Decoding detuned reactors: What and why

In this blog, I will acquaint you with detuned reactors and analyse their usage and benefits. Detuned reactors, that are three-phase inductors dedicated to attenuate the amplification of harmonics in harmonic rich networks,  protect the different components of the installation.

What are detuned reactors?

Detuned reactors prevent harmonic amplification caused due to RESONANCE and avoid the risk of overloading capacitors, thereby significantly reducing voltage and current harmonic distortion in the network. All connected equipment, and even remote substations are subject to voltage fluctuations which may result in equipment malfunction or failure. To avoid this problem, it is common to insert reactors in series with capacitor banks.

The reactor also by its nature will safeguard capacitor and associated switch gears against switching inrush, which other may damage capacitors, circuit breakers and contactors.

Why use detuned reactors?

Presence of Harmonic distortion due to the  non-linear loads within the network or due to import of harmonic from grid or power source will increases the current flowing through capacitors as the capacitive reactance is inversely proportional to the frequency , consequently capacitors will be subjected to over load. The over load on capacitors can cause premature failure in capacitor due to increased voltage and thermal stress on dielectric.

On the other hand, the inductive reactance XL of a Reactor is directly proportional to frequency: The magnitude of inductive reactance will increase with high frequency harmonics thus blocking the harmonic current. Hence, use of detuned reactor in series with capacitor will offer higher impedance for harmonics, thus eliminating risk of over load in capacitors.

The inductance value of detuned reactor is selected such that the resonance frequency is less than 90% of dominant harmonic in the spectrum. For example: if 5^th harmonic is dominant in the spectrum, any series LC circuit having resonance frequency 90% of 250Hz (for 50Hz system), i.e. if the natural resonance frequency of LC is less than 225Hz, it is categorized as detuned filters or detuned capacitors.

Applications of detuned reactors

Detuned reactors are widely used in modern electrical networks to improve power quality and protect equipment from harmonic distortions. One of their primary applications is in conjunction with capacitor banks to form detuned or harmonic filter circuits. These reactors help stop harmonic currents from increasing, which can happen when capacitors work with non-linear loads like variable frequency drives, UPS systems, and industrial machinery. By doing so, detuned reactors help maintain voltage stability and reduce overheating in transformers, motors, and other critical equipment.

Another significant application of detuned reactors is in industrial plants and commercial buildings where harmonic pollution is high. Installing detuned reactors in such environments ensures compliance with IEEE and IEC harmonic standards, extending the life of electrical devices and reducing maintenance costs. Additionally, detuned reactors are used in reactive power compensation systems to avoid resonance conditions that can damage the network. Their role in mitigating harmonics also improves energy efficiency and overall system reliability.

Detuned reactors are essential components in electrical distribution systems, particularly in industrial and commercial applications. They safeguard sensitive equipment, enhance power quality, and support long-term operational efficiency by controlling harmonic distortions effectively.

What are the benefits of using a detuned reactor?

The typical benefits of a detuned reactor are as follows:

• It eliminates harmonic amplification
• It enhances the life of capacitors by reducing voltage and thermal stress due to harmonics.
• Prevents the constant nuisance of input fuse blowing or circuit breaker tripping
• Reduces over heating of the transformer, busbars, cables, switchgear etc caused due to harmonic amplification.
• Reduces the harmonic current in the electrical supply system
• Addresses the harmonic problems created by non-linear loads.
• Improves Power Factor in harmonic rich environment.

How detuned reactors differ from other solutions

Detuned reactors offer a unique approach to controlling harmonics compared to other harmonic mitigation methods. Unlike active filters, which use power electronics to dynamically detect and cancel harmonic currents, detuned reactors are passive components that operate without complex control systems. This makes them simpler, more reliable, and maintenance-friendly, especially in industrial and commercial installations.

Detuned reactors are also different from tuned harmonic filters. Tuned filters are designed to target specific harmonic frequencies, providing precise mitigation but requiring careful design and adjustment for each application. Detuned reactors, on the other hand, are intentionally designed to avoid resonance with typical harmonic frequencies. They provide broader protection by preventing harmonic amplification without needing exact tuning, making them a safer choice for capacitor banks.

Compared to basic capacitor banks without reactors, detuned reactors also stand out. Capacitor banks alone can unintentionally amplify harmonic currents, causing overheating, equipment stress, and potential system instability. By adding detuned reactors in series with capacitors, this risk is greatly reduced.

Detuned reactors combine simplicity, reliability, and broad-spectrum harmonic protection, making them a preferred solution.

Technical data

They form a complete product range from  6 to 100 kvar and are available in the most common tunings like 135, 190 and 210 Hz for network voltage of 400/415V 50Hz. They must be chosen according to the capacitors they are associated with.

To prevent disturbances in a remote installation, select a tuning frequency that is at a lower value than the ripple control frequency (applicable for networks having Remote Utility metering system). In a detuned filter application, the voltage across the capacitors will be higher than the nominal system voltage due to Vector sum of voltage drop, hence  the capacitors must be designed to withstand higher voltages. Typical capacitor voltages for 400/415V network are 480V, 525V etc.

Future of detuned reactors in power systems

The role of detuned reactors in power systems is evolving as electrical networks become more complex and digitized. As the adoption of renewable energy sources, power systems are encountering more harmonic distortions and voltage instabilities. Detuned reactors will continue to play a critical role in mitigating these harmonics, protecting sensitive equipment, and maintaining overall system stability.

In modern smart grids, detuned reactors are increasingly being integrated with digital monitoring and control systems. This allows real-time analysis of harmonic levels and better coordination with reactive power compensation devices. As non-linear loads like electric vehicle chargers, variable frequency drives, and energy storage systems become more widespread, detuned reactors will remain a cost-effective, reliable solution for improving power quality.

Overall, detuned reactors are set to remain a key component in future-ready electrical networks, supporting both traditional and renewable-based power systems.