自愈式電容器采用單層聚丙烯膜做為介質(zhì)，表面蒸鍍了一層薄金屬作為導(dǎo)電電極。電解電容廠家為您詳細(xì)介紹下自愈式電容的自愈過程：當(dāng)施加過高的電壓時(shí)，聚丙烯膜電弱點(diǎn)被擊穿，擊穿點(diǎn)阻抗明顯降低，流過的電流密度急劇增大，使金屬化鍍層產(chǎn)生高熱，擊穿點(diǎn)周圍的金屬導(dǎo)體迅速蒸發(fā)逸散，形成金屬鍍層空白區(qū)，擊穿點(diǎn)自動(dòng)恢復(fù)絕緣。
The self-healing capacitor uses a single layer of polypropylene film as the dielectric, and a thin layer of metal is evaporated on the surface as the conductive electrode. When the high voltage is applied, the electric weakness of polypropylene film is broken down, the impedance of breakdown point is obviously reduced, the current density is increased rapidly, which makes the metallized coating produce high heat, the metal conductor around the breakdown point evaporates and dissipates rapidly, forming a metal coating blank area, and the breakdown point automatically recovers the insulation.
1、定電壓
Constant voltage
電容器額定電壓優(yōu)先值如下0.23，0.4，0.525及0.69kV。電容器額定電壓選取一般比電氣設(shè)備額定運(yùn)行電壓高5%。
The priority values of capacitor rated voltage are as follows: 0.23, 0.4, 0.525 and 0.69kv. The rated voltage of capacitor is generally 5% higher than that of electrical equipment.
2、電容
Capacitance
電容器的電容是極板上的電荷相對(duì)于極板間電壓的比值，該值與極板面積、極板間絕緣厚度和絕緣介質(zhì)的介電系數(shù)有關(guān)，其計(jì)算式為C=14πε×SD式中ε為極板間絕緣介質(zhì)的介電系數(shù);S為電容器極板面積;D為電容器絕緣層厚度。
The capacitance of a capacitor is the ratio of the charge on the electrode plate to the voltage between the plates, which is related to the area of the plate, the insulation thickness between the plates and the dielectric coefficient of the insulating medium. The formula is C = 14 π ε × SD, where ε is the dielectric coefficient of the insulating medium between the plates; s is the area of the capacitor plate; D is the thickness of the insulation layer of the capacitor.
靜態(tài)電容一般投運(yùn)后第一年電容值下降率應(yīng)在2%以內(nèi)，第二年至第五年電容值下降率應(yīng)在1%～2%，第五年后因電介質(zhì)老化，電容值將加速下降，當(dāng)電容值下降至出廠時(shí)的85%以下，可認(rèn)為該電容器壽命期結(jié)束。
Generally, after the static capacitor is put into operation, the reduction rate of capacitance value in the first year shall be within 2%, and that from the second year to the fifth year shall be between 1% and 2%. After the fifth year, due to dielectric aging, the capacitance value will decrease rapidly. When the capacitance value drops to less than 85% of the original value, the life of the capacitor can be considered to be over.
3、無功功率
Reactive power
在交流電路中，無功功率QC=UIsinφ由于電容器電介質(zhì)損耗角極小，φ=90°，所以sinφ=1，則無功功率QC=UI=ωCU2×10-3=2πfCU2×10-3（μF），從該式可見，電容器無功功率不僅取決于電容C，而且還與電源頻率f、端電壓U直接相關(guān)，電容器額定無功功率的準(zhǔn)確定義應(yīng)是標(biāo)準(zhǔn)頻率下外接額定電壓時(shí)靜態(tài)電容C所對(duì)應(yīng)的無功率。
In AC circuit, the reactive power QC = uisin φ, because the dielectric loss angle of capacitor is very small, φ = 90 °, so sin φ = 1, then reactive power QC = UI = ω Cu2 × 10-3 = 2 π fcu2 × 10-3 (μ f). From this formula, it can be seen that the reactive power of capacitor is not only determined by capacitor C, but also directly related to power frequency f and terminal voltage u. The accurate definition of rated reactive power of capacitor should be under standard frequency No power corresponding to static capacitance C when external rated voltage is connected.
當(dāng)電網(wǎng)電壓低于電容器額定電壓時(shí)，電容器所輸出的無功功率將小于標(biāo)定值。因此如果電容器額定電壓選擇偏高，電容器實(shí)際運(yùn)行電壓長(zhǎng)期低于額定值，很可能因電容器無功出力低于設(shè)計(jì)值造成電網(wǎng)無功短缺。
When the output voltage of the capacitor is lower than the rated voltage of the capacitor. Therefore, if the rated voltage of the capacitor is too high and the actual operating voltage of the capacitor is lower than the rated value for a long time, it is likely that the reactive power of the power grid will be short because the reactive power output of the capacitor is lower than the design value.
電容器在外施電壓作用下，由于介質(zhì)中的雜質(zhì)或氣隙等弱點(diǎn)的存在或發(fā)展引起介質(zhì)擊穿形成導(dǎo)通電路；接著在導(dǎo)通電路處附近很小范圍內(nèi)的金屬層中流過一個(gè)前沿很陡的脈沖電流。鄰近擊穿點(diǎn)處金屬層上的電流突然上升，按其離擊穿點(diǎn)的距離而成反比分布。在順時(shí)刻t，半徑為Rt的區(qū)域內(nèi)金屬層的溫度達(dá)到金屬的熔點(diǎn)，于是在此范圍內(nèi)的金屬熔化并產(chǎn)生電弧。該電流引起電容能量釋放，在弧道局部區(qū)域溫度突然升高，壓力突然增大。
Under the action of applied voltage, the dielectric breakdown of the capacitor is caused by the existence or development of impurities or air gap in the medium to form a conducting circuit; then a pulse current with a very steep front edge flows through the metal layer within a small range near the conduction circuit. The current on the metal layer near the breakdown point suddenly rises and is inversely proportional to the distance from the breakdown point. At the time t, the temperature of the metal layer in the region with radius RT reaches the melting point of the metal, so the metal in this range melts and generates an arc. The current results in the release of capacitance energy and the sudden increase of temperature and pressure in the local area of arc channel.
隨著放電能量的作用，半徑為Rt的區(qū)域內(nèi)金屬層劇烈蒸發(fā)并伴隨噴濺。在該區(qū)域半徑增大的過程中電弧被拉斷，金屬被吹散并受到氧化與冷卻，破壞了導(dǎo)電通路，在介質(zhì)表面形成一個(gè)以擊穿點(diǎn)為中心的失掉金屬層的圓形絕緣區(qū)域，電容器的自愈過程結(jié)束。
With the effect of discharge energy, the metal layer in the region with radius RT evaporates violently, accompanied by splashing. In the process of increasing the radius of the region, the arc is broken, the metal is blown away and oxidized and cooled, which destroys the conductive path, and forms a circular insulation area with the breakdown point as the center, and the self-healing process of the capacitor ends.