How to suppress harmonics?
May 06, 2025| Harmonic Problems:
At present, most reactive power compensation in low-voltage power distribution systems is achieved by installing parallel-type capacitor compensation cabinets on the load side. However, the presence of harmonics may cause the capacitors for reactive power compensation to be affected by harmonics and thus be damaged, and it can also amplify the harmonic current. Let's take a look at specific examples to see what effects harmonics have on pure capacitor compensation cabinets and how to carry out harmonic control.
A certain company has adopted a pure capacitor compensation cabinet on-site. In a harmonic environment, some harmonics will enter the capacitor compensation cabinet, causing the current of the capacitor to be too large and resulting in overheating. Even at a certain harmonic frequency, resonance occurs with the system, the harmonics are amplified, causing damage to the capacitor compensation cabinet, making it unable to operate normally. The power factor drops, resulting in fines, increased electricity loss and equipment replacement loss, causing economic losses to the enterprise.
Solutions:
To eliminate the influence of harmonics, the following two methods are recommended:
Method 1: Modify the capacitor compensation cabinet to form a series connection of the capacitor bank and the reactor. The specific reactance rate of the reactor should be determined based on the main harmonic content in the system. If the system mainly contains 5th and 7th harmonics, it is recommended to use a reactor with a reactance rate of 7%.
Method 2: Implement harmonic control using active power filters. An active power filter (APF: Active power filter) is a new type of power electronic device used for dynamically suppressing harmonics and compensating reactive power. It can quickly track and compensate for harmonics of different magnitudes and frequencies. The term "active" is in contrast to passive LC filters, which can only passively absorb harmonics of a fixed frequency and magnitude. The APF can sample the load current and separate each harmonic and reactive power, control and actively output the size, frequency and phase of the current, and respond quickly to counteract the corresponding current in the load, achieving dynamic tracking compensation. Moreover, it can also compensate for harmonics, reactive power and imbalance.