The fundamental cause of harmonic generation in power systems is due to nonlinear loads. When the current flows through the load, it does not have a linear relationship with the applied voltage, and a non-sinusoidal current is formed, that is, harmonics are generated in the circuit. Harmonic frequency is an integral multiple of the fundamental frequency. According to the analysis principle of the French mathematician M. Fourier, any repeated waveform can be decomposed into a sine wave containing the fundamental frequency and a series of harmonics that are multiples of the fundamental wave. Portion. Harmonics are sine waves, each harmonic has a different frequency, amplitude and phase angle. Harmonics can be divided into even-order and odd-order harmonics. The 3rd, 5th, and 7th harmonics are odd-order harmonics, while the 2nd, 4th, 6th, and 8th harmonics are even-order harmonics. For example, when the fundamental wave is 50Hz, 2 The second harmonic is 100Hz, and the third harmonic is 150Hz. Generally speaking, odd harmonics cause more harm than even harmonics. In a balanced three-phase system,

due to symmetry, even harmonics have been eliminated and only odd harmonics exist.

There is a concept of third harmonic in physics and electrical subjects

f(t)=∑(k=0,n)cos(kwt+ak)

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Any wave function can be Fourier decomposed

The above form

When k=0, the component f (t) = cos (a0) becomes Fundamental wave component

By analogy

When k=3, f(t)=cos(3wt+a3) is called the third harmonic.

In the third In the phase transformer group, the three-phase magnetic circuits have nothing to do with each other, and the third harmonic magnetic flux and the fundamental magnetic flux are closed along the same magnetic circuit. Since the magnetic resistance of the magnetic circuit is small, the third harmonic magnetic flux is larger. In addition, the frequency of the third harmonic is three times the fundamental frequency, so the third harmonic phase electromotive force induced by it is quite large. However, in the three-phase line electromotive force, the third harmonic electromotive force cancels each other, so the waveform of the line electromotive force is still a sine wave.

Harmonic analysis in the transformer refers to analyzing the propagation and distribution of harmonic currents and harmonic voltages in the transformer to evaluate the response and tolerance of the transformer to harmonics, thereby determining whether corresponding measures need to be taken. harmonic suppression measures.

The harmonic current and harmonic voltage in the transformer can be obtained through theoretical analysis and experimental measurement of the circuit. Generally speaking, harmonics in transformers mainly include secondary side harmonic currents and harmonic voltages, which will produce some adverse effects and hazards in transformers, such as damaging insulation materials, causing overvoltage, reducing efficiency, etc. Therefore, the harmonic response and tolerance of the transformer need to be evaluated to determine whether harmonic suppression measures are needed.

Harmonic analysis can be achieved through computer simulation software. Generally speaking, you can use circuit simulation software to establish an equivalent circuit model of the transformer, and perform harmonic analysis on the model to obtain the distribution and propagation of harmonic currents and harmonic voltages. In addition, the harmonic current and harmonic voltage in the transformer can also be obtained through experimental measurements and analyzed and evaluated.

When conducting harmonic analysis of a transformer, it is necessary to consider the frequency and amplitude of harmonics, as well as the impact of factors such as the rated capacity, winding structure, and core material of the transformer on the harmonic response. By analyzing the propagation and distribution of harmonics, the harmonic response and tolerance in the transformer can be determined, and corresponding harmonic suppression measures can be taken to ensure the normal operation of the transformer and the safety of the equipment.

Harmonic analysis can also be used to design harmonic suppression measures for transformers. Common harmonic suppression measures include harmonic filters, harmonic dampers, harmonic capacitors, etc. These measures can be verified through simulation software to determine their inhibitory effects and implementation options.

In practical applications, harmonic analysis of transformers is also very important. Especially in power systems, harmonic problems have become one of the important factors affecting power equipment and power quality. For transformers, the existence of harmonics will cause the rated capacity transformer to become non-rated capacity, causing voltage distortion and imbalance of the rated voltage transformer, accelerating insulation aging and reducing the life of the transformer. Therefore, when designing and operating a transformer, it is necessary to evaluate the harmonic response of the transformer and take corresponding measures for harmonic suppression to ensure the safety and stability of the equipment.