low-power capacitor

конденсатор малой мощности
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[Я.Н.Лугинский, М.С.Фези-Жилинская, Ю.С.Кабиров. Англо-русский словарь по электротехнике и электроэнергетике, Москва, 1999 г.]

Тематики

• электротехника, основные понятия

EN

• low-power capacitor

виды коррекции коэффициента мощности
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There are 2 types of power factor correction: fixed or automatic.
Fixed power factor correction consists of inserting, in parallel on the network, a capacitor bank whose total power is provided by the assembly of capacitors of identical or different ratings. The bank is energized by a contactor that simultaneously supplies all the capacitors (a single step).
The inrush current peak, in the case of fixed correction, can reach 30 times the nominal current of the capacitor bank.
An automatic power factor correction system, on the other hand, consists of several capacitor banks of identical or different ratings (several steps), energized separately according to the value of the power factor to be corrected.
An electronic device automatically determines the power of the steps to be energized and activates the relevant contactors.
The inrush current peak, in the case of automatic correction, depends on the power of the steps already on duty, and can reach 100 times the nominal current of the step to be energized.
[ABB]

PFC Types
There are two types of Power Factor Correction - Passive PFC and Active PFC.
Passive PFC uses passive elements like a ferrite core inductor on the AC input. It is very easy to implement in existing power circuits although the power factor is low at 60-80%. The proper AC input voltage (115V or 230V) must also be chosen manually. In addition, significant EMI can still result with a 115V AC source. Of course, a 230V AC source will not have this problem!.
Active PFC, on the other hand, uses a switching regulator with active elements like an IC, FETs (Field Effect Transistors) and diodes to create an active PFC circuit. This circuit allows the power supply to achieve a power factor of up to 95%, significantly reduce harmonics and automatically adjusts the AC input voltage. This means you do not have to manually select the AC input voltage. It works with all voltages from 110V to 240V.
[ http://www.techarp.com/showarticle.aspx?artno=81&pgno=1]

 

Тематики

• компенсация реактивной мощности

EN

• PFC types
• types of power factor correction

импульсный источник электропитания с коммутацией тока на первичной стороне
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In primary switch mode power supplies, the AC mains voltage is first rectified and smoothed and then chopped ("switched"). Chopping means that the DC voltage is switched periodically at a frequency of 40 to 200 kHz using a power transistor.
In contrast to linearly regulated power supplies, the power transistor does not act as a variable resistor but as a switch instead. This generates a square-wave AC voltage that is transformed to the secondary circuit using a high-frequency transformer. In the secondary circuit, the voltage is rectifi ed and smoothed. The quantity of energy transformed to the secondary circuit is controlled, depending on the load, by varying the chopping rate. The longer the transistor is conductive, the higher is the quantity of energy transformed to the secondary circuit ( pulse width modulation).
Due to the use of high-frequency AC voltage, primary switch mode power supplies have the decisive advantage that their transformer can be of much smaller size than required for the transformation of low frequencies. This reduces the weight and the dissipation inside the unit. The effi ciency of these units is between 85 and 95 %. Since the output voltage does not directly depend on the input voltage, these units can be used for a wide input voltage range and can even be supplied with DC voltage. Furthermore, it is possible to buffer short-time mains voltage breakdowns up to 200 ms. However, the power failure buffering time is limited by the size of capacitor C1 since a longer buffering time requires a higher capacity and thus a bigger size of the capacitor. Especially in case of small power supplies this is not desirable.
Therefore, a practicable compromise has to be made between the size of the power supply and the buffering time.
Primary switch mode power supplies can be used for all purposes. For example, they are suitable for the supply of all kind of electronics as well as for electromechanical applications.
[ABB]

Тематики

• источники и системы электропитания

EN

• primary switch mode power supply