Improved graduated spark gap design for internally gapped surge arresters.

Abstract

A lightning arrester including a metal oxide varistor (MOV) disk and a spark gap assembly electrically connected in series with the MOV disk, the spark gap assembly including a spark gap and a frequency dependent grading capacitor electrically connected in parallel with the spark gap.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 313,050, filed February 23, 2022, the contents of which are incorporated by reference in their entirety.

[0002] FIELD OF THE DISCLOSURE Embodiments relate to surge arresters. [Background technology]

[0003] Surge arresters, which provide a current path from a conductor to electrical ground, protect power systems and associated components from power surges due to, for example, lightning strikes, electrical switching events, and / or other causes. Surge arrester designs may include a metal oxide varistor (MOV) stack comprised of one or more MOV devices or disks, which are highly nonlinear ceramic semiconductors that switch from an insulating state during normal operation to a conductive state in the presence of a power surge. During a power surge, the resistance of the MOV stack decreases, allowing the arrester to direct the surge current to ground. Thus, the voltage rise on the conductor during a power surge can be limited to a level that will not damage the power system or components. Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, the MOV disks in surge arresters can protect equipment from short duration power surges due to lightning strikes or electrical switching. However, MOV disks in surge arresters may not be effective in protecting against sustained overvoltage conditions that occur at typical line frequencies such as 50-60 Hz. Sustained overvoltages can increase the conductivity of the MOV disks by causing the arrester to overheat, thus increasing power losses. This can result in thermal runaway and short circuit failure within the arrester as it reaches a critical temperature. Short circuit failure of the arrester can cause severe power arcing and may even release hot debris into the environment, creating a dangerous situation for nearby personnel and equipment. [Means for solving the problem]

[0005] A first aspect provides a lightning arrester that includes a metal oxide varistor (MOV) disk and a spark gap assembly electrically connected in series with the MOV disk. The spark gap assembly includes a spark gap and a frequency dependent grading capacitor electrically connected in parallel with the spark gap.

[0006] A second aspect provides an accessory device electrically connected in series with a lightning arrestor, the accessory device including a spark gap assembly including a spark gap and a frequency dependent grading capacitor electrically connected in parallel with the spark gap.

[0007] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 illustrates a lightning arrestor according to some embodiments. [Diagram 2] 2 is a schematic diagram of the lightning arrestor of FIG. 1 according to some embodiments. [Diagram 3] 1 is a graph of dielectric constant versus frequency in accordance with some embodiments. [Figure 4A] 1A-1D are schematic diagrams of various lightning arrestor embodiments. [Figure 4B] 1A-1D are schematic diagrams of various lightning arrestor embodiments. [Figure 4C] 1A-1D are schematic diagrams of various lightning arrestor embodiments. [Diagram 5] FIG. 1 is a schematic diagram of a lightning arrestor according to some embodiments. [Figure 6] FIG. 1 is a schematic diagram of a lightning arrestor attachment device according to some embodiments. [Figure 7] 2 is a schematic diagram of materials used in the grading capacitor of the lightning arrestor of FIG. 1 according to some embodiments. [Figure 8] 1 is a graph of dielectric constant versus frequency in accordance with some embodiments. [Figure 9] 1 is a graph of dielectric constant versus frequency in accordance with some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 illustrates a lightning arrestor 100, such as a surge arrestor, according to some embodiments of the present application. The surge arrestor is included in an electrical system, such as an electrical power transmission grid, an electrical distribution grid, or other power supply system. The surge arrestor 100 includes a housing 105, a first stud 110 extending from a top of the housing 105, and a bottom stud 115 extending from a bottom of the housing 105. The first stud 110 electrically connects the surge arrestor 100 to an electrical power system 120. The second stud 115 electrically connects the surge arrestor 100 to a ground 125. The housing 105 may be formed of any suitable material, such as, but not limited to, ceramic, silicone rubber, and / or ethylene propylene diene monomer (EPDM) rubber.

[0010] The surge arrestor 100 further includes one or more metal oxide varistor (MOV) disks 130 and a spark gap assembly 135. In some embodiments, the MOV disk 130 is composed primarily of zinc oxide (ZnO) with one or more additives, such as bismuth (Bi), manganese (Mn), cobalt (Co), nickel (Ni), antimony (Sb), tin (Sn), chromium (Cr), aluminum (Al), silver (Ag), and / or boron (B).

[0011] As shown in the circuit diagram of Figure 2, the MOV disk(s) 130 are electrically connected in series with a spark gap assembly 135. The spark gap assembly 135 includes a spark gap 140 electrically connected in parallel with a grading capacitor 145. In some embodiments, the spark gap assembly 135 includes additional elements, such as electrode plates, springs, and / or insulating materials. For example, Figure 1 illustrates an embodiment in which the spark gap assembly includes a spring 150 electrically connected to the grading capacitor 145.

[0012] The grading capacitor 145 is frequency dependent. That is, in operation, the electrical properties (e.g., capacitance, dielectric constant, etc.) of the grading capacitor 145 depend on the frequency of the system 120 to which the surge arrester 100 is connected, and thus on the frequency of the voltage applied to the grading capacitor 145. The grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 decreases as the frequency of the system 120 increases. Specifically, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 decreases by at least 40% as the frequency of the system 120 increases from 60 Hz to 500 kHz. The grading capacitor 145 is preferably designed such that the effective or measured capacitance of the grading capacitor 145 decreases by at least 75% over the frequency range of the system 120 from 60 Hz to 500 kHz.

[0013] In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 is reduced by at least 45% over the frequency range of the system 120 from 60 Hz to 500 kHz. In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 is reduced by at least 50% over the frequency range of the system 120 from 60 Hz to 500 kHz. In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 is reduced by at least 55% over the frequency range of the system 120 from 60 Hz to 500 kHz. In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 is reduced by at least 60% over the frequency range of the system 120 from 60 Hz to 500 kHz. In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 decreases by at least 65% over the frequency range of the system 120 from 60 Hz to 500 kHz. In some embodiments, the grading capacitor 145 is designed such that the effective or measured capacitance of the grading capacitor 145 decreases by at least 70% over the frequency range of the system 120 from 60 Hz to 500 kHz. The grading capacitor 145 can be linear or non-linear. A linear grading capacitor 145 has a capacitance that is independent of the applied voltage. A non-linear grading capacitor has a capacitance that changes with the applied voltage.

[0014] To achieve the above-mentioned capacitance reduction, the materials comprising the grading capacitor 145 can be selected to be one or more capacitive materials having a frequency-dependent permittivity. That is, the grading capacitor 145 can be constructed or formed of any material that produces a suitable permittivity that is strongly enhanced at low system frequencies. For example, the grading capacitor 145 can be formed of one or more of "soft" or donor-doped ferroelectric ceramics, relaxor ferroelectric ceramics, and / or various composite materials (e.g., conductor-insulator composites) that exhibit enhanced low-frequency permittivity due to space charge effects.

[0015] FIG. 3 illustrates an exemplary graph 300 of the target permittivity (real and imaginary) of the grading capacitor 145 versus frequency. As illustrated, at low system frequencies, the real permittivity 305 of the grading capacitor 145 is much higher than the imaginary permittivity 310 of the grading capacitor 145. The dielectric loss tangent of the material used to form the grading capacitor 145 is the ratio between the imaginary permittivity of the material and the real permittivity of the material. In some embodiments, it is desirable for the grading capacitor 145 to have a dielectric loss tangent of 15% or less at a system frequency of 50 / 60 Hz. However, in some embodiments, it is preferable for the grading capacitor 145 to be configured to have an even lower dielectric loss tangent at a system frequency of 50 / 60 Hz. For example, it is particularly preferable for the grading capacitor 145 to be configured to have a dielectric loss tangent of less than 5% at a system frequency of 50 / 60 Hz. In some embodiments, it is desirable for the grading capacitor 145 to have a dissipation factor of 10% or less at a system frequency of 50 / 60 Hz. In some embodiments, even higher dissipation factors (50% or more) at a system frequency of 50 / 60 Hz are acceptable.

[0016] In addition to including the frequency dependent grading capacitor 145, the spark gap assembly 135 is designed such that the voltage sharing between the spark gap assembly and the MOV disk 130 is optimized. For example, the spark gap assembly 135 is designed to enable a particular voltage sharing between the MOV disk 130 and the spark gap 140 included in the spark gap assembly 145 when necessary for the application and desired performance of the surge arrestor 100. Additionally, the spark gap assembly 135 is designed such that the impulse sparkover voltage of the surge arrestor 100 is minimized at high frequencies (e.g., 500 kHz to 1 MHz).

[0017] In some embodiments, the spark gap assembly 135 is designed such that the impedance of the grading capacitor 145 is coordinated with the series impedance of the MOV disk 130. In some embodiments, the impedance of the grading capacitor 145 is designed or selected to be a first percentage of the total impedance of the surge arrestor 100 at a maximum continuous operating voltage (MCOV) of 50 / 60 Hz. In such embodiments, during a system voltage surge at a frequency between 30 kHz and 1 MHz, the relative impedance of the grading capacitor 145 increases to a second percentage higher than the first percentage of the total impedance of the surge arrestor 100. For example, during operation at 50 / 60 Hz MCOV, the impedance of the grading capacitor 145 can be 20-50% of the total impedance of the surge arrestor 100. However, as the frequency increases to 30 kHz-1 MHz for the same voltage, the impedance of the grading capacitor 145 increases to a value between 80-100% of the total impedance of the surge arrestor 100. That is, when the surge arrestor 100 is subjected to a high frequency surge event generated within the system 120, the percentage of the grading capacitor 145 in the total impedance of the surge arrestor increases.

[0018] In some embodiments, during 50 / 60 Hz MCOV operation, the impedance of the grading capacitor 145 is lower than the impedance of the MOV disk(s) 130 and therefore may account for less than 50% of the total impedance of the surge arrestor 100. During surges occurring at frequencies between 30 kHz and 1 MHz, the frequency dependent capacitance of the grading capacitor 145 reduces the impedance of the gap assembly 135 below the impedance of the MOV disk 130. This results in a change in the voltage sharing between the MOV disk(s) 130 and the gap assembly 135, reducing the voltage across the MOV disk(s) 130 and increasing the voltage across the gap assembly 135, which results in earlier ignition of the spark gap 140 at higher frequencies.

[0019] In comparison to existing spark gap assemblies, the spark gap assembly 135 utilizes only a single grading capacitor 145 that is rated to withstand the gap discharge inception voltage. The use of a single grading capacitor 145, as opposed to multiple grading circuit elements, reduces the cost and size of the spark gap assembly 135. Also, a spark gap assembly that includes only a single grading capacitor can dissipate less heat than a spark gap assembly that includes multiple circuit grading elements, especially during a surge event.

[0020] It should be understood that the embodiment of the surge arrestor 100 shown in Figures 1-2 and described above is merely an example, and that the surge arrestor 100 is not limited to the structure shown in Figures 1 and 2. For example, while shown as including a single MOV disk 130 and a single spark gap assembly 135, it should be understood that in some embodiments, the surge arrestor 100 includes multiple MOV disks 130 and / or multiple spark gap assemblies 135. In such embodiments, the total series impedance of the one or more spark gap assemblies 135 is coordinated with the total series impedance of the one or more MOV disks 130 to be 20-50% of the total impedance of the surge arrestor 100 during operation at 50 / 60 Hz MCOV. Furthermore, in such embodiments, the total series impedance of the one or more spark gap assemblies 135 is 80-100% of the total impedance of the surge arrestor 100 during a surge event at a frequency between 30 kHz and 1 MHz.

[0021] 4A-4C illustrate various embodiments of surge arrestor 100 including one or more MOV disks 130 and / or one or more spark gap assemblies 135. It should be understood that the embodiments illustrated in Figures 4A-4C are provided by way of example only and are not intended to limit surge arrestor 100 to include other combinations of series-connected MOV disks 130 and spark gap assemblies 135 not shown or described herein.

[0022] Further, it should be understood that the embodiment of the spark gap assembly 135 shown in Figures 1-2 and described above is by way of example only, and that the spark gap assembly 135 is not limited to the structure shown in Figures 1 and 2. For example, while a single spark gap 140 is shown as being electrically connected in parallel with a single grading capacitor 145, it should be understood that in some embodiments, the spark gap assembly 135 includes multiple spark gaps 140 and / or multiple grading capacitors 145. In such embodiments, the total series impedance of the one or more grading capacitors 145 is coordinated with the total series impedance of the MOV disk(s) 130 to be 20-50% of the total impedance of the surge arrestor 100 during operation at 50 / 60 Hz MCOV. Further, in such embodiments, the total series impedance of the one or more grading capacitors 145 is 80-100% of the total impedance of the surge arrestor 100 during a surge event at a frequency between 30 kHz and 1 MHz.

[0023] As an example, Figure 5 illustrates an embodiment in which the spark gap assembly 135 includes two series connected grading capacitors 145A, 145B electrically connected in parallel with the spark gap 140. It should be understood that the embodiment illustrated in Figure 5 is provided by way of example only and is not intended to limit the spark gap assembly 135 to include other combinations of series and / or parallel connected grading capacitors 145 electrically connected in parallel with the spark gap 140. In some embodiments, the spark gap assembly 135 also includes a resistor or a non-frequency dependent capacitor in addition to the at least one frequency dependent capacitor 145.

[0024] In some instances, it may be desirable to provide the protection provided by the spark gap assembly 135 described herein to existing and / or new surge arrestors that do not include their own spark gap assembly. Thus, in some embodiments, a spark gap assembly as described herein and / or illustrated in Figures 1-5 may be included in an accessory device configured to be electrically connected in series with a surge arrestor that does not include its own spark gap assembly.

[0025] 6 illustrates an exemplary embodiment of a spark gap assembly attachment 600. The attachment 600 includes a housing 605, a first stud 610 extending from a top of the housing 605, and a bottom stud 615 extending from a bottom of the housing 605. The first stud 610 electrically connects the attachment 600 to a surge arrestor 700 that does not include its own spark gap assembly. For example, the surge arrestor 700 can be a conventional MOV-based surge arrestor that includes one or more resistive components, such as the MOV disk 130, but does not include a spark gap assembly. The second stud 615 electrically connects the attachment 600 to ground 125. The housing 605 of the attachment 600 can be formed of any suitable material, such as, but not limited to, ceramic, glass, and / or nylon.

[0026] As shown, the attachment 600 further includes a spark gap assembly 135. Thus, when the attachment 600 is connected in series with the surge arrestor 800, the impedance of the grading capacitor 145 included in the spark gap assembly 135 coordinates with the series impedance of the MOV disk(s) 130 included in the surge arrestor 700 as described above.

[0027] In some instances, it is preferred that the grading capacitor be formed from a dielectric ceramic that contains both capacitive and resistive microstructural elements when sintered in air. One example of such a dielectric ceramic is Cu. 0.75 Ca 0.25 The dielectric ceramic is a perovskite ceramic with a chemical formula of TiO3. By nature, perovskite ceramics exhibit heterogeneous electrical conductivity and contain insulating grain boundaries and conductive grains such that the material behaves as a complex RC circuit. FIG. 7 is a general equivalent circuit diagram of a dielectric ceramic 700. The dielectric ceramic includes a grain circuit 810 connected in series with a grain boundary circuit 820. The grain circuit 810 includes a grain resistor 830 connected in parallel with a grain capacitor 840. The grain boundary circuit 820 includes a grain boundary capacitor 850 connected in parallel with a grain boundary capacitor 860. In some embodiments, the grain capacitor 840 and / or the grain boundary capacitor 860 can be represented as constant phase elements (CPEs). In one example, the gap grading element is made of 90-99.5% Cu. 0.75 Ca 0.25It is composed of TiO3 and 0.5-10% of additional doping elements selected to aid in microstructural formation or to modify the electrical properties of the ceramic. Two preferred dopants are aluminum oxide (Al2o3) and silica (SiO2). 0.75 Ca 0.25 Ti 0.97 FIG. 9 shows an example graph 900 of the target dielectric constant of a perovskite ceramic (used as the grading capacitor 145) having the structure CuO3+0.03Al2O3. 0.75 Ca 0.25 1 shows an example graph 1000 of the target dielectric constant of a perovskite ceramic (used as the grading capacitor 145) having the structure TiO3+0.03Al2O3+0.03SiO2.

[0028] Accordingly, the present disclosure provides a lightning arrester for protecting power systems from, among other things, high frequency surge events. Various features and advantages of the present disclosure are set forth in the following claims. [Explanation of symbols]

[0029] 100 Lightning arrester 105 Housing 110 First Stud 115 Second Stud 120 Power Systems 125 Grounding 130 Metal Oxide Varistor (MOV) Disk 135 Spark Gap Assembly 140 Spark Gap 145 Grading Capacitor 150 Spring

Claims

1. A lightning arrester comprising: A metal oxide varistor (MOV) disk; a spark gap assembly electrically connected in series with the MOV disk; Equipped with The spark gap assembly includes: Spark gap and a frequency dependent grading capacitor electrically connected in parallel with the spark gap; A lightning arrester comprising:

2. the capacitance of the frequency dependent grading capacitor decreases as the frequency of the voltage applied to the frequency dependent grading capacitor increases; 2. The lightning arrester according to claim 1.

3. when the frequency of the voltage applied to the frequency dependent grading capacitor increases from 60 Hertz (Hz) to 500 kHz, the capacitance of the frequency dependent grading capacitor decreases by at least 40%; The lightning arrester according to claim 2.

4. when the frequency of the voltage applied to the frequency dependent grading capacitor increases from 60 Hertz (Hz) to 500 kHz, the capacitance of the frequency dependent grading capacitor decreases by at least 75%; The lightning arrester according to claim 2.

5. the frequency dependent grading capacitor is constructed from materials including at least one of a donor doped ferroelectric ceramic, a relaxor ferroelectric ceramic, and an insulator-conductor composite that exhibits an enhanced low frequency dielectric constant due to space charge effects; The lightning arrester according to claim 2.

6. the frequency-dependent grading capacitor has a dielectric loss tangent of less than 15% when the frequency of a voltage applied to the frequency-dependent grading capacitor is 60 Hz; The lightning arrester according to claim 2.

7. the frequency-dependent grading capacitor has a dielectric loss tangent of less than 5% when the frequency of a voltage applied to the frequency-dependent grading capacitor is 60 Hz; The lightning arrester according to claim 2.

8. when a frequency of a voltage applied to the frequency dependent grading capacitor is a first frequency, an impedance of the frequency dependent grading capacitor is a first percentage of a total series impedance of the surge arrester; when the frequency of the voltage across the frequency dependent grading capacitor increases to a second frequency, the impedance of the frequency dependent grading capacitor increases to a second percentage of a total series impedance of the surge arrester.

2. The lightning arrester according to claim 1.

9. When the frequency of the voltage applied to the frequency-dependent grading capacitor is 60 Hz, the impedance of the frequency-dependent grading capacitor is less than 50% of the total series impedance of the surge arrester; when the frequency of the voltage across the frequency dependent grading capacitor increases from 30 kHz to 1 MHz, the impedance of the frequency dependent grading capacitor increases to at least 80% of the total series impedance of the surge arrester; 2. The lightning arrester according to claim 1.

10. one or more of the included MOV disks are comprised primarily of zinc oxide; 2. The lightning arrester according to claim 1.

11. An accessory device electrically connected in series with the lightning arrester, Spark gap and a frequency dependent grading capacitor electrically connected in parallel with the spark gap; a spark gap assembly including: An accessory device characterized in that

12. the frequency dependent grading capacitor is constructed from materials including at least one of a donor doped ferroelectric ceramic, a relaxor ferroelectric ceramic, and a conductor-insulator composite material that exhibits an enhanced low frequency dielectric constant due to space charge effects; 12. The accessory device of claim 11.

13. the capacitance of the frequency dependent grading capacitor decreases as the frequency of the voltage applied to the frequency dependent grading capacitor increases; 12. The accessory device of claim 11.

14. when the frequency of the voltage applied to the frequency dependent grading capacitor increases from 60 Hertz (Hz) to 500 kHz, the capacitance of the frequency dependent grading capacitor decreases by at least 40%; 14. The accessory device of claim 13.

15. when the frequency of the voltage applied to the frequency dependent grading capacitor increases from 60 Hertz (Hz) to 500 kHz, the capacitance of the frequency dependent grading capacitor decreases by at least 75%; 14. The accessory device of claim 13.

16. the frequency-dependent grading capacitor has a dielectric loss tangent of less than 15% when the frequency of a voltage applied to the frequency-dependent grading capacitor is 60 Hz; 14. The accessory device of claim 13.

17. the frequency-dependent grading capacitor has a dielectric loss tangent of less than 5% when the frequency of a voltage applied to the frequency-dependent grading capacitor is 60 Hz; 14. The accessory device of claim 13.

18. when a frequency of a voltage applied to the frequency dependent grading capacitor is a first frequency, an impedance of the frequency dependent grading capacitor is a first percentage of a combined series impedance of the frequency dependent grading capacitor and the lightning arrestor; when the frequency of the voltage across the frequency dependent grading capacitor increases to a second frequency, the impedance of the frequency dependent grading capacitor increases to a second percentage of a combined series impedance of the frequency dependent grading capacitor and the surge arrestor.

12. The accessory device of claim 11.

19. When the frequency of the voltage applied to the frequency-dependent grading capacitor is 60 Hz, the impedance of the frequency-dependent grading capacitor is less than 50% of the combined series impedance of the frequency-dependent grading capacitor and the lightning arrester.

20. The accessory device of claim 18.

20. When the frequency of the voltage applied to the frequency dependent grading capacitor is greater than 30 kHz, the impedance of the frequency dependent grading capacitor is at least 80% of the combined series impedance of the frequency dependent grading capacitor and the surge arrester.

20. The accessory device of claim 19.

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