Tan Delta and Capacitance Test on Transformer

Herewith some information relating to Tan Delta (Power Factor) and Capacitance Test on transformers from our perspective. With regards to your statement relating to whether Tan Delta testing could have any adverse effect on transformer health, the following:

- This test is a diagnostic insulation assessment tool that is a measurement of the fundamental AC electrical characteristics of insulation. These electrical characteristics could provide an indication of moisture, insulation deterioration, destructive agents, or ionization that can affect the dielectric strength and serviceability of the insulation.

- The test is non-destructive, however, it is important that the appropriate test voltage is selected before applying a test voltage to any equipment. It is recommended that the rated phase to phase voltage for windings below 12kV (phase to phase) on small distribution transformers is not exceeded.

- Tan Delta / Capacitance tests are normally performed as part of factory acceptance testing, pre-commissioning testing, on-site condition monitoring test, and also as part of Condition Assessment testing following electrical disturbances.

With regards to the failure that was experienced on the 1600kVA dry-type transformer, there could be various reasons for the failure and as with most transformer failures, this may require a thorough investigation to ascertain the root cause. Repair of dry transformers are in most cases only possible via the OEM as this relates to the unique cast resin winding technology of each manufacturer.