Modular substations and dry-type transformers offer a number of advantages for renewable energy projects such as those relying on solar and wind power, says Trafo Power Solutions’ David Claassen.

He explains that solar photovoltaic (PV) and wind farms have an important characteristic in common: they both have to deal with multiple sources of generated energy. At a solar plant, for instance, there is a large area of solar panels – especially when the project is of utility scale – that require many individual substations at different locations within the project.

“Depending on the output of the plant, it could require 30 to 100 substations to service the generation capacity,” says Claassen. “This means that there is a large volume of essentially identical substations, which lends itself to factory-based production. In this way, projects gain the quality benefit of dedicated workshop conditions, as well as the cost benefits related to economies of scale when it comes to sheet metal, structural steel and other components.”

When production is streamlined in this way, the completion of the units is also quicker, he says, and is likely to be accomplished by a smaller team than would be required to build brick-and-mortar structures on a distant site. He noted that the locations chosen for these renewables projects – especially for wind farms – are usually quite remote, making logistics challenging.

The usual inputs for on-site construction such as water, sand and aggregate are often not close at hand and can be costly to transport. The wind turbines are often best placed in hilly or mountainous areas where there is little infrastructure to support early on-site operations.

Claassen affirms that dry-type transformers fit easily into compact modular substations along with the inverter, switchgear and ancillary equipment. In addition, the design and operation of the transformers aligns closely with the promotion of clean, renewable energy.

“Unlike conventional transformers, which are cooled by oil, dry-type transformers are air-cooled and are much more environmentally friendly.”

The absence of oil as a coolant means that there is no risk of oil contamination through leakage, and higher levels of safety. The safety ranking of dry-type transformers allows them to be situated close to human traffic and even indoors – as there is little danger of fire or explosion.

“While the manufacture of substations in a modular format saves on the upfront capital, the dry-type transformers require minimal maintenance and save on the plant’s running costs,” he says. “In contrast, oil-cooled transformers need to be regularly inspected and the oil must also be changed; on renewable projects where there could be 100 of these units to be maintained, there are substantial costs involved.”

There are additional technical reasons for using dry-type transformers for renewable power applications. For example, high ambient temperatures must be considered in the design, especially for solar plants. The cooling system must be able to manage the heat, so that the performance and service life of the transformer is optimised.

“Within our design for modular substations in the renewable energy space, we have multiple options for cooling, depending on the prevailing conditions,” says Claassen. “This includes naturally ventilated air, forced ventilated air or cooling strategies using heat exchangers based on either air or water.”

He notes that Trafo Power Systems’ transformer units for these applications are rated as Class H on both the low voltage and medium voltage windings.

“Another key aspect of the design is the fact that transformers in a PV application experience a daily cycle of full load and no load, so there is frequent expansion and contraction of the windings that needs to be accommodated,” he says. “Further to that is the non-linear supply from the inverter, so the transformer has to be designed for high harmonic content, which also translates into a temperature consideration.”

He emphasises that Trafo Power Systems has the design experience to meet these requirements, and project management expertise for engaging with clients, engineers and other stakeholders.