Patent Publication Number: US-11038347-B2

Title: Overvoltage protection for power systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 15/487,690, filed Apr. 14, 2017, which application claims priority to Ser. No. 14/185,458, filed Feb. 20, 2014, now U.S. Pat. No. 9,660,441 which application claims from U.S. Provisional Patent Application Ser. No. 61/767,143, filed Feb. 20, 2013; U.S. Provisional Patent Application Ser. No. 61/817,762, filed Apr. 30, 2013; and U.S. Provisional Patent Application Ser. No. 61/880,345, filed Sep. 20, 2013; which applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to power system features, and in particular to an overvoltage protection arrangement for power systems. 
     BACKGROUND 
     Traditionally, critical electrical systems are required to be protected against over voltages caused by faults in such electrical systems. These faults can generate much higher than normal currents and voltages across critical devices and can exceed their safe limit. For example, power systems, which correspond to an example of critical infrastructure, can experience ground faults, which result in high voltage signals being grounded, causing a current spike through equipment, and often causing damage to critical electrical equipment. 
     Systems have historically been developed that protect such systems during fault events. For example, in some cases, a spark gap was historically used to allow relief of overvoltage events, by allowing for a spark to form across an open air gap or in a non-combustible gas within a container to cause relief of voltage events that exceed a predetermined threshold. However, spark gaps are highly variable, and the voltage that causes such a spark to occur can vary by up to 10%-15% based on humidity and condensation or other environmental conditions. Furthermore, the total amount of energy that can be dispersed via the spark gap before the gap electrode material is destroyed by the energy of the electrical arc. 
     In more recent protection systems, surge arresters have been placed in parallel with power line transformers to protect during lightning strikes, ground faults, or other voltage and/or current spike conditions. In such circumstances, surge arresters provide voltage clipping at a first threshold, in which overvoltage events can be routed to ground without damaging electrical systems positioned in parallel with such surge arresters. The surge arresters have a limit to the amount of energy they can shunt to ground. If the event continues after that energy limit is exceeded, the surge arrester enters a pressure relief mode. In this event, the surge arrester is designed to safely carry the current to ground and to limit the voltage on the protected system (e.g. as described in IEEE C62.11) but is unusable afterwards. 
     Accordingly, the various systems and methods that have been used experience disadvantages in operation that render them, at times, to be suboptimal for reliable protection for electrical systems. 
     SUMMARY 
     In accordance with the following disclosure, the above and other issues are addressed by the following: 
     In a first aspect, an electrical protection device includes a first electrical connection, a second electrical connection, a first electrical discharge device, and a second electrical discharge device. The first electrical discharge device includes a first conductive bus connected to the first electrical connection and a second conductive bus connected to the second electrical connection, wherein the first electrical discharge device has a first breakdown voltage and wherein when a voltage differential between the first conductive bus and the second conductive bus exceeds the first breakdown voltage, a first electrical current passes between the first conductive bus and the second conductive bus. The second electrical discharge device includes a third conductive bus connected to the first electrical connection and a fourth conductive bus connected to the second electrical connection, wherein the second electrical discharge device has a second breakdown voltage and wherein when a voltage differential between the third conductive bus and the fourth conductive bus exceeds the second breakdown voltage, a second electrical current passes between the third conductive bus and the fourth conductive bus. 
     In a second aspect, an electrical protection device includes a first electrical connection, a second electrical connection, a first spark gap, and a second spark gap. The first spark gap is formed between a first electrode and a second electrode, the first electrode is connected to the first electrical connection and the second electrode is connected to the second electrical connection, wherein the first spark gap has a first breakdown voltage. The second spark gap is formed between a third electrode and a fourth electrode, the third electrode is connected to the first electrical connection and the fourth electrode is connected to the second electrical connection, wherein the second spark gap has a second breakdown voltage. 
     In a third aspect, an electrical protection device includes a first electrical connection, a second electrical connection, a first spark gap, a second spark gap, a third spark gap, an upper plate, a lower plate, and an insulating standoff. The first spark gap is formed between a first electrode and a second electrode, the first electrode is connected to the first electrical connection and the second electrode is connected to the second electrical connection, wherein the first spark gap has a first breakdown voltage. The second spark gap is formed between a third electrode and a fourth electrode, the third electrode is connected to the first electrical connection and the fourth electrode is connected to the second electrical connection, wherein the second spark gap has a second breakdown voltage. The third spark gap is formed between a fifth electrode and a sixth electrode, the fifth electrode is connected to the first electrical connection and the sixth electrode is connected to the second electrical connection, wherein the third spark gap has a third breakdown voltage. The upper plate formed from an electrically conductive material. The lower plate formed from an electrically conductive material. The insulating standoff is disposed between the upper plate and the lower plate. The first electrode, the third electrode, and the fifth electrode are oriented vertically and are mounted in the upper plate. The second electrode, the fourth electrode, and the sixth electrode are oriented vertically and mounted in the lower plate. The first electrode is separated from the second electrode by a first gap distance corresponding to the first breakdown voltage. The third electrode is separated from the fourth electrode by a second gap distance corresponding to the second breakdown voltage. The fifth electrode is separated from the sixth electrode by a third gap distance corresponding to the third breakdown voltage. The first electrical connection is connected to a grounding terminal, and the second electrical connection is connected to a power transmission line or to the neutral of a transformer for the protection of connected electrical equipment from an electrical ground fault current. 
     In a fourth aspect, an overvoltage protection system includes an overvoltage protection assembly and a self-test assembly. The overvoltage protection assembly includes a first electrical connection and a second electrical connection. It also includes a first electrical discharge device, including a first conductive bus connected to the first electrical connection and a second conductive bus connected to the second electrical connection, wherein the first electrical discharge device has a first breakdown voltage and wherein when a voltage differential between the first conductive bus and the second conductive bus exceeds the first breakdown voltage, a first electrical current passes between the first conductive bus and the second conductive bus. The overvoltage protection assembly also includes a second electrical discharge device, including a third conductive bus connected to the first electrical connection and a fourth conductive bus connected to the second electrical connection, wherein the second electrical discharge device has a second breakdown voltage and wherein when a voltage differential between the third conductive bus and the fourth conductive bus exceeds the second breakdown voltage, a second electrical current passes between the third conductive bus and the fourth conductive bus. The self-test assembly is electrically connected in parallel with the overvoltage protection assembly and useable to detect at least one of the first and second breakdown voltage between an electrical component and ground. 
     In another aspect, an electrical protection device includes a first electrical connection and a second electrical connection, and a surge arrester including a first side connected to the first electrical connection and a second side connected to the second electrical connection. The surge arrester has a breakdown voltage at which it begins to conduct and clipping occurs and a pressure relief voltage above which the surge arrester enters a pressure relief mode nearly instantaneously (here less than 10 s of microseconds). The electrical protection device includes a spark gap formed between first and second electrodes, the first electrode connected to the first electrical connection and the second electrode connected to the second electrical connection, wherein the spark gap has a first side and a second side, the distance between the first side and the second side selected such that a breakdown voltage of the spark gap is greater than the conduction voltage and less than the voltage withstand limit of the connected electrical equipment. The electrical protection device further includes a first conductor including a first end and a second end, the first end connected to the first side of the spark gap, and a second conductor, including a first end and a second end, the first end connected to the second side of the spark gap. The distance between the second end of the first conductor and the second end of the second conductor is greater than the distance between the first end of the first conductor and the first end of the second conductor. The surge arrester and the spark gap are thus electrically connected in a parallel configuration. 
     In yet another aspect, an electrical protection device includes first and second electrical connections and a surge arrester, including a first side connected to the first electrical connection and a second side connected to the second electrical connection. The electrical protection device includes a pair of arcing horns (or Jacob&#39;s ladder) formed from a conducting material, the first arcing horn in the pair connected to the first electrical connection, the second arcing horn in the pair connected to the second electrical connection. The distance between the middle of the first arcing horn and the middle of the second arcing horn (or Jacob&#39;s ladder) forms a spark gap with a breakdown voltage that is greater than the conduction voltage of the surge arrester and less than the voltage withstand limit of the connected electrical equipment . The surge arrester and the arcing horns are thus electrically connected in a parallel configuration. 
     In a further aspect, an electrical protection device includes a first electrical connection, a second electrical connection, and a surge arrester. The surge arrester includes a first side connected to the first electrical connection and a second side connected to the second electrical connection, the surge arrester having a breakdown voltage at which clipping occurs. The device further includes a spark gap formed by a pair of concentric cylindrical conductors spaced apart by a predetermined distance. The spark gap has a breakdown voltage that is greater than the conduction voltage of the surge arrester and less than the voltage withstand limit of the connected electrical equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an overvoltage protection assembly; 
         FIG. 2  is a perspective view of an overvoltage protection assembly, according to a first alternative example embodiment; 
         FIG. 3  illustrates example voltage levels depicting a design of the overvoltage protection assemblies discussed herein, in some example embodiments; 
         FIG. 4  is a perspective view of an overvoltage protection assembly, according to a second example embodiment; 
         FIG. 5A  is a perspective view of an overvoltage protection assembly including an integrated Gabriel, according to a further example embodiment; 
         FIG. 5B  is a close up perspective view of a portion of the overvoltage protection assembly of  FIG. 5A ; 
         FIG. 6  is a schematic view of an overvoltage protection assembly, according to a further example embodiment; 
         FIG. 7  is a schematic view of an overvoltage protection assembly, according to a further example embodiment; 
         FIG. 8  is a schematic view of a cylindrical spark gap assembly, according to a further example embodiment; 
         FIG. 9  is a cross-sectional schematic view of a cylindrical spark gap assembly, according to a further example embodiment; 
         FIG. 10A  is a perspective view of an overvoltage protection assembly according to a further example embodiment; 
         FIG. 10B  is a close-up, perspective view of a portion of the overvoltage protection assembly of  FIG. 10A ; 
         FIG. 10C  is another perspective view of the overvoltage protection assembly of  FIG. 10A ; 
         FIG. 11A  is a perspective view of an embodiment of the electrodes in an overvoltage protection assembly; 
         FIG. 11B  is a close-up, perspective view of the embodiment of the electrodes of  FIG. 11A ; 
         FIG. 12  is a perspective view of an overvoltage protection assembly according to another example embodiment; 
         FIG. 13A  is a perspective view of an overvoltage protection assembly according to another example embodiment; 
         FIG. 13B  is an perspective view of the of the inside of the overvoltage protection assembly of  FIG. 13A ; 
         FIG. 14A  is a perspective view of an overvoltage protection assembly according to another example embodiment; 
         FIG. 14B  is a side view of a subassembly of the overvoltage protection assembly of  FIG. 14A ; 
         FIG. 14C  is a perspective view of an alternate embodiment of the overvoltage protection assembly of  FIG. 14A ; 
         FIG. 14D  is a perspective view of an alternate embodiment of the overvoltage protection assembly of  FIG. 14A ; 
         FIG. 14E  is a side view of an alternate embodiment of the conductors of the overvoltage protection assembly of  FIG. 14A ; 
         FIG. 14F  is a side view of another alternate embodiment of the conductors of the overvoltage protection assembly of  FIG. 14A ; 
         FIG. 15A  is a perspective view of an overvoltage protection assembly according to another example embodiment; 
         FIG. 15B  is another perspective view of the overvoltage protection assembly of  FIG. 15A ; 
         FIGS. 15C  is a perspective view from below of the overvoltage protection assembly of  FIG. 15A ; 
         FIG. 15D  is a close-up, perspective view from below of the overvoltage protection assembly of  FIG. 15A ; 
         FIG. 15E  is a perspective view from below of the roof and the cage of the overvoltage protection assembly of  FIG. 15A ; 
         FIG. 15F  is a perspective view of the cage of the overvoltage protection assembly of  FIG. 15A ; and 
         FIG. 16  is a circuit diagram of an overvoltage protection system according to another example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
     In general the present disclosure relates to a protective device for other electrical components, such as a capacitor bank or other electrical system, from ground fault voltage surges in power systems. Embodiments of the systems and methods of the present disclosure incorporates the integration of a surge arrester, spark gap, and a Jacob&#39;s ladder (or arcing horns) such that the gap distance and the surge arrester electrical characteristics are selected to give reliable protection at a given voltage level. Still other embodiments of the electrical protection systems described herein employ spark gap configurations that provide overvoltage protection of electrical systems, and in particular for use in large scale power systems (e.g. power transmission systems) that require relatively large power and current dissipation amounts, while remaining cost-effective for use in power transmission networks. Such embodiments can include features which are tailored for use in protection against induced currents experienced on a neutral of a power line transformer, and are configured to provide a relatively low-cost configuration which also can accommodate such large current dissipation events as may occur in a power grid. 
     Referring now to  FIGS. 1-2 , an assembly  100  is shown that is configured to provide protection to a high power electrical component, such as a capacitor bank or other power system component, from high voltage during ground fault events, according to example embodiments. The assembly includes a surge arrester  102 , a Jacob&#39;s ladder (or arcing horns)  104 , and a spark gap  106  integrated therein, and connected in parallel with one another across circuit leads  108   a - b,  which connect to the component to be protected. 
     In the embodiment shown, the surge arrester  102  can take many forms. In an example embodiment, the surge arrester  102  is a metal oxide varistor (MOV) surge arrester. It can be located in a variety of locations; in the example of  FIG. 2 , the surge arrester  102  is mounted at the base of the assembly. The surge arrester  102  clips any resonant or other voltages that might appear across a capacitor or capacitor bank or a series combination of a capacitor and resistor, thereby providing voltage clipping and resulting dampening for any unwanted series, ferro, or other resonances. In the embodiment shown, the surge arrester  102  is electrically connected at opposing sides to first and second electrical connections, at circuit leads  108   a - b.    
     Attached to the surge arrester is a combination Jacob&#39;s ladder (or arcing horns)  104  with a spark gap  106 . The Jacob&#39;s ladder  104  includes first and second conductors  105   a - b,  between which the spark gap is formed, and in which the distance between the top end of the first electrode and the top end of the second electrode is greater than the distance between the bottom end of the first electrode and the bottom end of the second electrode. The first and second conductors  105   a - b  can be constructed from, in various embodiments, brass, nickel coated copper, tungsten, niobium, alloys thereof, or other types of highly conductive materials. 
     The spark gap  106  is, in the embodiment shown in  FIG. 2 , a narrow gap between the two conductors  105   a - b  of a narrow section of the Jacob&#39;s ladder  104 , forming electrodes  110   a - b.  The spark gap  106  has, in the embodiment shown, a few millimeter gap distance, and is built into the Jacob&#39;s ladder  104 . When a high current ground fault is experienced, an arc will form at the spark gap  106  to limit the voltage across the component to be protected (i.e. a capacitor or capacitor bank or other component, connected at leads  108   a - b ). 
     The Jacob&#39;s ladder  104  includes complementary metal structures forming a gap of increasing distance extending away from the spark gap  106 . The Jacob&#39;s ladder  104  is, in example embodiments, constructed of a suitable conducting metal such as brass, nickel coated copper, tungsten, niobium, alloys thereof, or other suitable metal, and provides a means for the arc to travel away from the spark gap  106  (e.g., up the ladder) where it can dissipate large amounts of energy to the air. 
     In some embodiments, the gap separation on the Jacob&#39;s ladder  104 , and hence the breakdown voltage, is designed to be a fixed distance to achieve a fixed breakdown voltage in air. In alternative embodiments, the gap could be adjustable, and hence the breakdown voltage of the gap could be adjustable. The relationship between the breakdown voltage and gap spacing for various gases is given by Paschen&#39;s Law, which describes a breakdown voltage of gas between parallel plates as a function of pressure and gap distance. 
     During operation, and upon occurrence of an overvoltage event, typically the initial arc after forming at the spark gap  106  will rapidly climb the Jacob&#39;s ladder  104  and then continue to arc across the tips of the ladder for several power cycles, typically a few (4-6) power cycles at 60 Hz (i.e. 60 to 100 milliseconds). During this arc energy dissipation phase, some of the tips of the Jacob&#39;s ladder  104  will experience heating and a small amount of the metal electrode tips could be vaporized. 
     The surge arrester provides voltage clipping and in turn dampening of any unwanted resonances which might be encountered. If the surge arrester&#39;s energy absorption limit is exceeded, the spark gap remains to protect connected equipment from further overvoltage events. A Jacob&#39;s ladder is also connected in parallel with the surge arrester and the spark gap. The Jacob&#39;s ladder function is to protect the surge arrester and spark gap once an arc conduction path has been established. That is, the arc when initiated at the gap will rapidly rise to the top of the ladder where the arc energy is dissipated into the air. In this way the combination of the surge arrester, spark gap and the Jacob&#39;s ladder provide an extremely reliable device for high power components such as capacitor banks, static VAR compensators (SVCs), or other high power electrical system components. 
       FIG. 3  illustrates an example voltage level diagram  300  depicting a design of the overvoltage protection assemblies discussed herein, in some example embodiments. In the diagram  300  as shown, operation of the protection assemblies illustrated above, as well as those in  FIGS. 4-5  below, are described. In particular, one application of this protection assembly is the protection of a capacitor bank used for blocking Geomagnetically Induced Current (GIC) in the neutral of a grounded transformer, SVC or other power component. 
     As seen in the diagram  300  of  FIG. 3 , when ground fault voltages are encountered, the surge arrester  102  in an example assembly will conduct current and will perform a voltage clipping function for example in the 5 kV to 7 kV range. This provides damping to control unwanted resonances that may appear in a power system. If the amount of energy being shunted to ground by the surge arrester exceeds its functional limit, it will enter pressure relief and be consumed. In subsequent fault events, if the voltage exceeds the breakdown voltage of the spark gap (e.g., above the 11 kV range), an arc will form at the spark gap. In this case, the gap distance would be selected such that the arc would form for example at a nominal voltage on the order of 11 kV to 25 kV. It has been established that this breakdown voltage is dependent on humidity, condensation, atmospheric pressure variations, etc. However, variations over humidity, condensation, and pressure conditions will not greatly affect the breakdown voltage in the spark gap  106 ; rather, a variation in breakdown voltage will be relatively small (i.e. on the order of +/−10% to 15%), and is tolerable for this protection application. In alternative embodiments, additional surge arresters having different characteristics could be incorporated, such that each surge arrester may be configured to enter a pressure relief mode at the same level, or different levels. 
       FIG. 4  is a perspective view of an overvoltage protection assembly  400 , according to a second example embodiment. The assembly  400  includes a surge arrester  402 , as well as a Jacob&#39;s ladder  404  and spark gap  406 , analogous to those described above. In this example embodiment, the assembly  400  is configured using a “blade” configuration of the Jacob&#39;s ladder  404  that is designed to provide increased mechanical stability to the Jacob&#39;s ladder  404  and a hence a more stable spark gap distance (i.e. a more consistent gap breakdown voltage). The assembly  400  as shown includes the surge arrester  402  (e.g., the MOV) mounted horizontally at the bottom of the assembly. Conductors  405   a - b  of the Jacob&#39;s ladder  404  are electrically connected in parallel with the surge arrester  402 , and extend vertically. If the surge arrester&#39;s current carrying ability is exceeded, it will enter the pressure relief mode and an electrical arc will form. Subsequent overvoltage events would create an arc at the spark gap if the voltage differential reaches the gaps preset breakdown voltage. In either case, the arc energy is then dissipated at the tips of the Jacob&#39;s ladder  404  reducing the amount of damage to the surge arrester  402  and material of conductors  405   a - b  that define the gap dimensions and therefore the breakdown voltage of the spark gap. The assembly  400  is configured to be connected to the component to be protected at circuit leads  408   a - b.    
     Now referring to  FIGS. 5A-5B , a further example protective assembly  500  is shown that includes an integrated “Gabriel” configuration. In this embodiment, the assembly again includes a surge arrester (not shown), Jacob&#39;s ladder  504 , and spark gap  506 . However, in the embodiment shown, the spark gap  506  includes a Gabriel electrode  510   c  in addition to the existing electrodes  510   a - b.  This provides a more reliable breakdown voltage of the gap. In the embodiment shown the third electrode  510   c  is implemented by including in this example a spark plug  512  at the spark gap  506 , with the tip of this third electrode (in this example a spark plug) positioned in the spark gap  506 . This electrode  510   c  is connected electrically to the high voltage ladder electrode  510   b  through a series resistor (not shown, but typically on the order of a few mega ohms resistance). The function of electrode  510   c  is to initiate an ionized column of gas at a more precise voltage level to start the formation of the arc in the gap. The resistor then limits the current through this electrode so that the arc current is carried through the first and second electrodes of the Jacob&#39;s ladder or arcing horns. The third electrode  510   c  thereby provides a smaller range of voltages over which the spark gap fires and the assembly enters its protection mode. The assembly  500  is configured to be connected to the component to be protected at circuit leads  508   a - b.    
     Referring now to  FIG. 6 , a further embodiment of an overvoltage protection assembly  600  is shown. In the embodiment shown, a spark gap  602  is used for ground fault protection for high voltage (HV) and extra high voltage (EHV) power equipment. In the embodiment shown, a Jacob&#39;s ladder  604  can be used in connection with the spark gap  602  to create a protection device which has a long life and allows reuse for many (e.g., about 100 to 1,000) ground fault events. The spark gap  602  includes electrodes  603   a - b,  positioned at a predetermined distance from one another. 
     The overvoltage protection assembly  600  of  FIG. 6 , as with the other embodiments discussed herein, overcomes a problem with many spark gaps when used in high voltage, high current situations, in that the high current arc melts and destroys the metal in the area of the gap unless a special geometry and materials are used in the device. In an example embodiment as shown in  FIG. 6 , this destructive situation can be overcome using a Jacob&#39;s ladder  604  associated with the spark gap  602 , and which will move the arc out of the initial gap area to allow energy dissipation over a larger volume and at the tip of the ladder electrodes. By this means, an overvoltage protection assembly, such as overvoltage protection assembly  600 , can be designed that will not degrade but instead be re-useable for many ground faults. 
     Additionally, it is noted that the overvoltage protection assembly  600  further encourages any spark formed at the spark gap  602  to quickly move up the Jacob&#39;s ladder by applying a Lorentz force from the return conductor ( 612 ) located below the region of the arc. One side of the assembly is connected to the hot side of the electrical device that is to be protected. The second side of the spark gap is grounded at a grounding point  610 . A conductive bar  612  or other electrical bus can be connected to the grounded return path side of the spark gap  602  and positioned below the spark gap  602 . 
     In operation, a Lorentz force occurs between the conductive path on the positive side of the spark gap and Jacob&#39;s ladder assembly (at the first side of the spark gap  602 ) and the return path side of the spark gap  602 , which repels the arc plasma and thereby pushes the arc up the Jacob&#39;s ladder  604 . In the embodiment shown, a gap distance between the two electrodes is selected such that the required breakdown voltage can be achieved. This distance can be calculated using a Paschen&#39;s law relationship, expressed as a relationship between the breakdown voltage, the gas in the spark gap (i.e., air), the pressure experienced, and the distance of the spark gap. 
     In a further embodiment of the present disclosure illustrated in  FIG. 7 , overvoltage protection assembly  700  is shown. In this embodiment, a spark gap  702  can include electrodes  703   a - b,  and can be introduced into the arrangement illustrated in  FIG. 6  by way of a Gabriel electrode  704 . In this embodiment, a current conduction path is similar to that shown in  FIG. 6 ; however, in the overvoltage protection assembly  700 , the width of the spark gap  702  can be wider. For example, in some embodiments, the spark gap  702  can have a width of about 6 to 10 millimeters. In this configuration, an initial spark occurs between the third electrode  704  and the ground electrode  703   b.  A typical gap distance between this third electrode and the electrode  703   b  can be on the order of about 1 to 4 millimeters depending on the required breakdown voltage. The current in the initial spark is limited by a resistor  706  connected to this third electrode  704 . Once a spark is initiated, a high current arc will be established between the high voltage electrode  703   a  and the ground electrode  703   b.  The larger gap size, typically 6 to 20 millimeters, allows for better arc energy dissipation over a larger volume and hence less chance for melting and destruction of the electrodes. The third electrode  704  can be, in various embodiments, made of tungsten or niobium or other high melting point metal to reduce wear occurring on this electrode. Additionally, in some embodiments the third electrode can be mounted securely in an insulating material  708  located under the gap area but above the lower electrical bus  709  (i.e. conductor), which is electrically connected to a grounding point  712 . 
     In some embodiments, additionally the spark gap electrodes  703   a - b  can be constructed of tungsten to decrease the melting and/or destructive effect of a high current event on an electrode. This can be accomplished by using either two blocks of tungsten to which a Jacob&#39;s ladder  710  is attached as shown in  FIG. 7 , or alternatively by using tungsten horns for the entire assembly of the Jacob&#39;s ladder  710 . In still other embodiments, other partial portions of the spark gap  702  and/or Jacob&#39;s ladder  710  can be made from tungsten or equivalent resilient conductive material. 
     An example cylindrical spark gap assembly  800  is illustrated in  FIGS. 8-9 . In this embodiment, two concentric metallic cylinders  802 ,  804  create a large area spark gap to achieve a long life ground fault protection device. In this embodiment, an arc is allowed to move around to the region of the smallest gap distance. Should metal ablation or melting occur the gap size in the region will increase. Hence, the arc will move to a different location within the device. A large spark gap area can be created by increasing the diameter and height of the cylinders shown in  FIG. 8 . Electrical leads  810   a - b  can connect to the overvoltage protection assembly  800 , for example for grounding or connecting to the electrical network to be protected, as in  FIGS. 7-8 . 
       FIG. 9  shows details of the cylindrical spark gap assembly  800  in cross-sectional form. In particular, the details illustrated in  FIG. 9  illustrate mounting the cylindrical spark gap assembly  800  including two concentric metallic cylinders  802 ,  804 . An insulating material can be used to form top and bottom housing pieces  806   a - b.  Using a bolt  808  or other fastener, the center electrode cylinder can be secured relative to the outer electrode cylinder. Using the bolt  808  and associated cylinder shells, a uniform gap distance can be maintained between the two electrodes. 
       FIG. 10A  is a perspective view of an overvoltage protection assembly  1000  according to another example embodiment. The assembly  1000  includes a Jacob&#39;s ladder  1004 , a spark gap  1006 , and standoffs  1012   a - b.    
     In the embodiment shown, the Jacob&#39;s ladder  1004  includes conductors  1005   a - b  having electrodes  1010   a - b  (shown more clearly in conjunction with the embodiment described below in connection with  FIG. 10C ) and is configured to carry an arc that forms in the spark gap  1006  along the conductors  1005   a - b  where large amounts of arc energy can be dissipated into the air. The conductors  1005   a - b  are generally vertically disposed and, in some embodiments, have a cylindrical shape. The conductors  1005   a - b  are angled such that the distance between the middle of the conductors  1005   a - b  is less than the distance between the tops or the bottoms of the conductors  1005   a - b.  The spark gap  1006  is formed between the conductors  1005   a - b  at the point where the electrodes are closest together. Below the spark gap  1006 , the distance between the conductors  1005   a - b  is widened sufficiently to prevent the arc from travelling down, or towards the equipment being protected. As described above, the spacing of the spark gap  1006  is selected using Paschen&#39;s Law to achieve a desired break down voltage. For example, in an embodiment configured to achieve a break down voltage of 10,000 volts in nitrogen at atmospheric pressure, the width of the spark gap  1006  is 2.3 mm. 
     In the embodiment shown, the current in the conductors  1005   a - b  just below the spark gap  1006  provides the Lorentz force on the arc formed in the spark gap  1006  and causes the arc to travel along the conductors  1005   a - b.  In some embodiments, the current moving up conductors  1005   a,  through the arc (i.e., across the spark gap  1006 ), and then down the conductors  1005   b  gives rise to a magnetic field in the area of the spark gap  1006 . This magnetic field interacts with the current in the arc to give rise to the Lorentz force on the arc plasma, which pushes the arc up the conductors  1005   a - b.    
     In some embodiments, the conductors  1005   a - b  are coupled to standoffs  1012   a - b.  The standoffs  1012   a - b  are formed from a rigid, insulating material and are configured to ensure that the electrodes do not move while the arc is present. In some embodiments, the standoffs  1012   a - b  are additionally coupled to another rigid external structure. 
     The conductors  1005   a - b  are connected to conducting buses  1007   a - b.  In some embodiments, the Jacob&#39;s ladder  1004  is connected in parallel to the equipment that is to be protected. In some embodiments, one of conductors  1005   a - b  is connected to the hot side of the electrical device that is to be protected and the other is connected to ground. 
     In some embodiments, the overvoltage protection assembly  1000  additionally includes a Gabriel electrode  1010   c.  Other embodiments do not include a Gabriel electrode  1010   c.    
     Now referring to  FIG. 10B , a close-up, perspective view of overvoltage protective assembly  1000  is shown. In the embodiment shown, overvoltage protective assembly  1000  includes as an integrated “Gabriel” electrode  1010   c.    
     In the embodiment shown in  FIGS. 10A-B , a Gabriel electrode  1010   c  is disposed in the spark gap  1006  between electrodes  1010   a - b.  In some embodiments, the Gabriel electrode  1010   c  is an electrical conducting point that is much smaller than electrodes  1010   a - b.  The Gabriel electrode  1010   c  is configured to initiate the arc at a controlled voltage. The Gabriel electrode  1010   c  allows for the initiation of the arc at a reasonably low breakdown voltage and allows for a larger gap so as to withstand the energy dissipation of a high-current arc. In some embodiments, the Gabriel electrode  1010   c  is disposed and rigidly held at a position that is closer to electrode  1010   a  than electrode  1010   b.  In these embodiments, the initiation of the arc across the spark gap  1006  is dependent on the distance between the tips of electrode  1010   a  and Gabriel electrode  1010   c.  Further, in these embodiments, the initiation of the arc across spark gap  1006  is less dependent on the distance between electrode  1010   a  and electrode  1010   b.  Accordingly, embodiments that include Gabriel electrode  1010   c  have greater tolerance for environmental, material, and fabrication variances. 
     In the embodiment shown, the Gabriel electrode  1010   c  is a conductor disposed in an insulating material  1011 . The insulating material  1011  holds the Gabriel electrode  1010   c  in place. The tip of the Gabriel electrode  1010   c  is positioned within the gap of the two electrodes such that it provides a shorter gap distance to one of the electrodes so that electrical breakdown will occur at a lower voltage than that if the Gabriel electrode were not present. The Gabriel electrode  1010   c  is connected through a series resistor (not shown, but typically on the order of a few mega ohms resistance). The function of the Gabriel electrode  1010   c  is to initiate an ionized column of gas at a more precise voltage level to start the formation of the arc in the gap. The resistor then limits the current through this electrode so that the arc current is carried through the conductors  1005   a - b  of the Jacob&#39;s ladder  1004 . The Gabriel electrode  1010   c  thereby provides a smaller range of voltages over which the spark gap  1006  fires and the assembly  1000  enters its protection mode. 
       FIG. 10C  is another perspective view of the overvoltage protection assembly  1000 . The standoffs  1012   a - b  are coupled to the support elements  1013   a - b.  Generally, the support elements  1013   a - b  are rigid and are formed from an insulating material, such as concrete. The standoffs  1012   a - b  and support elements  1013  are configured to secure the conductors  1005   a - b.  This helps stabilize the conductors  1005   a - b  against the forces generated when an arc current forms. Accordingly, use of such standoffs  1012   a - b  and support elements  1013  may be advantageous in circumstances where the current across the spark gap is great, for example up to 60,000 amps or more, which might otherwise cause substantial Lorentz forces and resulting damage to the assembly. 
     Additionally, in the embodiment shown, the spacing between the conductors  1005   a - b  is further secured by the insulators  1014   a - b.  The insulators  1014   a - b  are rigid and formed from an insulating material, such as concrete. The insulators  1014   a - b  are configured to secure the spacing between the conductors  1005   a - b  and, accordingly, the width of the spark gap  1006 . 
     Referring now to  FIGS. 11A-B , conductors  1101   a - b  of a Jacob&#39;s ladder  1100  are shown, according to an example embodiment. The conductors  1101   a - b  have electrodes (shown in detail in  FIG. 11B ), and are configured to be used in the overvoltage protection systems described throughout this application. The conductors  1101   a - b  include lower portions  1102   a - b  and upper portions  1103   a - b.    
     Generally, the materials selected for the conductors  1101   a - b  should have at least some of the following properties: high conductivity, stiffness, a high melting point to withstand the plasma energy that will be dissipated during arcing events, and the ability to be molded into the shape of a Jacob&#39;s ladder  1100 . For example, some materials having these properties to varying degrees include tungsten, tungsten/copper alloy, niobium, and copper. Because the demands on the material used in the lower portions  1102   a - b  are different from the demands upon the material used to form the upper portions  1103   a - b,  a different material may be used to form the lower portions  1102   a - b  than is used to form the upper portions  1103   a - b.    
     Generally, in the embodiment disclosed the lower portions  1102   a - b  are cylindrical, include an angled portion, and are configured to form a spark gap  1106  there between. In some embodiments, the diameter of the lower portions  1102   a - b  is ⅜ inch. Other embodiments are possible utilizing other cross-sectional shapes, or otherwise utilizing different diameters of electrodes. In some embodiments, the subtended angle of the conductors  1101   a - b  below the gap  1106  is larger than the subtended angle between the conductors  1101   a - b  above the gap  1106  so that the arc will move “up” the ladder. The subtended angle of the conductors above the gap  1106  should be sufficiently small to ensure that the arc does in fact move away from the connections at which equipment is protected. For example, a subtended angle between the conductors  1101   a - b  above the gap  1106  in the range of 50 to 80 degrees would be suitable for most high current arc applications. In some embodiments, the lower portions  1102   a - b  are formed from copper because it is amenable to forming the angled shape of the lower portion using forming die and pressing techniques. The methods of forming the shape of the lower portions  1102   a - b  using tungsten, tungsten/copper alloy, or niobium are more difficult. 
     Generally, the upper portions  1103   a - b  are cylindrical, straight, and configured to withstand the energy dissipated by an arcing event. In some embodiments, the diameter of the upper portions  1103   a - b  is ⅜ inch. Other embodiments are possible. In some embodiments the upper portions  1103   a - b  are formed from tungsten because tungsten has a high melting point. In other embodiments, the upper components are formed from tungsten/copper alloy or niobium. Tungsten, tungsten/copper alloy, and niobium have higher melting points and are stiffer than copper and thus allow the upper portions  1103   a - b  to withstand the energy dissipated by arcing events better than would many other conductive materials, such as copper. 
     In the embodiment shown, the lower portions  1102   a - b  are joined to the upper portions  1103   a - b  using a silver soldering process. The lower ends  1105   a - b  of the upper portions  1103   a - b  are machined to have a spherical surface. The upper ends of the lower portions  1102   a - b  are machined to accept the spherical surface of the lower end of the upper portions  1103   a - b.  In this manner, the conductors  1101   a - b  are formed using two different materials using common manufacturing techniques. In addition, conductors  1101   a - b  have a superior ability to withstand the energy dissipated by arcing events than if the conductors  1101   a - b  were formed from copper alone. 
       FIG. 12  is a perspective view of an overvoltage protection assembly  1200  according to another example embodiment. The assembly  1200  includes conductors  1201   a - b  and a spark gap  1206 . 
     Generally, the conductors  1201   a - b  are large-diameter, cylindrical rods with electrode ends  1202   a - b  having spherical surfaces. The diameter of the conductors  1201   a - b  is selected based on the expected arc current for a given application of the overvoltage protection assembly  1200 . The conductors  1201   a - b  are disposed horizontally such that the electrode ends  1202   a - b  are adjacent to one another. The electrode ends  1202   a - b  are separated by the spark gap  1206 . In some embodiments, the conductors  1201   a - b  are formed from tungsten. In other embodiments, the conductors  1201   a - b  are formed from a different material with a high melting point, such as tungsten/copper alloy or niobium. In other embodiments, other materials may be used as well. Due to the spherical surfaces of electrode ends  1202   a - b  of the conductors  1201   a - b,  the arc will move around the spherical surfaces and will not ablate a single spot on the surface. Accordingly, in this embodiment the overvoltage protection assembly  1200  has a long life and may be reused for many ground fault events. In some embodiments, a Gabriel electrode is included in the spark gap  1206  to initiate the arc as has been described above. 
     In other embodiments, the conductors  1201   a - b  are not positioned horizontally but instead are positioned at an angle with respect to each other. In this manner, when the arc forms in the spark gap  1206 , it will move upward on the spherical surfaces due to the Lorentz force as has been described above. This movement of the arc will allow for better dissipation of the arc energy and less ablation of the electrode material. In some embodiments, a Gabriel electrode is also included in the spark gap  1206  to initiate the arc at a given voltage as has been described above. 
     In some embodiments, springs  1203   a - b  are used in mounting the conductors  1201   a - b  to respective mounts  1204   a - b.  In such embodiments, the springs  1203   a - b  can compress and allow conductors  1201   a - b  to recoil away from one another. During normal operation, the two springs  1203   a - b  hold the conductors  1201   a - b  in normal positions, pointing at each other with an initial small gap there between. In cases where large electrical forces between the electrodes occur, a force between the electrodes will cause the electrodes to recoil, allowing for faster dissipation of the electrical effect, or arcing, between the electrodes. This will provide additional protection against damage to the electrodes in the event of arcing, since the arcing can be quickly dissipated. 
       FIG. 13A  is a perspective view of an overvoltage protection assembly  1300  according to another example embodiment. The assembly  1300  includes a Jacob&#39;s ladder  1304 , a spark gap  1306 , and support structure  1312 . 
     The Jacob&#39;s ladder  1304  includes conductors  1305   a - b,  which form electrodes  1310   a - b.  The Jacob&#39;s ladder  1304  is similar to the Jacob&#39;s ladder  1004  that is illustrated and described in greater detail with respect to  FIGS. 10A-B . In some embodiments, the conductors  1305   a - b  have a diameter of 1-1.5 inches and a length of 10-18 inches. In some embodiments, the conductors  1305   a - b  are formed from a copper/tungsten alloy. 
     In the embodiment shown, the spark gap  1306  is similar to the spark gap  1006  that is illustrated and described in greater detail with respect to  FIGS. 10A-B . In some embodiments of the assembly  1300 , the width of the spark gap  1306  is 2-3 mm. 
     In example embodiments, the support structure  1312  is a physical structure formed from a rigid insulating material, such as ceramic or molded concrete, and is configured to support the conductors  1305   a - b.  During large ground fault currents, the conductors  1305   a - b  may carry extremely large currents (e.g., up to 60,000 amps or more), which may generate large Lorentz forces on the conductors  1305   a - b.  The support structure is configured to support and stabilize the conductors  1305   a - b  so that the conductors  1305   a - b  are less likely to be pushed apart or twisted by the Lorentz forces. Additionally, the support structure  1312  is configured to prevent or minimize the conductors  1305   a - b  from moving or warping. The support structure  1312  increases the mechanical stability of the Jacob&#39;s ladder  1304  and hence creates a more stable spark gap distance and a more consistent gap breakdown voltage. 
     The support structure  1312  includes base  1313 , support walls  1314   a - b,  lower clamps  1315   a - b,  middle clamps  1316   a - b,  and upper clamps  1317   a - b.  Additionally, in some embodiments, the support walls  1314   a - b  include apertures  1318   a - b.  In some embodiments, the base  1313 , the support walls  1314   a - b  and the lower clamps  1315   a - b  are formed from a rigid conducting material. The middle clamps  1316   a - b  are formed from an electrically insulating material. The upper clamps  1317   a - b  are formed integrally from a rigid conducting or insulating material. In other embodiments, the support structure  1312  is formed from multiple independent components that are coupled together with one or more fasteners, such as adhesives or screws. 
     In embodiments, the base  1313  is a rigid structure that provides strength to resist bending so that the conductors  1305   a - b  cannot be pushed apart by the Lorentz forces generated between conductors  1305   a - b.    
     The support walls  1314   a - b  are formed from a rigid insulating material and are configured to support and secure the lower clamps  1315   a - b,  the middle clamps  1316   a - b,  and the upper clamps  1317   a - b.  Additionally, the support walls  1313   a - b  provide lateral support to prevent the conductors  1305   a - b  from twisting when subject to large Lorentz forces. 
     The apertures  1318   a - b  are openings in the support walls  1314   a - b.  The apertures  1318   a - b  are adjacent to the spark gap  1306  and are configured to allow the plasma blast that is created by the initial arc formed in the spark gap  1306  to escape. In this manner, the apertures  1318   a - b  allow the pressure created by the plasma blast to be released without damaging the support structure  1312 . 
       FIG. 13B  is an perspective view of the inside of the overvoltage protection assembly  1300 . In this figure, the support wall  1314   a  is not shown so that the inside of the overvoltage protection assembly  1300  is visible. 
     The lower clamps  1315   a - b  are devices to secure the bottom of the conductors  1305   a - b.  In some embodiments, the lower clamps  1315   a - b  each includes a hole in which the bottom of its respective conductor  1305   a  or  1305   b  is disposed. In this manner, the lower clamps  1315   a - b  each fully surrounds its respective conductor  1305   a  or  1305   b  to provide increased stability and resistance to Lorentz forces. 
     In some embodiments, the lower clamps  1315   a - b  are separated by a gap  1319 . The gap  1319  is sufficiently large enough to prevent the arcing across this gap between the lower clamps  1315   a - b.    
     The middle clamps  1316   a - b  are devices to secure the middle of the conductors  1305   a - b.  In some embodiments, the middle clamps  1316   a - b  include one or more support surfaces configured to abut the surface of the conductors  1305   a - b.  In some embodiments, the support surfaces abut approximately half of the outer surface of the conductors  1305   a - b.  In this manner, the middle clamps  1316   a - b  support the conductors  1305   a - b,  but do not interfere with the formation of the arc in the spark gap  1306  or impede the arc from travelling up the conductors  1305   a - b.  Additionally, in some embodiments, the middle clamps  1316   a - b  do not abut the conductors  1305   a - b  at the spark gap  1306 . In this manner, the middle clamps  1316   a - b  allow space for the plasma blast to escape from the spark gap  1306 . 
     The upper claims  1317   a - b  are devices to secure the top or a region near the top of the conductors  1305   a - b.  In some embodiments, the upper clamps  1317   a - b  include one or more support surfaces configured to abut the surface of the conductors  1305   a - b.  In some embodiments, the support surfaces abut approximately half of the outer surface of the conductors  1305   a - b.  In this manner, the upper clamps  1317   a - b  support the conductors  1305   a - b,  but do not impede the arc from travelling up the conductors  1305   a - b.    
     In some embodiments, multiple assemblies, such as assembly  1300 , are disposed in a container and connected in parallel to the same conductor buses. During large ground fault currents, an arc current forms across the spark gap of one of the assemblies. The arc current forms in the assembly with the lowest breakdown voltage. The arc current may ablate a portion of the electrodes adjacent to the spark gap, causing the spark gap to widen and the breakdown voltage to increase. In some circumstances, the breakdown voltage increases beyond that of one of the other assemblies. During a second large ground fault current, an arc current then forms across the spark gap of one of the other assemblies. In this manner, overvoltage protection is provided over a longer lifetime than would be possible with a single assembly. An example embodiment that includes parallel spark gaps is illustrated and described in greater detail with respect to  FIGS. 14A-D . 
     Further, in some embodiments of assembly  1300 , the conductors  1305   a - b  are formed from multiple materials and are joined using silver soldering as is illustrated and described in greater detail with respect to  FIGS. 11A-B . 
       FIG. 14A  is a perspective view of an overvoltage protection assembly  1400  according to another example embodiment. The assembly  1400  includes a plurality of subassemblies  1401   a - c  and circuit leads  1402   a - b.  The subassemblies are connected in parallel to the circuit leads  1402   a - b.  Additionally, each of the subassemblies  1401   a - c  includes a spark gap  1406   a - c.  Although there are three subassemblies shown in this figure, other embodiments include more or fewer subassemblies. 
     In some embodiments, the widths of the spark gaps  1406   a - c  are substantially the same. When a large ground fault current triggers the breakdown voltage of one of the spark gaps  1406   a - c,  a portion of the corresponding electrodes surrounding the spark gap ablates and the width of the spark gap increases. This increase in spark gap width will cause a corresponding increase in breakdown voltage. In some cases, the breakdown voltage of the spark gap after ablation caused by a large ground fault current will be greater than the breakdown voltage of one of the other spark gaps. Accordingly, during the next large ground fault current, the arc will initiate in a different spark gap. In this manner, the assembly  1400  will have an increased lifespan and will withstand a greater number of large ground fault currents. 
       FIG. 14B  is a side view of the subassembly  1401   a  of assembly  1400 . The subassembly  1401   a  includes mounts  1404   a - b,  conductors  1405   a - b,  electrodes  1410   a - b,  insulators  1414   a - b,  and cylindrical shields  1416   a - d.    
     The mounts  1404   a - b  are rigid support structures that are configured to secure and support the conductors  1405   a - b  at a desired angle. In some embodiments, the mounts are configured to position the conductors  1405   a - b  at an angle of 2.5-20 degrees from vertical. The mounts  1404   a - b  are configured to withstand the Loretnz force generated between the conductors  1405   a - b  when an arc current is formed. 
     Generally, the conductors  1405   a - b  are large-diameter, cylindrical rods with tapered ends that form electrodes  1410   a - b.  The diameter of the conductors  1405   a - b  is selected based on the expected arc current for a given application of the overvoltage protection assembly  1400 . The conductors  1405   a - b  are angled towards each other, such that the electrodes  1410   a - b  are adjacent to one another. In some embodiments, the subtended angle between the conductors  1405   a - b  is 5-40 degrees. The electrodes  1410   a - b  are separated by the spark gap  1406   a.    
     In some embodiments, the conductors  1405   a - b  and the electrodes  1410   a - b  are formed integrally from a rigid, conducting material with a high melting point. For example, in some embodiments, the conductors  1405   a - b  and the electrodes  1410   a - b  are formed from a copper/tungsten alloy. In other embodiments, the conductors  1405   a - b  and the electrodes  1410   a - b  are formed from different materials such as tungsten, copper, and niobium. In some embodiments, a Gabriel electrode is included in the spark gap  1406  to initiate the arc as has been described above. 
     Additionally, the spacing between the electrodes  1410   a - b  is further secured by the insulators  1414   a - b.  The insulators  1414   a - b  are rigid and formed from an insulating material, such as concrete. In some embodiments, the insulators  1414   a - b  have a cylindrical shape. The insulators  1414   a - b  are configured to secure the spacing between the mounts  1404   a - b,  the conductors  1405   a - b,  and the electrodes  1410   a - b,  and accordingly, the width of the spark gap  1406  as well. 
     In some embodiments, cylindrical shields  1416   a - d  are included. The cylindrical shields are hollow cylinders that are disposed around the insulators  1414   a - b  and are configured to interfere with the formation of a conductive path (from deposited carbon or materials expelled during an arc) along the surface of the insulators  1414   a - b.  In some embodiments, the radius of each of the cylindrical shields  1416   a - d  is 0.5-1 inches greater than the radius of the insulators  1414   a - b.    
       FIG. 14C  is a perspective view of an overvoltage protection assembly  1400  according to another example embodiment. The assembly  1400  shown in FIG.  14 C is similar to the assembly  1400  shown in  FIGS. 14A-B  except that it does not include the cylindrical shields  1416   a - d.    
       FIG. 14D  is a perspective view of an overvoltage protection assembly  1400  according to another example embodiment. The assembly  1400  shown in  FIG. 14C  is similar to the assembly  1400  shown in  FIGS. 14A-B  except that it additionally includes barriers  1417   a - b.    
     The barriers  1417   a - b  are physical structures formed from an insulating material and are configured to separate the subassemblies  1401   a - c  from each other. In some embodiments, the barriers  1417   a - b  are configured to prevent an arc current from forming between subassemblies  1401   a - c.  Additionally, in some embodiments, the barriers  1417   a - b  are configured to prevent plasma and other material expelled from one of the subassemblies  1401   a - c  during an arc current from reaching the others of the subassemblies  1401   a - c.    
       FIG. 14E  is a side view of conductors  1455   a - b,  electrodes  1460   a - b,  and spark gap  1456  according to another example embodiment. The conductors  1455   a - b  are an alternate embodiment of the conductors  1405   a - b,  the electrodes  1460   a - b  are an alternate embodiment of the electrodes  1410   a - b,  and the spark gap  1456  is alternate embodiment of the spark gap  1406   a.  In some embodiments of assembly  1400 , some or all of assembly  1401   a - c  include the conductors  1455   a - b,  the electrodes  1460   a - b,  and the spark gap  1456  instead of the conductors  1405   a - b,  the electrodes  1410   a - b,  and one of the spark gaps  1406   a - c.    
     The conductors  1455   a - b  include upper portions  1468   a - b  and lower portions  1469   a - b.  Additionally, the conductors  1455   a - b  form electrodes  1460   a - b,  which define the spark gap  1456   a . The upper portions  1468   a - b  are angled away from each other such that after an arc forms in the spark gap  1456   a , it will climb the upper portions  1468   a - b  and dissipate greater amounts of energy as it does so. In some embodiments, the upper portions  1468   a - b  have a length of 2.5 inches. In other embodiments, the upper portions  1468   a - b  are shorter or longer. In some embodiments, the upper portions  1468   a - b  are formed from a different material than the lower portions  1469   a - b.  In these embodiments, the upper portions  1468   a - b  are joined to the lower portions  1469   a - b  using a silver soldering process, as has been illustrated and described with respect to  FIGS. 11A-B . 
     In  FIG. 14E , the electrodes  1460   a - b  have a curved surface with a radius R. In some embodiments, the radius R is 2 inches. In other embodiments, the radius R is 1-3 inches. In other embodiments of the electrodes  1460   a - b,  the radius R is smaller or larger. 
     The electrodes  1460   a - b  are configured to initiate an arc current across the spark gap  1456   a  when the breakdown voltage of the spark gap  1456   a  is exceeded. As has been described previously, the breakdown voltage of the spark gap  1456   a  is based on its width. Often, material from the electrodes  1460   a - b  is ablated by the heat and plasma generated by the arc current. This causes the spark gap  1456   a  to widen and consequently the break down voltage to increase. Due to the curved surfaces of electrodes  1460   a - b,  the arc will move around the curved surfaces and will only minimally ablate a single spot on the surface. Accordingly, in this embodiment the electrodes  1460   a - b  may have a long life and may be reused for many ground fault events. 
       FIG. 14F  is a side view of conductors  1475   a - b,  electrodes  1480   a - b,  and spark gap  1476  according to another example embodiment. The conductors  1475   a - b  are an alternate embodiment of the conductors  1405   a - b,  the electrodes  1480   a - b  are an alternate embodiment of the electrodes  1410   a - b,  and the spark gap  1476  is alternate embodiment of the spark gap  1406   a.  In some embodiments of assembly  1400 , some or all of assembly  1401   a - c  include the conductors  1475   a - b,  the electrodes  1480   a - b,  and the spark gap  1476  instead of the conductors  1405   a - b,  the electrodes  1480   a - b,  and one of the spark gaps  1406   a - c.    
     The conductors  1475   a - b  include upper portions  1488   a - b  and lower portions  1489   a - b.  The embodiment shown in  FIG. 14F  is similar to the embodiment shown in  FIG. 14E , except that the surface of the electrodes  1480   a - b  are flat rather than curved. In some embodiments, the tops of the electrodes  1480   a - b  are separated by a smaller distance than the bottoms of the electrodes  1410   a - b.  For example, in some embodiments the tops of the electrodes  1480   a - b  are separated by a first width W 1  and the bottoms of the electrodes  1480   a - b  are separated by a slightly larger second width W 2 . In some embodiments, the width W 1  is 3.9 millimeters and the width W 2  is 4.3 millimeters. In some embodiments, the flat surfaces of the electrodes  1480   a - b  have a height H. In some embodiments, the height H is 1 inch. However, other embodiments with other heights and other first and second widths are possible as well. During an initial high ground fault voltage, the arc current will form at the top of the electrodes  1480   a - b.  As material is ablated during high ground fault current events, the arc will start at lower positions in the spark gap  1476 . 
       FIG. 15A  is a perspective view of an overvoltage protection assembly  1500  according to another example embodiment. The assembly  1500  is circular and includes a plurality of subassemblies  1501   a - c,  circuit leads  1502   a - b,  lower plate  1503 , upper plate  1504 , stand-off insulators  1507   a - c,  and lower insulators  1523   a - c.  The subassemblies  1501   a - c  are equally spaced around the assembly  1500 , being separated from each other by a 120 degree angle, and are connected in parallel to the circuit leads  1502   a - b.  Additionally, each of the subassemblies  1501   a - c  includes a pair of conductors that form a pair of electrodes and a spark gap  1506   a - c  (these elements are best seen in  FIG. 15B ). Although there are three subassemblies shown in this figure, other embodiments include more or fewer subassemblies. 
     The lower plate  1503  is a round disc-like structure formed from a rigid conductive material. Similarly, the upper plate  1504  is also a round disc-like structure formed from a rigid conductive material. In some embodiments, one or both of the lower plate  1503  and the upper plate  1504  are not round but instead have a different shape, such as a rectangle. The subassemblies  1501   a - c  are disposed and secured between the lower plate  1503  and the upper plate  1504 . 
     The stand-off insulators  1507   a - c  are rigid structures formed from a rigid insulating material and are configured to secure the upper plate  1504  to the lower plate  1503 . The upper plate  1504  is separated from the lower plate  1503  by the height of the stand-off insulators  1507   a - c.  In some embodiments, the stand-off insulators  1507   a - c  are 8 inches high and 4 inches in diameter. In other embodiments, the stand-off insulators  1507   a - c  are taller or shorter or have a different diameter. 
     The lower insulators  1523   a - c  are rigid structures formed from a rigid insulating material and are configured to support the assembly  1500 . The lower insulators  1523   a - c  are secured to the lower plate  1503 . 
       FIG. 15B  is another perspective view of the overvoltage protection assembly  1500 . In  FIG. 15B , the upper plate  1504  is not shown to provide a clearer view of the subassemblies  1501   a - c  and the stand-off insulators  1507   a - c.  Also shown are cylindrical shields  1513   a - c  and insulating discs  1514   a - c.    
     The subassemblies  1501   a - c  include upper conductors  1505   a - c,  lower conductors  1508   a - c,  and half-cylinder shields  1512   a - c.  In some embodiments, the upper conductors  1505   a - c  and the lower conductors  1508   a - c  have a diameter of 1-1.5 inches. The upper conductors  1505   a - c  and the lower conductors  1508   a - c  are oriented vertically. The bottom of the upper conductors  1505   a - c  form upper electrodes  1510   a - c.  Similarly, the top of the lower conductors  1508   a - c  form lower electrodes  1511   a - c.  The spark gaps  1506   a - c  are vertical gaps formed between the upper electrodes  1510   a - c  and the lower electrodes  1511   a - c  in each of the subassemblies  1501   a - c.  The lower conductors  1508   a - c  are secured to the lower plate with lower clamps  1517   a - c  (best seen in  FIGS. 15C-D ). The lower clamps  1517   a - c  can be used to individually adjust the height of the lower conductors  1508   a - c  and consequently the size of the spark gaps  1506   a - c.  In some embodiments, the assembly  1500  is configured so that each of the spark gaps  1506   a - c  has a different size and consequently a different breakdown voltage. Additionally, in some embodiments, the upper conductors  1505   a - c  are raised or lowered using upper clamps  1515   a - c  instead of or in addition to raising or lowering the lower conductors  1508   a - c.    
     The half-cylinder shields  1512   a - c  are physical structures with the shape of a hollow half-cylinder and are formed from either a conducting an insulating material. The half-cylinder shields  1512   a - c  are disposed around the inner side of the upper conductors  1505   a - c.  The half-cylinder shields  1512   a - c  are configured to prevent the arc from one subassembly from initiating an arc in another subassembly. The half-cylinder shields  1512   a - c  are also configured to prevent plasma and materials that are expelled when an arc is formed from reaching the stand-off insulators  1507   a - c.  Additionally, the half-cylinder shields  1512   a - c  direct the blast created when an arc current forms towards the outside of the assembly  1500 . The half-cylinder shields  1512   a - c  are oriented vertically and are secured to and hang down from the upper plate  1504 . The half-cylinder shields  1512   a - c  do not extend to the lower plate  1503  and thus do not provide a surface upon which a conductive path (i.e., short circuit) could form from materials deposited during arc events. 
     The cylindrical shields  1513   a - c  are physical structures with the shape of a hollow cylinder and are formed from either a conducting or an insulating material. The cylindrical shields  1513   a - c  are disposed around the stand-off insulators  1507   a - c.  The cylindrical shields  1513   a - c  are configured to prevent plasma and materials that are expelled when an arc is formed in the subassemblies  1501   a - c  from depositing on the stand-off insulators  1507   a - c.  The cylindrical shields  1513   a - c  are oriented vertically and are secured to and hang down from the upper plate  1504 . The cylindrical shields  1513   a - c  do not extend to the lower plate  1503  and thus do not provide a surface upon which a conductive path (i.e., short circuit) could form from materials deposited during arc events. 
     The insulating discs  1514   a - c  are disc-shaped physical structures that are disposed between the cylindrical shields  1513   a - c  and the upper plate  1504  and are formed from an insulating material. In some alternative embodiments, other types of discs could be used, such as conductive discs. In some embodiments, the insulating discs  1514   a - c  are 0.5-1 inches thick. The insulating discs  1514   a - c  are configured to further minimize or eliminate the possibility that a conduction path will form between the upper plate  1504  and the lower plate  1503  due to the materials emitted during arc events. 
       FIGS. 15C-D  are perspective views from below of the assembly  1500 . The upper plate  1504  is not shown in these figures. The roof  1519  and the adjustment mechanism  1518   a  of the lower clamp  1517   a  are shown in this figure. 
     The roof  1519  is a cone-shape physical structure and is configured to prevent rain and snow from entering the assembly  1500 . 
     The adjustment mechanism  1518   a  is a component of the lower clamp  1517   a  and is configured to adjustably control the tightness of the lower clamp  1517   a.  When the lower clamp  1517   a  is loosened using the adjustment mechanism  1518   a,  the position of the lower conductor  1508   a  may be adjusted. When the lower clamp  1517   a  is tightened using the adjustment mechanism  1518   a,  the lower conductor  1508   a  is held securely in place and cannot be moved or adjusted. In some embodiments, the adjustment mechanism  1518   a  includes thumb screws. Other embodiments of adjustment mechanism  1518   a  are possible as well. The lower clamps  1517   b - c  include adjustment mechanisms as well. 
       FIG. 15E  is a perspective view from below of the roof  1519  and the cage  1520  of the assembly  1500 . The cage  1520  is a physical structure that surrounds the subassemblies  1501   a - c  and is configured to prevent people and objects from touching the subassemblies  1501   a - c.  In some embodiments, the cage  1520  is not solid, but has openings to permit pressure, material, and gasses that are released during an arc event to escape. 
       FIG. 15F  is a perspective view of the cage  1520  of the assembly  1500 . The cage is formed from rings  1521   a - b,  which are joined by a plurality of columns, including columns  1522   a - c.  Other embodiments of cage  1520  are possible as well. 
       FIG. 16  is a circuit diagram of an overvoltage protection system  1600  according to another example embodiment. The system  1600  includes overvoltage protection assembly  1601  and self-testing assembly  1602 . Using the self-testing assembly  1602  a power system operator can ensure that the assembly  1601  will provide protection if a ground fault occurs after the thyristor (or the MOV) has failed to operate. 
     The assembly  1601  is a system configured to protect power systems from overvoltage events. In some embodiments, the assembly  1601  is attached the transformer neutral line. In some embodiments, the assembly  1601  is a spark gap. In other embodiments, the assembly  1601  is one of the other assemblies disclosed herein. 
     The self-testing assembly  1602  includes a voltage source  1603 , voltage probe  1604 , a fuse  1605 , and a current probe  1606 . Some embodiments do not include the current probe  1606 . 
     The voltage source  1603  is a voltage source capable of generating a high voltage. In some embodiments, the voltage source  1603  is an AC voltage source. 
     In operation, the voltage source  1603  is used to apply a high voltage but limited current to the assembly  1601  to allow measurement of the breakdown voltage of the assembly  1601 . The voltage source  1603  increases the voltage being applied to the assembly  1601  over time. For example, in some embodiments, the voltage is increased over 0.2-0.5 seconds. When the breakdown occurs, only a limited current from the voltage source  1603  will be allowed to flow through the assembly  1601 . In some embodiments, this is achieved by using a voltage source  1603  that is not capable of supplying large currents, such as some AC voltage sources. 
     The breakdown voltage of the spark gap can be determined by monitoring the voltage with the voltage probe  1604  as the voltage is increased to determine the voltage level at which breakdown occurs. In this manner, the operation of the assembly  1601  can be verified and confirmed to meet the specified breakdown voltage requirements. In some embodiments, the determined breakdown voltage is then sent to the power system operator and/or to the supervisory control and data acquisition (SCADA) system. 
     In the rare case that the assembly  1601  is activated by a power system ground fault, the fuse  1605  opens to protect the voltage source  1603 . 
     In alternate embodiments, the voltage source  1603  is a DC voltage source, which is also configured to increase the voltage over time (e.g., over 0.2-0.5 seconds in some embodiments). In this embodiment, the current probe  1606  monitors the current and deactivates the voltage source  1603  when a current is detected. 
     Referring to  FIGS. 1-16  generally, it is noted that in alternative embodiments, one or more of the features of the arrangement may be excluded. For example, in one possible embodiment, the surge arrester and Jacob&#39;s ladder may be integrated. In a further example embodiment, the surge arrester and spark gap could be used in combination, in the absence of the Jacob&#39;s ladder configuration extending from the spark gap. In such embodiments, arcs formed in the spark gap can be used to discharge electrical energy, but are not easily carried away from the spark gap once formed. It is further recognized that other implementations of this concept could be developed which in principle employ a set or subset of similar components which are arranged in a parallel electrical connection to provide protection for other components. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.