CC-PAON01 51410070-175 is a harmonic equivalent circuit for compensating capacitors and grid impedance parallel resonance. Among them, C is the compensation capacitor capacity, Ls and rs are the equivalent reactance and resistance of the power grid, Ilf and Ilh are the fundamental current and harmonic current intensity of the load, Isf and Ish are the fundamental current and harmonic current intensity on the grid side, and Us is the harmonic voltage of the power grid.

The ratio of grid side harmonic current Ish to load harmonic current Ilh is defined as the harmonic amplification factor, and the relationship between Ish/Ilh and harmonic frequency is shown in Figure 5

As a typical reference value, assuming that the short-circuit impedance of the distribution transformer is 6% and the compensation capacity is 50% (or 30%) of the rated capacity of the transformer, if the short-circuit impedance of the high-voltage line is ignored, the resonant frequency f0 of CC-PAON01 51410070-175 is about 288Hz (or 372Hz). After considering the short-circuit impedance of high-voltage lines, f0 will still be slightly lower. Therefore, if the load current contains 5th and 7th harmonic components, it will be significantly amplified.

The function of series reactors

The effective method to solve the problem of harmonic amplification caused by compensating capacitors is to connect appropriate reactors in series in the capacitor branch. As shown in Figure 6.

After the CC-PAON01 51410070-175 series reactor L is connected, the parallel resonant frequency f0 of the system moves towards the low-frequency direction, which is determined by equation (2). At the same time, L and C form a series resonant branch, and the resonant frequency f1 is determined by.