• Taking Care of Transformers, Part 7

    Nov. 26, 2012

    In-house maintenance staff can typically handle the two periodic tests needed for dry-type transformers: 1) insulation resistance testing, and 2) core ground (if applicable). One advantage of oil-filled transformers over dry type is you can tell a whole lot more about their condition. However, the tests you must perform to get this information are typically beyond the capabilities of in-house maintenance staff.

    Use a qualified testing firm to conduct a full program that includes the dry-type tests plus:

    • Insulation PF testing
    • Oil samples (sent out for analysis)
    • Oil gas analysis
    • Detailed internal inspection and connection testing
    • Other tests as warranted (e.g., impedance, excitation current)

    Required frequency ranges from three months to five years, depending upon transformer condition and criticality. When scheduling the shutdown, allow for contingencies.

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