Metal Oxide Varistor Formulation

Abstract

Provided are metal oxide varistors including a sintered ceramic, wherein the ceramic comprises by weight about 91.0% to about 97.0% ZnO, at least 0.3% Mn, at least 0.4% Bi, at least 1.0% Sb, and 0.50% or less Co. The metal oxide varistors as disclosed herein may exhibit reduced power consumption, improved thermal stability, and may be produced at a lower cost relative to conventional MOV devices.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to U.S. Provisional Application No. 62 / 951,183, filed on December 20, 2019, the contents of which are incorporated herein by reference in their entirety, and priority is hereby claimed. Technical Field

[0003] The present disclosure relates to metal oxide varistor formulations that can reduce production costs and improve thermal stability compared to conventional formulations. Background Art

[0004] Surge protection in both high-voltage and low-voltage circuits is typically provided by surge arresters using one or more metal oxide varistors (MOVs). MOVs act as varistors that reversibly switch between a low-resistivity state and a high-resistivity state over a narrow voltage range. Near the switching voltage, the voltage-current relationship is often a power-law relationship, I=CV α , where α is a nonlinear coefficient and C is a constant. In some materials, the peak value of α can exceed 40-50. MOVs are typically rated by manufacturers for various characteristics, which can include maximum continuous operating voltage (MCOV), temporary overvoltage (TOV) capability, and residual voltage during a specified surge event (e.g., 8×20μs surge at 10000A). Commercially available MOVs for high voltage applications are rated for specific duty levels according to the guidelines given by the US IEEE C62.11 standard or the international IEC 60099-4 standard.

[0005] The nonlinear VI characteristics of MOVs originate from the addition of elements. The MOV microstructure consists of n-type semiconductor ZnO grains and resistive grain boundaries. The composition of the grain boundaries is quite different, containing Bi2O3 and other modifying elements such as Mn, Co and Sb. The interface states located at the grain boundaries behave as electron traps and capture the conduction band electrons in the adjacent n-type ZnO. This process causes a double Schottky barrier at the grain boundaries that hinders the flow of electrons. The current leakage through the Schottky barrier is thermally activated, and the power consumption of the MOV in the range of 1.0-1.25*MCOV is generally very temperature dependent. If the MOV is repeatedly exposed to surge loads and overheats, the power consumption at the MCOV may exceed the level that the arrester housing can dissipate, causing the arrester to fail due to thermal runaway.

[0006] Therefore, there is still a need for alternative MOV formulations to improve thermal stability and nonlinear characteristics. Summary of the invention

[0007] In one aspect, the present disclosure provides a metal oxide varistor, comprising:

[0008] Sintered ceramics, containing by weight:

[0009] about 91.0% to about 97.0% ZnO;

[0010] At least 0.3% Mn;

[0011] At least 0.4% Bi;

[0012] At least 1.0% Sb; and

[0013] 0.50% or less Co.

[0014] In another aspect, the present disclosure provides a surge arrester for protecting one or more conductors from a power surge, the surge arrester comprising the metal oxide varistor described herein, wherein the surge current is diverted from the one or more conductors to ground through the metal oxide varistor.

[0015] The metal oxide varistors described herein exhibit reduced power consumption, improved thermal stability, and can be produced at a lower cost relative to conventional MOVs.

[0016] Other aspects of the application will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The variation of W / kV MCOV with temperature is shown for the three MOV formulations provided in Table 1. The reference material ("REF") is a commercially available MOV used in IEEE C62.11-2012 "Normal Duty" surge arresters. DETAILED DESCRIPTION

[0018] Before explaining any embodiments of the present application in detail, it will be understood that the present application is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The present application is capable of realizing other embodiments and can be practiced or implemented in various ways.

[0019] As used herein, the terms "includes," "comprising," "having," "having," "can," "containing," and variations thereof are intended to be open-ended transitional phrases, terms, or words that do not exclude the possibility of additional actions or structures. The singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments that "include," "consist of," and "consist essentially of," the embodiments or elements presented herein, whether or not explicitly stated.

[0020] The modifier "about" used in conjunction with a quantity includes the nominal value and has the meaning dictated by the context (e.g., including at least the degree of error associated with the measurement of a particular quantity). The modifier "about" should also be considered to disclose a range defined by the absolute values ​​of the two endpoints. For example, the expression "from about 2 to about 4" also discloses a range of "from 2 to 4". The term "about" can refer to plus or minus 10% of the indicated number. For example, "about 10%" can mean a range of 9% to 11%, while "about 1" can mean from 0.9 to 1.1. Other meanings of "about" will be apparent from the context, such as rounding, so, for example, "about 1" may also mean from 0.5 to 1.4.

[0021] For the recitation of numerical ranges herein, each intervening number with the same degree of precision is expressly contemplated. For example, for the range of 6 to 9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range of 6.0 to 7.0, the numbers 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 and 7.0 are expressly contemplated.

[0022] The term "metal oxide varistor (MOV)" refers to an oxide ceramic material, or an electrical unit fabricated therefrom, that exhibits a highly nonlinear relationship between voltage and current, such that the resistivity of the material decreases significantly as voltage increases.

[0023] The term "maximum continuous operating voltage (MCOV)" means 0.4 mA / cm at 20°C. 2 80% of the reference voltage measured at a peak current density of 60 Hz. Unless otherwise stated, all voltages and currents are defined as peak values ​​for 60 Hz. Voltage values ​​may alternatively be expressed in RMS units.

[0024] Unless otherwise stated, chemical elements (e.g., Mn, Co, Bi, Sb) as disclosed herein may be included in the formulation in any suitable molecular form. These include, for example, commercially available oxides, carbonates, hydroxides, nitrates, mixed oxide precursors, and other molecular forms of the element known in the art.

[0025] The present disclosure relates to a chemical formulation for making MOVs that can be used in high voltage surge arresters, such as those governed by IEEE C62.11, IEC 60099-4, or similar standards.

[0026] In one aspect, the present disclosure provides a metal oxide varistor, comprising:

[0027] Sintered ceramics, including by weight:

[0028] about 91.0% to about 97.0% ZnO;

[0029] At least 0.3% Mn;

[0030] At least 0.4% Bi;

[0031] At least 1.0% Sb; and

[0032] 0.50% or less Co.

[0033] As described herein, sintered ceramic refers to a sintering recipe that provides a ceramic body for a metal oxide varistor (MOV). It should be understood that the present sintering recipe is adapted to the operating conditions of the MOV in accordance with standards known in the art, such as temperature, voltage, and current. The metal oxide varistor may also include a first electrode having a first electrode surface and a second electrode having a second electrode surface. For example, the sintered ceramic may be sandwiched between two metal plates that serve as electrodes of the varistor.

[0034] The formulation may include at least 91.0%, at least 92.0%, at least 93.0%, at least 94.0%, at least 95.0%, or at least 96.0% ZnO by weight. The formulation may include less than 97.0%, less than 96.0%, less than 95.0%, less than 94.0%, less than 93.0%, or less than 92.0% ZnO by weight. The formulation may include about 92.0% to about 97.0%, about 93.0% to about 97.0%, about 94.0% to about 97.0%, or about 95.0% to about 97.0% ZnO by weight. In some embodiments, the formulation includes about 95.0% to about 97.0% ZnO by weight, such as about 95.5%, about 96.0%, or about 96.5% ZnO by weight.

[0035] The formulation may contain 0.4% or less, 0.3% or less, 0.2% or less, or 0.1% or less cobalt (Co) by weight. In some embodiments, the formulation contains 0.20% or less Co by weight, such as 0.18% or less, 0.15% or less, 0.12% or less, 0.10% or less, 0.09% or less, 0.08% or less, 0.07% or less, 0.06% or less, 0.05% or less, 0.04% or less, 0.03% or less, 0.02% or less, 0.01% or less, 0.005% or less, or 0.001% or less Co by weight. In some embodiments, the formulation is free of Co.

[0036] Co may be included in the formulation at least in part in the form of cobalt oxide, such as Co3O4. For example, the formulation may contain 0.68% or less by weight Co3O4, corresponding to 0.50% or less by weight Co. In some embodiments, the formulation contains 0.60% or less by weight Co3O4, such as 0.50% or less, 0.40% or less, 0.30% or less, 0.20% or less, 0.10% or less, 0.05% or less, 0.01% or less, 0.005% or less, or 0.001% or less by weight Co3O4. In some embodiments, the formulation contains no Co3O4.

[0037] The formulation may include at least 0.3% manganese (Mn) by weight, such as at least 0.4%, at least 0.5%, at least 0.6%, at least 0.7%, at least 0.8%, at least 0.9%, or at least 1.0% Mn by weight. The formulation may include less than 1.0%, less than 0.9%, less than 0.8%, less than 0.7%, less than 0.6%, less than 0.5%, or less than 0.4% Mn by weight. The formulation may include at least 0.3% to about 1.0%, about 0.4% to about 1.0%, about 0.4% to about 0.9%, or about 0.4% to about 0.8% Mn by weight. In some embodiments, the formulation includes about 0.4% to about 0.8% Mn by weight, such as about 0.4%, about 0.5%, about 0.6%, about 0.7%, or about 0.8% Mn by weight.

[0038] Mn can be included in the formulation at least in part in the form of manganese oxide, such as MnO. For example, the formulation may contain at least 0.39% by weight of MnO, corresponding to at least 0.30% by weight of Mn. In some embodiments, the formulation contains at least 0.40% to about 1.30%, about 0.50% to about 1.30%, about 0.50% to about 1.20%, about 0.50% to about 1.10%, or about 0.50% to about 1.00% MnO by weight. In some embodiments, the formulation contains about 0.50% to about 1.00% MnO by weight, such as about 1.00%, about 0.90%, about 0.80%, about 0.70%, about 0.60%, or about 0.50% by weight of MnO.

[0039] In some embodiments, the combined amount of Mn(x) and Co(y) in the formulation satisfies z=1.29x+1.36y, wherein x is at least 0.31%, y is 0.00% to 0.50%, and z is about 0.75% to about 1.25%. The z value can be about 0.80%, about 0.90%, about 1.00%, about 1.10%, or about 1.20%.

[0040] The formulation may include at least 1.0% antimony (Sb) by weight, such as at least 1.25%, at least 1.50%, at least 1.75%, at least 2.00%, at least 2.25%, at least 2.50%, or at least 2.75% Sb by weight. The formulation may include less than 3.00%, less than 2.75%, less than 2.50%, less than 2.25%, less than 2.00%, less than 1.75%, less than 1.50%, or less than 1.25% Sb by weight. The formulation may include at least 1.00% to about 3.00%, at least 1.00% to about 2.50%, about 1.25% to about 2.50%, or about 1.50% to about 2.50% Sb by weight. In some embodiments, the formulation comprises about 1.50% to about 2.50% by weight Sb, such as about 1.70%, about 1.80%, about 1.90%, about 2.00%, about 2.10%, or about 2.20% by weight Sb.

[0041] Sb may be included in the formulation at least in part in the form of antimony oxide, such as Sb2O3. For example, the formulation may contain at least 1.20% by weight Sb2O3, corresponding to at least 1.00% by weight Sb. In some embodiments, the formulation contains at least 1.20% to about 3.60%, about 1.50% to about 3.60%, about 1.80% to about 3.60%, about 1.80% to about 3.40%, about 1.80% to about 3.20%, or about 1.80% to about 3.00% Sb2O3 by weight. In some embodiments, the formulation contains about 1.80% to about 3.00% by weight Sb2O3, such as about 2.00%, about 2.25%, about 2.50%, or about 2.75% by weight Sb2O3.

[0042] The formulation may include at least 0.4% by weight bismuth (Bi), such as at least 0.50%, at least 0.60%, at least 0.70%, at least 0.80%, at least 0.90%, at least 1.00%, at least 1.10%, at least 1.20%, at least 1.30%, at least 1.40%, at least 1.50%, at least 1.60%, at least 1.70%, at least 1.80%, or at least 1.90% Bi by weight. The formulation may contain less than 2.00%, less than 1.90%, less than 1.80%, less than 1.70%, less than 1.60%, less than 1.50%, less than 1.40%, less than 1.30%, less than 1.20%, less than 1.10%, less than 1.00%, less than 0.90%, less than 0.80%, less than 0.70%, less than 0.60%, or less than 0.50% Bi by weight. The formulation may contain at least 0.40% to about 2.0%, about 0.50% to about 2.00%, about 0.50% to about 1.80%, about 0.50% to about 1.50%, about 0.50% to about 1.20%, or about 0.50% to about 1.00% Bi by weight. In some embodiments, the formulation comprises about 0.50% to about 1.00% by weight Bi, such as about 0.60%, about 0.70%, about 0.80%, about 0.90%, or about 1.00% by weight Bi.

[0043] Bi may be included in the formulation at least in part in the form of bismuth oxide, such as Bi2O3. For example, the formulation may contain at least 0.44% by weight Bi2O3, corresponding to at least 0.40% by weight Sb. In some embodiments, the formulation contains at least 0.44% to about 2.20%, about 0.50% to about 2.20%, about 0.60% to about 2.00%, about 0.60% to about 1.50%, or about 0.60% to about 1.20% Bi2O3 by weight. In some embodiments, the formulation contains about 0.60% to about 1.20% Bi2O3 by weight, such as about 0.70%, about 0.80%, about 0.90%, about 1.00%, about 1.10%, or about 1.20% Bi2O3 by weight.

[0044] The formulation may include Sb and Bi in a molar ratio of Sb:Bi=2:1 or greater. The molar ratio of Sb to Bi may be, for example, at least 2.5:1, at least 3.0:1, at least 4.0:1, at least 5.0:1, at least 6.0:1, or at least 7.0:1. In some embodiments, the molar ratio of Sb:Bi is from about 2.5:1 to about 5.0:1, such as about 3.0:1, about 4.0:1, about 4.5:1, or about 4.8:1.

[0045] In a first embodiment, the formulation comprises, by weight of the formulation, 91.0% to about 97.0% ZnO, at least 0.30% to about 1.00% Mn, about 1.00% to about 3.00% Sb, about 0.40% to about 2.00% Bi, and 0.50% or less Co. For example, such a formulation may comprise, by weight, at least 0.39% to about 1.29% MnO (corresponding to at least 0.30% to about 1.00% Mn), about 1.20% to about 3.59% Sb2O3 (corresponding to about 1.00% to about 3.00% Sb), about 0.44% to about 2.23% Bi2O3 (corresponding to about 0.40% to about 2.00% Bi), and about 0.68% or less Co3O4 (corresponding to 0.50% or less Co).

[0046] In a second embodiment, the formulation comprises, by weight of the formulation, 91.0% to about 97.0% ZnO, about 1.50% to about 2.50% Sb, about 0.50% to about 1.00% Bi, about 0.40% to 0.80% Mn, and 0.50% or less Co. For example, the formulation may comprise, by weight, about 1.80% to about 2.99% Sb2O3 (corresponding to about 1.50% to about 2.50% Sb), about 0.56% to about 1.11% Bi2O3 (corresponding to about 0.50% to about 1.00% Bi), about 0.52% to about 1.03% MnO (corresponding to about 0.40% to about 0.80% Mn), and about 0.68% or less Co3O4 (corresponding to 0.50% or less Co).

[0047] In the first and second embodiments, the total amount of Mn and Co can be in the range of about 0.70% to about 1.00% by weight of the formulation. For example, the formulation can include Mn in the form of MnO and Co in the form of Co3O4, and the combined amount of MnO and Co3O4 is about 0.75% to about 1.25% by weight of the formulation.

[0048] In the first and second embodiments, the amount of Co can be reduced to 0.20% or less. For example, the formulation can contain 0.27% or less Co3O4 (corresponding to 0.20% or less Co). In the first and second embodiments, the molar ratio of Sb to Bi can be 2:1 or greater, such as 4:1 or greater.

[0049] In a third embodiment, the formulation includes, by weight of the formulation: 91.0% to about 97.0% ZnO, about 0.50% to about 1.00% MnO, about 1.75% to about 2.25% Sb2O3, about 0.50% to about 1.00% Bi2O3, and 0.2% or less Co3O4. In a third embodiment, the total amount of Mn and Co can be about 0.50% to about 1.00% by weight of the formulation, and the molar ratio of Sb to Bi can be 4:1 or greater.

[0050] The formulations described herein may also include one or more additives known in the art, such as Ag, Al, B, Cr, K, Ni, Si, Sn, or combinations thereof. The additives in the MOV formulation may promote the processing, sintering, and / or microstructural evolution of the ceramic. The additives may be included in the formulation in various molecular forms such as oxides, carbonates, hydroxides, or nitrates. Suitable oxides for additives include, for example, AgO, Ag2O, Al2O3, B2O3, Cr2O3, K2O, NiO, SiO2, and SnO2. In some embodiments, the formulation may preferably include B and / or K to promote liquid phase formation, and may also include other dopants or sintering aids. In some embodiments, the formulation may include Al and / or other dopant species (e.g., 5-20ppm) to provide conductivity within the ZnO grains.

[0051] Any other additives present in the formulation may comprise from about 0.001% to 0.500% or more by weight. For example, the formulation may comprise one or more additives selected from AgO, Ag2O, Al2O3, B2O3, Cr2O3, K2O, NiO, SiO2, and SnO2, each of which, if present, is about 0.005%, about 0.010%, about 0.020%, about 0.030%, about 0.040%, or about 0.045% by weight. In some embodiments, the formulation includes one or more additives selected from Ag2O, Al2O3, B2O3, and K2O, each of which, if present, is about 0.020%, about 0.025%, or about 0.030% by weight. In some embodiments, the formulation includes Ag2O, Al2O3, B2O3, and K2O, each of which is about 0.020%, about 0.025%, or about 0.030% by weight.

[0052] In some embodiments, each of the first electrode surface and the second electrode surface has at least 4 cm 2 The surface area can be about 5.0 cm 2 、About 8cm 2 , about 10cm 2 , or about 15cm 2In some embodiments, the distance between the first electrode surface and the second electrode surface is at least 15 mm. For example, the distance can be the distance between two metal plates that act as varistor electrodes. The distance between the first electrode surface and the second electrode surface can be about 16 mm, about 18 mm, about 20 mm, about 22 mm, or about 25 mm. The surface area and distance can be adjusted for a particular application. In some embodiments, the area of ​​each of the first electrode surface and the second electrode surface is at least 4 cm 2 , and the distance between the first electrode surface and the second electrode surface is at least 15 mm.

[0053] In some embodiments, the metal oxide varistor as described herein has a maximum continuous operating voltage (MCOV) of at least 3.0 kV RMS, such as at least 4.0 kV, at least 4.5 kV, at least 5.0 kV, at least 5.5 kV, at least 6.0 kV, or at least 6.5 kV RMS. For example, the MCOV may be about 4.8 kV, about 5.0 kV, about 5.2 kV, about 5.4 kV, about 5.6 kV, about 5.8 kV, or about 6.0 kV.

[0054] In some embodiments, the metal oxide varistor as described herein has a power consumption of less than 0.1 W / kV at 60 Hz at a maximum continuous operating voltage (MCOV) at 100° C., or less than 0.2 W / kV at 60 Hz at a maximum continuous operating voltage (MCOV) at 150° C. The power consumption at 60 Hz at MCOV at 100° C. may be less than 0.07 W / kV, less than 0.05 W / kV, or less than 0.02 W / kV. The power consumption at 60 Hz at MCOV at 150° C. may be less than 0.18 W / kV, less than 0.15 W / kV, less than 0.12 W / kV, or less than 0.10 W / kV.

[0055] In some embodiments, the ratio of the power consumption of the metal oxide varistor at 150°C to the power consumption at 20°C, both measured at 60Hz under MCOV, is less than 20. For example, the ratio of the power consumption at 150°C to the power consumption at 20°C can be less than 15, less than 10, less than 5, or less than 2.

[0056] The MOV formulations as described herein can be manufactured by methods known in the art. A typical manufacturing process may include pre-reacting the raw materials via a mixing or grinding process, calcining, remixing with zinc oxide, and spray drying to form a powder. The powder can then be pressed into the desired shape and heat treated in one or more stages at up to 1150°C. During this period, any organic binder is removed and the material is sintered to form a dense ceramic. Typical post-processing operations include grinding and metallization of the electrode faces, application of an electrically insulating glaze, and additional heat treatment steps.

[0057] MOVs produced using the formulations described herein have performance advantages over existing commercial MOV devices. In particular, the present formulations and MOVs exhibit reduced power consumption in the range of 1.0-1.25*MCOV at high temperatures (e.g., 100-180°C). The reduced risk of thermal runaway can allow surge arresters to use smaller MOVs to meet functionally equivalent design specifications. When Mn is used to replace Co in the MOV formulation, the power consumption at V=l.2-l.25*MCOV and T≥100°C is improved relative to a similar formulation containing both Mn and Co. The degree of improvement increases as Mn / (Mn+Co) increases from 0.5 to 1.0. Increasing Mn / (Mn+Co) reduces the nonlinear coefficient (α) at ​​higher current densities, and the formulation can be adjusted for specific application conditions. The formulation can also be adjusted to optimize other properties of interest, such as the stability of electrical properties relative to time under AC excitation or relative to pulse loads.

[0058] As a result of improved heat recovery, MOVs as described herein generally meet or exceed the performance of conventional MOVs used in high voltage surge arresters. In arrester designs limited by thermal performance, the present disclosure can allow the volume of the MOV to be reduced by 10% or more. This reduction in volume can be achieved, for example, by reducing the cross-sectional area of ​​the MOV block or increasing the voltage gradient V res / mm to achieve, where V res Indicates the residual voltage of the MOV for a given pulse wave.

[0059] For measuring the V of MOV res The pulse condition is defined herein as a nominal 8×20μs waveform at a peak of 5kA for MOVs used in IEEE "normal load" or IEC "medium distribution" arresters, and 8×20μs at a peak of 10kA for MOVs used in IEEE "high load" or IEC "high distribution" arresters and MOVs used in station arresters. MOVs used in distribution arresters are preferably manufactured to V res / mm is between 420-625, and most preferably between 450-525. For station-level MOV, V res / mm is preferably 325-525. The voltage gradient can be adjusted, for example, by adjusting the sintering temperature or the MOV recipe.

[0060] In addition to improved thermal stability and reduced nonlinearity, MOVs as described herein can be produced at significantly reduced costs over existing commercial MOVs due to reduced use of expensive raw materials. In particular, reducing or eliminating Co in MOV formulations is of strategic importance due to price fluctuations and high demand pressures from other commercial applications such as lithium battery manufacturing. The degree of Co used can be adjusted to meet the specific needs of the surge arrester design. A completely cobalt-free formulation can meet or exceed the typical performance of known high voltage MOV devices.

[0061] In another aspect, the present disclosure provides a surge arrester for protecting one or more conductors from power surges, the surge arrester comprising a metal oxide varistor as described herein, wherein the surge current travels from the conductor to ground through the metal oxide varistor. The surge arrester can be constructed using one or more metal oxide varistors according to known methods.

[0062] In some embodiments, surge arresters as described herein are designed for high voltage applications covered by applicable national or international standards (such as IEEE C62.11, IEC 60099-4, or other national standards derived therefrom) and are rated for a 4×10 μs surge current of approximately 65 kA or higher.

[0063] Example

[0064] Example 1

[0065] Example formulations (A, B, and C) with different amounts of Mn and Co were prepared according to Table 1. The properties of these formulations are shown in Table 2. The "REF" material is a commercially available MOV used in IEEE C62.12 "normal load" surge arresters. For all MOVs, nonlinear coefficient (α) values ​​were calculated between 3 mA and 5 kA, and the physical dimensions of these MOVs are almost the same. Each α value represents an average value between 3 mA and 5 kA. These three formulations show α values ​​comparable to or better than commercial materials. It is worth noting that as Co is replaced by Mn, the α value decreases.

[0066] Table 1: MOV formulations AC (weight percentage values)

[0067] MnO <![CDATA[Co3O4]]> <![CDATA[Sb2O3]]> <![CDATA[Bi2O3]]> <![CDATA[B2O3]]> <![CDATA[K2O]]> <![CDATA[Ag2O]]> <![CDATA[Al2O3]]> ZnO A 0.97％ 0％ 2.39％ 0.82％ 0.024％ 0.025％ 0.018％ 0.0015％ 95.8％ B 0.90％ 0.09％ 2.41％ 0.82％ 0.024％ 0.025％ 0.018％ 0.0015％ 95.7％ C 0.54％ 0.54％ 2.51％ 0.86％ 0.025％ 0.026％ 0.019％ 0.0023％ 95.5％

[0068] Table 2: Dimensions and properties of MOV formulations

[0069]

[0070] like Figure 1As shown, power dissipation at MCOV (shown as RMS Watts per kV of MCOV) was measured for three example formulations and a commercial MOV ("REF"). Formulations A, B, and C demonstrate approximately an order of magnitude improvement in power dissipation at MCOV over the commercial MOV. These formulations also demonstrate a reduced temperature dependence of power dissipation. Formulations A (0% Co3O4) and Formulation B (0.09% Co3O4) show additional reductions in power dissipation over a temperature range of approximately 75-180°C compared to Formulation C (0.54% Co3O4), which is attributed to the use of Mn instead of Co in these formulations.

[0071] Additional MOV formulations were prepared and tested. Table 3 shows the weight percentages of the elements calculated based on the corresponding oxides included in the formulations. Formulations B, D, and G showed the overall best performance under the conditions tested.

[0072] Table 3: MOV formulation DG (weight percentage values)

[0073]

[0074] Various features and advantages of the present application are set forth in the following claims.

Claims

1. A metal oxide varistor, comprising: Sintered ceramic comprising, by weight: 91.0% to 97.0% ZnO; At least 0.3% to 1.0% Mn; At least 0.4% to 2.0% Bi; at least 1.0% to 3.0% Sb; and 0.5% or less Co.

2. The metal oxide varistor according to claim 1, wherein: The ceramic contains 0.3% or less Co by weight of the formulation.

3. The metal oxide varistor according to claim 1, wherein: The ceramic contains 0.2% or less Co by weight of the formulation.

4. The metal oxide varistor according to claim 1, wherein: The ceramic contains 0.1% or less Co by weight of the formulation.

5. The metal oxide varistor according to claim 1, wherein: Ceramics do not contain Co.

6. The metal oxide varistor according to claim 1, wherein: The ceramic comprises by weight: 0.4% to 0.8% Mn; 0.5% to 1.0% Bi; and 1.5% to 2.5% Sb.

7. The metal oxide varistor according to any one of claims 1 to 6, wherein: The combined amount of MnO and Co3O4 is 0.75% to 1.25% by weight.

8. The metal oxide varistor according to any one of claims 1 to 6, wherein: The molar ratio of Sb to Bi is 2:1 or more.

9. The metal oxide varistor according to any one of claims 1 to 6, wherein: The molar ratio of Sb to Bi is 4:1 or more.

10. The metal oxide varistor according to any one of claims 1 to 6, wherein: The ceramic further comprises an additive comprising Ag, Al, B, Cr, K, Ni, Si, Sn or a combination thereof.

11. The metal oxide varistor according to any one of claims 1 to 6, further comprising: A first electrode having a first electrode surface and a second electrode having a second electrode surface, wherein an area of ​​each of the first electrode surface and the second electrode surface is at least 4 cm 2 , and wherein the distance between the first electrode surface and the second electrode surface is at least 15 mm.

12. The metal oxide varistor according to any one of claims 1 to 6, wherein: The metal oxide varistor has a maximum continuous operating voltage (MCOV) of at least 3.0 kV RMS.

13. The metal oxide varistor according to claim 12, wherein: The maximum continuous operating voltage (MCOV) is at least 4.5 kV RMS.

14. The metal oxide varistor according to any one of claims 1 to 6, wherein: The power consumption of the metal oxide varistor at 60 Hz under a maximum continuous operating voltage (MCOV) at 100° C. is less than 0.1 W / kV, or the power consumption at 60 Hz under a maximum continuous operating voltage (MCOV) at 150° C. is less than 0.2 W / kV.

15. The metal oxide varistor according to any one of claims 1 to 6, wherein: The ratio of power consumption at 150°C to power consumption at 20°C is less than 20, both measured at 60Hz under MCOV.

16. A surge arrester for protecting one or more conductors from power surges, the surge arrester comprising a metal oxide varistor according to any one of claims 1 to 15, wherein a surge current travels from the conductor to ground through the metal oxide varistor.

17. A surge arrester according to claim 16, designed for high voltage applications covered by an applicable national or international standard such as IEEE C62.11 or IEC 60099-4 or other national standards derived therefrom, and rated for a 4 x 10 μs surge current of 65 kA or more.

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