Field Diagnosis on Transformers for Wind Turbine Applications

Distribution transformers used in wind turbine applications are exposed to additional stress caused by permanent mechanical vibrations, strong load cycling and harsh climatic conditions. These influences can cause an accelerated ageing of the insulation system and shortening of the life expectancy of these essential components of wind power stations. To avoid spontaneous failure of the transformer, regular on site diagnosis contributes to an increased reliability of the whole power system by early detection of the degradation of the insulation system. An induced voltage test with partial discharge measurement is the most significant and productive method for the assessment of the dielectric condition. The most efficient way with respect to availability and logistics is to perform the induced voltage test on-site. Because of the very limited space inside the wind power systems, specialized test equipment was developed for the regular on-site inspection. This compact test voltage source is based on a small IGBT inverter with filter and step-up transformer. It comprises a state of the art control computer to enable a closed loop control of the test voltage. The test voltage source is divided into three small transport units (boxes) and can be used directly in the nacelle. First field tests in 2017 proved the suitability of the compact test voltage source to perform induced voltage tests with accompanying partial discharge measurement. Such field tests were executed continuously throughout the last years and it could be proven that the test system could be integrated into the different service regimes. The test system is suitable for the on-site diagnosis of any kind of cast-resin and distribution transformer too.