Air Core Reactors

An air core reactor is an inductive device that limits current, filters harmonics, or provides reactive impedance in an electrical system — without using a magnetic core. Instead of steel or laminated iron, it relies on the magnetic field created in free air around its coils to provide inductance. This eliminates core saturation, hysteresis losses, and magnetic coupling issues. Rex Power Magnetics air core reactors are designed for applications requiring stable inductance and linear performance under high current and harmonic conditions.

An air core reactor maintains a consistent inductance regardless of current magnitude, as there is no magnetic core to saturate. This makes it ideal for systems exposed to transient overcurrents, high harmonic distortion, or switching surges. Iron-core reactors, by contrast, experience reduced inductance and increased distortion at high currents due to core saturation. Air core designs offer superior linearity, thermal stability, and minimal magnetic coupling to nearby components — essential in precision filtering or high-energy circuits.

Air core reactors are widely used in harmonic filtering, capacitor bank protection, short-circuit current limiting, and line/load filtering in power systems. They are also used in renewable energy installations, DC link circuits, and drive systems to control inrush currents or dampen transients. Rex Power Magnetics designs these reactors for use in harmonic filters, tuned circuits, and custom power conditioning systems that demand high electrical accuracy and durability in continuous-duty environments.

Each reactor consists of precision-wound aluminum or copper coils supported by a non-magnetic fiberglass or epoxy structure. The coils are dipped in polyester resin to increase mechanical strength, insulation stability, and environmental protection. The resin coating minimizes vibration, reduces corona discharge, and protects against moisture and contamination. The air core design ensures linear inductance, while the structural materials withstand high mechanical forces from short-circuit events and thermal cycling. Designs are optimized for low loss and long service life.

In harmonic filter applications, air core reactors are connected in series with capacitors to form tuned or detuned filter banks. The reactor’s inductance limits the flow of harmonic currents into the capacitor, preventing resonance at harmonic frequencies and improving overall power quality. Because of their linear behavior, air core reactors maintain predictable filtering characteristics across the full operating current range, ensuring effective harmonic attenuation even under variable load conditions.

The main parameters include inductance (measured in millihenries or microhenries), rated current, voltage class, frequency, and thermal limit. The mechanical design considers magnetic forces, conductor spacing, and thermal dissipation. Rex Power Magnetics engineers design reactors with precise inductance tolerances and optimized coil geometry to meet each system’s electrical and mechanical requirements. Optional enclosures, terminal arrangements, and cooling enhancements can be specified for demanding applications.

Yes. When required, air core reactors can be supplied with ventilated NEMA 3R or 4 enclosures for outdoor use. The polyester resin coating and fiberglass support structure provide strong resistance to moisture, UV exposure, and corrosion. For extreme environments, additional epoxy sealing or stainless steel hardware can be used. Proper installation spacing and ventilation ensure adequate cooling and prevent magnetic interference with nearby metal structures.

Air core reactors are low-maintenance devices. Periodic inspections should include checking for secure terminal connections, signs of overheating, or accumulation of debris that might restrict airflow. The polyester resin coating eliminates the need for re-impregnation or varnish reapplication. In high-contamination areas, occasional cleaning of the coil surfaces helps maintain cooling and insulation performance. With proper installation and monitoring, these reactors provide decades of reliable service.

Yes. Rex Power Magnetics specializes in custom air core reactor designs for harmonic filtering, current limiting, or neutral grounding applications. Customization options include inductance value, current rating, physical dimensions, and mounting configuration. Engineering teams can also design reactors with specific tuning frequencies, voltage ratings, or dielectric clearances for utility, renewable energy, or industrial systems. Each custom-built reactor is fully tested for electrical, thermal, and mechanical compliance before delivery.