Harmonic hazards and control solutions
Release time:
2024-06-19
Harmonic control is not only directly related to the distribution network, but also a measure that enterprises can take to improve the quality of power supply. Its importance also needs to be taken seriously by business operators. This article will popularize relevant knowledge.
Harmonic control is not only directly related to the distribution network, but also a measure that enterprises can take to improve the quality of power supply. Its importance also needs to be taken seriously by business operators. This article will popularize relevant knowledge.
Ways of harmonic generation
First, we need to know the causes of harmonics. Generally speaking, there are two ways to generate them:
1. Nonlinear electrical equipment, which is related to industrial AC and DC conversion devices from low-voltage and small-capacity household appliances to high-voltage and large-capacity;
2. Harmonics generated by the power supply system, such as odd harmonics generated by the gap between generator processes, odd harmonics generated by transformer no-load or over-excitation; when no-load transformers or capacitors are switched in the power grid, the closing of the switch forms a sudden harmonic source.
When the generated grid harmonics accumulate to a certain extent, they will cause harm to the power grid, electrical equipment in the power grid, debt terminals and lines. We need to have sufficient understanding of this.
Harm of harmonics
Grid side:
1. Voltage resonance occurs, resonant overvoltage is generated on the line, insulation of the line and equipment is broken down, causing short circuit;
2. Cause relay protection and automatic device to malfunction, affecting the normal operation of the system; cause monitoring instruments to have errors
3. Interfere with the communication system
4. Affect the power factor compensation effect
Electricity measurement:
1. The existence of high-order harmonic electromotive force makes the electromotive force waveform of the generator worse, increases the stray loss of the generator, increases the temperature rise, and the harmonic current connected to the grid will also interfere with communication;
2. Eddy current loss is generated in the transformer, the transformer efficiency becomes lower, and the service life of the transformer is shortened;
3. When the harmonic current passes through the capacitor, the capacitor presents a smaller impedance to the harmonic current. The higher the harmonic order, the smaller the impedance, so the capacitor is easily overloaded or even burned.
Harmonic control scheme
There are several ideas for harmonic control
1. Filtering: Remove some unnecessary AC signals in the power grid or power equipment. There are three forms: series filtering, parallel filtering and low-pass filtering (series-parallel hybrid). This is done by using capacitor compensation and series reactor.
2. Grounding: Through the correct grounding method, the interference of the equipment itself to the outside world is reduced, and external interference such as grid harmonics can also be controlled.
3. Shielding: Use the method of shielding interference sources for control. The inverter itself is shielded with an iron shell to prevent its electromagnetic interference from leaking; the output line is better to be shielded with a steel pipe, and double-core shielding is adopted.
4. Multi-phase pulse rectification: When the harmonic limit is relatively small, the multi-phase rectification method can be adopted. However, this method requires a dedicated rectifier transformer, which is more expensive.
5. Reactor: Inserting a reactor in series in the input circuit is a method to control lower harmonic currents.
Summary
The control of grid harmonics is of great significance to the power system. This article discusses the generation and harm of harmonics, and studies the methods and measures for controlling grid harmonics from the perspective of technology and management. With the in-depth development of power quality management in my country, we should continue to update technology and vigorously innovate the system, strive to achieve greater achievements in grid harmonic management, and ensure the provision of clean energy for society.
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