Patent Publication Number: US-7910852-B2

Title: Encapsulated pole unit conductor assembly for an encapsulated pole unit and medium voltage circuit interrupter including the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to circuit interrupters and, more particularly, to medium voltage circuit breakers including a plurality of poles. The invention also relates to pole units for circuit interrupters. The invention further relates to pole unit conductor assemblies for pole units. 
     2. Background Information 
     Circuit interrupters provide protection for electrical systems from electrical fault conditions such as, for example, current overloads and short circuits. Various circuit interrupters include a spring powered operating mechanism, which opens electrical contacts to interrupt the current through the conductors of an electrical system in response to abnormal conditions, although a wide range of mechanical, electromechanical or other suitable driving mechanisms may be employed. 
     Vacuum circuit interrupters (e.g., vacuum circuit breakers; vacuum reclosers; other vacuum switching devices) include separable contacts disposed within an insulating housing. Vacuum circuit interrupters, such as, for example, power circuit breakers for systems operating above about 1,000 volts, typically utilize vacuum switches (not to be confused with vacuum switching devices), such as vacuum interrupters (not to be confused with vacuum circuit interrupters), as the switch element. 
     U.S. Pat. No. 5,912,604 discloses a recloser including a housing to which is attached a number of pole assemblies. A separate pole assembly is provided for each pole. Each pole assembly generally includes three subassemblies, namely a molded pole assembly, a connecting assembly and an actuator assembly. Protruding from each pole assembly are connection studs. The poles are molded from polyurethane, polymer concrete, epoxy or EPDM (ethylene propylene diene methylene). During a molding or casting operation, a vacuum interrupter and studs are placed in a mold and held in place by securing the studs. Any sensors, such as a current sensor and a voltage sensor, are held in place using porous insulating material. The current and voltage sensors are concentric rings positioned around a portion of one stud. The porous material is placed between the concentric rings and the stud. The polyurethane encapsulating material in its liquid state fills all mold voids including those voids in the porous insulating material. 
     It is known to provide circuit breaker pole assembly bottom conductors in the form of copper bars (or tubes) with an epoxy insulator on the outside. However, such known bottom conductors do not include any current transformer (CT) or any electronic sensing circuit. Since known CTs for corresponding circuit breakers are relatively very large and relatively very heavy, they are not disposed at the circuit breaker. Furthermore, such CTs would likely fail during circuit breaker testing. 
     There is room for improvement in medium voltage circuit interrupters. 
     There is also room for improvement in pole units for circuit interrupters. 
     There is further room for improvement in pole unit conductor assemblies for circuit interrupter pole units. 
     SUMMARY OF THE INVENTION 
     These needs and others are met by embodiments of the invention, which provide a removable unit for an encapsulated pole unit of a pole of a circuit interrupter in which an insulative housing encapsulates a line or load conductor along with an electronic device structured to sense a characteristic of the pole. 
     In accordance with one aspect of the invention, a medium voltage circuit interrupter comprises: a circuit interrupter housing; a plurality of poles, each of the poles including a characteristic, each of the poles comprising an encapsulated pole unit comprising: a first unit comprising: a first conductor, a second conductor, a vacuum interrupter electrically connected between the first conductor and the second conductor, and a first housing housing the vacuum interrupter, and a removable second unit comprising: a third conductor, a fourth conductor including a first portion electrically connected to the third conductor and a second portion removably electrically connected to one of the first conductor and the second conductor, an electronic device structured to sense the characteristic, and a second insulative housing encapsulating the third conductor, the first portion of the fourth conductor and the electronic device; and an operating mechanism structured to open and close the vacuum interrupter of each of the poles. 
     The second conductor may be below the first conductor; and the second portion of the fourth conductor may be removably electrically connected to the second conductor. 
     The electronic device may be a voltage sensor comprising a capacitive voltage divider structured to sense the voltage. 
     In accordance with another aspect of the invention, an encapsulated pole unit includes a characteristic and comprises: a first unit comprising: a first conductor, a second conductor, a vacuum interrupter electrically connected between the first conductor and the second conductor, and a first housing housing the vacuum interrupter; and a removable second unit comprising: a third conductor, a fourth conductor including a first portion electrically connected to the third conductor and a second portion removably electrically connected to one of the first conductor and the second conductor, an electronic device structured to sense the characteristic, and a second insulative housing encapsulating the third conductor, the first portion of the fourth conductor and the electronic device. 
     The electronic device may be selected from the group consisting of a current sensor, a temperature sensor, a partial discharge sensor and a voltage sensor. 
     As another aspect of the invention, an encapsulated pole unit conductor assembly includes a characteristic and comprises: a first conductor; a second conductor electrically connected to the first conductor, the second conductor being structured to be removably electrically connected to a pole unit of a circuit interrupter; an electronic device structured to sense the characteristic; and an insulative housing encapsulating the first conductor and the electronic device, the insulative housing being structured to be mounted with respect to the circuit interrupter along with a number of other encapsulated pole unit conductor assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is an isometric view of an encapsulated pole unit in accordance with embodiments of the invention. 
         FIG. 2  is an exploded isometric view of the encapsulated pole unit of  FIG. 1 . 
         FIG. 3  is a partial cross-sectional view of the encapsulated pole unit of  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a removable bottom conductor assembly for an encapsulated pole unit in accordance with another embodiment of the invention. 
         FIG. 5  is a vertical end elevation view of the removable bottom conductor assembly of  FIG. 4 . 
         FIGS. 6 and 7  are cross-sectional views of removable bottom conductor assemblies for encapsulated pole units in accordance with other embodiments of the invention. 
         FIG. 8  is an isometric view of a three-pole circuit breaker in accordance with another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Directional phrases used herein, such as, for example, left, right, upper, lower, above, below, clockwise, counterclockwise and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     As employed herein, the term “fastener” refers to any suitable connecting, tightening or fastening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts. 
     As employed herein, the statement that two or more parts are “coupled” together means that the parts are joined together either directly or joined through one or more intermediate parts. 
     As employed herein, the term “number” means one or an integer greater than one (i.e., a plurality). 
     As employed herein, the term “encapsulated” means at least substantially surrounded by a number of insulative structures. 
     As employed herein, the term “encapsulating” means at least substantially surrounding a conductive structure by a number of insulative structures. For example, when a conductive structure is encapsulated by a number of insulative structures, the conductive structure is at least substantially embedded within such number of insulative structures. 
     As employed herein, the term “characteristic” means a trait, a quality, or a property of a structure that is capable of being sensed, such as, for example and without limitation, a voltage, a current or a temperature. 
     As employed herein, the term “sensed” means to perceive or detect by an electronic device, such as a sensor or detector. 
     As employed herein, the term “electronic device” include devices structured to sense a number of characteristics of a structure. Electronic devices include, for example and without limitation, voltage sensors, current sensors, partial discharge sensors and temperature sensors. 
     The invention is disclosed in association with a medium voltage vacuum circuit breaker having three independent poles, although the invention is applicable to a wide range of circuit interrupters (e.g., without limitation, reclosers, circuit switching devices and other interrupters, such as contactors, motor starters, motor controllers and other load controllers) including any suitable count of poles for a wide range of voltages. 
     Referring to  FIGS. 1-3 , an encapsulated pole unit  2  includes a number of embedded sensors  4 , 6  (shown in  FIG. 3 ), as will be discussed. The example sensors  4  and  6  are electronic devices structured to sense characteristics of a circuit interrupter pole corresponding to the encapsulated pole unit  2 , such as, for example and without limitation, current and temperature, respectively. However, a wide range of electronic devices for other characteristics of circuit interrupter poles may be employed, such as for example and without limitation, partial discharge sensors and voltage sensors. The encapsulated pole unit  2  includes a first unit  8  including a first conductor  10 , a second conductor  12 , a vacuum interrupter  14  electrically connected between the first conductor  10  and the second conductor  12 , and a first housing  16  housing the vacuum interrupter  14 . The encapsulated pole unit  2  also includes a removable second unit  18  including a third conductor  20 , a fourth conductor  22  including a first portion  24  electrically connected to the third conductor  20  and a second portion  26  removably electrically connected to one of the first and second conductors  10 , 12 . The removable second unit  18  forms an encapsulated pole unit conductor assembly. Preferably, the first housing  16  is an insulative housing, such as an outer silicone sleeve, encapsulating the vacuum interrupter  14 . Although the third and fourth conductors  20 , 22  are shown as separate distinct structures, it will be appreciated that the third and fourth conductors  20 , 22  may be parts of a single integrated structure. 
     In the example of  FIGS. 1-3 , the second portion  26  is removably electrically and mechanically connected to the second conductor  12 , as will be explained. A second insulative housing  28  encapsulates the third conductor  20 , the first portion  24  of the fourth conductor  22  and the example sensors  4 , 6 . The second conductor  12  is below the first conductor  10  with respect to  FIGS. 1-3 . The vacuum interrupter  14  includes an upper conductor  30 , which is electrically connected to the first conductor  10 , and a lower conductor  32 , which is electrically connected to the second conductor  12 . The lower conductor  32 , which is the movable contact of the separable contacts  180  ( FIG. 8 ), is preferably electrically connected to the second conductor  12  by a pair of conductive spring contacts  33 . A conductive spring housing  35  carries the lower conductor  32  and the spring contacts  33  and is movably coupled to the drive rod assembly  72 . 
     Although two example embedded sensors  4 , 6  are shown, one, three or more embedded sensors may be employed. The example encapsulated pole unit  2  also includes a removable top conductor assembly  34  in addition to the removable second unit  18 , which is a removable bottom conductor assembly having the example embedded sensors  4 , 6 . The removable top conductor assembly  34  includes a conductor in the form of a conductive conduit  36  encapsulated with an insulative layer, such as an epoxy layer  38  ( FIG. 3 ). Similarly, the removable bottom conductor assembly  18  includes the third conductor  20  in the form of a conductive conduit encapsulated with an insulative layer, such as an epoxy layer  40  ( FIG. 3 ). The removable bottom conductor assembly  18  also includes a section formed as an epoxy mold  42 . 
     As shown in  FIGS. 2 and 3 , a first threaded plug, such as conductive disk  44 , is threaded into a first end  46  of the conductive conduit  36  ( FIG. 3 ). Similarly, the fourth conductor  22  is threaded plug, such as a conductive disk, threaded into a first end  48  of the conductive conduit  20  ( FIG. 3 ). A suitable fastener, such as a lock washer  50  and a bolt  52 , removably couple the conductive conduit  36  through the conductive disk  44  to the first conductor  10 , which is the fixed top conductor of the pole unit  2 . In a similar manner, a suitable fastener, such as a lock washer  54  and a bolt  56 , removably couple the conductive conduit  20  through the fourth conductor  22  to the second conductor  12 , which is the fixed bottom conductor of the pole unit  2 . A third threaded plug, such as conductive disk  58 , is threaded into the opposite second end  60  of the conductive conduit  36  ( FIG. 3 ), and a fourth threaded plug, such as conductive disk  62 , is threaded into the opposite second end  64  of the conductive conduit  20 . Then, two finger cluster assemblies  66  are coupled to the conductive disks  58 , 62  with suitable fasteners, such as lock washers  68  and bolts  70 . As is conventional, the vacuum interrupter  14  is driven by a drive rod assembly  72 . The first unit  8  also includes an insulative section formed as an epoxy mold  74 . 
     In the example of  FIGS. 1-3 , an embedded air core coil, such as the example Rogowski coil  4 , and an embedded temperature sensor  6  are mounted within the removable bottom conductor assembly  18  of the encapsulated pole unit  2 . The Rogowski coil  4  is a current sensor. Alternatively, the embedded air core coil may be a current transformer. Alternating current (AC) current flows through the conductive conduits  36 , 20  at the respective top and bottom of the encapsulated pole unit  2 . Preferably, the example Rogowski coil  4  is separated from the conductive conduit  20  with about 0.25 inch to about 0.50 inch of a suitable epoxy insulator. One difference between the upper and lower removable conductor assemblies  34 , 18  is that the removable bottom conductor assembly  18  includes the embedded sensors  4 , 6 . Hence, if something were to go wrong with any one or more of those sensors  4 , 6 , then the removable bottom conductor assembly  18  could be readily replaced instead of replacing the entire encapsulated pole unit  2 , which would be relatively more costly. 
     The following discussion assumes that a load terminal and the corresponding load voltage are provided at the lower finger cluster assembly  66  ( FIGS. 1-3 ) and that the corresponding line voltage is present at the upper finger cluster assembly  66  ( FIGS. 1-3 ). It will, however, be appreciated that these example voltages may be reversed. In this example, the AC current is the current at load side, and the example Rogowski coil  4  is structured to sense the current at load side. If the voltages are reversed, then the Rogowski coil  4  senses the current at line side and the conductive conduit  20  is a line conductor. The conductive conduit  20  is a generally cylindrical conductor including the end portion  48 . The Rogowski coil  4  includes a generally circular opening  49  disposed about the generally cylindrical conductive conduit  20  proximate the end portion  48  thereof. The fourth conductor  22  is disposed from that end portion  48 . 
     The example temperature sensor  6  is structured to sense the temperature of the adjacent conductive conduit  20 , which is a load conductor in this example. For example, the conductive conduit  20  is a generally cylindrical conductor including an elongated generally cylindrical surface. The temperature sensor  6  is disposed proximate that elongated generally cylindrical surface as shown in  FIG. 3 . 
     Preferably, the external insulation  38 , 40 , 42 , 74  of the encapsulated pole unit  2  is a suitable epoxy that supports all the internal components thereof (e.g., the epoxy is molded around them). The encapsulated pole unit  2  is insulated in order to avoid a voltage breakdown issue (e.g., a Lightning Impulse Withstand Voltage (LIWV) or Basic Impulse Level (BIL) test requirement). Shielded internal electrical connections enable characteristic sensing, such as current and voltage sensing, as will be discussed below in connection with  FIGS. 4-7 . 
       FIGS. 4 and 5 ,  6 , and  7  show examples of other removable bottom conductor assemblies  76 ,  78 , and  80 , in which the voltage sensor is a capacitive voltage divider  82 ,  84 , and  86 , respectively, structured to sense the line or load voltage. These example voltage dividers employ two capacitors to divide the relatively high line or load voltage and output a relatively much lower output voltage. For example, the line or load voltage at the vacuum interrupter  14  ( FIG. 3 ) is provided to the corresponding one of the voltage dividers  82 , 84 , 86 . Except for these voltage sensors  82 , 84 , 86 , the removable bottom conductor assemblies  76 , 78 , 80  are the same as or similar to the removable bottom conductor assembly  18  of  FIGS. 1-3 . Hence, it will be appreciated that the example removable bottom conductor assemblies  76 , 78 , 80  are usable with the first unit  8  of  FIGS. 1-3 . 
     The following discussion assumes that a line terminal and the corresponding line voltage are provided at the lower finger cluster assembly  66  ( FIGS. 1-3 ) and that the corresponding load voltage is present at the upper finger cluster assembly  66  ( FIGS. 1-3 ). It will, however, be appreciated that these example voltages may be reversed. 
       FIGS. 4 and 5  show the example voltage divider voltage sensor  82 , which is in the form of a double cup assembly. The voltage sensor  82  includes a first bell-shaped conductive member  88  electrically connected to the second conductor  20 , a second bell-shaped conductive member  90  electrically connected to ground  92 , an elongated insulative member  94  disposed between the first and second bell-shaped conductive members  88 , 90 , and a conductive ring  96  disposed about the elongated insulative member  94  and between the first and second bell-shaped conductive members  88 , 90 . The conductive ring  96  and the second bell-shaped conductive member  90  output a second voltage  98 , which is substantially smaller than the voltage between the second conductor  20  and ground  92 . 
     Although the voltage sensor  82  is described, above, as being suitable for sensing a line or load voltage, it will be appreciated that the voltage sensor  82  is also suitable for sensing a partial discharge of the second conductor  20 . For example, when a partial discharge is occurring, the line-to-load voltage drops to the discharge voltage, which usually is about a few hundred volts to about a thousand volts, and is much lower than the line voltage. Partial discharge voltage values are sensed from voltage differences between the line or load voltage and ground  92 . A printed circuit board (PCB)  102  senses the voltage differences by using the example voltage sensor  82 . The voltage sensor  82  includes the two bell-shaped conductive members  88 , 90 , which have electrical potentials of the line or load voltage and ground, respectively. The upper bell-shaped conductive member  88  is preferably directly electrically connected to the adjacent second conductor  20 . The lower bell-shaped conductive member  90  is electrically connected to ground  92  by a number of ground conductors  100 . The capacitive voltage divider  82 , is formed by the example rod  94 , which is disposed between the two bell shaped conductive members  88 , 90 . The rod  94  is an insulator with a conductive coated ring or solid conductive ring  96  disposed on it and somewhat closer to the lower bell-shaped conductive member  90 , in order to form the capacitive voltage divider  82 . The PCB  102  includes a first electrical connection  104  to ground  92  and a second electrical connection  106 , which forms the tap of the capacitive voltage divider  82 . The upper bell shaped conductive member  88  and the conductive ring  96  form a first capacitor. The lower bell shaped conductive member  90  and the conductive ring  96  form a second capacitor that outputs the voltage  98 , which is proportional to the line voltage, but significantly smaller. Alternatively, the conductive ring  96  can be a conductive plate (not shown). 
     The example removable bottom conductor assembly  76  further includes a Rogowski coil assembly  108  having an output  110  to the PCB  102 , which is referenced to ground  92  by the conductor  112 , and a parasitic power supply  114  having an output  116  to the PCB  102 . 
       FIG. 6  shows the voltage sensor  84  in the example form of a double plate assembly. The capacitive voltage divider  84  includes an elongated insulative member  118  having a first end  120  engaging the second conductor  20  and an opposite second end  122 . A first conductive ring member  124  is disposed about the elongated insulative member  118  and is electrically connected to ground  92  by a number of conductors  126 , 128 . A second conductive ring member  130  is disposed about the elongated insulative member  118  and is apart from and between the first end  120  thereof and the first conductive ring member  124 . The first and second conductive ring members  124 , 130  output a voltage  132 , which is substantially smaller than the line voltage between the second conductor  20  and ground  92 . These example conductive ring members  124 , 130 , which may alternatively be conductive plates (not shown), along with the elongated insulative member  118  form the capacitive voltage divider  84 . The voltage  132  is input by the PCB  134  through conductors  136 , 138 . The PCB  134 , thus, receives both the voltage sensor output and ground  92  through the conductors  136 , 138 . 
     The example removable bottom conductor assembly  78  further includes a Rogowski coil assembly  140  having an output  142 , and a parasitic power supply  144  having an output  146 . Both of the outputs  142 , 146  are received by the PCB  134 . 
       FIG. 7  shows the voltage sensor  86  in the example form of an integrated current and voltage sensing assembly. The capacitive voltage divider  86  includes a first conductive ring-shaped member  148  surrounding and spaced apart from the generally cylindrical second conductor  20 , and a second conductive ring-shaped member  150  surrounding and spaced apart from the first conductive ring-shaped member  148 . The second conductive ring-shaped member  150  is electrically connected to ground  92  by a number of conductors  152 , 154 . The example first and second conductive ring-shaped members  148 , 150  are at least generally concentric and output a voltage, with respect to ground  92 , which voltage is substantially smaller than the line voltage. 
     The example second conductive ring-shaped member  150  has an example generally U-shaped cross-section. A current sensor, such as a coil  158 , surrounding and spaced apart from the second conductor  20  is disposed within the generally U-shaped cross-section. The example coil  158  is preferably a Rogowski coil. The Rogowski coil  158  and the capacitive voltage divider  86  cooperate to form an integrated voltage and current sensor. A parasitic power supply  160  includes an output  162 . A PCB  164  receives the output  162  and the voltage through the conductors  165  and  156 , respectively. The PCB  164  receives the ground  92  through conductors  154 , 152 , 153 . 
     For each of the capacitive voltage dividers  82 , 84 , 86  of  FIGS. 4-7 , Equation 1, below, provides the secondary voltage output, V OUTPUT .
 
 V   OUTPUT   =V   LINE   *C 1/( C 1 +C 2)  (Eq. 1)
 
wherein:
 
V LINE  is the line or load voltage;
 
C 1  is the capacitance of the first capacitor; and
 
C 2  is the capacitance of the second capacitor.
 
     Referring to  FIG. 8 , a circuit interrupter, such as a medium voltage vacuum circuit breaker  170 , includes a circuit interrupter housing  172  and three independent poles  174 , 176 , 178 . Each of the independent poles  174 , 176 , 178  includes separable contacts  180  (shown in hidden line drawing with pole  178 ), a number of sensors (e.g., a corresponding one of the example capacitive voltage divider  86  of  FIG. 7 , which includes the Rogowski coil  158 ), and a linkage  182  to the drive rod assembly  72  ( FIG. 3 ). The medium voltage vacuum circuit breaker  170  also includes an operating mechanism  184  structured to open and close the vacuum interrupter  14  ( FIG. 3 ) of each of the poles  174 , 176 , 178  through the linkages  182  and drive rod assemblies  72 . 
     For each of the poles  174 , 176 , 178 , the circuit breaker  170  includes an encapsulated pole unit  2 ′, which is similar to the encapsulated pole unit  2  ( FIGS. 1-3 ) except that the removable bottom conductor assembly  80  of  FIG. 7  is employed in this example. Alternatively, any of the removable bottom conductor assemblies  18 ,  76  and  78  of  FIGS. 1-3 ,  4  and  5 , and  6 , respectively, can be employed. The example removable bottom conductor assembly  80  forms an encapsulated pole unit conductor assembly. The example section  42  ( FIGS. 1-3 ) formed as an epoxy mold encapsulates the conductor  20 , the example capacitive voltage divider  86  and the example Rogowski coil  158  of  FIG. 7 . The resulting insulative housing is, thus, mounted with respect to the circuit interrupter  170  along with two additional encapsulated pole units  2 ′ having corresponding removable bottom conductor assemblies  80  (as shown with pole  178 ). 
     Although the capacitive voltage divider  86  of  FIG. 7  is shown as an example sensor, any suitable sensor may be employed for sensing a number of the characteristics of a pole of the example medium voltage vacuum circuit breaker  170 . For example and without limitation, the encapsulated pole unit  2  of  FIGS. 1-3  may be employed with the removable bottom conductor assembly  18  thereof, or with the removable bottom conductor assemblies  76  ( FIGS. 4 and 5 ) or  78  ( FIG. 6 ). 
     The disclosed encapsulated pole unit  2 ′ permits the example medium voltage circuit interrupter  170  to be relatively small compared to known circuit interrupters. 
     The disclosed removable bottom conductor assembly  18  encapsulates the various sensors. In known circuit interrupters, such sensors are in the switchgear, which causes the overall assembly to be much larger. Also, this enables the encapsulated pole unit  2  or  2 ′ to be certified as a complete tested assembly. This eliminates further extensive testing by a supplier because the complete assembly is pre-tested versus separate sub-assemblies being tested separately. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.