In low-voltage power factor correction systems, detuned reactors are widely used together with capacitor banks to prevent harmonic amplification and protect capacitors. Among the most common configurations, 7% and 14% detuned reactors serve different purposes and require different capacitor specifications.

A 7% detuned reactor typically creates a tuning frequency of approximately 189 Hz in a 50 Hz system, which is below the 5th harmonic frequency (250 Hz). It is commonly used in electrical networks with moderate harmonic levels, especially where 5th harmonic distortion is the main concern.

A 14% detuned reactor, with a lower tuning frequency of approximately 134 Hz, provides stronger detuning and is generally selected for networks with more severe harmonic conditions or a higher risk of harmonic resonance.

The reactor selection also directly affects the capacitor voltage requirement. Because the reactor and capacitor form a series circuit, the capacitor may experience a voltage higher than the nominal system voltage.

For example, in a 400 V system:

• 7% reactor: Capacitors are commonly rated at 440 V or higher.

• 14% reactor: Capacitors are commonly rated at 480 V or higher, depending on the actual system harmonic conditions and design requirements.

In addition, the capacitor kvar rating should be carefully matched with the reactor. The reactor changes the impedance of the circuit and affects the actual reactive power output of the capacitor bank.

Therefore, choosing between 7% and 14% reactors should not be based only on capacitor bank capacity. A proper harmonic analysis is essential to ensure safe operation, avoid resonance, and extend capacitor service life.

In short: 7% is a common solution for moderate harmonic environments, while 14% provides stronger detuning for more demanding power quality conditions.