Oil power transformers use liquid insulation and cooling, which supports higher voltage classes, higher MVA ratings, and better thermal management. Dry-type transformers use solid insulation with air cooling, which reduces spill concerns and can be suitable for indoor facilities. Oil units require containment, oil testing, and leak management, while dry-type units require ventilation control and are limited at very high voltages. Grid level transmission applications overwhelmingly use oil units, while dry-type is common for buildings, hospitals, and indoor industrial distribution.
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