Application of APF in Harmonic Control of Power Plant Flue Gas Dedusting System

1.Project Problem Description

This project was the procurement and installation project of the flue gas dust removal system equipment of a power plant. A total of 30 sets of dust removal equipment were provided. The dust removal system included a large number of power electronic equipment such as high voltage electrostatic dust removal power supply, frequency conversion drive unit, pulse control unit and dust removal control system. Such equipment contained typical nonlinear load, which will inject a large amount of harmonic current into the power grid during operation, resulting in distortion of voltage waveform of the power grid, and problems such as low power factor and large fluctuation of reactive power existed.

The harmonic current and reactive power impact had multiple adverse effects on the auxiliary power system: first, it accelerated the heating of transformers, cables, switch cabinets and other electrical equipment, increased the loss and shorten the service life of equipment; The second was to cause malfunction of protective relay device, decrease of metering accuracy and interference of control system, threatening safe and stable operation of generator and auxiliary equipment system; The third was to reduce the power quality of the power grid, affected the normal operation of other sensitive electrical equipment in the plant, and even led to abnormal control of the dust removal system and reduced dust removal efficiency.

2.APF Solution 

On-site solution: each dust collector was installed with APF-200A+passive scheme. The APF was mainly used to treat 5-7 harmonics, and the passive filter was used to control higher harmonics

3.The actual situation of APF after use

For power system, harmonic is a kind of pollution, which will affect and damage surrounding equipment. Harmonics can increase the additional losses of power components such as transformers and cause equipment overheating. The existence of harmonic wave will cause resonance between compensation capacitor and power distribution system, amplify harmonic wave, damage capacitor or even explosion. Harmonics will cause malfunction of relay protection device and inaccurate measurement of measuring instrument.

With the use of APF active power filters, the following benefits are obtained for the site LV distribution system:

• Reduce harmonic content, avoid burning caused by possible parallel resonance of capacitor bank and system circuit, and ensure normal operation of reactive compensation cabinet.
• Reduce the effective value of current flowing through the distribution line, improve the power factor and eliminate the harmonic wave flowing through the distribution line. Therefore, the line loss is greatly reduced, the temperature rise of the distribution cable is reduced, and the load carrying capacity of the line is improved.
• Reduce misoperation or rejection of control equipment and relay protection device, and improve safety and reliability of power supply.
• Compensate for three-phase current imbalance, reduce copper loss and neutral current of transformer and line, and improve power supply quality.
• Reduce the additional loss of transformer, reduce the noise and improve the loading capacity of transformer.
• APF access can also improve the carrying capacity of transformers and distribution cables, which is equivalent to an expansion of the system, reducing the investment of the power system in expansion capacity.