How to suppress transformer harmonics

With the development of modern power electronics technology, more and more nonlinear load devices (such as frequency converters, LED lighting, arc furnaces, etc.) are connected to the power grid, which leads to the increasing harmonic content in the power grid. As one of the core devices in power system, transformer may not only become the medium of harmonic propagation, but also cause problems such as overheating, increased loss and increased noise due to harmonics. Therefore, it is of great practical significance to study and take effective measures to suppress the harmonic influence of transformers.

First, the source and influence of transformer harmonics

The transformer itself is a linear device, and it will not actively generate harmonics under normal circumstances. However, in actual operation, due to the magnetic saturation characteristics of the iron core and the influence of nonlinear load, the transformer may produce harmonic current when transmitting current, especially the third, fifth and seventh harmonics. In addition, when the load connected to the transformer is nonlinear, it will also cause harmonic current to flow into the power grid through the transformer.

These harmonics will bring a series of problems, including: the increase of copper loss and iron loss of transformer, which will lead to the increase of temperature; Excessive neutral current may cause fire; Distortion of voltage waveform reduces power quality; Affect the correct action of relay protection device, etc.

Second, the main methods to suppress transformer harmonics

1. Reasonable selection of transformer structure and parameters.
In the design stage, you can choose a transformer with high anti-harmonic ability, such as the transformer with Dy (Delta-Star) connection mode, which is helpful for the third harmonic to circulate without entering the power grid. In addition, properly increasing the short-circuit impedance of transformer can limit the growth of harmonic current to some extent.

2. Use a filtering device
Installing passive filter or active filter is a common means to suppress harmonics. Passive filter absorbs harmonics of specific frequency through LC circuit; The active filter detects and injects the reverse harmonic current in real time through the power electronic device to cancel the original harmonic. The combination of the two is better.

3. Adopt harmonic isolation transformer.
Harmonic isolation transformer realizes isolation and attenuation of higher harmonics through special winding structure, which is especially suitable for places with high requirements for power quality, such as data centers and hospitals.

4. Strengthen system management and monitoring.
Using intelligent monitoring system to monitor the running state and harmonic content of transformer in real time, find anomalies in time and take countermeasures, which can effectively prevent equipment damage and system failure caused by harmonics.

5. Standardize nonlinear load access.
Unified planning and management of nonlinear load equipment connected to the power grid, setting access threshold, limiting the access ratio of equipment with high harmonic content, and reducing harmonic pollution from the source.

Third, the conclusion

To sum up, suppressing transformer harmonics is an important link to ensure the safe, stable and efficient operation of power system. By optimizing transformer design, installing filtering devices, using isolation equipment and strengthening system monitoring and other comprehensive measures, the influence of harmonics on transformer and the whole power grid can be effectively reduced. In the future, with the further popularization of power electronic equipment and the continuous improvement of power quality standards, harmonic control technology will develop in a more intelligent and efficient direction, providing strong support for building a green and safe power system.