Why Active Harmonic Filters Are Critical in Managing Electrical Resonance?

Power quality challenges, such as harmonic distortion, are a major cause for concern in modern electrical systems. Distortion occurs when the electric circuit faces a non-linear load, leading to the generation of non-sinusoidal waveforms. Harmonic distortion can lead to overheating, overconsumption of energy, damage to equipment and a whole host of other problems. Harmonic filters, particularly active harmonic filters, are used to tackle this issue. Another issue plaguing the electrical system is known as resonance. This is a more nuanced phenomenon where there is a surge in voltage at certain frequencies.

Resonance occurs when the inductive and capacitive reactances in an electrical system are equal in magnitude, but completely opposite in phase. This blog aims to cover the basics of resonance, its effects, and how active harmonic filters aid in tackling this phenomenon.

Understanding Resonance in Power Systems

As mentioned already, resonance occurs when the inductive and capacitive elements of the system interact with one another in an electrical circuit, that is, their reactances are equal in magnitude and opposite in phase. But what is a reactance? It is a form of opposition or impedance to the flow of alternating current. Therefore, it means that electrical resonance occurs when the impedances of both inductive and capacitive elements of the circuit are equal in power but opposite in phase, leading to a marked increase in voltage.

With this basic understanding of resonance, it is time to explore the classification of this phenomenon.

- Series Resonance: This occurs in a series circuit. The inductive reactance and the capacitive reactance are equal in this case, leading to the minimization of this impedance at the resonant frequency. This leads to a significant increase in current in the circuit.

- Parallel Resonance: This takes place in a parallel circuit. In this case, too, the inductive reactance and capacitive reactance are equal in magnitude. However, the effect is very different. Instead of minimizing impedance, as was the case in series resonance, the impedance is maximized at the said resonant frequency. Consequently, there is a marked increase in the voltage of the circuit.

Therefore, in the first case, the impedances cancel each other out, reducing the overall resistance in the circuit. In the second case, however, even when the impedances cancel out, the resistance in the circuit is maximized. This difference is primarily due to the nature of the circuits in question.

Causes and Effects of Resonance

Here is a brief look at the possible causes and effects of resonance.

Causes Of Resonance:

- Use of capacitor banks: While capacitor banks are highly useful for power factor correction, they can lead to electrical resonance. This is because capacitor banks have the tendency to resonate with the system's inductance at particular harmonic frequencies.

- Non-linear loads: Much like harmonic distortion, non-linear loads are also a common cause of resonance. The most common culprits behind non-linear loads include rectifiers, inverters and variable frequency drives, generating harmonics that interact negatively with the circuit elements.

- System Configuration: Sometimes, the system configuration is the cause of resonance. This includes transformers, cables and other elements that make it conducive to create resonance at certain frequencies.

- Load Changes: Lastly, load changes can also adversely affect the system’s performance by generating resonance. This is because the load shift can change the resonant frequency, making previous preventative measures obsolete.

Effects Of Resonance:

Some common effects of resonance include:

Overcurrent and Voltage Surge: The presence of too much current and voltage causes detrimental effects on the system. The most notable effects are damage to equipment and failure of insulation.

Harmonic Amplification: Harmonic distortion is also closely connected with resonance. Unchecked resonance can amplify any harmonics within the circuit, leading to an increase in Total Harmonic Distortion (THDi). The negative effects of high THDi are well known.

Equipment Malfunction: Sensitive equipment is susceptible to malfunctioning due to resonance, and can even face complete damage.

Overheating: If nothing else, the increase in harmonics will directly translate to overheating of equipment. This can cause undue damage to transformers, cables, motors and other sensitive equipment used during operation.

This is why it's paramount to combat resonance with harmonic filters, and active harmonic filters have emerged as one of the best possible solutions.

Introduction to Active Harmonic Filters

As mentioned above, active harmonic filters are touted as a popular solution to combat resonance. By definition, active harmonic filters are a harmonic mitigation solution that uses compensating harmonics to counteract the effects of the original. Hence, they are a dynamic solution to counter resonance and distortion.

Operational Principles:

The operating principle of an active harmonic filter can be divided into three sections: detection, compensation, and injection.

- Detection: The active harmonic filter uses sensors to assess the incoming harmonics in an electrical circuit.

- Compensation: The harmonic filter generates a counter current that is equal in magnitude to the incoming harmonics, but is totally opposite in phase.

- Injection: Lastly, the compensatory current is injected into the circuit, and the problematic harmonics are neutralized. This is an ongoing process depending on the harmonics.

Advantages Over Passive Filters:

So what sets active harmonic filters apart from passive filters, with the latter being a more widespread solution for handling harmonics? Active harmonic filters set themselves apart in the following ways:

- Dynamic Adjustment: Unlike passive harmonic filters, which can only handle harmonics of a specific frequency, their active counterpart can handle dynamic loads and harmonics, making them a versatile, one-size-fits-all solution.

- Handling Wide Range Of Harmonics: To further emphasize on the first point, active harmonic filters can handle harmonics in a wide range of frequencies. By contrast, multiple passive filters are required to handle multiple harmonic frequencies.

- Improves Power Quality: Lastly, active harmonic filters are an excellent solution to reduce total harmonic distortion (THDi) and improve the power quality and reliability of the entire electrical system.

Role Of Active Harmonic Filters In Managing Resonance

How do active harmonic filters combat the effects of resonance in an electrical system? It does so in 4 major ways:

- Harmonic Cancellation: By cancelling out harmonics occurring in the system, active harmonic filters reduce the risk of damage caused by resonance, as harmonics worsen resonance due to harmonic amplification.

- Detuned Reactors And Other Measures: Detuned reactors and capacitor banks are often used to keep the resonant frequency away from harmonics, as their combination can amplify problems. Active harmonic filters, when combined with these measures, can lead to further reduction in harmonics, as well as prevention of resonance and its adverse effects.

- System Analysis and Fine Tuning: Although active harmonic filters are known for dynamically tackling non-linear loads, they can operate even better if the resonance is properly analyzed. By conducting this analysis, it is easy to identify the common points of resonance within an electrical system, so these harmonic filters can be used expertly to avoid them altogether.

- Continuous Monitoring: Even without proper analysis, active harmonic filters are an excellent choice for combating harmonics as they continuously monitor the system. Thus, when they witness any harmonics, they are sensed, compensated, and adjusted in real time, leading to an electrical system that is highly stable. This reduces the probability of resonance in the circuit in the first place.

Best Practices For Implementing Active Harmonic Filters

While active harmonic filters are the solution for resonance, following these practices will lead to the best results:

- System Assessment: Before implementing the solution, it is important to understand the problem. This is only possible with a thorough analysis, where the harmonic profile of the system can be gauged and possible resonance points are understood.

- Equipment Selection: Not all active harmonic filters are suited for all conditions. Find the right AHF that is rated for a particular system’s harmonics and overall load. They must also be installed in strategic points in the circuit where there are high chances of resonance generation.

- Integration Strategies: It is also recommended to combine active harmonic filters with other types of equipment that are geared towards power factor correction. Since these harmonic filters are somewhat expensive, they can be combined with something like hybrid harmonic filters. The latter is a power quality solution that combines the features of both active and passive harmonic filters, but is more cost-effective.

- Maintenance and Monitoring: Lastly, make sure the active harmonic filters are maintained properly so they remain effective. Regular inspection and calibration are important steps to follow in this regard. Monitoring tools can also be combined with inspection to detect any anomalies before it causes any performance issues.

Conclusion

To sum it up, resonance is a big issue plaguing electrical systems as it can lead to a lot of detrimental effects, such as an increase in current and voltage, amplification of harmonic distortion, damage to equipment, and overheating. Active harmonic filters emerge as the perfect solution to counter this phenomenon as they can aid in dynamic harmonic mitigation and real-time monitoring of the electrical system.

Looking for quality harmonic filters for your system? ADM Engineering Inc. can help. A leading distributor of power quality solutions, numerous industries and OEM manufacturers rely on our harmonic solutions to improve power factor and system reliability. To know which harmonic filter is right for you, contact us at 877-236-8337 today.