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IEC 60289: Reactors — The Air Gap Stores Energy, the Iron Core Transfers It
The Fundamental Difference Between a Reactor and a Transformer: Air Gap = Energy Storage, Closed Core = Energy Transfer
IEC 60289 specifies reactor requirements. Though reactors resemble transformers externally, the magnetic circuit design objectives are fundamentally different — transformers seek minimum exciting current (gapless closed magnetic circuit); reactors seek linear inductance-current characteristics (gapped magnetic circuit for energy storage).
| Characteristic | Transformer | Reactor | Design Reason |
|---|---|---|---|
| Magnetic Circuit | Closed core, zero gap | Core with intentional air gap | Gap stores magnetic energy→linear L-I |
| Energy Flow | Primary to secondary transfer | Store and release magnetic energy | Reactor has single winding (or series/parallel without isolation) |
| Exciting Current | Very small (<1% In) | Equal to rated current | The reactor “excitation” IS its operating current |
Air gap engineering design: Gap length determines reactor linearity. Too small → core saturates at high current → inductance collapses → current-limiting lost. Too large → more turns needed → increased copper loss. Typical iron-core reactor total gap is 0.5–5% of magnetic path length. Filter reactors requiring high linearity often use distributed gaps (multiple small gaps vs. one large gap) to reduce fringing-flux-induced winding eddy-current losses.
TN Lab — The reactor vs. transformer distinction: the air gap determines whether it is an energy storage device or an energy transfer device.
