Harmonic filters are designed to eliminate or reduce harmonic currents and voltages in electrical systems, which can be detrimental to the overall power quality and efficiency. There are various types of harmonic filters, but they are primarily classified into two main categories: passive and active.
Passive Harmonic Filters:
- Tuned Passive Filters: These are the most common type of passive filter and consist of a combination of reactors (inductors) and capacitors. They are tuned to a specific harmonic frequency and provide a low impedance path for that harmonic, effectively reducing its magnitude.
- Broadband Passive Filters: These offer a wider frequency range of harmonic suppression compared to tuned filters. They are designed to handle multiple harmonics simultaneously.
- High Pass Filters: These filters allow high-frequency harmonics to pass through while blocking lower frequency harmonics. Advantages:
- Relatively low cost.
- Simple design without the need for complex control systems. Disadvantages:
- Fixed to a particular harmonic and might not be effective against others.
- Potential for resonance with other system components.
Active Harmonic Filters:
- Active filters monitor the harmonic currents in a system and generate counteractive currents to nullify or cancel out the harmonics.
- They use power electronics and are usually controlled by a microprocessor. Advantages:
- Can adapt to varying system conditions and harmonics.
- Can target multiple harmonics simultaneously.
- Can improve power factor and correct imbalances. Disadvantages:
- More expensive than passive filters.
- Require more maintenance due to power electronics.
Selection and Implementation:
- The choice between passive and active filters depends on the specific application, the nature of the harmonic problems, and economic considerations.
- Before installing harmonic filters, a thorough harmonic study should be conducted to determine the sources of harmonics, their magnitude, and frequencies. This will help in designing and tuning the filter effectively.
- Installation should also consider the potential for future changes in the system that might introduce new harmonic sources.
Additional Measures:
Apart from filters, there are other methods to manage harmonics, such as using harmonic mitigating transformers, double wound transformers, and altering the design and operation of equipment producing harmonics.