Mov for line discharge

 Варисторы оксидно-цинковые Movs manufacturer Arresters which used TGEMOV have below advantages: --With the same referencevoltage, hold more excellent protective characteristics; --With the same protectionlevel, arrester have higher reference voltage andcontinuous operating voltage. Therefore, arrester could withstandlower electric stress and for safe operation.

metal oxide varistor basics metal oxide varistor theory

Basic Specification

type: metal oxide varistors/ Blocks

size: diameter38mm, height 29mm

coating: organic coating and glass coating

rated voltage: 4.5kV

craft: metal oxide

package type: wooden cases and carton

NDC:5kA

Description

DC U1mA voltage is 6.38+0.3kV

Reference current is 1mA

Reference voltage is 6.38kV

Residual voltage is 11.5+0.5kV

Long duration current is 400A

Nominal discharge current is 10kA

Applications:

Used for distribution arresters.

Arresters which used TGE MOV have below advantages:

--With the same referencevoltage, hold more excellent protective characteristics;

--With the same protectionlevel, arrester have higher reference voltage andcontinuous operating voltage. Therefore, arrester could withstandlower electric stress and for safe operation.

Варисторы оксидно-цинковые

metal oxide varistor basics 

metal oxide varistor theory

The basic properties of metal oxide blocks

(1) metal oxide blocks has protection feature, when the impact of the strong impact of the source does not exceed a predetermined value, the varistor voltage limit must not exceed the protected object can withstand voltage shock resistance.
(2) the impact resistance, the varistor itself should be able to withstand the impact of current, impact energy, and several attacks have appeared when the average power.
(3) There are two characteristics of life, one continuous working voltage life, namely varistor specified ambient temperature and system voltage conditions should be able to work reliably specified time. Second, the impact of life, that is able to reliably withstand the impact of a predetermined number of times.
(4) After the metal oxide varistor basics intervention system, in addition to protect a "safety valve", it will also bring some additional impact, which is the so-called "secondary effects", it should not reduce the normal performance of the system. Then the main factors to be considered, there are three, one varistor own capacity, the second is the system voltage, leakage current, the third is non-linear current through the varistor coupled source impedance effects on other circuits.

The note of ZnO Resistors

Temperature fuse ZnO Resistors should have good thermal coupling when varistors fail (high-impedance short circuit), the heat it generates the temperature fuse fuse, varistor and separation circuit failure to ensure that the equipment Safety. When a high frequency temporary over-voltage applied to the varistor , the varistor may cause momentary short-circuit breakdown (low impedance short circuit), the temperature fuse fuse had a chance, but also may cause fire. To avoid this phenomenon may be further connected in series to each varistor fuse a high impact frequency (single frequency fuse employment at the time of aging failure may not fuse)

The role of Zinc blocks

Zinc blocks are widely used in electronic circuits, because of the protection circuit to damage the instantaneous voltage power supply system of the mutation may be. When the high pressure comes, the varistor resistance decreases and current shunt to be safeguarded against excessive transient voltage damage or interference. Thereby protecting sensitive electronic components.
However, I do not think the role of the varistor too, varistors are not able to provide a complete voltage protection varistors can withstand the energy or power is limited, do not provide sustained overvoltage protection . Sustained overvoltage will destroy the protection device (varistor), and damage to equipment, and there may be a fire hazard.Zinc Oxide block not provide protection part are: the inrush current at power-on, over-current short circuit, voltage dips, etc., these cases require other forms of protection. In addition, there are a few protection device detects the power supply voltage, such as the power supply will be cut off when the relay exceeds dangerous limits.

Metal Oxide Varistors (MOV)

While an Metal Oxide Varistors (MOV) is designed to conduct significant power for very short durations (about 8 to 20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a mov metal oxide varistor can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.

A 130 volt, 150 J MOV that has undergone catastrophic failure, apparently as a result of a lightning strike, showing evidence of heat and smoke. The 3 amp fast-blow fuse immediately in front of the varistor blew during the same event.
A series connected thermal fuse is one solution to catastrophic MOV failure. Varistors with internal thermal protection are also available.
There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. Depending on the level of conducted current, dissipated heat may be insufficient to cause failure, but may degrade the MOV device and reduce its life expectancy. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. A user may have no indication when the surge suppressor has failed. Under the right conditions of over-voltage and line impedance, it may be possible to cause the MOV to burst into flames,[5] the root cause of many fires[6] and the main reason for NFPA’s concern resulting in UL1449 in 1986 and subsequent revisions in 1998 and 2009. Properly designed TVSS devices must not fail catastrophically, resulting in the opening of a thermal fuse or something equivalent that only disconnects MOV devices.

The Specifications of metal oxide varistor application

MOVs are specified according to the voltage range that they can tolerate without damage. Other important parameters are the metal oxide varistor application energy rating in joules, operating voltage, response time, maximum current, and breakdown (clamping) voltage. Energy rating is often defined using standardized transients such as 8/20 microseconds or 10/1000 microseconds, where 8 microseconds is the transient's front time and 20 microseconds is the time to half value.
Response time
The response time of the varistors is not standardized. The sub-nanosecond MOV response claim is based on the material's intrinsic response time, but will be slowed down by other factors such as the inductance of component leads and the mounting method. That response time is also qualified as insignificant when compared to a transient having an 8 μs rise-time, thereby allowing ample time for the device to slowly turn-on. When subjected to a very fast, <1 ns rise-time transient, response times for the MOV are in the 40–60 ns range.
Capacitance

Typical capacitance for consumer-sized (7–20 mm diameter) varistors are in the range of 100–1,000 pF. Smaller, lower-capacitance varistors are available with capacitance of ~1 pF for microelectronic protection, such as in cellular phones. These low-capacitance varistors are, however, unable to withstand large surge currents simply due to their compact PCB-mount size.

The Applications of High voltage varistor

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.

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.

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).

Metal Oxide Varistors (MOV)

Metal Oxide Varistors (MOV) current-voltage characteristics for zinc oxide (ZnO) and silicon carbide (SiC) devices
The most common type of varistor is the metal-oxide varistor (MOV). This type contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction,Porcelain housed arrester allows current to flow in only one direction.

The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.

Traditional Metal oxide varistors schematic symbol

Traditional Metal oxide varistors schematic symbol. It expresses the diode-like behavior in both directions of current flow.
Modern varistor schematic symbol.
A metal oxide varistors application is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. In contrast to a diode however, it has the same characteristic for both directions of traversing current. At low voltage it has a high electrical resistance which decreases as the voltage is raised.

Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered.
The development of the varistor, in the form of a new type of rectifier (copper oxide), originated in the work by L.O. Grondahl and P.H. Geiger in 1927. The name varistor is a portmanteau of varying resistor. The term is only used for non-ohmic varying resistors. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics.

the metal oxide varistors application Limitations

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.

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.

characteristics for Metal Oxide Varistors (MOV)

Metal Oxide Varistors (MOV) current-voltage characteristics for zinc oxide (ZnO) and silicon carbide (SiC) devices
The most common type of varistor is the metal-oxide varistor (MOV). This type contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, Porcelain housed arrester allows current to flow in only one direction.

The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.

XATGE ZnO Blocks with MOV glasses

TGE offers a selection of glasses suitable for use as insulating coatings on Metal Oxide Varistors (ZnO “blocks”). TGE offers powders sized for wet application by dipping, rolling or spraying as well as application by dry electrostatic techniques. Typical firing temperatures are 550°C, resulting in pore-free insulating coatings of suitable toughness to withstand potential damage due to lapping of the block ends prior to metallization. Along with PbO-containing glass options, lead-free versions are also available. If lead-free MOV glasses are of interest, ask for our industrial evaluation report for TGE Glass V1467. Our glasses are melted in platinum lined vessels ensuring consistency of physical properties and preventing unwanted impurities. Glass powders are custom milled to your particle size specifications and can be co-milled with additives to increase surface roughness for handling purposes.

Being an ISO 9001-2008 accredited manufacturer and exporter in the market, we put froth a dependable, durable and remarkable range of  ZnO Blocks. In addition to this, our widely appreciated range is made keeping in mind the exact requirements of the industry. As an outcome, it is extensively in demand nowadays. Besides, by using authentic raw material, we gain appreciation for ZnO Blocks from the masses. As per the requirements of the domain, we deliver the product right on time. 

Zinc Oxide blocks

Nano-block body,ZnO varistor refined grains make the material easy to cause transgranular fracture, will help improve the toughness; grain refinement contributes to slip between the grains, the material has plastic behavior; grain refinement the strength of the ceramic material can also greatly increased [6,7]. Currently nano Sintering more are ZrO2, AI2O3, TiO2 [8,9]. Semiconductor nano-ZnO low-density bulk impedance spectroscopy has been reported [10]. But during sintering of nano Zinc Oxide blocks nanocrystals growth it has not been reported. Studied law during sintering grain growth of ZnO 20nm average particle size of paper as the raw material, the application of grain growth phenomenological theory of kinetic equations to determine the index of grain growth kinetics and the apparent activation energy, and with the rough sintered polycrystalline material was compared, we discussed the mechanism of nano xatge MOV sintered. It laid the foundation for the sintering and application of semiconductor material nanometer ZnO.

ZnO blocks

TGE Metal Oxide Varistors(MOV) ceramic because of its non-linear current-voltage characteristics (and non-linear coefficient is the highest of all semiconductor materials) are widely used in electronic devices [1-5]. ZnO varistors are typically the grain size, grain boundary structure control their macroscopic properties of materials. ZnO grain size and the number of grain boundary layer directly affects the breakdown voltage level. In addition, many other properties are also dependent on the polycrystalline ceramic its microstructure. In recent years, sintering and grain growth of ZnO based ceramics have been many reports of research [1-5]. People around the crystal densification and control of the sintered body sintered body grow a lot of research. According to reports, doped ZnO nano-ZnO Resistors coarse grain has a higher breakdown voltage, the greater the nonlinearity coefficient, low leakage current. And said performance increases with the amount of nano-Zinc Oxide discs [3]. Nano-sintering is the second after the emergence of nanomaterials developed a new sintering technology. The so-called nano-sintering, is to use nano-powder sintering under certain conditions, the microstructure of the phase of the nano-phase materials. Nano-sintering with the conventional sintering coarse grain compared to: (1) low sintering temperature; the nano-powder small size, high surface energy, compressed into a block material after the interface has a high energy, high in sintering interface can become the driving atomic motion force, is conducive to the interface holes shrink, annihilation vacancy clusters, thus enabling the sintering temperature is lowered.

ZnO varistor

In the preparation of nanomaterials and nano-structure, there are many people in different ways.metal oxide varistor theory These methods may be divided according to the state of the reaction medium during the preparation of two categories: solution-based liquid phase reaction of gas phase reaction based on gas phase process. Growth by gas inorganic nano materials and nano-bodies have VLS mechanism main mechanism, VS mechanism, ZnO Resistors growth (OAG) mechanism, SLS mechanism. There is now a zinc oxide fine synthesis of nanostructures with different morphologies are pulsed laser deposition (PLD), chemical vapor deposition (CVD), metal organic chemical vapor deposition (MOCVD), chemical transport method (CTM),overvoltage arrester thermal evaporation, carbothermal reduction. Solvothermal, hydrothermal method.

Promotional Zinc Oxide Disc

In recent years, nano-materials due to its quantum size effect and macroscopic quantum tunneling, etc. ZnO varistorexhibit special optical, electrical, magnetic and catalytic properties, aroused great interest. After the zinc oxide and zinc sulfide nano materials, no doubt given on the basis of the original features of its range of new features, it will help to improve the material performance and functionality. In recent years, studies have shown that Zinc Oxide blocks and zinc sulfide nano-materials with ordinary zinc oxide and zinc sulfide compared to the bulk material, the mechanical properties, high temperature resistance, luminescence, catalysis and many other aspects have improved significantly. Zinc Oxide discsStudy on preparation and performance of materials science has become a very active area.

Zinc oxide varistors Features

TGE AC and DC High Performance MOV are widely used in electronic circuits, transient voltage surge protection because of the power supply system may harm the circuit. Varistor is generally used in parallel with the circuit when the voltage across the resistor changes rapidly, resistance short circuit current fuse blows, play a protective role. varistor metal oxide in the circuit, commonly used in the power supply voltage protection and regulation. Decrease the resistance of the TGE metal oxide varistor identification will be shunt currents, to protect against excessive transient voltage damage or interference.