1 Introduction
In recent years, various modern building buildings have rapidly developed into building automation, and have gradually become an important reference for urban and national development. A large number of automation equipment in high-rise building automation systems (equipment automation systems, office automation systems, communication automation systems) require high-quality power supplies, but quite a few of these devices have non-linear load characteristics and are low-voltage power supply systems. Disturbance source for wave distortion. These harmonic sources cause serious pollution to the power supply system and degrade the power quality, which not only brings serious harm and adverse effects to the electrical equipment and electronic equipment in the building, but even threatens the entire building intelligent system.
Therefore, it is of great significance to analyze the various types of harmonic sources that cause harmonic distortion in the power supply of office buildings and to propose countermeasures against harmonic distortion hazards, which is of great significance to the safe operation of building automation systems in high-rise office buildings.
2. Harmonic sources
Harmonics in building distribution systems mainly come from two aspects. First, the load itself has a large number of harmonic sources. These harmonic sources generate a large amount of harmonic currents, which cause harmonic voltages in the system voltage through the line impedance. Second, the utility grid itself also has a certain amount of harmonic voltage, which can be transmitted from the grid side to the power distribution system.
The load in the building distribution system has the following characteristics: (1) Single-phase load is large. In the building distribution system, single-phase load accounts for more than half, which may cause zero-sequence harmonics, causing problems such as three-phase unbalanced one-phase three-phase phase difference asymmetry.
(2) The nonlinear load ratio is high. Personal computers, copiers, communication equipment, lighting equipment, and UPS, primary power supply and other loads in building distribution systems are the main harmonic sources.
(3) Harmonic source harmonic distortion rate is large. According to tests, harmonic sources in building distribution systems have large harmonic distortion rates, such as PC computer harmonic current distortion rate of 100%, UPS distortion rate of about 20%-30%, primary power supply harmonic current The distortion rate is usually 40%-50%.
(4) Most intelligent and automated equipment in building power distribution have high requirements on power quality and are sensitive to harmonics.
3. Harmonic hazards
The harmonic voltage and harmonic current existing in the building distribution system cause great pollution to the power distribution system, which not only deteriorates the power quality of the power grid, but also causes certain harm to various power equipment: (1) The additional loss of power components is increased, which is easy to cause fire.
Harmonics cause additional losses in components in the utility grid, reducing the efficiency of power generation, transmission, and electrical equipment. A large number of third harmonics flowing through the center line can overheat the line and even cause a fire.
(2) Affect the normal operation of electrical equipment.
Harmonics can affect the normal operation of electrical equipment, causing mechanical vibration and noise of the motor, causing severe overheating of the transformer, causing overheating of capacitors, cables and other equipment, insulation aging, and shortened service life, resulting in damage.
(3) Cause grid resonance.
This resonance may cause the harmonic current to be amplified several times or even tens of times, posing a great threat to the system, especially to capacitors and reactors connected in series, often causing capacitors and reactors to burn out.
(4) The relay protection is malfunctioned and the electrical measurement error is too large.
Harmonics will lead to relay protection, especially the microcomputer integrated protector and automatic device malfunction, resulting in unnecessary power interruption and production loss; harmonics will make the electrical measurement instrument measurement inaccurate, produce measurement error, give power management Economic losses caused by departments or power users.
(5) The industrial control system collapses.
The adjacent harmonic source or higher harmonics will cause interference to the communication and information processing equipment, and light noise will be generated, the communication quality will be lowered, the computer will not work normally, and the information will be lost and the industrial control system will collapse.
4. Building distribution harmonic solution
Current harmonic management equipment mainly includes passive filters and active filters. Traditional passive filters are widely used due to their simple structure. However, as the power quality requirements of various power distribution centers continue to increase, the limitations of passive filters are becoming increasingly prominent. Compared to traditional passive filters, active filters are widely used due to their excellent harmonic compensation performance.
4.1ANAPF active filter working principle ANAPF series active power filter device is connected to the grid in parallel mode. By detecting the harmonic and reactive components of the load in real time, PWM converter technology is used to generate one and current from the converter. The inverse component corresponding to the harmonic component and the reactive component is injected into the power system in real time, thereby achieving harmonic control and reactive power compensation.
The principle is as follows:
4.3ANAPF Active Filter Application Case Description The following is a detailed description of the comparative analysis of the power quality test of the distribution system before and after the ANAPF active filter is put into operation in the distribution transformer busbar of the distribution room.
After testing, the total harmonic current in the system before the active filter is put into about 75A, the main harmonic content is 3 times, 5 times, 7 times, of which the 3rd harmonic current is about 60A, and the 5th harmonic current is 40A, after the Ankerui ANAPF100-400/B active filter, has a significant filtering effect, as shown below:
No input of ANAPF current distortion rate into ANAPF current distortion rate
This paper analyzes the hazards of harmonics on building construction, and introduces the principle and function of ANAPF low-voltage active filters. Through the application case of the active filter in a building's low-voltage distribution system, it can be seen that the harmonics of the system can be effectively filtered out, eliminating various additional losses caused by harmonics, reducing the noise of the transformer and reducing the harmonics. Adverse effects on electrical equipment. The power quality has been improved, and the operating efficiency of the equipment and the efficiency of using the power energy have been improved overall. In addition, the neutral current is reduced, the midline temperature is lowered, and the hidden danger caused by excessive current in the neutral line and even life safety is eliminated. It can be seen that the active filter is the preferred solution for harmonic control in building distribution centers.
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