1. What is harmonic control?
Harmonic control is to install a filter at the harmonic source, and absorb the harmonic current generated by the harmonic source nearby. The widely used filters are passive filters, and there are active filters that use the principle of time domain compensation. The advantage of this type of filter is that it can be compensated in a timely manner without adding capacitive components of the power grid, but the cost is higher. The passive filtering device absorbs the higher harmonics, and all the filtering branches are capacitive to the fundamental wave, which just meets the requirements of reactive power compensation. There is no need to install a parallel capacitor compensation device. This method is economical, simple, and widely used at home and abroad.
2. Why do we need harmonic control?
When there is a non-linear load in the power system, even if the power supply is powered by the power frequency 50HZ, when the power frequency voltage or current acts on the non-linear load, it will generate sinusoidal voltage or current of other frequencies different from the power frequency. These are different from The sinusoidal voltage or current of the power frequency is the power harmonic. Power harmonics can cause the following hazards:
1. Cause series resonance and parallel resonance, amplify harmonics, and cause dangerous overvoltage or overcurrent;
2. Harmonic loss is generated, which reduces the efficiency of power generation, transformation and power equipment;
3. Accelerate the aging of electrical equipment insulation, make it easy to breakdown, and shorten their service life;
4. Make equipment (such as motors, relay protection, automatic devices, measuring instruments, power electronic devices, computer systems, precision instruments, etc.) run abnormally or cannot operate properly;
5. Interfering with the communication system, reducing the transmission quality of the signal, destroying the correct transmission of the signal, and even damaging the communication equipment.
3.Monitoring method of harmonic control
1. The harmonic monitoring points are generally selected on the main power plants, hub substations, and buses with voltage levels of 220kV and below that are connected to a large number of harmonic source loads or capacitor banks. Harmonic monitoring points should be adjusted in time with the development of the power grid.
2. For the harmonic voltage at the harmonic monitoring point and the harmonic current of the main harmonic source user, continuous or regular monitoring should be performed according to the specific situation.
3. The harmonic voltage (phase voltage) at any point in the power grid must not exceed the limit value specified in the National Standard of the People's Republic of China-Power Quality Harmonic of Public Power Grid (GB / T14549-93).
4. Harmonic treatment mainly adopts passive filter device and active filter. Commonly used methods for harmonic control are passive filtering and active filtering.