Varistor - choose to comply with rules Knowledge of electrical resistance

by:Thermistor-Mov     2020-06-22
Varistor choose to comply with the rules of this article mainly introduced the varistor is chosen to follow rules, this article about 1100 words, read the full article 11 minutes. Varistor work environment: should be within the prescribed scope of technical conditions: temperature: - 40 c ~ + 85 ℃; Relative humidity: + 40 & plusmn; When 2 ℃, 96%; The atmospheric pressure: up to 8. 5 kpa。 (2) the selection of pressure-sensitive voltage selection according to the supply voltage. Fully consider the grid ( Or circuit) The working voltage of the volatility, the selection of piezoresistive pressure sensitive voltage value, to leave enough margin. Domestic general volatility of 30%. There is also considering the continuous sinusoidal voltage on opposite sides of the varistor, cannot exceed the specifications listed in the table & other Continuous working voltage & throughout; Value. For 220 v to 240 v ac power lightning protection device, should choose pressure-sensitive voltage of 470 v to 620 v varistor is more appropriate. Choose pressure-sensitive voltage higher pressure sensitive resistance, can reduce the failure rate, prolong service life, but the residual pressure is slightly increased. (3) the selection of flux flow pressure sensitive resistance of nominal discharge current should be greater than demand surge current or possible surge current at a time. Nominal discharge current should be pressure sensitive resistance surge in the number of life rating curve hit more than 10 times of numerical calculation, about 30% of the impact on traffic, Is 0. 3IP) The left and right sides. (4) clamping voltage selection of varistor clamping voltage must be smaller than the protected components or equipment to withstand voltage ( The safety voltage) 。 (5) pressure sensitive resistance in parallel when a varistor can't satisfy the request for the nominal discharge current, should use multiple pressure sensitive resistor in parallel. Sometimes in order to reduce the limit voltage, even if the nominal discharge current required also USES multiple pressure sensitive resistor in parallel. Pay special attention to the pressure sensitive resistance in parallel when using, must strictly selected parameters are consistent, For example: Δ U1mA & le; 3 v,Δα≤ 3) Match, for the evenness of current distribution. 6 failure protection of varistor varistor failure modes are usually short circuit, to prevent the failure caused by pressure sensitive resistance power short circuit and fire, can be in series on each varistor tube or heat from a temperature insurance agency. Tube temperature insurance should pressure sensitive resistance and good thermal coupling, when varistor failure ( High impedance short-circuit) Temperature, the heat generated by the it to insurance tube fuse, so that the failure of the varistor from circuit, ensure the safety of the equipment. When high power frequency overvoltage temporarily on the varistor, could make the varistor instantaneous breakdown circuit ( Low impedance short-circuit) , and insurance tube could fusing temperature, may also be a fire. In order to avoid this kind of phenomenon, can again on each varistor series a impact resistance fuse (power frequency Single labor frequency fuse when aging failure may not fuse) 。 Also can put varistor and ceramic gas discharge tube in series, ceramic gas discharge tube is not in normal working conditions conduction, varistor no leakage current, can greatly prolong the service life; Is impacted by the surge, ceramic gas discharge tube breakdown first, and then by pressure sensitive resistance limit surge voltage, the total pressure equal to the sum of the residue, slightly larger ( Dozens of V) ; After shocks in the past, due to the pressure sensitive resistance limit the current, discharge tube can not maintain conduction and arc, returned to normal working state; After the pressure sensitive resistance short-circuit failure, because of ceramic gas discharge tube through the large power frequency current quickly fails, but its failure mode is most open, and therefore is not easy to cause fire. 文章/ ymdzxyzsdg。 HTML this paper label: an article on resistance pressure sensitive resistance: varistor fails to cause circuit under the influence of an article, several applications of pressure sensitive resistance in the circuit
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