Converter Embedded Testing of Inter-Laminar Core Insulation of Step-Up Transformers for Wind Energy Applications

Transformers used in wind power applications for stepping up the low voltage output of wind generators are known to have high failure rate due to the harsh operating conditions and environment. It is a challenge to perform on-site tests regularly because wind turbines are difficult to access due to their remote location. This makes remote and automated condition assessment of wind turbine transformers (WTT) crucial for preventing failure. In this paper, the feasibility of a new off-line method for testing the quality of the inter-laminar insulation of the step-up transformer core using the back-to-back converter is evaluated. The idea is to use the converter available in the wind turbine as the test equipment for injecting test signals into the WTT for remote and automated testing, whenever the wind turbine is disconnected from the grid. It is shown that inter-laminar core faults can be clearly detected with sensitivity comparable to the core loss test and commercial FRA equipment. An experimental study was performed on a 380/690 V transformer under emulated inter-laminar insulation fault conditions to verify the new test concept. It is shown that the proposed method can provide remote, automated testing of WTTs for reliable detection of core faults.