A More Insightful Dimension of Standard Electrical Field Tests for Transformer Diagnostics

The variable frequency power factor (PF) (VFPF), frequency response of stray losses (FRSL), and dynamic dc winding resistance tests are reviewed in this paper. These electrical field tests provide new and significant diagnostic detail and thereby enable a more comprehensive assessment of the condition of a transformer. These tools are not radically different from three standard electrical tests that have been in use for decades in the industry. In fact, the test setup, connections, and test implementation requirements from a tester's perspective are identical to those for the PF, leakage reactance, and dc winding resistance tests, respectively. The subject electrical field tests have progressed from these traditional tests, gaining their unique assessment capabilities by simply expanding the related standard test's measurement(s) in the frequency or time domain. VFPF, FRSL, and dynamic dc winding resistance tests do not displace these older diagnostic tools but rather supplement them, bringing considerable and, in the case of the VFPF test, disproportionately more value.