What Are The Performance Differences Between Iron-core And Air-core High-voltage Series Reactors?

The performance difference between core and air core high voltage series reactor is mainly shown in their inductance characteristics, loss, heat dissipation, application scenarios, structure and cost. The specific analysis is as follows:
1.Inductance Characteristics
* **Iron-core Reactors:** iron core significantly increases inductance through a centralized magnetic field, providing a larger inductance for the same capacity and suitable for low-frequency applications (e.g. reactive power compensation in power systems). However, magnetic saturation iron core occurs easily, and when the current is too high, the inductance value drops sharply, resulting in poor linearity.
**Typical application:** 6kV–35kV power systems used in series with capacitor banks to limit short-circuit currents and suppress harmonics (e.g., third and fifth harmonics).
* **Air-core Reactors:** The core-free design results in a smaller but stable inductance value that do not change significantly with current variations and exhibit good linearity. The magnetic field is evenly distributed, has no saturation issues and is suitable for high frequency or high current conditions (e.g. filtering and harmonic mitigation).
**Typical applications:** Orbital transportation, metallurgy, petrochemicals, etc., require continuous operation and high harmonic suppression.
2. Loss and efficiency
Iron-core Reactors: Losses are mainly due to hysteresis and eddy current losses iron core, which results in the generation of large amounts of heat and requires effective heat dissipation measures (e.g. silicone rubber shock absorbent pads and epoxy resin encapsulation). Long-term operation can lead to heat failure, especially in summer or under high loads.
Case study: after a subway substation adopts an iron-core reactor, the third harmonic distortion rate exceeded the standard. Switching to a 12% reactance rate reduced harmonic amplification, but heat generation is still a concern.
Air-core Reactors: No iron core losses, only conductor resistance loss (copper losses). Low heat, high efficiency. Air cooling (e.g. mandatory air cooling design) can be operated continuously for 24 hours without the risk of heat accumulation.
Case study: In a long-cable pressurization test, a single section of an air-core reactor weighed only 24kg and could withstand a 22kV high voltage, dispelling fears of thermal rupture in high temperatures.
3. Heat Dissipation Performance
Iron-Core Reactors: designed to rely on external heat dissipation design (e.g., self-cooling, oil-cooling), but the loss of the core leads to elevated temperatures and requires rigorous monitoring of operating temperatures.
Technical Parameters: average coil temperature increased ≤75K and continuous overload capacity ≤1.35 times current.
Air-Core Reactors: Air cooling is efficient, heat is taken away by air and no internal heat accumulation. Compact structure, suitable for outdoor or confined spaces.
Technical Parameters: long glass fiber bundle coated with epoxy resin impregnation, coil curing has good integrity and short circuit resistance.
4.Application Scenarios
Iron-Core Reactors:
Strengths: Small size, light weight (35kg~100kg), easy to carry and low cost.
Limitations: Suitable for small capacity situations (e.g. series resonant reactors of less than 1,000 kVA); large capacity applications require multiple series units, increasing cost and complexity.
Typical Scenarios: urban power grid substations, underground substation and other locations with high fire protection requirements and limited space.
Empty-core reactors:
Advantages: large rated current capacity, good reliability, suitable for large current transmission and frequent switching applications.
Limit: Bigger size (you'll require a larger size to achieve the same inductance value) but still manageable weight (24kg per section).
Typical scenario: rail transit, metallurgy, petrochemical and other areas requiring long-term operation and high harmonic suppression.
V. Structure and costs
Iron Core Reactor:
The structure is complex, the iron core requires stacking of silicon steel sheets and air gap (filled with insulating materials such as epoxy glass plates), and the manufacturing requirements are high. Costs are mainly influenced by iron core materials such as directional silicon steel sheets.
Case study: A 110kV substation uses 6% reactance iron-core reactors, which are cheaper than emptycore reactors but require regular harmonic monitoring.
Empty-core reactors:
The structure is simple, including winding and supporting insulation; the coreless design reduces material costs. However, the manufacturing process is very demanding (e.g., multilayer parallel winding and epoxy resin pouring) and the total cost may be higher than that of an iron-core reactor.
Case study: after adopting air-core reactor in a subway project, although the initial cost was higher, the long-term operating efficiency is higher and maintenance cost is lower.