關于CELEM電容選型指導
1. 根據需要選擇電容器
在為應用選擇電容器時，選擇具有最大額定電壓RMS、電流和無功功率的電容器，該電容器應與應用的最高工作電壓和頻率最接近。考慮操作過程中可能出現的任何紋波和任何DV偏置，因為即使是短暫的過壓也會損壞電容器并縮短其使用壽命。每個電容器的數據表上都清楚地顯示了最大額定值。
無功功率公式為：
Qc= V2rms x C x 2πf x 10-6
注：
Qc是無功功率，單位為kVAr
Vrms是以伏特為單位的RMS電壓
C是以μF為單位的電容
f是以kHz為單位的頻率
1. Choosing the Best Capacitor for Needs
When choosing a capacitor for an application, select a capacitor with maximum rated voltage RMS, current and reactive power that most closely matches the highest operating voltage and frequency of the application. Take into account any ripple and any DV bias that can occur during operation, as even momentarily over voltage damages the capacitor and reduces its life time. The maximum ratings appear clearly on the data sheet of each capacitor.
The reactive power formula is:
Qc= V2rms x C x 2πf x 10-6
where
Qc is reactive power in kVAr
Vrms is RMS voltage in volts
C is capacitance in μF
f is frequency in kHz
2. 功率電容器的適當冷卻和端接
Celem電導冷卻功率電容器以相對較小的體積處理大量功率。為了正確運行，電容器必須正確端接以確保所有內部元件的均勻冷卻。
使用傳導冷卻電容器時必須滿足四個關鍵要求：
1) 冷卻。電容器的整個接觸面必須使用導熱膏與散熱器接觸，以確保最佳的熱傳導。當電容器以最大極限工作時，這一點尤其重要。切勿超過最大允許扭矩擰緊螺栓。
2) 傳導損耗。大多數電力電容器能夠提供數百安培的電流。當多個電容器連接到一個公共集電極時，由于集膚效應，可能會導致集電極表面積不足，導致收集電流的母線極度發(fā)熱，即使適當冷卻也會導致電容器過熱。
3) 電容器的感應加熱。當多個傳導冷卻電容器組裝在兩個匯流條之間時，那些離輸出端子最近的電容器可能會受到感應加熱。這種情況應通過如圖B所示安裝電容器或通過在母線之間構建低電感路徑（如圖C所示）來避免這種情況。C-Cap技術克服了這一缺陷。
4) 雜散電感。即使電容器組沒有直接連接到工作線圈，也要避免電路中的雜散電感。電感與母線的長度成正比，與它們的寬度成反比，與母線之間的距離成反比。
2. Proper Cooling and Termination for Power Capacitors
Celem conduction-cooled power capacitors handle a large amount of power in relatively small volume. In order to operate correctly, capacitors must be terminated properly to ensure uniform cooling of all internal elements.
Four critical requirements must be addressed when using conduction cooled capacitors:
1) Cooling. The entire area of the capacitor’s contacts surface must be placed in contact with the heat sink using a thermal conductive paste to ensure optimal heat conductance. This is particularly critical when the capacitor is working at its maximum limits. Never tighten the bolts beyond the maximum allowed torque.
2) Conduction losses. Most power capacitors are able to supply hundreds of amperes. When several capacitors are connected to a common collector, insufficient collectors’ surface area may result, due to the skin effect, in extreme heating of the bus bar where the current is collected, and overheating of the capacitor despite proper cooling.
3) Induction heating of capacitors. When several conduction-cooled capacitors are assembled between two bus bars, those located closest to the output terminals may experience induction heating. This situation should be avoided by mounting the capacitors as illustrated in diagram B or by building a low inductance path between the bus bars as illustrated in diagram C. The C-Cap technology overcomes this deficiency.
5) Stray inductance. Even when a capacitor bank is not connected directly to a work coil, it is good practice to avoid stray inductance in the circuit. Inductance is proportional to the bus bars’ lengths, inversely proportional to their widths and inversely proportional to the distance between the bus bars.
3. 電容器組損耗
電容器組由電容器以及電容器與輸出端子之間的連接組成。損失可能與這些要素中的任何一個有關。
電容損耗。電容器的損耗極低，通常約為無功功率的5 x 10-4 x。
連接損耗。在正確構造的電容器組中，連接損耗將與電容器損耗大致相同。
總電容器組損耗等于電容器損耗和連接損耗之和。 因此，它通?？傆嫾s為無功功率的10-3。
3. Capacitor Bank Losses
A capacitor bank consists of capacitors and connections between the capacitors and output terminals. Losses may be associated with either of these elements.
Capacitor losses. Losses in the capacitors are extremely low, generally about 5 x 10-4 x the reactive power.
Connection losses. In a properly constructed capacitor bank, connection losses will be approximately the same as the capacitor losses.
Total capacitor bank loss is equivalent to the sum of the capacitor losses and connection losses. As such, it generally totals about 10-3 of the reactive power.
4. 電容器組冷卻所需的水流量
聚丙烯電容器可以在高達90°C的溫度下安全運行。聚丙烯元件的最熱點與Celem電容器的銅表面之間的溫度梯度為40-45°C。因此，電容器的外表面不得超過45°C。在實際應用中，冷卻回路出口處的冷卻水溫度不應超過40°C。
當電容器組與工作線圈串聯冷卻時，工作線圈的損耗至少是電容器組的十倍。因此，應先冷卻電容器組，然后再冷卻工作線圈。
4. Required Water Flow for Capacitor Bank Cooling
Polypropylene capacitors can safely run at temperatures of up to 90°C. The temperature gradient between the hottest points of the polypropylene element and the copper surface of Celem capacitors is 40-45°C. Therefore, external surfaces of the capacitors must not exceed 45°C. In practice, the cooling water temperature at the outlet of the cooling circuit should not exceed 40°C.
When the capacitor bank is cooled in series with the work coil, the losses of the work coil are at least ten times that of the capacitor bank. Therefore, the capacitor bank should be cooled first, followed by the work coil.
