Application of parameter calculation formulas of capacitors and reactors in reactive power compensation devices

What are the formulas for calculating the parameters of reactors and capacitors in reactive power compensation devices

Single tuned branch parameter calculation method

The calculation of single-tuned branch parameters mainly includes determining the sizes of C, L, and R, rated current, rated voltage, etc.

1. Determine the resonant frequency f of the single-tuned branch according to the harmonic current of the system;

2. Calculate the required capacity of capacitor C based on the size of the harmonic current. The calculation formula is

Qc=Up*Ih

If reactive power compensation is considered, Qc can be increased according to the principle of equal distribution to meet system requirements. Among them, Qc is the capacitor capacity, Up is the effective value of phase voltage, and Ih is the effective value of current harmonics.

3. Based on the calculated size of the required capacitor C, the calculation formula is

Qc=U1^2ωC

where ω is the fundamental angular velocity of the system, and U1 is the rated voltage of the capacitor;

4. Calculate the size of the inductor L based on C and the branch resonant frequency. The calculation formula is

nωL=1/nωC1

where n is the order of harmonic current. In order to increase the robustness of the system, the fundamental frequency is taken to be 49.7Hz during calculation;

5. Select the filter branch quality print number Q according to the filtering effect. Generally, the Q selection range is 30-60. Assuming that the reactor resistance is R1, the size of the resistor R that needs to be added is

R=nωL/Q-R1

Taking into account the heat dissipation and cost issues, if the filtering effect meets the requirements, the resistor may not be added;

6. After obtaining the filter parameters C, L, and R, calculate the frequency characteristics of the branch impedance, and calculate the harmonic current flowing into the power grid based on the harmonic equivalent circuit diagram model. If the harmonic current flowing into the power grid meets the national standards , proceed to the next step of verification. If the requirements are not met, reduce the size of R and fine-tune the C and L parameters to further reduce the harmonic current flowing into the power grid;

7. Calculate whether the filtering performance can meet the standard when the filter is normally detuned. If it cannot meet the standard, further adjustments to the C, L, and R parameters are required;

8. Calculate the grid impedance and the equivalent parallel impedance of the filter branch, and check whether parallel resonance occurs at the characteristic frequency. If parallel resonance occurs, further fine-tuning of the C, L, and R parameters is required;

9. When the C, L, and R parameters meet all the above requirements, further check the rated current and rated voltage of each device so that the rated current and voltage capacity of the capacitor meets the standard requirements;

How to calculate the capacity power current of a capacitor for reactive power compensation

Measure active and reactive power to get the original power factor,

Then get the compensation amount based on the power factor you need to compensate.

Suppose the power factor is a a=P/S

S=Under the root sign (p^2 q^2)

p active power, s is apparent power, q is reactive power

The original q1 can be obtained through measurement, and the reactive power q2 provided by the system after compensation can be obtained through the required power factor,

Required compensation amount = q1-q2 As long as you remember the above two formulas, you can calculate it no matter what the data is.

The selection of capacitor must be determined based on the actual situation of your load, which cannot be explained clearly at once.

In addition, if there are harmonics in the system, the series and parallel resonance caused by the harmonics must be considered, so a reactor must be connected in front of the capacitor. The choice depends on the harmonic type.

The capacitor withstand voltage must consider the fundamental voltage, reactor voltage rise, and harmonic voltage

You can directly find out the capacitance value and current of the capacitor if you have the capacity. You can find formulas in books on how to calculate them specifically.

If you have any questions, you can leave a message to communicate.

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