Inspecting the appearance and structural dimensions of the iron core is a fundamental procedure used primarily to verify the core's forming process and assembly precision, thereby preventing structural defects. The inspection requires a comprehensive check of the silicon steel sheet surfaces to ensure the absence of rust, paint loss, coating damage, edge curling, deformation, or cracks, and to confirm that the spaces between sheets are clean and free of oil or accumulated impurities. Precision measuring tools are used to measure the external dimensions of core limbs and yokes, lamination thickness, and joint gaps; dimensions and tolerances are verified against design standards to ensure tight stacking, precise alignment, and uniform gaps. Additionally, the assembly of auxiliary components-such as clamps, tie plates, insulation blocks, and grounding strips-must be checked to ensure they are correctly positioned and structurally symmetrical, with no issues like looseness, misalignment, or missing parts, thus guaranteeing the quality of the core assembly from a structural perspective.
Testing the iron core's insulation and grounding performance is a critical safety procedure that directly determines the transformer's operational safety and stability. Key tests focus on core-to-ground insulation resistance and inter-laminar insulation performance; specialized insulation testers (megohmmeters) are used to measure resistance values, ensuring robust insulation between the core and the tank, clamps, and windings. Values must meet industry standards to eliminate risks such as low insulation resistance, current leakage, or inter-laminar short circuits. Simultaneously, the grounding status is rigorously verified: connections of grounding strips are checked for reliability, and the core is confirmed to have a **proper single-point ground connection**. Issues such as multi-point grounding, loose connections, or floating grounds are thoroughly investigated to prevent floating potentials during operation, which could otherwise trigger safety faults like partial discharge, localized overheating, or core overheating.
Testing iron core losses and operational performance is a crucial step in verifying the core's efficiency and quality. These tests-primarily covering no-load loss, no-load current, noise levels, and temperature rise-evaluate the core's electromagnetic performance under standard test conditions. For an acceptable core, no-load loss and no-load current must remain within rated standard limits without excessive values or abnormal fluctuations, ensuring high electromagnetic conversion efficiency and low energy consumption. At the same time, transformer operating noise is monitored to identify issues such as abnormal sounds or excessive noise caused by loose core stacking, uneven magnetic circuits, or excessive gaps. For certain operating conditions, temperature rise tests are also required to verify that the core's temperature rise remains stable under rated load without localized overheating, ensuring stable magnetic performance and the absence of magnetic saturation defects, thereby meeting the requirements for long-term, continuous, and stable transformer operation.
