Hi, manh_hoa99,
Both harmonic filter banks and SVC (static VAR compensators) utilize PF capacitors and inductors. They are arranged quite differently and have different logic (control). The purpose of each is different.
Harmonic filter banks are known as “detuned capacitor banks.” The detuning means series reactors are inserted on the line side of the PF capacitors. Detuning can be detuned to keep harmonic currents away from the PF capacitors to prevent harmonic overheating. This device is used for PF correction only.
Detuning can also 'tune' the filter bank to remove a specific harmonic frequency and as such are harmonic filters and PF correction banks. Commonly, the frequency to be removed is the 5th harmonic.
These devices can be fixed (all PF caps on line all the time) or stepped. Stepped banks utilize contactors or thyristors to switch discrete amounts of VARs per step. Generally, these devices are slow switching – 10-30 seconds on to off or vice versa.
SVC use thyrsitor switched PF capacitors and inductors all aranged in parallel with the loads. SVC logic is designed to inject leading reactive current (leading VARs) to help maintian a short duration voltage sag caused by loads. The inductors are utilized to prevent resonance conditions that may exist when the electrical system goes leading due to a lot of PF capacitors being added. SVC are fast operating – cycle by cycle.
Thanks for the comments.
Regards, Jim