By Brandon Dupuis

The Power Factor measurement has long been accepted as an invaluable tool for identifying insulation defects such as aging, deterioration, moisture ingress, and localized failures involving the winding and bushing insulation of a power transformer. Historically, Power Factor measurements have been performed at a single test-frequency (typically 60 Hz) and at a single test-voltage (typically 10 kV); however, modern test instruments can perform Power Factor measurements at several different test-frequencies and at several different test-voltages with minimal additional time and effort.

Based on experience, performing Power Factor frequency-sweep and voltage-sweep measurements can help identify and confirm:
* Compromised insulation
* User-error
* Influences of the test environment

Power Factor sweep measurements help the industry:
* Better assess the condition of an insulation system
* Determine whether a given Power Factor measurement is even valid

Although Power Factor sweep measurements can be performed when testing the overall winding insulation of a power transformer, this paper focuses on the benefits of applying sweep measurements to the C1 insulation of bushings. Several case studies are presented, which highlight the value of these underutilized diagnostic tests.

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This article was originally published in the June 2019 issue of the New Technology Changing the Heart of Power Systems magazine.

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