Patent Publication Number: US-11043317-B2

Title: Conbined tubular metal oxide varistor and gas discharge tube

Description:
FIELD OF THE DISCLOSURE 
     The disclosure relates generally to the protection of electrical and electronic circuits and equipment from power surges and, more particularly, to a combined tubular metal oxide varistor and gas discharge tube. 
     BACKGROUND OF THE DISCLOSURE 
     A variety of devices are available on the market that are designed to protect devices that are susceptible to damage by voltage surge when the voltage applied between power terminals exceeds a maximum acceptable threshold. For example, some prior art approaches include metal oxide varistors (MOVs), based on semiconductors and the like, as well as gas discharge tube (GDT) devices. MOV devices are generally fast acting, which is very desirable in certain applications, but with the inconvenience of not being able to absorb an unlimited number of surges. That is, MOVs degrade with use and in the end fail. The number of times an MOV device shall function correctly depends on the energy absorbed each time it functions. Furthermore, there is the inconvenience that the MOV device may short circuit in case of malfunction, necessitating some other type of protection against this inconvenience. 
     With regard to GDT devices, which are generally slower acting devices that function by producing an electric arc in their interior when nominal voltage is surpassed, impedance between their terminals during use diminishes drastically, potentially causing a short circuit. Furthermore, GDT devices have relatively small capacitance. 
     One prior art solution uses separate GDT and MOV devices connected in series between the terminals of the element to be protected. This combination has the advantage that taken together, capacitance is approximately equal to that of the GDT device (a few pF). Generally, if the MOV device and the GDT device are similar in size, then protection capability depends on the MOV device because capacitance of the GDT device is higher. When the MOV device and the GDT device act in a protection stage, the combined resistance is reduced significantly. However, this solution has significant size constraints, which limit use in space saving condition. 
     Thus, there presently exists a need for a combined MOV and GDT that overcomes the deficiencies of the prior art. 
     SUMMARY OF THE DISCLOSURE 
     In one approach according to the present disclosure, a protection device, may include a tubular ceramic part having a first end coupled to a first electrode and a second end coupled to a second electrode, and a tubular metal oxide varistor (MOV) having a first end coupled to the second electrode and a second end coupled to a third electrode. The tubular MOV may include a central cavity aligned with a central cavity of the tubular ceramic part, the central cavity of the tubular MOV and the central cavity of the tubular ceramic part containing an inert gas. The protection device may further include an enclosure surrounding the tubular ceramic part and the tubular MOV. 
     In another approach according to the present disclosure, a protection module, may include a tubular ceramic part having a first end directly coupled to a first electrode and a second end directly coupled to a second electrode, and a tubular metal oxide varistor (MOV) having a first end directly coupled to the second electrode and a second end directly coupled to a third electrode, wherein the tubular MOV includes a central cavity aligned with a central cavity of the tubular ceramic part, and wherein the central cavity of the tubular MOV and the central cavity of the tubular ceramic part contains an inert gas. The protection module may further include an enclosure surrounding the tubular ceramic part and the tubular MOV within a same internal cavity. 
     In another approach according to the present disclosure, a protection device includes a tubular ceramic part having a first end directly coupled to a first electrode and a second end directly coupled to a second electrode, and a tubular metal oxide varistor (MOV) having a first end directly coupled to the second electrode and a second end directly coupled to a third electrode, wherein a central cavity of the tubular ceramic part is fluidly connected with a central cavity of the tubular MOV, and wherein an inert gas is disposed within the central cavity of the tubular MOV and the central cavity of the tubular ceramic part. The protection device may further include an enclosure surrounding the tubular ceramic part and the tubular MOV. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate exemplary approaches of the disclosed embodiments so far devised for the practical application of the principles thereof, and in which: 
         FIG. 1  depicts a circuit diagram of a GDT electrically connected with a tubular MOV according to embodiments of the present disclosure; 
         FIG. 2  depicts a side view of a protection device including a protection device including a tubular ceramic part coupled with a tubular MOV according to embodiments of the present disclosure; 
         FIG. 3  depicts a side cross-sectional view of the protection device of  FIG. 2  according to embodiments of the present disclosure; 
         FIG. 4  depicts an exploded view of the protection device of  FIG. 2  according to embodiments of the present disclosure; 
         FIG. 5  depicts a circuit diagram of a GDT electrically connected with a tubular MOV according to embodiments of the present disclosure; 
         FIG. 6  depicts a side cross-sectional view of a protection device including a protection device including a tubular inductor coupled with a tubular MOV according to embodiments of the present disclosure; 
         FIG. 7  depicts an exploded view of a portion of the protection device of  FIG. 6  according to embodiments of the present disclosure; and 
         FIGS. 8A-8B  depict perspective views of an inductor of the protection device of  FIG. 6  according to embodiments of the present disclosure. 
     
    
    
     The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict typical embodiments of the disclosure, and therefore should not be considered as limiting in scope. In the drawings, like numbering represents like elements. 
     Furthermore, certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. Still furthermore, for clarity, some reference numbers may be omitted in certain drawings. 
     DETAILED DESCRIPTION 
     Embodiments in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The device/circuit may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the system and method to those skilled in the art. 
     For the sake of convenience and clarity, terms such as “top,” “bottom,” “upper,” “lower,” “vertical,” “horizontal,” “lateral,” and “longitudinal” will be used herein to describe the relative placement and orientation of various components and their constituent parts. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
     As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or operations, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     Furthermore, in the following description and/or claims, the terms “on”, “overlying,” “disposed on” and “over” may be used in the following description and claims. “On,” “overlying,” “disposed on” and “over” may be used to indicate that two or more elements are in direct physical contact with each other. However, “on,”, “overlying,” “disposed on,” and over, may also mean that two or more elements are not in direct contact with each other. For example, “over” may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect. 
     As will be described herein, embodiments of the present disclosure address the GDT follow-on current issue of the prior art by providing a tubular MOV in series with a tubular ceramic part, which can advantageously cut off the follow-on current because the tubular MOV will resume a high resistance state immediately when voltage is reduced to normal levels as a surge subsides. Furthermore, embodiments of the present disclosure address the MOV degradation issues of the prior art, as there is no voltage applied on the tubular MOV in a normal state, thus allowing the life of the tubular MOV to be significantly longer. Still furthermore, embodiments of the present disclosure address the deficiencies of the prior art by alternatively providing the tubular MOV and GDT in parallel, which provides most of the current to flow through the tubular GDT during a surge event. In some embodiments, because the tubular MOV reacts faster than the tubular GDT, present embodiments advantageously provide an inductor to coordinate the reaction of the tubular GDT and MOV. 
     To accomplish the above advantages, provided herein are protection devices having a tubular ceramic part and a tubular MOV electrically coupled in a series or parallel arrangement. In some series connection-type embodiments, the protection device includes a ceramic part (e.g., Al 2 O 3 ) connected between a first electrode and a second electrode, and a ceramic MOV (e.g., ZnO) connected between the second electrode and a third electrode. The protection device further includes an enclosure surrounding the tubular ceramic part and the tubular MOV, wherein leads of the first electrode, the second electrode, and the third electrode extend outside the enclosure. In some parallel connection-type embodiments, the tubular ceramic part includes a tubular inductor positioned between the tubular ceramic part and the tubular MOV, which are electrically connected in parallel. In some embodiments, the protection device includes an inductor, wherein the inductor is electrically connected to the first electrode and the second electrode. 
     In some embodiments of the present disclosure, the protection device is a surge protector including the tubular MOV and the tubular ceramic part along with a resistor. The inert gas of the tubular ceramic part may be non-conductive below a trigger voltage, and conductive above the trigger voltage. The tubular MOV and the tubular ceramic part may be connected in parallel with each other, and the resistor may be connected in series with the tubular MOV and the tubular ceramic part. 
     The protection device of the present disclosure may provide protection for any electrical component such as an electrical device, an electrical machine, or electrical equipment. In some embodiments, the component to be protected is a motor drive for an electric machine. In embodiments, the electric machine is a direct-current (DC) or alternating-current (AC), fractional horsepower (HP) electric machine. The electric machine may be powered by a voltage signal (AC or DC), and generates power under 1 HP. 
     Turning now to  FIGS. 1-4 , a protection module or device  100  according to embodiments of the present disclosure will be described in greater detail. As shown, the protection device  100  may include a cylindrical or tubular shaped ceramic part  104  connected between a first electrode  106  and a second electrode  108 , and a cylindrical or tubular shaped metal oxide varistor (MOV)  110  connected between the second electrode  108  and a third electrode  114 . The tubular ceramic part  104  and the tubular MOV  110  may be electrically connected in series. In some embodiments, the tubular ceramic part  104  and the tubular MOV  110  are coupled together on opposite sides of the second electrode  108 . More specifically, the tubular ceramic part  104  may include a first end  105  opposite a second end  107 , wherein the first end  105  is directly physically and electrically coupled to the first electrode  106 , and the second end  107  is directly physically and electrically coupled to the second electrode  108 . The tubular MOV  110  may also include a first end  111  opposite a second end  113 , wherein the first end  111  is directly physically and electrically coupled to the second electrode  108  and the second end  113  is directly and physically coupled to the third electrode  114 . 
     An enclosure  118 , such as a coating, encapsulation layer and/or a housing, may be formed over the tubular ceramic part  104  and the tubular MOV  110 , wherein leads of the first electrode  106 , the second electrode  108 , and the third electrode  114  extend outside of the enclosure  118 . In some embodiments, the enclosure  118  may include first and second halves, for example as depicted in  FIG. 4 . As shown, the tubular ceramic part  104  and the tubular MOV  110  may have a same, or substantially the same, shape and outer circumference to permit the combined elements to be efficiently retained within the enclosure  118 . Furthermore, the first electrode  106 , the second electrode  108 , and the third electrode  114  may all have a same, or substantially the same, outer circumference, which may also be the same or similar to the that of the tubular ceramic part  104  and the tubular MOV  110 . 
     The tubular ceramic part  104  and the tubular MOV  110  may be coupled together to form a continuous cavity  120  extending between the tubular ceramic part  104  and the tubular MOV  110 . In some embodiments, an inert gas  122  is disposed within the cavity  120 . To accommodate flow of the inert gas  122  between the tubular ceramic part  104  and the tubular MOV  110 , the second electrode  108  may include a central opening  124 . In some embodiments, as best shown in  FIG. 4 , the tubular ceramic part  104  may include a projection or rim  125  configured to engage an inner circular surface  127  of the second electrode  108  to align the second electrode  108  with the tubular ceramic part  104 . 
     As further shown, each of the first electrode  106  and the third electrode  114  may include a centering projection  130  extending inwardly towards the second electrode  108 . For example, the centering projection  130  of the first electrode  106  may extend into a central cavity  132  of the tubular ceramic part  104 , while the centering projection  130  of the third electrode  114  may extend into a central cavity  134  of the tubular MOV  110 . 
     In some embodiments, an insulation layer  135  ( FIG. 3 ) may be provided along an interior surface of the cavity  120 . More specifically, the insulation layer  135  may be provided along an interior surface  140  of the tubular ceramic part  104  and along an interior surface  142  of the tubular MOV  110  so that current flows from the first lead  106  to the third lead  114  and then to the second lead  108 . In exemplary embodiments, the central cavity  132  of the tubular ceramic part  104  is fluidly connected with the central cavity  134  of the tubular MOV  110 , thus permitting the inert gas  122  to fill both central cavities  132  and  134 . 
     During use, the tubular MOV  110  is designed to limit surge voltages by clamping the voltage. For example, the tubular MOV  110  may provide a variable resistance that is based on the voltage across the tubular MOV  110 . The tubular MOV  110  includes a corresponding voltage threshold or break-over voltage. Exemplary break-over voltages (Vn) for the tubular MOV  110  may be between approximately 200V and 800V. When voltage across the tubular MOV  110  is less than its break-over voltage, the tubular MOV  110  has a high resistance that limits current flow. When the voltage across the tubular MOV  110  is above its break-over voltage, the tubular MOV  110  has a relatively low resistance that limits the voltage. 
     The tubular ceramic part  104  also limits voltage. The tubular ceramic part  104  may include an inert gas within a ceramic housing that is capped by the first electrode  106  and the second electrode  108 . The tubular ceramic part  104  may have a trigger voltage, above which the tubular ceramic part  104  becomes conductive. An exemplary trigger voltage may be between 3000V and 3500V, for example. In other embodiments, the trigger voltage may be between 200V and 800V. When the voltage across the tubular ceramic part  104  is below the trigger voltage, the tubular ceramic part  104  is non-conductive (i.e., no current flow therethrough). When the voltage across the tubular ceramic part  104  is above the trigger voltage, the tubular ceramic part  104  is conductive and current flows therethrough. Once the tubular ceramic part  104  is triggered, it becomes highly conductive. This further limits the voltage and reduces the possibility of damage from the voltage surge. The tubular ceramic part  104  may form or comprise a spark gap, and a resistor may be placed across this spark gap. 
     Turning now to  FIGS. 5-8B , a protection module or device  200  according to embodiments of the present disclosure will be described in greater detail. As shown, the protection device  200  may include a tubular ceramic part  204 , which in this embodiment may be a tubular inductor. The tubular inductor  204  may be connected between a first electrode  206  and a second electrode  208 , and a tubular MOV  210  is connected between the second electrode  208  and a third electrode  214 . The tubular inductor  204  and the tubular MOV  210  are electrically connected in parallel. As shown, the protection device  200  may include an inductor  250  connected in series with the tubular inductor  204  and the tubular MOV  210 . In some embodiments, the tubular inductor  204  and the tubular MOV  210  are coupled together on opposite sides of the second electrode  208 . More specifically, the tubular inductor  204  may include a first end  205  opposite a second end  207 , wherein the first end  205  is directly physically and electrically coupled to the first electrode  206 , and the second end  207  is directly physically and electrically coupled to the second electrode  208 . The tubular MOV  210  may also include a first end  211  opposite a second end  213 , wherein the first end  211  is directly physically and electrically coupled to the second electrode  208  and the second end  213  is directly and physically coupled to the third electrode  214 . 
     An enclosure  218  ( FIG. 6 ), such as a coating, encapsulation layer and/or a housing, may be formed over the tubular inductor  204  and the tubular MOV  210 , wherein leads of the first electrode  206 , the second electrode  208 , and the third electrode  214  extend outside of the enclosure  218 . As shown, the tubular inductor  204 , the tubular MOV  210 , the first electrode  206 , the second electrode  208 , and the third electrode  214  may all have a same, or substantially the same, outer circumference to permit the internal elements of the protection device  200  to be efficiently retained by the enclosure  218 . 
     The tubular inductor  204  may be a cylindrical ceramic component, wherein a cavity  220  extends between the tubular inductor  204  and the tubular MOV  210 . In some embodiments, an inert gas  222  is disposed within the cavity  220 . To accommodate flow of the inert gas  222  between the tubular inductor  204  and the tubular MOV  210 , the second electrode  208  may include a central opening  224 . As further shown, each of the first electrode  206  and the third electrode  214  may include a centering projection  230  extending inwardly towards the second electrode  208 . For example, the centering projection  230  of the first electrode  206  may extend into a central cavity  232  of the tubular inductor  204 , while the centering projection  230  of the third electrode  214  may extend into a central cavity  234  of the tubular MOV  210 . In some embodiments, an insulation layer  235  ( FIG. 6 ) may be provided along an interior surface of the cavity  220 . More specifically, the insulation layer  235  may be provided along an interior surface  240  of the tubular inductor  204  and along an interior surface  242  of the tubular MOV  210 . In exemplary embodiments, the central cavity  232  of the tubular inductor  204  is fluidly connected with the central cavity  234  of the tubular MOV  210 . 
     In this embodiment, the protection device  200  may include the inductor  250  disposed between the tubular inductor  204  and the tubular MOV  210 . As shown, the inductor  250  may be a tubular inductor including a spiral coil  252  surrounded by a ceramic (e.g., Al 2 O 3 ) tube insulation  254 . The spiral coil  252  has a first end  255  electrically connected to the first electrode  206  and a second end  258  electrically connected to the second electrode  208 . As shown, the spiral coil  252  may be substantially surrounded by the tube insulation  254 , while the outer surfaces of the first and second ends  255 ,  258  remain exposed at the first and second ends  205  and  207 , respectively, for connection with adjacent layers. In some embodiments, the tubular inductor  250  may be made by tape-casting and lamination, similar to techniques used for multi-layer varistors. 
     While the present disclosure has been described with reference to certain approaches, numerous modifications, alterations and changes to the described approaches are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claims. Accordingly, it is intended that the present disclosure not be limited to the described approaches, but that it has the full scope defined by the language of the following claims, and equivalents thereof. While the disclosure has been described with reference to certain approaches, numerous modifications, alterations and changes to the described approaches are possible without departing from the spirit and scope of the disclosure, as defined in the appended claims. Accordingly, it is intended that the present disclosure not be limited to the described approaches, but that it has the full scope defined by the language of the following claims, and equivalents thereof.