Patent Publication Number: US-9418810-B2

Title: Multiphase medium voltage vacuum contactor

Description:
RELATED APPLICATIONS 
     This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2012/071924 which was filed as an International Application on Nov. 6, 2012 designating the U.S., and which claims priority to European Application 11191052.7 filed in Europe on Nov. 29, 2011. The entire contents of these applications are hereby incorporated by reference in their entireties. 
     FIELD 
     The present disclosure relates to a multiphase medium voltage (MV) vacuum contactor which is suitable to be connected to an associated multiphase electric circuit. 
     For the purpose of the present disclosure, the term medium voltage refers to applications with nominal operating voltages ranging between about 1 kV and some tens of kV, for example, 3.6 kV, 7.2 kV, 12 kV, or greater. 
     Electric contactors have controlled users/loads involving a high number of hourly operations, for example to switch on/off electric motors, and are directed to satisfying a number of conditions which can be important to guarantee proper functional performances during their service life in electrical networks; for example, switching off maneuvers should be carried out in due time, often as quickly as possible, in order to prevent possible damage to the equipment; the actuating mechanism should be designed so as to ensure an adequate operational repeatability and an optimized reliability, and so on. 
     Examples of known and widely used medium voltage contactors are vacuum contactors; for each phase, they include (e.g., consist essentially of) an interrupter assembly having a sealed evacuated enclosure or chamber surrounding a fixed contact and a movable contact. 
     The movable contacts of the various phases are actuated by an actuator, e.g. an electromagnetic actuator, which is controlled by an associated main control/driving circuit or unit. 
     The contactor can also have some auxiliary circuits, accessories et cetera. 
     All components, e.g. vacuum interrupters, actuators, the main control/driving circuit unit, and auxiliary circuits are mounted on a contactor frame. 
     Current-limiting fuses can be associated to the vacuum interrupters of the contactor in order to deal with fault conditions, e.g. short circuit-currents; current-limiting fuses can be of a disposable type and include a cartridge inside which there is a heat-melting conductor. 
     Today, there are many different constructive solutions of medium voltage contactors which, despite allowing adequate execution of desired performances, still present some aspects which could be further improved. 
     For example, the energy for operating the auxiliary and/or main control circuits of the contactor is fed by components separate and distinct from the whole body of the contactor itself; the same applies for the components used to monitor the correct flow of currents. 
     Some additional protection devices may be also desired; e.g. additional disposable fuses of the type previously mentioned, can be used to specifically protect the elements used to supply the auxiliary and/or main control circuits. 
     Clearly, such aspects are not entirely satisfying since they can entail specific cabling and space occupation which in some cases can create practical difficulties, for example, when considering that contactors are often installed in switchgear panels wherein available spaces can be limited and maybe also difficult to access. 
     SUMMARY 
     A multiphase medium voltage vacuum contactor is disclosed for connection to an associated multiphase electrical circuit, comprising: a mounting frame on which there are positioned: for each phase, a current interrupter for operative connection to a corresponding phase of a multiphase electrical circuit, said current interrupter having a vacuum bulb which contains a fixed contact and a corresponding movable contact; an actuator for moving the movable contacts between a closed position where the movable contacts are coupled each to a corresponding fixed contact and an open position where the movable contacts are each electrically separated from the corresponding fixed contact; an electronic unit driving the actuator; a voltage transformer for feeding said electronic unit, the voltage transformer being mounted on said frame and at least partially encased by an electrically insulating coating; and one or more sacrificial fault-protection devices which are operatively associated to said voltage transformer and are embedded into said electrically insulating coating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages will become apparent from the description of exemplary preferred but not exclusive embodiments of a multi-phase medium voltage vacuum contactor according to the disclosure, illustrated by way of non-limitative examples in the accompanying drawings, wherein: 
         FIG. 1  is a perspective view showing an exemplary multiphase medium voltage vacuum contactor according to the present disclosure, seen from the front; 
         FIGS. 1 a    and  2  are perspective views showing the multiphase medium voltage vacuum contactor of  FIG. 1 , with some components omitted for the sake of better illustration; 
         FIG. 3  is a plan view of  FIG. 2 ; 
         FIG. 4  is a plan view of the multiphase medium voltage vacuum contactor of  FIG. 1 ; 
         FIG. 5  is a perspective view schematically illustrating an exemplary sacrificial fault protection device usable in a multiphase medium voltage vacuum contactor according to the present disclosure; 
         FIG. 6  is a perspective view illustrating in detail two exemplary sacrificial fault protection devices associated with a voltage transformer in a multiphase medium voltage vacuum contactor according to the present disclosure; 
         FIG. 7  is a perspective view illustrating three exemplary current monitoring devices associated with a voltage transformer in a multiphase medium voltage vacuum contactor according to the present disclosure; and 
         FIG. 8  is a schematic view illustrating a block diagram of exemplary components used in a multiphase medium voltage vacuum contactor according to the present disclosure. 
     
    
    
     It should be noted that in the detailed description that follows, identical or similar components, either from a structural and/or functional point of view, have the same reference numerals, regardless of whether they are shown in different embodiments of the present disclosure; it should also be noted that in order to clearly and concisely describe the present disclosure, the drawings may not necessarily be to scale and certain features of the disclosure may be shown in somewhat schematic form. 
     The present disclosure is directed to improving the constructive layout of known contactors. 
     Exemplary embodiments are directed to a multiphase medium voltage vacuum contactor which is suitable to be connected to an associated multiphase electrical circuit and can include:
         a mounting frame on which there are positioned:   for each phase, a current interrupter suitable to be operatively connected to a corresponding phase of the multiphase electrical circuit, the current interrupter including a vacuum bulb which contains a fixed contact and a corresponding movable contact;   an actuator for moving the movable contacts between a closed position where the movable contacts are coupled each to a corresponding fixed contact and an open position where the movable contacts are each electrically separated from the corresponding fixed contact;   an electronic unit driving the actuator;   a voltage transformer for feeding the electronic unit, the voltage transformer being mounted on the frame and at least partially encased by an electrically insulating coating; and   one or more sacrificial fault-protection devices which are operatively associated to the voltage transformer and are embedded into the electrically insulating coating.       

     An exemplary multiphase medium vacuum contactor according to the present disclosure will be described by making reference to an exemplary three-phase medium voltage vacuum contactor; clearly, the following description can be applied to a multiphase medium vacuum contactor having any suitable number of poles or phases. 
       FIGS. 1-4  show an exemplary three-pole (or three-phase) medium voltage vacuum contactor generally indicated by the reference numeral  100 , hereinafter referred to as the “contactor  100 ” for the sake of simplicity. 
     According to well-known solutions, each of the phases or poles of the contactor  100  is suitable to be connected to an associated phase of an electrical circuit in which the contactor is used, which circuit phases are all schematically illustrated in  FIG. 8  with the reference number  101 . 
     The contactor  100  can include a mounting frame  10  which can be formed by one single mono-bloc or by two or more pieces connected together. 
     For instance, in the exemplary embodiment illustrated in  FIGS. 1-4 , the frame  10  includes a first mono-bloc, realized for example with electrically insulating material, which has a couple of side walls  11 , and an intermediate region having intermediate walls  12  parallel to the side walls  11 ; the mono-bloc is mechanically connected to a base wall  13  which, in the exemplary embodiment illustrated, is for instance made of metallic material. 
     The contactor  100  can include, for each phase, a current interrupter which is mounted on the frame  10 , e.g. between a side wall  11  and the adjacent intermediate wall  12 , or between two adjacent intermediate walls  12 , and is suitable to be operatively connected to a corresponding phase  101  of the associated multiphase electrical circuit. 
     As better visible in  FIGS. 2 and 3 , each current interrupter includes a vacuum bulb or bottle  1  which contains a fixed contact  2  and a corresponding movable contact  3  (illustrated for simplicity only for one pole in  FIG. 3 ); possible constructional embodiments of the bulb  1  and ways in which the vacuum is maintained inside it are widely known in the art and therefore are not described in details herein. 
     At the top part of the frame  10 , and according to well-known solutions, there is placed a fuse holder  9  for housing current-limiting fuses for example of traditional types, e.g. with cartridges containing each a corresponding heat-melting conductor. 
     On the frame  10  there is mounted an actuator  20  which is for instance connected to the base wall  13  and is suitable to move the movable contact  3  of each phase of the contactor  100  between a closed position where the movable contacts  3  are coupled each to a corresponding fixed contact  2 , and an open position where the movable contacts  3  are each electrically separated from the corresponding fixed contact  2 , according to solutions well known in the art or readily available to those skilled in the art. 
     As a person skilled in the art would appreciate, any suitable type of actuator can be used; for instance, the actuator  20  can be an electromagnetic actuator, e.g. a permanent-magnet actuator marketed by the ABB® group under the name of MAC. 
     An electronic unit, which is also positioned on the frame  10  and is schematically represented in  FIGS. 1 and 1   a  by the reference number  40 , controls and drives the operation of the actuator  20  according to solutions well known in the art and therefore not described in detail herein. Also the electronic unit  40  can be constituted by any suitable electronic unit available on the market; for example the electronic unit  40  can be constituted by an electronic device type MAC R2 marketed by the ABB® group. 
     The contactor  100  includes a voltage transformer  30  for feeding the electronic unit  40 ; as illustrated, the voltage transformer  30  is positioned directly on board on the contactor  100 , namely mounted on the frame  10 , and is least partially, for example, completely, encased by an electrically insulating coating  31 , made for example of resin such as any suitable epoxy or polyurethane resin already available on the market. 
     For the sake of better illustrating some internal parts, the insulating coating  31  is not shown in  FIGS. 1 a   ,  2 ,  3 , while it is shown partially cut in  FIGS. 6 and 7 . 
     The voltage transformer  30  is adapted (e.g., configured) to be electrically connected, once installed, only to two phases of the associated electric circuit  101 , e.g. a first side phase and a second side phase schematically indicated in the  FIGS. 6, 7 and 8  by the reference letters “R” and “T”, respectively. 
     In the exemplary embodiment illustrated, the voltage transformer  30  is positioned at the front, upper part of the contactor  100  close to the vacuum interrupters and between the two side walls  11  of the frame  10 ; as better illustrated in  FIG. 4 , some support dumpers  14 , made for example of rubber, are positioned between and operatively connect the lower part of the voltage transformer  30  and the frame  10 . 
     The voltage transformer  30  can include a magnetic core  32  on which there are wound a primary winding  33  which is suitable to be electrically connected to the first and second phases “R”, “T” of the multiphase electrical circuit  101 , and a secondary winding  34  which is suitable to feed power to the electronic unit  40  at the suitable voltage. 
     The primary winding  33  is for example realized in two or more sections which are wound on the magnetic core  32  spaced apart from each other and are electrically connected in series. 
     In the exemplary embodiments illustrated, the primary winding  33  includes at least a first lateral section  33   a , a second central section  33   b  and a third lateral section  33   c  which are wound on the magnetic core  32  spaced apart from each other, and are electrically connected in series. 
     The central section  33   b  can be formed by a unique part as illustrated for example in  FIGS. 6-7 , or it can be split in two or more subsections. 
     One or more sacrificial fault-protection devices, schematically illustrated in figures by the reference number  50 , are operatively associated to the voltage transformer  30  and are embedded into the electrically insulating coating  31 . 
     As schematically illustrated in  FIG. 5 , the one or more sacrificial fault-protection devices  50  can each include an electrically insulating board or support  51  on which there is securely fixed, e.g. printed, at least one track  52  of electrically conductive material; the at least one track  52  is adapted to melt when the level of current flowing in it exceeds a predefined threshold which can be set based on the specific application. 
     For example, the board  51  can be made of ceramic, or fiber-glass, or plastics or any other suitable material or combination of materials; the track  52  can be made of copper, or silver, or any other suitable electrically conductive material or combination of materials. 
     As it will be appreciated by those skilled in the art, the track  52  can be easily sized according to the specific applications, for example using Onderdonk&#39;s or Preece&#39;s equations. 
     In the embodiments illustrated, the contactor  100  can include two sacrificial fault protection devices  50 . 
     For example, a first sacrificial fault-protection device  50  and a second sacrificial fault-protection device  50  are positioned form an electrical point of view upstream and downstream the primary winding  33  of the voltage transformer  30 , respectively; the first sacrificial fault-protection device  50 , the primary winding  33  and the second sacrificial fault-protection device  50  are electrically connected in series one next to the other. 
     As illustrated in  FIG. 6 , the first sacrificial fault-protection device  50  is embedded into the electrically insulating coating  31  at a position between the first and second sections  33   a ,  33   b , while the second sacrificial fault-protection device  50  is embedded into the electrically insulating coating  31  at a position between the second and third sections  33   b ,  33   c.    
     The exemplary contactor  100  according to the present disclosure can further include one or more current monitoring devices  60  that are also embedded into the electrically insulating coating  31 ; for example, in the exemplary embodiment illustrated in  FIG. 7 , for each phase there is a corresponding current monitoring device  60 . 
     Each current monitoring device  60  can include a supporting board  61  on which there are securely mounted a current sensor  62  and an associated microprocessor-based unit  63  which is operative communication with the electronic unit  40 . 
     For example, also in this case the support board  61  can be made of ceramic, or fiber-glass, or plastics or any other suitable material or combination of materials; and the current sensor  62  and/or the microprocessor-based unit  63  can be printed on the support board  63 . 
     For example, the current sensor  62  is a Hall-effect current sensor; in turn, the microprocessor-based unit  63  can be constituted by any suitable device available on the market, e.g. a microcontroller MSP430 marketed by Texas Instruments. 
     In practice when the contactor  100  is installed, the first sacrificial protection  50  is electrically connected in series between the first lateral phase “R” of the associated circuit  101  and the primary winding  33  of the voltage transformer  30 , while the second sacrificial fault protection device  50  is connected in series between the primary winding  33  and the second lateral phase “T” of the circuit  101 . For example, such current connections between the phases of the contactor  100  and the phases of the circuit  101  occur through the bolted terminals  102 . 
     The current monitoring devices  60  are each associated to the corresponding phase  101  with the current sensors  62  at a certain distance from the current conducting conductors. 
     In exemplary normal operating conditions, the current flows through the sacrificial fault-protection devices  50  and the voltage transformer  30  which feeds the electronic unit  40  (as well as other auxiliary circuits when present) with a power at a suitable level of transformed voltage. 
     In turn, each microprocessor-based unit  63  receives from the respective current sensor  62  signals of the current detected and outputs to the electronic unit  40  corresponding signals indicative of the current flowing into the corresponding phase of the multiphase electrical circuit  101 . 
     If there is a fault in the windings of the voltage transformer  30 , e.g. a short circuit, the overcurrent flowing along the track  52  heats up the track  52  itself until it melts and interrupts the flow of current. In practice the protection devices, and in particular the tracks  52 , are calibrated so as they start to melt down when the current flowing through them exceeds a defined threshold; such threshold represents in practice an equilibrium level at which there is a balance between heating of the track  52  due to the flow of current and cooling of the track itself through the supporting board  51  and/or the surrounding insulating coating  31 . 
     Hence, in case of over-currents above the defined threshold, the protection devices  50  sacrifice themselves but avoid damages on the closing parts of the voltage transformer  30  and in particular that the voltage transformer may blow up after an internal fault. Indeed, without the sacrifice of the protection devices  50  the voltage transformer  30  could even explode or catch on fire thus creating very dangerous and damaging conditions for the surrounding parts. Once the protection devices have intervened, the voltage transformer  30  together with the components embedded therein can be disposed and replaced by new ones. 
     In turn, the electronic unit  40  can be properly adapted, e.g. with software and/or electronic circuitry, to exploit the signals supplied by the various current monitoring devices. Indeed, it is possible for instance to easily set related thresholds and perform protection interventions for fault conditions regarding for example unbalanced phases, locked rotors (when the contactor is used to protect motors), thermal memory, et cetera. 
     In practice it has been found that exemplary medium voltage vacuum contactors according to the disclosure can provide improvements over the known prior art. 
     Indeed, as described herein and differently from known contactors, the contactor  100  can be a stand-alone device where the basic elements are directly on board on it; the voltage transformer  30  together with the components embedded therein form a sub-unit which can be easily mounted on board of the contactor  100  itself and easily replaced. Thanks to the division of the primary winding into sections and to the physical positioning of the sacrificial protection devices  50  in the insulating coating and between the winding sections, the voltage distribution over the primary winding of the voltage transformer and space occupation can be optimized at the same time. 
     These results can be achieved with a structure which is quite simple, compact and effective; as disclosed, for example the sacrificial protection devices  50  and/or the current monitoring devices  60  can be produced very simply as printed circuit boards. 
     This makes the contactor easy to be used in electric switchgear panels of the type having a cabinet internally divided into one or more compartments one of which accommodates a contactor  100 . Hence, the present disclosure encompasses also an electric switchgear panel having a multiphase medium voltage vacuum contactor as described herein. 
     The contactor  100  can be suitable for modifications and variations, all of which are within the scope of the inventive concept as defined by the appended claims and including any combination of the herein described embodiments; for example, depending on the applications, the frame  10  can be formed in a unique body, or it can include two or more pieces, or if the contactor is in the form of a withdrawable contactor, it can include a sliding truck, et cetera. The sacrificial devices  50  can be differently shaped; for instance, the track  52  can be formed by one or more layers of conductive material(s), where the material can be the same for all layers, or different materials can be used. For each sacrificial device there could be only one track or more tracks, e.g. fixed on different faces of the support board  51 . Track(s) can extend along any suitable path, e.g. rectilinear as illustrated in  FIG. 5 , curved, segmented (as illustrated in  FIG. 6 ), mixed et cetera. 
     In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to desired specifications and the state of the art. 
     It will thus be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.