to the repelling electrodes and to the case wall. There is an insulating structure electrically separating the collecting electrodes and repelling electrodes. 
     The rods are not electrically connected to the repelling electrodes. The rods do not have an electrical contact with the collecting electrodes. However, the creeping path between rods is along the surface of the insulating structure. When the insulating structure is clean, there is no electrical shortage between the first and second sets of conducting rods. When the insulating structure is dirty and contaminated with electrically conducive substances like metal powder or coal dust, it becomes slightly conductive. Due to high electrical potential difference between the rods, even a slightly conductive path may cause an electrical shortage. 
       FIGS. 1A and 1B  schematically illustrate a prior art configuration  101  for mounting collecting electrodes  102  and repelling electrodes  103  in an electrostatic air cleaner modified after the design shown in U.S. Pat. No. 2,526,402. The configuration is a plurality of collecting electrodes  102  alternating with a plurality of repelling electrodes  103 . The electrodes may be plate structures. Collecting electrodes  102  may be electrically connected to conducting rod  104 . The repelling electrodes may include apertures  107  which surrounds, but does not touch, conducting rods  104 . Repelling electrodes  103  may be electrically connected to conducting rod  105 . The collecting electrodes  102  may include apertures  108  which surround but do not touch connecting rods  105 . 
     The collecting electrodes  102  may be assembled on the conductive rods  104 . These rods  104  may be attached to the collecting electrodes  102  and to the case wall  106 . The repelling electrodes  103  are assembled by the conductive rods  105 . These rods  105  are attached to the repelling electrodes  103  and to the case wall  106 . The case wall  106 , or at least part of it, is made of non-conductive material like ABS plastic or porcelain. 
     The rods  104  do not have an electrical contact with the repelling electrodes  103 . The rods  105  do not have an electrical contact with the collecting electrodes  102 . The creeping path between these rods may be established along the insulating surface of the case wall  106 . When the wall  106  is clean, no electrical shortage between the rods  104  and  105  takes place. When the wall is dirty and contaminated with electrically conductive substances like metal powder or coal dust, the surface may become slightly conductive. Due to high electrical potential difference between the rods  104  and  105 , even a slightly conductive path may cause an electrical shortage. The creeping distance in the configuration illustrated in  FIGS. 1A and 1B  is shown as “a.” 
     Two-stage electrostatic air filters may have four types of electrodes. Corona electrodes and exciting electrodes form an ionization stage located at the air inlet. The exciting electrodes may be at or near ground potential. An electrical potential difference of several kilovolts or tens of kilovolts may be applied between the corona electrode and the exciting electrode in order to generate a corona discharge. A collecting stage may be downstream of the ionization stage and may include collecting and repelling electrodes. The collecting electrodes may be flat or corrugated plates parallel to each other and spaced from each other. The repelling electrodes may be flat or corrugated plates parallel to each other and located between the collecting electrodes. The collecting electrodes may be at or near ground voltage. The electrical potential difference of tens of kilovolts may be applied between the collecting and repelling electrodes. The electric field is therefore formed in the area between the collecting and repelling electrodes. Ions are emitted by the ionization stage. The ions may charge particles passing through this stage toward the collecting electrodes. When charged particles enter the area between the collecting and repelling electrodes, these particles are attracted toward the collecting electrodes by the electric force between those electrodes, and settle on the collecting electrodes. 
     Corona discharge between the corona electrode and the exciting electrode may generate so called ionic wind. It may be beneficial to place the corona electrodes at the inlet side of the electrostatic air filter and the exciting electrode further down along with air passing. That arrangement may accelerate air and assist fans or blowers with air movement. 
     All of the electrodes described above are attached to corresponding rigid fixtures. The corona electrodes, for instance, may be attached to a corona frame. The collecting electrodes as well as the repelling electrodes may be attached to their own rigid fixtures. Those rigid fixtures are, in turn, attached to a common case (or a cabinet). As an alternative, all or some of the above mentioned electrodes may be attached to a common case (or a cabinet). This common case is made from an insulating material, like plastic. 
     When electrodes having different electrical potentials are attached to the cabinet directly or via the corresponding rigid fixtures, the shortest distance between them along an insulating surface is called the “creeping path.” An electrical shortage between the electrodes may occur when this creeping path is short or becomes contaminated with electrically conductive substances such as metal powder or coal dust. 
     That phenomenon may lead to a power supply shortage or a failure, which may disrupt the operation of the electrostatic filter. Under certain conditions, i.e., when the incoming air contains conductive substances such as metal powder or coal dust, the electrostatic filters should be cleaned more often. This causes inconvenience and increases the cost of operation. In more harsh conditions, electrostatic air filters may not be useful at all. 
     An electrostatic air filter may have a case with walls and having an open air inlet and an open air outlet. The electrostatic air filter may have at least two electrode sets having different electrical potentials. Each electrode set may be assembled on a separate rigid fixture. The rigid fixtures may be secured to the case at separate spots. The separate spots may be spaced apart sufficient to establish an extended creeping distance. The electrode sets may be two or more of a collecting electrode set; a corona electrode set; an exciting electrode set; and a repelling electrode set. The collecting electrode set may have a plurality of collecting surfaces mounted parallel to each other and substantially parallel to a principal air flow direction. Repelling electrode sets may have a plurality of repelling surfaces mounted parallel to each other and in locations flanked by collecting surfaces. A corona electrode set may have one or more thin conductive wires mounted to traverse and air flow path in parallel and defining a plane that is substantially perpendicular to a principal air flow direction. An exciting electrode set may be one or more electrically conductive members in a plane that is parallel to a plane defined by a corona electrode set. The exciting electrode set may be an electrically conductive air penetrable web. The repelling electrode set may be at or near the electrical potential of the corona electrode set. The collecting electrode set may have an electrical potential at or near the electrical potential of the exciting electrode set. The collecting electrode set and the exciting electrode may have an electrical potential close to ground. 
     An electrostatic air filter may have an electrode assembly built upon an accordion rack. A first group of electrodes may be mounted in parallel on the accordion rack, and a second group of electrodes which operate at a different potential than the first group of electrodes may be mounted in parallel to the first group on the accordion rack wherein said electrodes are mounted in an alternating sequence. The accordion rack may have members secure to each other at pivot points to form the accordion rack. Some or all of the members may extend beyond the pivot points. An additional electrode set may be mounted on extended portion of the extended members. 
     In one configuration the collecting electrodes may have apertures and are connected to each other via rigid fixtures. The repelling electrodes may have apertures and may connect to each other via rigid fixtures. The repelling and collecting electrodes may be mounted in alternating order and parallel to each other. The rigid fixtures holding the collecting electrodes may be through rod-like members that pass apertures of the repelling electrodes but do not contact the repelling electrodes. In a similar fashion the rigid fixtures holding the repelling electrodes pass through apertures in the collecting electrodes but do not touch the collecting electrodes. The case may have two inner walls and two outer walls on opposing sides. These walls may be substantially parallel to the collecting electrodes and separated from each other by air gaps. The inner walls have apertures and the rigid fixtures of the collecting electrode set pass through the apertures of an inner wall on one side and may be secured to the outer wall on that same side. The fixtures for the repelling electrodes may pass through apertures in the inner wall on the opposing side and may be secured to the outer wall on that opposing side. When a rod or fixture is described as passing through an aperture of an electrode, it is intended that the rod or fixture does not contact that electrode. 
     Another mechanism that may be employed to hinder accumulation of conductive and/or semi-conductive particles is the use of a shield to block or reduce airflow in areas where it is critical to impair buildup and hinder creep. Yet another mechanism may be employed to that end which replaces flat elements that may be subject to particle accumulation with irregular, winding, or corrugated structures. 
     SUMMARY OF THE INVENTION 
     An electrostatic precipitator may have several types of electrodes. One type of electrode is a corona electrode. Another type may be collecting electrodes. There may be other types of electrodes such as an exciting electrode and a repelling electrodes. Each type of electrode referred to herein may be a single electrode or plural electrodes. Typically electrodes of the same type are kept at the same potential. The exciting electrode may be a single piece structure or more than one piece electrically connected to each other. A device may have corona electrodes. The corona electrodes may be a corona wire routed across the air flow path one time or more than one time and an electrostatic device may have one corona wire or multiple corona wires routed across an airflow path and electrically connected to each other. The term “electrode set” is intended to include one or more electrodes. 
     Electrodes that are under the same electrical potential may be attached to a common rigid fixtures or to a common case at or near the maximum available distance along the surface from each other. The surface separating the rigid fixtures from each other may be made winding or corrugated or convoluted in order to increase the creeping discharge path. The surface separating the electrodes from each other may be protected from contamination by particulate matter. Various objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
     Moreover, the above objects and advantages of the invention are illustrative, and not exhaustive, of those that can be achieved by the invention. Thus, these and other objects and advantages of the invention will be apparent from the description herein, both as embodied herein and as modified in view of any variations which will be apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a schematic illustration of a prior art electrode configuration.  FIG. 1B  shows a portion of  FIG. 1A  enlarged. 
         FIGS. 2A, 2B, 2C, 2D and 2E  show an electrostatic filter with a case. 
         FIGS. 3A and 3B  show a partial view of a filter with an inlet exciting electrode and corona wires located on the frame. 
         FIGS. 4A and 4B  show a second embodiment of an electrostatic filter. 
         FIGS. 5A and 5B  show the top view of an electrostatic filter in unfolder and folded configurations. 
         FIGS. 6A, 6B, 6C, 6D and 6E  show an alternative electrode support configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before the present invention is described in further detail, it is to be understood that the invention is not limited to the particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the exemplary methods and materials are described herein. 
     It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
     All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed. 
     The invention is described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention. 
     The term “creeping distance” is used to indicate the distance between the two closest points on the surface of an insulated structures between components having different potentials, for example corona electrodes and collecting electrodes. The term “creeping path” is used to indicate the path of current flow on the surface of an insulated structure between components having different potentials, for example corona electrodes and collecting electrodes. The creeping path is no shorter than the creeping distance as the creeping path is the actual current path and the creeping distance is a measure of the minimum distance along a surface between two points. 
     An electrostatic air filter may have several groups of electrodes. All electrodes in a group have the same or similar electrical potential. The electrical potential difference between the groups of electrodes may be ranged from several kilovolts to several tens of kilovolts. 
     Corona electrodes in an electrostatic air cleaner may be in the form of thin wires and may be located on a corona frame. The collecting electrodes may be secured on common rigid fixture. Sets of rods or brackets may be used to mount the collecting electrodes. 
     Electrodes that belong to the same group may be secured on a common rigid fixture. The rigid fixtures may be secured, integrated with, or attached to a non-conductive case in a manner where the attachment points for rigid fixtures that support the electrodes under different electrical potentials are spaced apart from each other along the surface of the case. The spacing may be selected to increase the creeping distance between electrodes of differing potentials. The spacing may be greater than the minimum spacing otherwise permitted 
       FIGS. 2A, 2B, 2C, 2D, and 2E  show an electrostatic air filter  201  with a case  202 . The case  202  may be non-conductive and may have two horizontal and two vertical walls attached to each other. The electrostatic air filter  201  may have a corona electrode frame  203  with parallel thin wires, an exciting electrode  204  with an air penetrable electrically conductive web, collecting electrodes  205  which may be secured by four brackets  208  to vertical walls of the case  202 , and repelling electrodes  209  which may be received in slots  213  provided in horizontal walls of the case  202 . The exciting electrode  204  may be secured to the case  202  by brackets  208 . The brackets  208  may be attached to the vertical walls of the case  202  with latches  212 . The exciting electrode  204  may be grounded or at a low (i.e., safe) electrical potential. The exciting electrode  204  may also serve as an electrical protection for people and as a rough pre-filter at the same time. The exciting electrodes  204  may be located on upstream or downstream side of the corona electrode  203 . 
     The exciting electrode  204  fixture may be attached to opposing parallel walls of the case, for example, at the vertical walls. The corona wires may be under high electrical potential in the order of several kilovolts to several tens of kilovolts. Therefore, the corona electrode  203  fixture may be attached to orthogonal walls, for example, the horizontal walls of the case  202 . Such a configuration provides an extended creeping path from the corona electrode frame  203  to the exciting electrode frame  204  via the surface of the case  202 . 
     The repelling electrodes  209  may be located between the collecting electrodes  205  and may be parallel to each other. The repelling electrodes  209  may be attached to the horizontal plates of the case  202  by the slots  213 . The repelling electrodes may be under high electrical potential that is close to or, in some instances, the same as the electrical potential on the corona electrode wires. Therefore there is no need to separate the corona electrode frame  203  and the repelling electrodes  209  by a long creeping path. 
     The collecting electrodes  205  may be secured by the brackets  208 . The collecting electrodes  205  may be located between the repelling electrodes and may be parallel to each other. The collecting electrodes  205  may be under a low electrical potential that is close to the electrical potential of the exciting electrodes  204 . The collecting electrodes  205  may be separated from the horizontal walls of the case by air gaps. 
     The brackets  208  may hold the collecting electrodes  205  and may be secured to the vertical walls of the case  202 , while the repelling electrodes  209  may be attached to the horizontal walls. Such an arrangement ensures an extended creeping path along the surface between the collecting electrodes  205  and the repelling electrodes  209 . 
     The shortest distance for the creeping discharge is from the outmost repelling electrodes  209  via part of the horizontal wall of the case  202 , then via part of the vertical wall of the case  202 , and finally via part of the brackets  208  to the outmost collecting electrodes  205 . This path is much longer than it would be if the collecting electrodes and the repelling electrodes were both supported by the horizontal wall of the case  202  like in the existing art. 
     Another feature further prevents a creeping discharge between the electrodes that are under different electrical potentials. The surfaces connecting such electrodes may be made winding or corrugated or convoluted in the same manner as surfaces of outdoor electrical insulators in transmission lines. That feature, along with the arrangement described above, ensures an even longer path for the creeping discharge along the surface. 
       FIGS. 3A and 3B  show a partial view of a filter with an inlet exciting electrode  304  and corona wires located on the frame  303 . A protecting shield  310  may be provided to impair, deflect, or block air passage along the walls of the case  202 . This reduces the amount of particulate that will settle and contaminate the walls of the filter case  202 . 
     The collecting electrodes  205  may advantageously be located on a separate fixture, i.e., on the brackets  208  or  308 . When the collecting electrodes  205  ( 305  in the  FIG. 3 ) become contaminated, the whole collecting electrodes assembly may be removed from the case  202 . Usually, the distance between the neighboring electrodes is larger than the thickness of the electrodes. In this case, two or more collecting electrodes assemblies may be inserted into each other. This way, they occupy much less space. A consumer or a customer, therefore, would enjoy cost and space savings on shipment and storage. 
       FIGS. 4A and 4B  show a second embodiment of an electrostatic filter. The electrostatic air filter  401  may contain collecting electrodes  403  and the repelling electrodes  404 . The collecting electrodes  403  and the repelling electrodes  404  may be assembled on an accordion rack  402 . The accordion rack may be constructed of folding bars connected at middle pivot points  408  and edge pivot points  409 . The collecting electrodes  403  and repelling electrodes  404  may be secured at the edge pivot points  409  of the bars of the accordion rack  402 . The bars may have shorter extensions  405  and longer extensions  406 . The exciting electrode  407  may be a conductive web similar to  204  in the  FIG. 1  and may be attached to the longer extensions. The corona electrodes (not shown) may be similar to electrodes  203  in  FIG. 1  and may be attached to the shorter extensions  406 . Alternatively, the corona electrodes may be attached to the longer extensions  405  while the exciting electrode may be attached to the shorter extension  406 . 
     In the configuration shown in  FIGS. 4A and 4B , the distance, along any structural component between collecting electrodes  403  and adjacent repelling electrodes  404  may be substantially greater than the space between the collecting electrodes  403  and adjacent repelling electrodes  404 . The shortest creeping path therebetween requires traversal of the folding bars. 
     As a practical example, assuming that the width (along the air flow direction) of the collecting electrode  403  is equal to 200 mm and the width of the repelling electrode  404  is equal to 180 mm, then the creeping path along the bars is approximately 150 mm. At the same time, the electrodes are separated from each other by about 10 mm. The arrangement shown in  FIGS. 4A and 4B  increases the creeping path by about 15 times compared with the shortest distance between the electrodes through the air. 
     The arrangement shown in the  FIGS. 4A and 4B  has still another advantage over the existing art. It is foldable.  FIG. 5A  shows a top view of an electrostatic air filter in an unfolded (operational) configuration.  FIG. 5B  shows a top view of an electrostatic air filter in a folded (stored) configuration. The unfolded configuration, shown in  FIG. 5A  may be about 530 mm (left to right), while the folded configuration shown in  FIG. 5B  may occupy just 63 mm. This is more convenient for filter maintenance (replacement) and also presents an advantage in cost savings for shipment and storage of the electrostatic air filter parts. In order to facilitate deployment of the electrodes, the pivots may have some sliding clearance and mechanism for locking the plate in the deployed (or open) position of the folding bars/pivot points. 
       FIGS. 6A, 6B, 6C, 6D and 6E  show an alternative electrode support configuration for increasing the creeping path length and has substantially improved filter performance in dirty atmospheres. 
     The electrostatic air filter  601  may contain a plurality of collecting electrodes  602  with apertures  608  and a plurality of repelling electrodes  603  with apertures  609 . The collecting and repelling electrodes may alternate. The collecting electrodes  602  may be assembled with the conductive rods  604 . These rods  604  may be attached to the collecting electrodes  602  and to the case wall  607 . The repelling electrodes  603  may be assembled on conductive rods  605 . Rods  605  may be attached to repelling electrodes  603  and to the case wall  606 . The case walls  606  and  607  may be made of non-conductive material like ABS plastic. 
     The rods  604  are not electrically connected to repelling electrodes  603  and the rods  605  are not electrically connected to collecting electrodes  602 . Therefore, the creeping path does not exist here. However, the creeping path is along the surface of the case wall  606  and  607 . The rods  604  may pass through an aperture  610  in the walls  606 . Aperture  610  may have a diameter greater than the diameter of the rod  604 . Therefore, there is no electrical contact between the collecting electrodes  602  and the wall  606 . The same provision may be provided for the rods  605  with apertures  608  and rods  604  with apertures  609 . 
     The creeping path between the collecting electrodes  602  and the repelling electrodes  603  may be substantially greater than in the existing art. The creeping path in the embodiment shown in  FIGS. 6A and 6B  is from the rod  605  along the wall  606  all way to the vertical wall of the case (not shown), then up along the vertical wall, and then back along the wall  607  to the place where the rod  604  is secured to the wall  607 . In addition, the electrostatic air filter may be equipped with a protecting shield similar to shield  310  shown in  FIG. 2 . In addition, the creeping path may be further increased by forming walls  606  and  607  with a corrugated shape. 
     The techniques, processes and apparatus described may be utilized to control operation of any device and conserve use of resources based on conditions detected or applicable to the device. 
     Thus, the specific systems and methods for the electrostatic air filter have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the disclosure. Moreover, in interpreting the disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “contains” and “containing” should be interpreted as referring to members, or components in a non-exclusive manner, indicating that the referenced elements and components, may be present, or utilized, or combined with other members and components that are not expressly referenced.