Virginia Transformer has a Solution for Gassing in Wind Farm Pad Mount Transformers

Wind farms have been rapidly added to the power grid in the last decade. Wind now contributes to more than 60,000 MW of generation capacity in USA and has been achieving double digit growth in the last couple of years. The wind turbines have become more matured over the years. But one of the crucial pieces of equipment, namely the Pad Mount Transformer that links the turbine to the grid has shown a major deficiency. Reports presented at the 2013 Doble conference have shown that pad mount transformers have experienced a gassing rate for conditions 3 & 4 of the IEEE standard at close to 11% level and though the turbines are designed for 25-30 year life cycle the pad mount transformers may be failing in as little as 3-5 years. This is alarming and will cause high O&M costs to the owners of these Wind Farms in the future.

Virginia Transformer has analyzed this ever increasing problem and brought its expertise of 40 years in the transformer business to resolve the problems and achieve 25 years of life matching that of the turbine. A brief description of the problems related to wave distortion, harmonic generation and gas production of the step-up transformers is provided. Standard distribution transformers have been used at these wind farms in the past though there is now a need for a much more stringent duty cycle with the newer turbines using electronic conversion of the power output. As such more care must be taken to design and manufacture these units.

The Wind Turbine Generators (WTGs), like other generators, produce generator related distortions which in turn produce harmonic waveforms. In addition to these harmonics, the solid state equipments used to control the output of the step-up transformers also produce damaging harmonics. The generator systems using rectifier/chopper circuits present a very special problem for the transformers. This requires a reduction of the eddy losses to compensate for the harmonic currents.

The specification used for the transformer which is working with rectifier/chopper type controllers should be similar to the transformer designed for arc furnace, drive duty, or rectifier transformer. If these concerns are not addressed the combined non-sinusoidal wave from the turbines and the wave forms from the switching induced harmonics will create excessive heating and hot spots within the transformer. If the conventional distribution transformers are used the extra burden imposed on them by such harmonic currents will shorten their life span considerably.

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