Patent Publication Number: US-9837224-B2

Title: Switchgear assembly

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a switchgear assembly and to a method for operating a switchgear assembly, in particular a ring cable switchgear assembly, by means of which a consumer or a generator is connected to an energy line of an energy distribution system. 
       FIG. 1  shows a schematic detail of an energy distribution system with a ring circuit. In this case, the electrical energy flow is passed via a ring or a ring cable  102 , to which spurs are connected, which are used for further supply and distribution. These spurs are configured as switchgear assemblies. In the arrangement shown in  FIG. 1 , these switchgear assemblies are referred to as ring cable switchgear assembly  101  or ring main unit. The ring cables  102  are connected to distribution systems  105 . 
     Such ring cable switchgear assemblies  101  usually have three connection points  103 , wherein two belong to the ring and one connection point is connected to a consumer or a generator. Embodiments with only two connection points are also known. 
     As variants, there are also ring cable switchgear assemblies  101  with more than one spur. All of the assemblies have the common factor that at least the spurs have a device  104  which is suitable for interrupting the flowing current. This interruption is usually achieved using circuit breakers or load break switches. In the sector of medium-voltage and high-voltage applications, often complex addons with circuit breakers and switch disconnectors are used in such circuits. In this case, the circuit breaker often represents the largest, heaviest and most complex individual component, in particular when the switchgear assembly is embodied as a gas-insulated switchgear assembly. 
     This results in complex addons which are sometimes implemented using air-insulated or SF6 gas-insulated technology. 
     For example, wind turbines are often connected to the energy supply grid via the ring cable switchgear assembly  101 . Such a ring cable switchgear assembly  101  is located, for example, at the foot of a tower of the wind turbine. Depending on the voltage level, the circuit and the size of the switchgear assembly, however, an additional building is required for this. Particularly in the case of offshore wind farms and high voltages (33 kV or 66 kV), the space requirement with modern-day technology is enormous; this is also problematic owing to the local conditions. 
     WO 2010/072622 A1 discloses an on-load tap changer for medium-voltage to low-voltage transformers which is based on one or more mechanical switches. During switchover, the current is passed via semiconductor switches in order to ensure the freedom from interruptions. WO 2010/072622 A1 also does not disclose an efficient possibility for a switch disconnector on the primary side of the transformer. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention consists in avoiding the abovementioned disadvantages and in particular in specifying an efficient approach for a ring cable switchgear assembly. 
     This object is achieved according to the features of the independent claims. Preferred embodiments are set forth in particular in the dependent claims. 
     In order to achieve the object, a switchgear assembly is proposed which comprises a thyristor circuit, which is arranged in parallel with a switch disconnector, a transformer, whose primary side is connected to an energy line via the parallel circuit comprising the thyristor circuit and the switch disconnector, wherein the secondary side of the transformer is provided for connection of a generator or a consumer. 
     This makes it possible to achieve efficient electrical disconnection of the generator or consumer from the energy line. The switch disconnector preferably has a certain degree of stability in respect of overvoltages (for example in accordance with the standard IEC62271). For example, the thyristor circuit can be matched flexibly to or designed for a current of up to 4000 A. Thus, the switchgear assembly can be matched in a targeted manner to the power of connected generators, for example wind turbines. This considerably reduces the complexity, the costs, the components required and the required installation space. Precisely for the connection of wind turbines, a switchgear assembly with small dimensions together with the wind turbine (for one or possibly a plurality of wind turbines) can thus be installed in a targeted manner. 
     In particular, the secondary-side circuit can also comprise at least one switchgear assembly. 
     A development consists in that the thyristor circuit is embodied with self-shutdown. 
     Thus, the actuation of the thyristor circuit is simplified. 
     Another development consists in that the thyristor circuit comprises two thyristor elements connected antiparallel. 
     Another development consists in that each thyristor element comprises at least one thyristor or at least one parallel and/or series circuit of thyristors. 
     Other electrical components can also be used jointly with the thyristors. 
     As an alternative to the thyristors, disconnectable semiconductor switches can also be used, in particular transistors, GTOs (Gate Turn-off Thyristors) or IGCTs (Integrated Gate-Commutated Transistors). 
     Particularly advantageously, thyristors consisting of superconductive semiconductor material, for example germanium, can also be used. The advantage in this case lies in the low resistance and the higher short-circuit withstand capability. 
     A development consists in that, in addition to the switch disconnector, a further switch disconnector is arranged in the branch of the thyristor circuit. 
     A development consists in that the switchgear assembly is a ring cable switchgear assembly and in that the energy line is a ring line of an energy distribution system. 
     Another development consists in that the switch disconnector is a gas-insulated switch disconnector, a vacuum interrupter or an air-break disconnector. 
     In particular, a development consists in that the actuation of the switch disconnector and/or the thyristor circuit takes place by means of a control device. 
     For example, the control device can activate or deactivate the thyristor circuit and/or the switch disconnector. The thyristor circuit can be actuated, for example, via a control current or light pulse firing, such as, for example, using the light of a laser diode. 
     For example, the control device can comprise a combination of contactors, relays and switching elements, such as rotary switches, or else can be embodied as a digital control unit, for example for remote control via a control center. The control device can be used to automatically disconnect the current in the event of the occurrence of a grid fault, for example a short circuit, or for switching in a targeted manner in order to actively influence the load flow in the ring cable. 
     Another development consists in that the switchgear assembly is connected to a generator or to a consumer, and wherein the generator or consumer is disconnectable from or connectable to the energy line by means of the switchgear assembly. 
     In addition, a development consists in that the secondary side of the transformer is connectable to the generator or the consumer via a changeover switch or a multiple changeover switch. 
     In respect of further details relating to the multiple changeover switch, reference is made to the document WO 2010/072622 A1 cited at the outset. 
     Within the scope of an additional development, a further thyristor circuit is provided by means of which the changeover switch or a multiple changeover switch is bypassable at least temporarily. 
     The object mentioned at the outset is also achieved by a method for operating a switchgear assembly, comprising a thyristor circuit, which is arranged in parallel with a switch disconnector, wherein the thyristor circuit and the switch disconnector are connected to the primary side of a transformer via an energy line, in which, prior to the switching operation of the switch disconnector, the thyristor circuit is switched so as to be conducting, in which the switch disconnector is opened, and in which the thyristor circuit is switched so as to be isolating. 
     In particular, the thyristor circuit is switched on in order to take over the load current during the switchover of the switch disconnector. 
     A development consists in that, during opening of the switch disconnector, the current is passed completely via the connected thyristor circuit. 
     One configuration consists in that the current through the switch disconnector and/or through the thyristor circuit is measured. 
     Based on this measurement, the switch disconnector and/or the thyristor circuit can be actuated correspondingly. 
     The abovedescribed properties, features and advantages of this invention and the way in which said properties, features and advantages are achieved will become clearer and more easily understandable in connection with the following schematic description of exemplary embodiments, which will be explained in more detail in connection with the drawings. In this case, identical or functionally identical elements can be provided with the same reference symbols for reasons of clarity. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       In the figures: 
         FIG. 1  shows a schematic detail of an energy distribution system with a ring circuit according to the prior art; 
         FIG. 2  shows a schematic ring circuit, which, in addition to the illustration in  FIG. 1 , also has a ring cable switchgear assembly  106 , which is configured in an advantageous manner with respect to the ring cable switchgear assembly  101 ; 
         FIG. 3  shows, in supplementary fashion to  FIG. 2 , a more detailed design of the ring cable switchgear assembly  106 ; 
         FIG. 4  shows, in supplementary fashion to  FIG. 2  and  FIG. 3 , a design of the ring cable switchgear assembly with an additional switch disconnector in the branch of the thyristor circuit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a schematic ring circuit which, in addition to the illustration in  FIG. 1 , also has a ring cable switchgear assembly  106 . The ring cable switchgear assembly  106  can in this case be embodied as an alternative to the ring cable switchgear assembly  101 . As will be explained in more detail below, the ring cable switchgear assembly  106  has some advantages over the ring cable switchgear assembly  101 . 
     Thus, the interruption  104  (for example the circuit breaker) is simplified, which enables a much more efficient design and use of the ring cable switchgear assembly  106 . 
       FIG. 3  shows, by way of supplementing  FIG. 2 , a more detailed design of the ring cable switchgear assembly  106 . 
     Thus, a switching unit  107  is proposed which has a switch disconnector  109 , which enables safe isolation, in combination with a thyristor circuit  111 . The switch disconnector is preferably arranged in parallel with the thyristor circuit  111 . The switching unit  107  enables effective disconnection of the secondary side from the ring cable  102 . 
     The switch disconnector  109  can be embodied as a simple switch or, as shown in  FIG. 3 , provided with an additional grounding function  112 . In combination with the grounding function  112 , the switch disconnector  109  provides the following switching states: on, off and grounded. Preferably, the switch disconnector  109  is embodied as a mechanical switch. 
     A multiple changeover switch  110 , which is arranged in parallel with a thyristor circuit  114 , is provided on the secondary side  108  of the transformer  113 . 
     Shortly prior to the switching operation of the switch disconnector  109  or shortly prior to the switching operation of the multiple changeover switch  110 , the thyristor circuit  111  is fired at least for the duration of the switching operation of the switch disconnector  109  and thus becomes conducting. After termination of the switching operation of the switch disconnector  109 , the thyristor circuit  111  becomes insulating again. 
     A control device  120  can activate or deactivate the thyristor circuit  111  and/or the switch disconnector  109 . For example, the control device  120  can comprise a combination of contactors, relays and switching elements, such as rotary switches, or else can be embodied as a digital control unit, for example for remote control via a control center. 
     By virtue of the proposed switching unit  107 , it is possible to dispense with the circuit breaker or load break switch (cf. device  104  in  FIG. 1 ). It is also possible for a corresponding thyristor circuit  111  to be used in functionally identical fashion as part of the multiple changeover switch of the secondary side  108 . 
       FIG. 4  shows, by way of supplementing  FIG. 2  and  FIG. 3 , a design of the ring cable switchgear assembly  106 , wherein the switching unit  107  in this case has an additional switch disconnector  115  in the branch of the thyristor circuit  111 . 
     By virtue of the proposed solution, the complexity and number of components required are reduced. 
     The invention can also advantageously be used when connecting photovoltaic systems to the supply grid. Furthermore, the invention provides an advantage in respect of costs in the case of the high numbers of components to be expected for future SMART grids. 
     Although the invention has been illustrated and described in detail using the at least one exemplary embodiment shown, the invention is not restricted to this exemplary embodiment and other variants can be derived from this by a person skilled in the art without departing from the scope of protection of the invention.