Parallel capacitor banks filter out harmonic problems

A series harmonic filter can be installed. Inverter harmonic filter.

The inverter is a typical six-pulse rectifier device. Therefore, it is a high harmonic generation source, the rectifier circuit of the inverter generates harmonic current, and after the harmonic current is injected into the power grid, it will have a disturbing effect on other electrical equipment and power supply equipment.

The harmonic filter is a kind of device-level harmonic filter developed for inverters (or other 3-phase 6-pulse rectifier circuits) in series ** circuit, for any 3-phase 6-pulse rectifier circuit, it can ensure that its harmonic current distortion rate (THID) is less than 10%, and when there are special requirements, it can be less than 5%.

The main features are as follows:

Determination of filtering effect: The filtering effect is independent of the system characteristics, and no debugging is required after on-site installation, ensuring that the total harmonic current distortion rate is < 10%.

No absorption of upstream harmonic current: The general harmonic filter presents high resistance to the upstream harmonic current, so it will not absorb the upstream harmonic current and there is no risk of overload;

Does not resonate with the system impedance: does not resonate with the system under any circumstances;

Small capacitive reactive power: the capacitive reactive power emitted by the general harmonic filter is less than 20% of the rated power, which ensures that the reactive power overcompensation phenomenon will not occur when the load is light;

Stable output voltage: The output voltage of the filter is kept at 5% of the input voltage;

Effective filtering of non-characteristic harmonics: The general harmonic filter not only filters out the harmonics generated by inverters, intermediate frequency furnaces and other equipment (5th, 7th, 11th, 13th), but also can effectively filter out various non-characteristic harmonics;

Stable performance and high reliability: the universal harmonic filter does not need maintenance within 3 years and works reliably;

Simple selection: When selecting DM universal harmonic filter, you do not need to know the value of harmonic current, nor do you need to know the parameters of the system, you only need to know the rated working voltage and power of the load.

010-82737748 Beijing Dammam Technology****.

This professor has not done engineering practice, so I take it for granted. Take a look at any TV circuit diagram, which medium and high frequency channel power line on the filter capacitor is not filtered with large electrolytic parallel small porcelain tiles!

This is not a problem of the size of the capacitor, but the manufacturing structure of the capacitor, the large capacitor, especially the electrolytic capacitor, is made in the form of a pole piece winding, containing parasitic inductance, should be equivalent to a capacitor and an inductor in series (if the loss is considered, there is also a resistance), if you don't believe it, please take an electrolytic capacitor to the RLC bridge to measure the parameters, test with a 50Hz frequency, the capacity is basically correct, increase the frequency of the test signal, the capacity will be greatly changed, more than a certain frequency, It's sensual. As we all know, the inductor is not connected to the high frequency, so this capacitor has no filtering effect on the high frequency, and a ceramic capacitor with a chip structure must be connected in parallel, because the chip structure does not contain the inductance component, so the high-frequency filtering is realized. However, if only chip capacitors are used, the capacitance is too small and has no effect on the interference of lower frequencies, so different varieties of capacitors are used for parallel filtering.

If the power cable is long and the printed cable also contains inductors, it is necessary to add capacitors in different physical locations (also see the TV circuit diagram, which can occasionally be found).

The problem of small capacitors in parallel with large capacitors, your professor has not yet understood the designer's intentions.

In order to reduce costs, large capacitors use electrolytic capacitors, and the high-frequency impedance of ordinary electrolytic capacitors is still large, and the filtering effect of high-frequency ripples is not ideal, and although there are high-frequency and low-resistance electrolytic capacitors, they are relatively expensive. Therefore, we use ordinary electrolytic capacitors to connect a small magneto-dielectric capacitor in parallel for filtering. As for the capacity selection of porcelain dielectric capacitors, it is generally selected according to the withstand voltage situation and actual producibility, and it is not the 1 3 capacitance of large capacitors that the professor said (don't say that it is the professor's words, laughing to death).

Hello, glad to answer for you. <>

In the operation of coupled capacitors, operators often encounter the following four common faults: (1) the wire is broken and loose, and the wire clamp connection is not firm. There is leakage and oil leakage in the hole (2).

3) The grounding is not good, and the grounding switch is in the wrong position. (4) The porcelain sleeve of the capacitor is damaged or discharged. Analysis:

1) The direct cause of the failure is caused by the severe corrosion of the soft connection line between the upper and lower sections of the coupling capacitor. The flexible wire is wound with multiple strands of copper wire, and due to corrosion caused by long-term operation, the discharge phenomenon occurs in the case of increased resistance and high voltage. (2) The indirect cause is that there are pollution sources around the substation, which causes the soft connection line to be seriously corroded, which causes the fault.

3) The color of the soft connection line Yuxian long-term transportation cavity line turns black, which is not easy to find when the operator inspects and inspects, and is also one of the reasons for the failure.

A capacitor bank with 6% reactance is not specifically filtered.

The device itself has the smallest impedance at 204 Hz (calculated as the impedance when the AC power is on), which means that it is a filter for 204 Hz. However, the 5th harmonic is 250Hz, so for the 5th harmonic, this capacitor bank is to protect itself, that is, it discharges most of the harmonic current into the grid, and only a small amount enters the capacitor. Then things like the 7th harmonic (350hz) and the second harmonic (550hz) also have the same effect.

Since it can't be filtered, why do you need string reactance? The answer is that if there is no string reactance, the pure capacitor will amplify the harmonic current.

For example, the harmonic current of the original equipment is 100A, and it is also 100A when there is no capacitance, but in the case of pure capacitance, the harmonic current will become larger, and in severe cases, it will be amplified by more than 5 times, that is, 500A. In this case, first of all, the capacitor will definitely burn out, and secondly, other equipment under the power grid will also be affected, and the specific loss depends on the situation at that time.

Therefore, the 6% capacitor bank in string, first, can protect itself, and second, it prevents the possibility of harmonic current amplification, that is to say, the harmonic current will not become larger (or 100A harmonic current, maybe 80A is discharged into the grid, and 20A capacitor bank is absorbed).

For this part of the harmonic current absorbed, the capacitor has a certain tolerance and can withstand itself.

There are three main functions of filter capacitors in power supply rectifier circuits!

1) Reduces pulsation ingredients! The rectified current is a one-way pulsating current! (50 (half-wave) or 100 (full-wave) seconds one-way wave)!

It's not a smooth DC current! And the role of the capacitor is to use its charging and discharging characteristics! Here charge high and low to level out these one-way pulsating waves!

At the same time, the average output DC voltage is also increased! (peak at no load).

2) The residual AC components of the circuit and the filtering out of higher harmonics! Due to the pass-and-cross separation of the capacitors, these clutter components are short-circuited and reflowed!

3) Increase the instantaneous overload capacity of the power output! The power filter capacitors are all large capacitance! Its energy storage effect can improve the instantaneous current characteristics of the circuit! to accommodate those momentary overcurrent loads!

Inductors also have these functions! But it's nowhere near as effective as capacitors! And it has a very low DC impedance! It can only be used as a series auxiliary component in the filter circuit!

Explain the filtering effect of capacitors in detail.

When the proportion of nonlinear electrical load in the distribution system is large and the capacitor bank is put into parallel connection, on the one hand, due to the small harmonic impedance of the capacitor bank, the harmonic current of the capacitor bank is injected.

large, so that the capacitor load and seriously affect its service life, on the other hand, when the capacitor bank harmonic capacitance.

Harmonic inductive reactance equivalent to the system.

Equals and resonates.

, causing the capacitor plexitant harmonic current to be seriously amplified, causing the capacitor to overheat and damage. Therefore, the voltage is harmonic.

For example, for the commonly used self-healing test parallel capacitor, the allowable overcurrent multiple is the frequency doubling constant current, when the current of the capacitor exceeds this limit, it will cause damage and hail. At the same time, the harmonic distorts the power frequency sinusoidal waveform and produces a jagged spire wave, which is easy to cause partial discharge in the insulating medium, and long-term partial discharge will also accelerate the aging of the insulating medium, and the self-healing performance will decline, which will easily lead to capacitor damage.

The power capacitor and the reactor together form an LC circuit, in the case of the fundamental line, the line is capacitive, the impedance is larger, for the higher harmonics because the inductance impedance becomes larger and the capacitance impedance becomes smaller, so the total impedance of the return road is very small, at this time, most of the higher harmonics will flow through the LC to achieve the purpose of filtering or suppressing harmonics.

These two questions, I try to answer for you, when using a 220V power supply, the DC output of the rectifier is not clean, which contains the current of the rectifier diode reverse leakage, so that this part of the AC component is sandwiched in the DC, so it is necessary to rely on the characteristics of the capacitor to filter out this part of the AC, leaving pure DC. When using the battery, the power supply is no problem, but due to the discrete nature of the components, when working, various harmful harmonics will be generated, which need to be filtered out, as well as various high and low frequency interference from space, if it is also amplified by the circuit, it will also destroy the normal operation of the circuit, and it is necessary to rely on different capacitors to filter out the interference of different frequencies.

The second problem is that data exchange is the task of the computer chip, and the capacitor only plays the role of transmitting the AC pulse here.

The third problem is that the crystal oscillator is a component that produces a certain frequency, but due to the discreteness of other components, the frequency generated by the crystal oscillator will be offset, but the crystal oscillator is a fixed frequency and cannot be adjusted, so it relies on the small porcelain capacitor to adjust and compensate, so that the circuit can accurately work at the set frequency.

The signals in the notebook are all high-frequency square waves, and the performance is good, the faster the frequency. The faster it runs, the faster.

At that time, it was inevitable that there would be interference clutter, and the capacitor was to filter out the unwanted waveform.

2. The impedance of the wave is different for capacitors with different capacitances. Select the capacity value according to the frequency. There are RC and RL oscillations (coupling) in the circuit

3. Crystal resonance requires capacitors to form an oscillation circuit, the same as 2 principles.

You need to study books like "Electronic Technology", and these questions cannot be explained in one or two sentences.

Let's talk about it, I don't know how to explain it to him, this man is a great mallet.