Testing a power transformer involves a combination of electrical, mechanical, and insulation diagnostics. Typical tests include winding resistance, turns ratio (TTR), insulation resistance (IR/PI), dielectric power factor (tan-delta), FRA/SFRA for core and winding displacement, leakage impedance, partial discharge assessment, and OLTC functional tests. Oil-filled units also undergo dissolved gas analysis (DGA), moisture measurements, and thermographic inspections. These tests evaluate insulation integrity, mechanical stability, core losses, and operational readiness before commissioning or after abnormal events.