What is the purpose of a transformer bushing test?

• A. Assess insulation integrity between winding and ground to prevent oil-leak or insulation failure.
• B. Measure copper loss.
• C. Determine oil viscosity.
• D. Check core saturation.

Answer: (A)

Bushing tests verify the dielectric isolation provided by the transformer bushing, ensuring the live winding is properly insulated from ground through the bushing oil and insulation path. The goal is to detect any compromise in that barrier that could create a leakage path, leading to oil leaks or insulation failure under operating voltages. If the insulation degrades, moisture, contamination, or mechanical damage can cause creepage or breakdown, risking arcing, oil loss, and transformer failure. This is why a bushing test focuses on insulation integrity between winding and ground. Copper loss, oil viscosity, and core saturation involve different parts or properties of the transformer and are not determined by bushing insulation tests.