The Applications of varistor metal oxide

To protect telecommunication lines, transient suppression devices such as 3 mil carbon blocks (IEEE C62.32), ultra-low capacitance varistor metal oxide , and avalanche diodes are used. For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized.[citation needed] A typical surge protector power strip is built using xatge MOV . Low-cost versions may use only one varistor, from the hot (live, active) to the neutral conductor. A better protector contains at least three varistors; one across each of the three pairs of conductors. In the United States, a power strip protector should have an Underwriters Laboratories (UL) 1449 3rd edition approval so that catastrophic MOV failure does not create a fire hazard.

MOV Block and metal oxide varistor application

In general, the primary case of varistor breakdown is localized heating caused as an effect of thermal runaway. metal oxide varistor application is to a lack of conformity in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress. If the energy in a transient pulse (normally measured in joules)MOV Block is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This (catastrophic) failure occurs when "Absolute Maximum Ratings" in manufacturer's data-sheet are significantly exceeded.

XAGET Metal oxide arrester features

high performance movs blocks varistor valve main ingredient is zinc oxide, zinc oxide varistor has a very excellent nonlinear characteristics. Under normal operating voltage of the resistance value is high, in fact, equivalent to an insulator, and over-voltage action, the resistance of the resistor is very small, residual pressure is very low. But under normal operating voltage, since the valve frequency voltage is applied to long-term exposure arising from deterioration caused by changes in resistance characteristics, resulting in increased flow through the valve leakage current. The resistive component of the current sharp increase in temperature will rise valves on thermal collapse, severe, or even cause explosion? AC and DC High Performance MOV . In accordance with the provisions of rules 1, XAGET Metal oxide arrester total of six test items, namely (1) Insulation resistance (2) leakage current DC U1mA and 0.75U1mA under (3) AC operation voltage leakage current (4) Power frequency frequency reference voltage (5) Base insulation resistance (6) Check discharge counter action case reference current.

MOV on the proper use of distribution transformers

Metal oxide arrester ?during normal operation and distribution transformers in parallel, the terminating line, the lower end of the ground. The pressure generated when the three parts? MOV for Counter When the line overvoltage occurs, this time over-voltage distribution transformer will be subjected by lightning, leads and grounding devices drop, known as residual pressure. In this three-part over voltage,?lightning arrester?residual pressure on its own performance related to its residual voltage value is constant. Residual voltage on the grounding device can be connected to the grounding deflectors distribution transformer housing, then connected to the grounding device and how to eliminate them. And how to reduce the residual voltage of the leads has become the key to the protection of distribution transformers.

Lead impedance and current frequency through, the higher the frequency, the inductance of the wire, the stronger the greater impedance. From U = IR shows that to reduce the residual pressure on the lead, you have to narrow the lead impedance, and possible ways to reduce the lead impedance is to shorten the distance between the arrester from the distribution transformer to reduce the lead impedance, lower lead drop, so arresters should be installed in a more appropriate distribution transformer near point distance.

Advantages and characteristics of the metal oxide surge arresters

MOVMetal oxide arrester is used to protect the transmission and distribution equipment, insulation against over-voltage protection of electrical hazards is important, it has a fast response, voltage characteristic flat, stable performance,Flow capacity, residual voltage, long life, simple structure, it is widely used in power generation,Transmission, substation, distribution and other systems. Composite coat metal oxide surge arresters is silicone rubber
Composite materials make coats, and traditional porcelain jacket Surge arrester , compared with a small size, light weight, rugged, stain resistance, proof performance and so on.

MOA varistor valve main ingredient is zinc oxide, Metal Oxide Varistors (MOV) has extremely excellent non-linear characteristics. Under normal operating voltage of the resistance value is high, in fact, equivalent to an insulator, and over-voltage action, the resistance of the resistor is very small, residual pressure is very low. But under normal operating voltage, since the valve frequency voltage is applied to long-term exposure arising from deterioration caused by changes in resistance characteristics, resulting in increased flow through the valve leakage current. The resistive component of the current sharp increase in temperature will rise valves on thermal collapse, severe, or even cause explosion arrester. In accordance with the provisions of rules 1, MOA total of six test items, namely (1) Insulation resistance (2) leakage current DC U1mA and 0.75U1mA under (3) AC operation voltage leakage current (4) Power frequency frequency reference voltage (5) Base insulation resistance (6) Check discharge counter action case reference current.

Electrical characteristics

A varistor metal oxide remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", thus varistors are typically used for suppressing line voltage surges. However, a polymer arrester may not be able to successfully limit a very large surge from an event like a lightning strike where the energy involved is many orders of magnitude greater than it can handle. Follow-through current resulting from a strike may generate excessive current that completely destroys the varistor.

Lesser surges still degrade it, however. Degradation is defined by manufacturer's life-expectancy charts that relate current, time and number of transient pulses. The main parameter affecting varistor life expectancy is its energy (Joule) rating. As the energy rating increases, its life expectancy typically increases exponentially, the number of transient pulses that it can accommodate increases and the "clamping voltage" it provides during each transient decreases. The probability of catastrophic failure can be reduced by increasing the rating, either by using a single varistor of higher rating or by connecting more devices in parallel. A varistor is typically deemed to be fully degraded when its "clamping voltage" has changed by 10%. In this condition it is not visibly damaged and it remains functional (no catastrophic failure).

The Limitations of metal oxide varistors application

A metal oxide varistors application inside a TVSS device does not provide equipment with complete power protection. In particular, a MOV device provides no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device. Other sustained and harmful overvoltages may be lower and therefore ignored by a MOV device.
A varistor provides no equipment protection from inrush current surges (during equipment startup), from overcurrent (created by a short circuit), or from mov varistor (also known as a brownout); it neither senses nor affects such events. Susceptibility of electronic equipment to these other power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means such as a UPS, a voltage regulator or a surge protector with built-in overvoltage protection (which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold).

the Limitations of metal oxide varistors application

A metal oxide varistors application inside a TVSS device does not provide equipment with complete power protection. In particular, a MOV device provides no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device. Other sustained and harmful overvoltages may be lower and therefore ignored by a MOV device.
A varistor provides no equipment protection from inrush current surges (during equipment startup), from overcurrent (created by a short circuit), or from mov varistor (also known as a brownout); it neither senses nor affects such events. Susceptibility of electronic equipment to these other power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means such as a UPS, a voltage regulator or a surge protector with built-in overvoltage protection (which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold).

Comparison to other transient suppressors
Another method for suppressing voltage spikes is the transient-voltage-suppression diode (TVS). Although diodes do not have as much capacity to conduct large surges as MOVs, diodes are not degraded by smaller surges and can be implemented with a lower "clamping voltage". MOVs degrade from repeated exposure to surges and generally have a higher "clamping voltage" so that leakage does not degrade the MOV. Both types are available over a wide range of voltages. MOVs tend to be more suitable for higher voltages, because they can conduct the higher associated energies at less cost.
Another type of transient suppressor is the gas-tube suppressor. This is a type of spark gap that may use air or an inert gas mixture and often, a small amount of radioactive material such as Ni-63, to provide a more consistent breakdown voltage and reduce response time. Unfortunately, these devices may have higher breakdown voltages and longer response times than varistors. However, they can handle significantly higher fault currents and withstand multiple high-voltage hits (for example, from lightning) without significant degradation.
Multi-layer varistor
Multi-layer varistor (MLV) devices provide electrostatic discharge protection to electronic circuits from low to medium energy transients in sensitive equipment operating at 0-120 volts dc. They have peak current ratings from about 20 to 500 amperes, and peak energy ratings from 0.05 to 2.5 joules.ratings from 0.05 to 2.5 joules.

metal oxide varistor application with high quality on xatge.com

In general, the primary case of varistor breakdown is localized heating caused as an effect of thermal runaway. metal oxide varistor application is to a lack of conformity in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress. If the energy in a transient pulse (normally measured in joules)MOV Block is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This (catastrophic) failure occurs when "Absolute Maximum Ratings" in manufacturer's data-sheet are significantly exceeded.

Electrical characteristics of varistor metal oxide

A varistor metal oxide remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", thus varistors are typically used for suppressing line voltage surges. However, a polymer arrester may not be able to successfully limit a very large surge from an event like a lightning strike where the energy involved is many orders of magnitude greater than it can handle. Follow-through current resulting from a strike may generate excessive current that completely destroys the varistor.

Lesser surges still degrade it, however. Degradation is defined by manufacturer's life-expectancy charts that relate current, time and number of transient pulses. The main parameter affecting varistor life expectancy is its energy (Joule) rating. As the energy rating increases, its life expectancy typically increases exponentially, the number of transient pulses that it can accommodate increases and the "clamping voltage" it provides during each transient decreases. The probability of catastrophic failure can be reduced by increasing the rating, either by using a single varistor of higher rating or by connecting more devices in parallel. A varistor is typically deemed to be fully degraded when its "clamping voltage" has changed by 10%. In this condition it is not visibly damaged and it remains functional (no catastrophic failure).

Line arrester

MOA grounding wire should be connected directly to the distribution transformer shell, then shell and then connect with the earth. That the surge arrester ground wire is connected directly to the earth, and then another from the ground stake lead a ground wire to the transformer housing practice is wrong. In addition, metal oxide varistor testing grounding line is to be as short as possible to reduce the residual pressure. Regularly Organic composite arrester insulation resistance measurement and leakage current test, if it is found MOA insulation resistance significantly reduced or breakdown should be replaced immediately in order to ensure safe and healthy operation of distribution transformer.

GIS Arresters

If the low-pressure side of the distribution transformer is not installed MOA, when the high-pressure side discharge lightning current polymer arrester to the earth when the grounding device to produce a pressure drop, the pressure drop through the distribution transformer housing while in the neutral point of the low pressure side of the winding. Therefore, low-voltage winding of the lightning arrester current will flow through the high-voltage winding turns ratio induced by a high potential (up to 1000 kV), the potential will thunder and high-voltage side winding voltage is superimposed, causing the high-voltage winding neutral point potential increased insulation breakdown near the neutral point. If the low-pressure side mounted MOA, MOA discharge when the potential of the high-pressure side grounding means is increased to a certain value, the low-pressure side xatge MOV begins to discharge, the low pressure side coil outlet and where the potential difference between the end point and the housing is reduced, so that to eliminate or reduce the impact of "anti-conversion" potential.

Composite arrester

MOA (MOA) during normal operation and distribution transformers in parallel, the terminating line, the lower end of the ground. When the line when an overvoltage occurs, then the distribution transformer will withstand over three parts dropout voltage generated through the arrester, wire and grounding device, called the residual pressure. In this three-part overvoltage, the metal oxide arrester residual voltage on its own performance related to its residual voltage value is constant. Residual voltage on the grounding device can be connected to the grounding deflectors distribution transformer housing, then connected to the grounding device and means to eliminate them. And how to reduce the residual voltage of the leads has become the key to the protection of distribution transformers. Leads through the current frequency impedance, varistors the higher the frequency, the stronger the wire inductance, impedance increases. Seen from U = IR, to reduce the residual pressure on the lead, you have to narrow the lead impedance, and possible ways to reduce the lead impedance is to shorten the distance between Composite arrester from distribution transformer to reduce the lead impedance, lower lead drop, so arresters should be installed in a more appropriate distribution transformer near point distance.

Metal oxide varistors

Mov varistor valve main ingredient is zinc oxide, zinc oxide varistor has a very excellent nonlinear characteristics. Under normal operating voltage of the resistance value is very high, in fact, the equivalent of an insulator, and in the over-voltage is applied, the resistance of the resistive sheet is small, residual pressure is very low. But under normal operating voltage, since the valve sheet to withstand long-term effect of power frequency voltage generated by the degradation caused by changes in resistance characteristics, resulting in increased flow through the valve leakage current. The resistive component of the current sharp increase in temperature will rise valves on thermal crashes, serious, mov metal oxide varistor or even cause explosion arrester. In accordance with the provisions of rules 1, MOA total of six test items, namely (1) Composite arrester Insulation resistance (2) Leakage Current DC U1mA and 0.75U1mA under (3) AC operating voltage under leakage current (4) Power frequency Power frequency reference voltage (5) Base insulation resistance (6) Check discharge counter action case reference current.

High-voltage surge arrester

MOA (MOA) is used to protect the transmission and distribution equipment insulated against overcurrent
Important protection of electrical pressure hazard, overvoltage arrester has fast response, voltage characteristic flat, stable performance,
Flow capacity, residual voltage, long life, simple structure, etc., it is widely used in power generation,
Transmission, substation, distribution and other systems. Composite coat metal oxide surge metal oxide varistor sizing is silicone rubber
Composite materials make coats, and traditional porcelain jacket metal oxide arrester, compared with a small size, light weight, rugged, stain resistance, good explosion-proof performance.

Metal oxide surge arresters

Metal oxide surge arresters are used to protect the transmission and distribution equipment, insulation against over-voltage protection of electrical hazards is important, it has fast response, voltage characteristic flat, stable performance, high flow capacity, low residual voltage, long life, simple structure etc., widely used in power generation, transmission, transformation, distribution and other systems. Composite coat metal oxide surge arresters composite material is made of silicone rubber jacket, and the traditional porcelain jacket arresters, compared with a small size, light weight, rugged, stain resistance, explosion-proof performance.

MOA on the proper use of distribution transformers

Distribution transformers shall be installed near side of the metal oxide surge arresters (MOA) during normal operation and distribution transformers in parallel, the terminating line, the bottom ground. When the line when an overvoltage occurs, this time with a change would put too three parts dropout voltage generated through the arrester, leads and grounding device, called a residual pressure. In this three-part overvoltage, the arrester residual voltage on its own performance related to its residual voltage value is constant. Residual voltage on the grounding device can be connected to the grounding deflectors distribution transformer housing, then connected to the grounding device and how to eliminate them.
Distribution transformer low-voltage side of distribution transformer should be installed if the low-pressure side is not installed AC and DC High Performance MOV, when the high-pressure side discharge lightning current arrester to the earth when the grounding device to produce a pressure drop, the pressure drop through the distribution transformer housing while in the low-pressure side coil The neutral point. Therefore, the low-pressure side of the lightning current flowing through the windings allow high voltage winding turns ratio induced by a high potential (up to 1000 kV), the potential will thunder and high-voltage side winding voltage is superimposed, resulting in high voltage winding neutral point potential increased insulation breakdown near the neutral point. If the low-pressure side mounted MOA, MOA discharge when the potential of the high-pressure side grounding means is increased to a certain value, the low-pressure side Glass Coating MOV begins to discharge, the low pressure side coil outlet and where the potential difference between the end point and the housing is reduced, so that eliminate or reduce the impact of "anti-conversion" potential.
MOA grounding wire should be connected to the distribution transformer housing MOA grounding wire should be connected directly to the power distribution transformer shell, then shell and then connected to ground. That the arrester ground wire directly connected to the earth, and then another from the ground stake lead a ground wire to the transformer housing approach is wrong
In strict accordance with the regulations require regular maintenance test regularly MOA insulation resistance measurement and leakage current test, if it is found MOA insulation resistance was significantly reduced or breakdown should be replaced immediately to ensure the safety and health of distribution transformer operation.

Advantages Surge arrester

Flow capacity. Arrester easy to absorb energy, no series gap constraints, only the strength of the valve itself relevant. Comparison with silicon carbide valves, through-flow capacity of the oxide valve unit area of ​​4 to 4.5 times larger. Therefore, the use of such valves made of lightning, not only can limit atmospheric over-voltage, and can be used to limit the operating voltage, they can even withstand certain short duration (frequency) overvoltage.
Simple structure, small size, easy to mass production, low cost
For a variety of special needs. Metal oxide surge AC High Gradient MOV good stain resistance, not due to changes in the surface potential distribution is filthy coat or charged cleaning affect the performance of the arrester. Meanwhile, the air valve from the environment, can adapt to a variety of insulation media, it also applies to a variety of special needs high altitudes and 6 SF - enclosed appliances.
Surge arrester has a number of advantages, great potential for development, is the main direction of development of the world arrester, will gradually replace the traditional band gap metal oxide arresters, it will also be key to the future of UHV system overvoltage protection device.
Flow capacity. Arrester easy to absorb energy, no series gap constraints, only the strength of the valve itself relevant. Comparison with silicon carbide valves, through-flow capacity of the oxide valve unit area of ​​4 to 4.5 times larger. Therefore, the use of such valves made of lightning, not only can limit atmospheric over-voltage, and can be used to limit the operating voltage, they can even withstand certain short duration (frequency) overvoltage.

Simple structure, small size, easy to mass production, low cost.

For a variety of special needs. Metal oxide surge arresters good stain resistance, not due to changes in the surface potential distribution is filthy coat or charged cleaning affect the performance of the arrester. Meanwhile, the air valve from the environment, can adapt to a variety of insulation media, it also applies to a variety of special needs high altitudes and 6 SF - enclosed appliances.

Surge arrester has a number of advantages, great potential for development, is the main direction of development of the world arrester, will gradually replace the traditional band gap arrester, it will also be key to the future of UHV system overvoltage protection device.

Advantages Surge arrester

Only new arrester Glass Coating varistors, varistors are sintered metal oxides such as zinc oxide made of polycrystalline semiconductor ceramic element, with the ideal valve characteristic. At the same time non-linear coefficient, good protection features, high energy absorption capacity, high flow capacity, simple structure and good stability.
Non-linear coefficient α is very small. When the metal oxide film by valve within the range of current 1mA ~ 10kA, α values ​​generally between 0.02 to 0.06. At the rated voltage is applied, the current through the small, so it can make the arrester without gaps. Good protection. It does not require the clearance operation, voltage rises once, you can quickly absorb the overvoltage energy, suppress over-development voltage; a good response characteristic steepness; gapless oxide arrester performance is almost independent of temperature, humidity, barometric pressure, Effect of contamination and other environmental conditions, and thus stable performance.
metal oxide arresters essentially free-wheeling action load light, resistant and repeat ability. Voltage characteristic is symmetrical, polarity does not matter, it can be made into DC arrester.

Structural characteristics Surge arrester

The basic structure of metal oxide arresters are valves [52], the valve with a zinc oxide (ZnO) as the main material, doped with small amounts of other metal oxide additives, high temperature roasting, varistor has a good non-linear characteristic , so called sensitive arrester.
The basic structure of this sintered body of zinc oxide grains in the high conductance [53], a resistivity of 1 Ω⋅ cm. Edge made of high-resistance (mainly metal oxide additions) surrounded by grain boundary layer, the resistivity is about 1010 ~ 1014Ω⋅cm at low electric field strength. At higher voltage is applied, the grain boundary layer of metal oxide varistor symboladditions to the valence electrons are pulled out, or because electron avalanche impact ionization of carriers leaving a significant increase [54]. When the electric field strength reaches 104 ~ 105V / cm, resistivity that is down to 1 Ω⋅ cm; when the applied voltage is reduced role, since the composite that carriers reduce resistance and bigger, so it has good nonlinear. And it is non-linear voltage characteristics in the positive and negative polarity is symmetrical.
Metal oxide valve under normal operating voltage through the resistive current is small, typically about 10 ~ 15μA, close to the insulating state. When acting on the valve voltage increases, current increases. The valve plate by resistive current of 1mA, the effect on the arrester voltage mA U1 as a starting operating voltage. Because zinc oxide valve has a good nonlinear characteristics, in the ratio by 10kA impulse current residual voltage and mA U1 is generally not more than 1.9, the pressure ratio is smaller, the better the performance of its protection. value mA U1 is about the maximum allowable operating voltage peak of 1.05 to 1.15 times.