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.