Publish Time: 2022-03-13 Origin: Site
A-harmonic generation
1. Definition of harmonics
2. When the voltage or current waveform in the power grid is not an ideal sine wave, it means that it contains voltage or current components with a frequency higher than 50Hz. We call the current or voltage components with a frequency higher than 50Hz harmonics. When the harmonic frequency is an integral multiple of the power frequency, we call it integer harmonic,.
3. For example, the harmonic whose frequency is 5 times of the power frequency (250Hz) is called the 5th harmonic, and so on. When the harmonic frequency is not an integral multiple of the power frequency, we call it fractional harmonic. Such harmonics are usually expressed directly by harmonic frequency. For example: harmonic with frequency of 1627hz.
4.2. There are many reasons for harmonic generation. There are two common types
5. The first type is harmonic generated due to nonlinear load, such as thyristor rectifier, switching power supply, etc. the harmonic frequency generated by this type of load is an integral multiple of power frequency. For example, the three-phase six pulse rectifier mainly produces the 5th and 7th harmonics, while the three-phase 12 pulse rectifier mainly produces the 11th and 13th harmonics.
6. The second type is the harmonic generated by the inverter load. This type of load produces not only integer harmonics, but also fractional harmonics with a frequency twice the inverter frequency.
B-harmonic hazard
When the harmonic current in the power grid is so large that the voltage waveform is distorted, we call it power grid pollution. The pollution degree of power grid is expressed by voltage waveform distortion rate, which is referred to as THDu for short. For details, please refer to the provisions of the national standard GB / T14549-93 power quality harmonics in public power grid.
1 - the core of the transformer is exposed to hazards such as higher noise, higher temperature and saturation of magnetic flux.
2 - precision electronic equipment (including electronic watt hour meter) will be seriously disturbed, resulting in failure to work normally or even burning.
3 - the loss and temperature rise of all equipment connected to the power grid will increase.
One of the transformer schemes given by our company to foreign hydrogen production projects:
Bridge thyristor rectifier: one voltage regulating transformer with two rectifier transformers, three common oil tanks, placed in a zigzag shape,
Forced oil water cooling and on load voltage regulation
The high-voltage phase shift of rectifier transformer is + 7.5 ° and - 7.5 °, and one group of D connection and one group of Y connection are adopted for the second time. In this way, the body of one rectifier transformer operates as a 12 pulse system, and the bodies of two rectifier transformers operate at the same time to form an equivalent 24 pulse wave.
Two rectifier transformers operate simultaneously to form an equivalent 24 pulse system.
The 24 pulse rectifier system basically eliminates the 5th, 7th, 11th, 13th, 17th and 19th harmonics and reduces the impact of harmonics on the power grid.
The transformer core adopts grain oriented silicon steel sheet and pull plate structure, and the magnetic density is about 1.68t to ensure that the core will not be saturated due to overvoltage and reduce loss and noise;
The current density of the conductor shall not exceed 4A / mm2, which can save energy, reduce the temperature rise and increase the stability and service life;
The low-voltage outgoing line adopts reverse parallel structure, which can reduce the loss of accessories;
The low-voltage outgoing line is box jacking, which is as convenient as possible for on-site installation and reduces material consumption.
The transformer scheme is applicable, energy-saving, low cost, small floor space, convenient installation and transportation, convenient maintenance, long service life, etc.