Importance of Insulation Testing After Oil Injection in High-Frequency Transformers

In the maintenance of high-frequency transformers, conducting insulation tests after oil injection is critical. Specifically, it’s recommended to perform the test 24 hours after the transformer has been sprayed with oil. This delay allows any moisture trapped within the insulation materials to migrate to the surface, where it can be detected during testing. Without this step, potential insulation defects might remain undetected, leading to significant issues later on. For instance, in a scenario involving a 110 kVA transformer with a 31.5 MWa low-voltage side, a 10kV copper rod support block's insulation was compromised, yet initial tests post-oil injection indicated no problems. It was only after 24 hours that the insulation resistance dropped to 1Ω, revealing a serious fault.
This example underscores the importance of waiting 24 hours post-oil injection before conducting insulation tests. This practice is essential for high-frequency pulse transformers and high-frequency switching transformers alike, ensuring that any latent insulation issues are identified and addressed promptly.