There are several facets to a transformer’s overall health (dielectric, magnetic, mechanical and thermal) and many components that must be tested to verify the transformer’s whole condition. These include: windings and winding leads, transformer insulation, transformer core, and accessories (tap changers, bushings, bushing CTs and surge arresters). For the assessment of each transformer component, a varying suite of electrical field tests is recommended. Each test in an individual component’s diagnosis test group has a characteristic strength(s) but also deficiencies. However together, with each test contributing unique diagnostic value, the group provides a robust representation of that transformer component’s health.
Many of the electrical field tests appearing in these suggested groups provide assessment information for several transformer components at once. So when the individual component test lists are merged, a thoughtful and smart overall test recommendation for transformers emerges. As some transformer tests are better suited as commissioning and diagnostic tests, the reason for testing (e.g., commissioning, routine screening and diagnostic test situations) will influence the electrical test recommendation for transformers.