Oil power transformers use liquid insulation and cooling, allowing higher voltage class, higher MVA capacity, and more compact insulation structures. Dry-type designs use solid insulation and air cooling, which reduces spill risk but limits power density and makes very high voltage designs impractical. Oil units require tanks, bushings, conservators, and containment systems, while dry-type units require ventilation management and may have higher audible noise in some cases. Grid design typically uses oil units for transmission and large substations.
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