Reactive power compensation capacitor reactance combination capacity calculation learning



One about reactive compensation learning

The concept of reactance:
In the capacitor bank for reactive power compensation or filtering, in order to reduce the closing inrush current and filter out harmonics, most of the capacitor bank series a group of reactors, the reactance of the series reactor XL and the capacitive reactance of the capacitor bank XC is the ratio of the reactance of the capacitor device. The induced reactance and capacitive reactance are calculated as follows:

XL=ωL=2πfL, XL is inductive reactance, in ohω, L is coil inductance, in Henry H;

Xc=1/ωC=1/(2πfC), where Xc is inductive reactance in ohω and C is capacitance in farad F.

Omega is the angular velocity of the alternator in radians per second, PI is PI, and f is the frequency in Hertz Hz.

Reactance =XL/Xc

Two, the terminal voltage of the capacitor will rise after series reactance:

After the capacitor is connected in series to the reactor, the voltage at the capacitor end will increase. For the convenience of analysis, the vector diagram of current and voltage is drawn, as shown in Figure 1 (For the convenience of understanding, take the partial complement as an example, the same as the co-complement).








As shown in the figure, based on current I, the upper voltage drop UL of the reactor is 90° leading current, and the upper voltage drop lag current of the capacitor is 90°. The difference between the two is 180°. The applied voltage, UN, is the sum of the vectors. As can be seen from the figure:

UC-UL=UN formula one

According to Ohm's law: UC=XC*I; UL=XL*I; Then:

UL=XL/XC*UC formula 2

Formula 2 is substituted into formula 1, and it is concluded that the reactance and capacitor are connected in series, and the voltage at both ends of the capacitor rises relative to the system voltage UN, and the voltage is UC=1/(1-XL /XC)UN Formula 3

UL=1/(XC/XL-1)UN formula four

Calculation of equivalent capacity output of capacitor series reactor

According to the 400V pure capacitor output power Qc=UN2/Xc formula 5

Capacitor string reactance output power QC "=UC2/XC, reactance consumption power QL=UL2/XL

Effective output power of the combination of actual reactance and capacitance Qc '=QC "-QL

After the substitution of the above formulas, we get Qc '=1/ (1-XL /Xc) Qc

That is, the equivalent output of the capacitor after series reactance is 1/ (1-reactance rate) times the capacity of the rated voltage of the grid kvar.

For example, the combination of a certain brand of capacitor bank and reactor is 480V 33.9kvar, 7% reactance of reactor 25kvar.

The effective output of capacitor after actual combination is: 1/(1-7%)*(400/480)2*33.9kvar≈25kvar.

Iv. Supplementary Note:

The ratio of inductive reactance to capacitive reactance and reactance of capacitance are related to their own characteristics and have nothing to do with voltage class. Its characteristics are related to the frequency of the power supply, in the same power loop is the same.

The so-called capacitor voltage class represents the working voltage resistance, and the actual output is associated with the working voltage rating.