OLTC field testing has a couple of new tools for the condition assessment of this moving transformer component. Dynamic testing can now provide information on the operational characteristics of the OLTC, as well as problems with contacts, mechanism and other subassemblies. Dynamic DRM test is an off-line, non-destructive test in which a DC current is injected through a winding and tap changer as it moves through all of its positions. Results from the current signatures are examined and compared against previous tests or similar unit test results. Another method is a vibration analysis that can be performed on-line also. Evaluation of time domain spectrum, as well as frequency spectrum can provide information that is complementary to the DRM results. With these two tools an exact position/component in trouble can be pinpointed based on early warning provided by ratio of gasses analyzed using DGA.