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By core Construction-Magnetic Path& Manufacturing, to Identify cores of transformer
Core‑Type Transformers
Windings surround the limbs. Stepped lap joints reduce joint losses; cores are assembled from laminations or wound strip. High‑permeability GO minimizes core cross‑section and copper losses.
Shell‑Type Transformers
Core surrounds the windings. Flux‑dividing structure with stacked laminations; precise stacking ensures magnetic symmetry. GO with excellent flatness and uniform coating for consistent stacking factor.
Wound Cores (C‑cores, toroidal)
Continuous strip wound into a ring, cut or uncut. Used in single‑phase distribution, instrument, and specialty transformers. GO requires high ductility, uniform tension, and narrow strip widths for toroids.
By Number of Phases – Stacking & Cutting Patterns for definition of transformer cores
Single‑Phase Cores
Two‑leg or three‑leg stacked cores. Wound cores are popular for distribution due to lower joint losses. GO utilization: higher flux density in legs; mitered overlaps critical to avoid local saturation.
Three‑Phase Cores
Three‑leg stacked (common for distribution) and five‑leg (for large power transformers to reduce height). GO utilization: yoke and limb sections require different cutting angles; advanced nesting software maximizes material yield from master coils.
By Insulation & Cooling Medium – Coating Compatibility, to define transformer cores
Oil‑Immersed
Most common for power and distribution. GO requires insulation coatings resistant to hot transformer oil (thermal stability up to 120°C+), high interlaminar resistance, and hydrolysis resistance.
Dry‑Type
Air‑cooled, used indoors or in fire‑sensitive areas. Coatings must withstand higher temperatures (class F/H insulation) and, for open environments, enhanced corrosion protection. Low‑loss GO maintains efficiency without liquid cooling.
Common Coating Need
Both benefit from insulation coatings that preserve low core loss after stress‑relief annealing.
By Voltage Class – Core Size & Magnetic Flux Density, to classify cores of transformer
· Low Voltage (LV): Up to 1 kV
· Medium Voltage (MV): 1 kV – 69 kV
· High Voltage (HV): 69 kV – 230 kV
· Extra High Voltage (EHV): >230 kV
Large cores require careful control of magnetostriction and joint losses. Domain‑refined GO is often used to reduce no‑load loss, a major part of lifecycle cost.
By Cooling Method – Thermal Management, for classification of transformer cores
Cooling method (ONAN, ONAF, OFAF, etc.) does not change core material but affects temperature rise. High‑cooling designs allow higher flux density since heat is removed more effectively. GO with stable magnetic properties up to 100–120°C ensures performance across all cooling regimes.
Whether for a compact dry‑type distribution transformer or a 500 kV power transformer, the core is the critical link between magnetic performance and long‑term value. By aligning core construction, material grade, and coating with the transformer’s classification, manufacturers can confidently deliver high‑efficiency, low‑loss solutions for today’s evolving energy landscape.
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