Let’s imagine the following analogy: you get in your car, put it in gear and accelerate as much as possible, maintaining this condition for a few hours. Then, you slam on the brakes abruptly until the car comes to a complete stop. Now repeat this several times a day, every day for years, and assess the wear and tear on your car. Clearly, much greater wear is generated compared to “normal” daily use of the car.
Bearing in mind the necessary comparisons and analogies, a transformer used in renewable energy generation systems is subjected to abrupt load variations daily during its operation. With each maximum and minimum incidence of solar radiation or wind, the transformers are subjected to a maximum and minimum load, respectively. This effect is more intense in transformers directly coupled to the generation systems, but can also be observed in collector power transformers that interconnect the generating plants to the electrical grid.
In addition to the mechanical stresses caused by load cycles in the transformer, we can also highlight the demands related to electromagnetic quantities (basically involving inverters with embedded power electronics). Several articles could be written about these electrical and magnetic phenomena, but in this initial approach I will only emphasize that in renewable energy generation parks there are many demands that, if not considered in the design phase, can compromise the lifespan of these transformers.
In summary, we can highlight the following design characteristics of transformers for renewable energy that should be evaluated from the technical specification, calculation and design to the final construction of the equipment:
• Construction concept with multiple secondary windings;
• Non-symmetrical voltage and current between phases;
• Transient and permanent undervoltages and overvoltages;
• Electrostatic shielding between primary and secondary to attenuate high frequencies;
• High-frequency electrical transients generated by switching and/or faults;
• Repeated stresses generated by the magnetizing current (inrush);
• Short-circuit conditions due to the multiple fault-prone components connected to the transformer;
• Installation environment (high temperature, salinity, pollution, humidity, among others);
• Current harmonics (this topic alone could generate material for several other posts);
• Mechanical stresses due to thermal variations during load cycles and/or ambient temperature;
• Mechanical vibrations (especially when the transformer has some coupling with the wind turbine, which typically generates a significant level of vibrations);
• Design variations with the use of vegetable fluid.