Commercial Building

A large number of automation equipment in high-rise building automation systems (equipment automation systems, office automation systems, communications automation systems) require high quality power supplies, but a significant portion of these devices, due to their non-linear load characteristics, also cause low voltage power supply systems Harmonic sources of distortions. These harmonic sources cause serious pollution of the power supply system, so that the power quality decline, not only to buildings in the electrical equipment, electronic equipment and even the entire building intelligent system to bring serious harm and adverse effects. Therefore, it is of great significance to analyze all kinds of harmonic sources that cause harmonic distortions in power supply of office buildings and put forward appropriate control measures for the harm of harmonic distortion, which is of great significance to the safe operation of building automation systems in high-rise office buildings.

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The existence of the problem

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1) Harmonic sources

Harmonic power distribution system mainly from two aspects, one load itself contains a large number of harmonic sources, these harmonic sources can produce a large number of harmonic currents, through the line impedance, but also can cause the system voltage harmonics Voltage. Second, the public power grid itself contains a certain amount of harmonic voltage, this part of the harmonics can be transmitted from the network side to the distribution system.

The load in the building distribution system has the following characteristics:

(1) single-phase load more. Building distribution system, single-phase load accounted for more than half, and single-phase load can cause zero sequence harmonics, and can cause three-phase imbalance and three-phase difference between the asymmetry and other issues.

(2) high nonlinear load ratio. Building distribution system in the main equipment are personal computers, copiers, communications equipment, lighting equipment. Part of the building distribution system will also have UPS, a power supply and other loads, these loads are the building distribution system, the main source of harmonics.

(3) harmonic source harmonic distortion rate. According to the test, the harmonic source in the building distribution system has a large harmonic distortion rate. For example, the harmonic distortion rate of a PC is 100%, the UPS distortion rate is about 20% -30%, and the power harmonic current The distortion rate is usually 40% -50%.

(4) Most intelligent and automation equipment in building distribution require high quality power supply, especially for harmonics.

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Harmonic harm

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The harmonic voltage and harmonic current of building distribution system cause great pollution to the distribution system, which not only deteriorates the power quality of the grid, but also harms all kinds of electric equipment. Harmonic damage to the building distribution system has two main parts:

1) Harm to the distribution network

(1) Additional power loss to the transformer, increased heat generation, and impulse torque and noise.

(2) accelerate the aging of insulated cables, increase the heat, life expectancy shortened. Serious system short circuit, power distribution failure or even cause personal injury.

(3) The circuit breakers, fuses, relays and other protective equipment interfere with, make it malfunction or move.

2) the hazards of electrical equipment

(1) to shorten the lighting equipment, lighting equipment on white light more influential. US IES lighting manual clearly pointed out that if the harmonic voltage distortion rate of 5%, the incandescent lamp life shortened 47%.

(2) make the voltage meter, ammeter and other types of electronic measuring equipment test error increases.

(3) easily lead to reactive power compensation device series resonance or parallel resonance. Cause the capacitor upside down or even explode. Can also lead to reactive power compensation equipment can not switch, the system power factor can not be increased.

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solution

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The current harmonic control equipment mainly passive filter and active filter. traditional

Passive filters have the advantages of simple structure, so it has a wide range of applications. However, with the various power distribution center on the improvement of power quality requirements, the limitations of passive filters have gradually become prominent. Based on this, Active Power Filter is widely used because of its excellent harmonic compensation performance. Compared with the traditional passive filter, the active filter has the following main advantages.

1) dynamic compensation, and can simultaneously harmonic, reactive power, three-phase imbalance compensation;

2) Affected by grid impedance is small, can restrain the grid resonance;

3) The compensation method is flexible. Can not only compensate for a specific harmonic source, but also compensate for multiple harmonic sources;