Why fault-current levels become a problem

As power systems expand, additional generators, transformers and network interconnections can raise the available short-circuit current. The resulting duty may approach or exceed the interrupting capacity of existing switchgear and the withstand ratings of cables, busbars and transformers. Replacing an entire substation can be expensive and disruptive. A current-limiting reactor offers a practical way to add controlled impedance and reduce fault current.

How a current-limiting reactor works

A current-limiting reactor is connected in series with a feeder, bus section, transformer circuit or other part of the network. Its inductive reactance has a limited effect on normal load current but opposes the rapid increase of current during a fault. The reactor therefore lowers the prospective short-circuit current and reduces the electrical and mechanical stress imposed on downstream equipment.

The final reactor impedance must be established through a system study. Too little reactance may not reduce the fault current enough; too much can create unacceptable voltage drop, affect motor starting or change system stability.

Common installation positions

Typical applications include feeder reactors that limit faults on individual outgoing circuits; bus-tie reactors that restrict fault contribution between bus sections; transformer secondary reactors that protect downstream equipment; and generator or industrial-plant circuits where network expansion has increased fault level. The best location depends on the one-line configuration and operational requirements.

Air-core and iron-core designs

Air-core reactors avoid magnetic core saturation and can maintain predictable inductance at high fault current. They are often used for medium- and high-voltage outdoor applications, although magnetic clearances and nearby metallic structures require careful layout. Iron-core reactors can provide a compact solution for certain ratings and installations. Their magnetic design, losses, noise and saturation performance must be evaluated for the specified duty.

Critical parameters for selection

A reactor inquiry should state rated voltage and frequency, continuous current, required inductance or percentage reactance, short-time current and duration, insulation level, system connection, permissible temperature rise, loss limits, indoor or outdoor service, altitude, pollution level, seismic requirements, terminal arrangement and applicable standard. The supplier should also receive the target fault-current reduction and the system study whenever available.

Avoiding common specification mistakes

Do not select a reactor only by current and voltage. Confirm thermal short-time withstand, peak mechanical forces, insulation coordination, conductor spacing, magnetic clearances, noise requirements and voltage-drop limits. Installation drawings should keep sensitive equipment, steel structures and closed metallic loops outside the required magnetic-clearance zone for air-core units.

Baoding Weifan Electrical Technology Co., Ltd. supplies MV and HV reactor solutions, including current-limiting reactor designs for project-specific electrical systems. Share your network parameters with Electric Valley to review the required reactor type and rating.