For the study of the hazards of harmonic currents, please consult the definition of harmonics, hazar

The harm of harmonics is mainly to reduce the life of electrical equipment, cause some equipment to malfunction, and cause unnecessary losses. In general, harmful harmonics are mainly more common. There are also many ways to govern it. We do energy conservation and emission reduction in Gansu.

The main effects of harmonics on the power grid are:

1. The main harm of harmonics to rotating equipment and transformers is to cause additional losses and increase in heating return.

Harmonics can also cause rotating equipment and transformers to vibrate and emit noise, and prolonged vibrations can cause metal fatigue and mechanical damage;

2. The main harm of harmonics to the line is to cause additional loss;

3. Harmonics can cause the inductance and capacitance of the system to resonate, so that the harmonics are amplified. When harmonics cause system resonance, the harmonic voltage increases and the harmonic current increases, causing malfunction of relay protection and safety automatic devices, damaging system equipment (such as power capacitors, cables, motors, etc.), causing system accidents and threatening the safe operation of the power system;

4. Harmonics can interfere with communication equipment, increase the power loss of the power system (such as line loss), make the reactive power compensation equipment unable to operate normally, etc., and bring harm to the system and users;

5. Harmonics will cause additional temperature rise outside the switch and reduce the load capacity of the fundamental current. The increase in temperature rise can reduce the service life of some insulating components.

The danger of harmonics to the power grid

In addition to the loss of DU lines, the more important thing is that the harmonic form of the ZHI power grid is polluted by DAO, and the quality of power supply and return is reduced, which endangers the normal operation of various power equipment. In addition to the previously mentioned damage to capacitors and reactors, there are other hazards.

The best harmonic control equipment at the moment is the LPAPF active filter.

The influence of harmonics on the electric BAI network is mainly du:

Harmonics are the main effects of resolvers and transformers

In addition, internal harmonics can cause rotating equipment and transformers to vibrate and emit noise, and long-term vibration can cause metal fatigue and mechanical damage.

The main hazard of harmonics to the line is to cause additional losses.

Harmonics can cause resonance of the inductance and capacitance of the system, so that the harmonics are amplified. When harmonics cause system resonance, the harmonic voltage increases and the harmonic current increases, causing malfunction of relay protection and safety automatic devices, damaging system equipment (such as power capacitors, cables, motors, etc.), causing system accidents and threatening the safe operation of the power system;

Harmonics can interfere with communication equipment, increase the power loss of the power system (such as line loss), make the reactive power compensation equipment unable to operate normally, etc., and bring harm to the system and users.

At present, the best device to control harmonics is the active filter HXAPF.

You can use an oscilloscope to measure the signal and perform FFT calculations, and find the position of the nth harmonic that needs to be calculated to calculate the frequency.

The red histogram below shows what the calibration square wave of the oscilloscope looks like after FFT (Fast Fourier Transform). As you can see from the red histogram, the nucleation voltage of a signal with a frequency of 0 Hz is 0, which means that the signal does not contain a DC component. The first red line is the fundamental wave of the signal, which has a frequency of 1kHz and an amplitude.

Through the difference between x1 and x2 of the x-axis cursor, we find that the frequency of the fifth line is 9 kHz, which is 9 times that of the lifting band fundamental, which is the ninth harmonic. From the difference between y1 and y2 of the y-axis cursor, we can see that the amplitude of this subharmonic is 104mV.

Harmonic generation: In an ideal clean power supply system, both current and voltage are sine waves. In a simple circuit with only linear components, the current flowing through is proportional to the applied voltage, and the current flowing through is a sinusoidal side-leakage wave.

In the actual power supply system, due to the existence of nonlinear loads, when the current flows through the load that is not linear to the applied voltage, a non-sinusoidal current is formed. Any periodic waveform can be broken down into a fundamental sine wave plus many harmonic frequencies. The harmonic frequency is an integer multiple of the fundamental frequency.

The solutions are: installing harmonic filters, isolating transformers and active harmonic regulators

1. Install harmonic filter: For the harmonics generated by the motor controller, the shape of the harmonics is very distinct, and the filter can be used to reduce the harmonic current.

2. Installation of isolation transformer: the problem of balanced third harmonic current flowing back to the power supply can be weakened by an isolation transformer with Dyn connection.

3. Equipped with an active harmonic regulator: the side bands and harmonics generated by the converter inverter cannot be filtered out well by ordinary filters, because the frequency searched on the side band changes with the speed of the transmission device, and is often very close to the fundamental frequency.

For the power grid, it is the harmonic current that is harmful.

However, the harmonic current is often caused by the harmonic voltage, because the power grid is equivalent to a power supply with very small internal resistance, after the voltage source containing harmonics is connected to the power grid, the output of the voltage source is forced to pull down the same as the grid voltage, that is: most of the voltage harmonics are eliminated, but the consequence of the elimination of voltage harmonics is to inject harmonic current into the power grid.

Harmonic current is the root of all harmonic problems, and harmonic voltage is also caused by harmonic current. Therefore, when studying the hazards caused by harmonics, it mainly refers to the hazards of harmonic currents.

causing the cable to overheat;

causing the transformer to overheat;

Damage to variable reactive power compensation device;

special hazards of the third harmonic;

adverse effects on other electronic devices;

resulting in accidental tripping;

Resulting in additional energy loss.

For the power grid, it is the harmonic current that is harmful.

However, the harmonic current is often caused by the harmonic voltage, because the power grid is equivalent to a power supply with very small internal resistance, after the voltage source containing harmonics is connected to the power grid, the output of the voltage source is forced to pull down the same as the grid voltage, that is: most of the voltage harmonics are eliminated, but the consequence of the elimination of voltage harmonics is to inject harmonic current into the power grid.