Capacitors: Structure, classification and calculation of capacitor capacityQPC
Table of Contents
- 1 What is a capacitor
- 2 Construction of compensating capacitor
- 3 Classification of capacitors
- 4 How to calculate capacitor capacity
- 5 Which type of capacitor should I choose?
What is a capacitor
Capacitor is an electrical device consisting of two conductors placed in a sealed vessel separated by an insulating dielectric layer, which discharges and charges in an electrical circuit.
Capacitance of a capacitor is a quantity that characterizes the ability of a capacitor to charge at a certain voltage. It is determined by the formula: C = Q/U. Where C is the capacitance, Q is the charge of the capacitor, and U is the potential difference between the two plates of the capacitor.
Capacitors are used to compensate for reactive power, improve power factor (cos phi) to improve operational efficiency, equipment durability, and help the power network to operate stably and without penalty according to regulations. Power industry.
Therefore installing capacitor cabinets Reduce fines significantly and save a lot of money later on. That savings far outweighs the initial condenser installation cost.
Different names such as: cos phi capacitor, power capacitor, capacitor capacitor, reactive power capacitor are all just capacitors.
Construction of compensating capacitor
Compensating capacitors are usually made of special oil-soaked paper capacitors, the two poles are long aluminum foils insulated by layers of paper. All are fixed in a sealed vessel, 2 terminals are brought up to the top of the jar, and there is a plastic cap to cover.
Classification of capacitors
Capacitors have different voltage levels, usually there are 2 main types of capacitors: oil capacitors and dry capacitors.
Classification of compensating capacitors
Dry compensating capacitors are high round capacitors. Compact, easy to install and replace, take up less space are the advantages of this type of capacitor. Dry capacitors have a lower cost than oil capacitors. Suitable for systems requiring small capacity compensation. The capacity commonly found in this type of capacitor is 10, 15, 20.25, 30Kvar. Particularly, the Spanish RTR capacitor has a smaller type of 2.5Kvar and a large type of 40, 50Kvar.
Oil compensating capacitor is a type of capacitor with rectangular, round or square sides. The advantage of this type of capacitor is the high side, but the cost is also higher, taking up more area. Often used in large systems, the quality of the power network is bad, with harmonics. Capacitor oil with common capacity is 10, 15, 20, 25, 30, 40, 50Kvar.
Classification of capacitors according to voltage
Single phase low voltage compensating capacitor
Single-phase low-voltage capacitors have voltage levels of 230v, 250v.
3 phase low voltage compensating capacitor
3-phase low-voltage capacitors have voltage levels of 230, 380, 400, 415, 440, 525, 660, 690, 720, 1100v. But only 2 types with voltage 415v and 440v are commonly used. Because the 415v capacitor is rated and used stably at 380v, while the 440v capacitor is often used in power networks with harmonics, it is necessary to use a harmonic filter reactor, and the network has a higher voltage than the mains. standard pressure.
How to calculate capacitor capacity
To choose a capacitor for a certain load, we need to know the power P of that load and the power factor Cosφ (cos phi) of that load:
Suppose we have the load capacity P.
The power factor of the load is Cosφ1 → φ1 → tgφ1 (before compensation, cosφ1 is small and tgφ1 is large).
The power factor after compensation is Cosφ2 → φ2 → tgφ2 (after compensation, cosφ2 is large and tgφ2 is small).
The reactive power to be compensated is Qb = P*(tgφ1 – tgφ2).
For example, we have a load capacity of P = 100 (kW).
The power factor before compensation is cosφ1 = 0.75 → tgφ1 = 0.88.
The power factor after compensation is Cosφ2 = 0.95 → tgφ2 = 0.33.
So the reactive power to be compensated is Qb = P*(tgφ1 – tgφ2).
Qb = 100*(0.88 – 0.33) = 55 (kVAr).
Which type of capacitor should I choose?
This is a question most customers are interested in because of how to make the most of the benefits of capacitors. This requires expertise and a deep understanding of the electrical system to decide which capacitor bank to install.
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