An oil filled current transformer uses oil as both insulation and cooling medium around the core and windings. The CT steps down primary current to a standardized secondary current for metering and protection while providing high voltage insulation to the primary conductor. The oil fills voids, improves dielectric strength, and helps dissipate heat from losses. Many designs include an expansion space, seals, and bushings to maintain insulation integrity. Periodic checks include oil level, leaks, and dielectric condition depending on design and criticality.
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