Once Harmonic is generated in system, it moves around and affects on the connected other electricity facilities.
- Overheating and loss of transformer
- Influx of over current of capacitor and noise
- Instability of control system
- Voltage change
- Overload of rotator
- Errors on the movement of circuit breaker
- Impediment in communication and interfering OA functions
- Heavy current in neutral and low voltage between phase and earthing
Harmonic filter is a device which represses and absorbs the outflow of harmonics generated in the electricity system, It consists of resistor, reactor and capacitor.
Basic harmonic filter consists of lower order (5-13th order) single shunt filter which is synchronized with the harmonics current generated.
For other higher order frequency, higher order filter shall be installed, if necessary.
- Improvement of power factor (invalid power in the electricity system is removed, resulting in the improvement of economics)
- Absorption and removal of harmonics
- Resolving the problem of resonance between inductive and caoacitive in the system
- Keeping the performance and lifetime of the facility high by keeping normal voltage

The effects of contained harmonic current by filter can be expressed as following :