Patent Publication Number: US-11657987-B2

Title: Dielectric shield for a switching device

Description:
PRIORITY 
     This application claims the benefit of Indian Patent Application No. IN 202031016049, filed on Apr. 14, 2020, which is hereby incorporated by reference in its entirety. 
     FIELD 
     The present disclosure relates to switching devices such as circuit breakers. More particularly, the present disclosure relates to enhancing dielectric performance of a circuit breaker without increasing clearances and/or physical dimensions of the circuit breaker. 
     BACKGROUND 
     Like Circuit breakers, grounding or earthing transformers are an important component of any power network. More particularly, grounding transformers are essential for renewable power generator plants, for example, in large multi-turbine wind farms where the substation transformer frequently provides a sole earthing source for distribution system. A grounding transformer placed on a wind turbine string provides a ground path in an event when the string becomes isolated from the system ground provided by the substation transformer. A ground fault on a collector cable causes the substation circuit breaker to open, and the wind turbine string becomes isolated from the system ground source. The wind turbines do not always detect this fault or the fact that the string is isolated and ungrounded. As a result, the generators continue to energize the collector cable, and the voltages between the un-faulted cables and the ground rise far above the normal voltage magnitude. This results in a staggering increase in operational costs. 
       FIG.  1 A  illustrates a wind power generation system  100 , according to the state of the art. The wind power generation system  100  has a string of wind turbines WTG 1 -WTGX each of which are connected to a medium voltage circuit breaker  101  and a grounding transformer  102 , via respective line transformers  103 A- 103 X. This wind power generation system  100  is then connected to a step-up transformer  104  to step up the voltage suitable for power transmission over the transmission system  105 .  FIG.  1 B  illustrates a wind power generation system  100  including a switching device  106  having a combined functionality of circuit breaking and ground switching, according to the state of the art.  FIG.  1 B  discloses a variation of the wind power generation system  100  shown in  FIG.  1 A . In this variation, the circuit breaker  101  and the grounding transformer  102  are integrated into a single switching device  106 . The switching device  106  performs the switching and grounding through a combined medium voltage circuit breaker and a grounding vacuum switch thereby, eliminating the grounding transformer  102 . 
     The switching device  106  is, for example, a three phase medium voltage switchgear having an operational rating of up to 38 kilo Volts and up to 40 kilo Amperes and includes at least one pole assembly, per phase, in an operable connection with a drive unit via a drive connection rod. Each pole assembly includes a first interrupter unit (e.g., a circuit breaker) providing a path for current flow therethrough in a closed state and interrupting the current flow in an open state, and a second interrupter unit operably connected to the first interrupter unit allowing the current flow through the first interrupter unit in an open state and grounding the switching device in a closed state (e.g., acting as a grounding switch). The pole assembly includes a pole plate supporting the two vacuum interrupters representing a circuit breaker and a grounding switch, respectively, via multiple post insulators. 
     During occurrence of a lightening impulse voltage in the switching device  106 , an electric field is generated around the live parts such as the vacuum interrupters. This electric field contains voltages of various magnitudes (e.g., varying potential across the field). Typically, a conductor, when placed in a voltage field having voltages of varying potential therein, experiences high levels of dielectric stress that may result in failure of the switching device  106  especially when exposed to high switching voltages. 
     For performing expected functions, aforementioned switching device  106  is required to withstand an impulse voltage of about 210 kVp. Further, the switching device  106  is required to withstand the impulse voltage with minimal increase in air clearances (e.g., a clearance of up to 335 mm between the pole plate and terminals of the interrupter units may be retained). This is because an increase in the air clearances beyond predefined limit leads to an increase in the overall physical dimensions of the product, thereby making the product bulky and increasing material and manufacturing overheads. 
     SUMMARY AND DESCRIPTION 
     The scope of the present invention is defined solely by the appended claims and is not affected to any degree by the statements within this summary. 
     The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a switching device that may successfully withstand rated switching impulse voltage without increasing physical dimensions of the switching device is provided. 
     A pole assembly of the switching device disclosed herein achieves this by a dielectric shield physically disposable between and operably connected to the post insulators supporting the interrupter units. In one embodiment, the dielectric shield is positioned longitudinally parallel to the pole plate and proximal to the first interrupter unit and the second interrupter unit to allow a near equipotential field to be created in the pole assembly around the dielectric shield. As used herein, “dielectric shield” refers to an elongate member constructed of a material exhibiting dielectric properties. The dielectric shield is configured to have a conducting material and/or an insulating material. In one embodiment, the dielectric shield is made of a conducting metal such as Copper, Aluminum, etc. that is then encapsulated with an insulating material such as a plastic compound, epoxy, etc. A thickness of the encapsulating material is dependent on dielectric properties of the insulating material chosen, such that the impulse voltage is withstood. A thickness of the conducting material is defined based on manufacturing constraints such as to avoid sharp edges, physical cracks, and deformities from occurring that may result in overall dielectric strength of the dielectric shield being affected. 
     According to an embodiment, distal surfaces and/or ends of the dielectric shield have insulating material extruded therefrom (e.g., these surfaces have conducting material without any insulating encapsulation). In one embodiment, these extrusions are present on both sides of the dielectric shield. These sides of the dielectric shield include a first side that operably connects to the post insulators and a second side that operably connects to an enclosure of an interlink arrangement positioned in between and in connection with the first interrupter unit and the second interrupter unit. The shapes and surface areas of the extrusions on the first side are equivalent to outer perimeters of post insulators connected to the dielectric shield. The shapes and surface areas of the extrusions on the second side are configured so as to establish contact with the enclosure of the interlink arrangement. In one embodiment, lack of insulating material on these extrusions allows for metal to metal connection, thereby enabling uniform distribution of the electric field around the interrupter units. According to another embodiment, the distal surfaces include an orifice centrally punched therethrough to allow conductors passing through the post insulators to be operably connected to the terminals of the respective interrupter units. 
     The first interrupter unit and the second interrupter unit are operably connected via the interlink arrangement that sets a stroke of the second vacuum interrupter without affecting a stroke of the first vacuum interrupter unit. The drive connection rod is used to set a stroke of the first interrupter unit (e.g., the circuit breaker). The interlink arrangement sets a stroke of the second vacuum interrupter (e.g., the grounding switch). The dielectric shield is positioned in proximity of the interlink arrangement. In one embodiment, at least one physical dimension of the dielectric shield is defined based on one or more physical properties associated with the interlink arrangement. With the interlink arrangement being a live component of the pole assembly, the electric field generated around the interlink arrangement is of a very high potential. In one embodiment, the dielectric shield is positioned longitudinally parallel to the interlink arrangement such that a length of the dielectric shield is equal to or more than a distance between a lower terminal of the first interrupter unit (e.g., a terminal proximal to the interlink arrangement) and an upper terminal of the second interrupter unit (e.g., a terminal proximal to the interlink arrangement). According to this embodiment, a width of the dielectric shield is defined to be greater than or equal to a width of the interlink arrangement. As used herein, interlink arrangement includes but is not limited to any enclosure in which the interlink arrangement may be secured and assembled in the pole assembly. According to another embodiment, the dielectric shield includes an orifice allowing passage of the drive connection rod therethrough for operably connecting to the interlink arrangement. In one embodiment, inner edges of this orifice have insulating material deposited thereon to prevent non-uniform distribution of the electric field. 
     According to an embodiment, the dielectric shield is configured of a generally rounded profile, for example, having gradual profiles along edges and/or around orifices positioned therein. A generally gradual profile such as rounded, beveled, etc. precludes electric flashovers from happening, thereby improving dielectric strength. 
     The dielectric shield, when positioned in the pole assembly in the aforementioned manner, enables uniform distribution of an electric field across the pole assembly when the switching device is in operation. By physically positioning the dielectric shield in a zone having high variation of potential, the electric filed is distributed nearly evenly thereby, reducing electric stresses faced by components of the pole assembly. This, for example, leads to withstanding of high impulse voltages without increasing air clearances and physical dimensions of the switching device. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the following description. The summary is not intended to identify features or essential features of the claimed subject matter. Further, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  illustrates a wind power generation system according to the state of the art. 
         FIG.  1 B  illustrates a wind power generation system including a switching device having a combined functionality of circuit breaking and ground switching, according to the state of the art. 
         FIG.  2    illustrates a pole assembly for one phase of a switching device, according to an embodiment of the present disclosure. 
         FIG.  3    illustrates a perspective view of a dielectric shield of the pole assembly shown in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments are described in detail. The various embodiments are described with reference to the drawings, where like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. Such embodiments may be practiced without these specific details. In other instances, well known materials or methods have not been described in detail in order to avoid unnecessarily obscuring embodiments of the present disclosure. While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. There is no intent to limit the disclosure to the particular forms disclosed; on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. 
       FIG.  2    illustrates one embodiment of a pole assembly  200  for one phase of a switching device  106  shown in  FIG.  1 B , according to an embodiment of the present disclosure. The pole assembly  200  includes a vacuum interrupter  202  operably connected to another vacuum interrupter  203  via an interlink arrangement  207 . The vacuum interrupter  202  represents the circuit breaker  101  shown in  FIG.  1 A , and the vacuum interrupter  203  represents the grounding switch  102  shown in  FIG.  1 A . The pole assembly  200  thus includes an integration of the circuit breaker and the grounding switch into a single switching device  106  shown in  FIG.  1 B . The interlink arrangement  207  is operably connected to a drive connection rod  204  that is connected to a drive unit  205  of a switching device  106 . The interlink arrangement  207  allows for an adjustment of a stroke of the vacuum interrupter  203  (e.g., the grounding switch without affecting the stroke of the vacuum interrupter  202 , the circuit breaker). 
     Post insulators  208 A- 208 D of the pole assembly support the two vacuum interrupters  202  and  203 . The vacuum interrupter  202  is supported by the post insulators  208 A and  208 B, and the vacuum interrupter  203  is supported by the post insulators  208 C and  208 D. The post insulators  208 A- 208 D are rigidly attached to a pole plate  206  of the pole assembly  200 . A dielectric shield  201  is positioned parallel to the pole plate  206  and in between the post insulators  208 B and  208 C, proximal to the interlink arrangement  207 . Accordingly, a length of the dielectric shield  201  is nearly equal to a distance D between outer edges of the post insulators  208 B and  208 C, and a width of the dielectric shield  201  is nearly equal to a width of the interlink arrangement  207  (e.g., an enclosure  207 A in which the interlink arrangement  207  is positioned). Thus, the dielectric shield  201  at least partially covers the interlink arrangement  207 . 
       FIG.  3    illustrates a perspective view of a dielectric shield  201  of the pole assembly  200  shown in  FIG.  2   . The dielectric shield  201  is an elongate member rigidly connected at an end  201 E to the post insulator  208 B and at another other end  201 E′ to the post insulator  208 C, shown in  FIG.  2   . The dielectric shield  201  is configured of an electrically conducting material encapsulated in an insulating material. The profile of the dielectric shield is configured such that connections of auxiliary components including but not limited to the drive connection rod  204 , the interlink arrangement  207 , the post insulators  208 B,  208 C, etc., of the pole assembly  200  are maintained with minimal changes in the assembly. 
     The dielectric shield  201  has extrusions  201 A and  201 B towards ends  201 E and  201 E′, respectively. The extrusions  201 A and  201 B are shaped based on the shapes of the post insulators  208 B and  208 C so as to allow the post insulators  208 B and  208 C to be connected to the vacuum interrupters  202  and  203 , respectively. The extrusions  201 A and  201 B have conducting material partially extruded from the dielectric shield  201  such that a thickness of the conducting material in areas defined by the extrusions  201 A and  201 B is lesser than an overall thickness of the conducting material elsewhere on the dielectric shield  201 . The extrusions  201 A and  201 B are made of conducting material without any encapsulation of the insulating material. The dielectric shield  201  has orifices  201 A′ and  201 B′ centrally positioned within the extrusions  201 A and  201 B, respectively, to allow passage of conductors (not shown) within the post insulators  208 B and  208 C for connection to the vacuum interrupters  202  and  203 , respectively. The dielectric shield  201  has another orifice (e.g., a cut-out  201 C positioned thereon such that the drive connection rod  204  may pass therethrough for rigid connection with the interlink arrangement  207 ). Inner walls  201 D of the cut-out  201 C are coated with the insulating material. 
     The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention disclosed herein. The embodiments described above are illustrative, not limiting. Further, although the invention has been described herein with reference to particular materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may effect numerous modifications thereto, and changes may be made without departing from the scope and spirit of aspects of the invention. 
     The elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent. Such new combinations are to be understood as forming a part of the present specification. 
     While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.