Power transformer testing includes routine, type, and special tests defined by IEC 60076/IEEE C57. Routine tests check ratio, winding resistance, insulation resistance, tan-delta, vector group, impedance, no-load/load losses, and induced/separate-source withstand. Type tests include lightning and switching impulse to verify dielectric coordination. Special tests may include partial discharge, FRA, sound level, temperature rise (heat run), and OLTC functional tests. Together they validate electrical, thermal, and mechanical robustness before energization.