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.