Renewable energy projects like those using solar and wind energy sources present particular demands on the electrical infrastructure, but there are opportunities for cost savings in both capital and operating expenditure. Managing Director of Trafo Power Solutions, David Claassen, highlights some key advantages of modular substations and dry-type transformers.
E-House or modular substation fitted with monitoring control panels for a renewable energy application.
The growing renewable energy generation sector in Africa is realising the value of modular substations in solar and wind projects, and the suitability of dry-type transformers in these installations.
Claassen notes that solar photovoltaic plants 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 typically a large area of solar panels – especially when the project is of utility scale – that requires 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,” Claassen says. “This means a large number of essentially identical substations is required – which lends itself to factory-based production. In this way, projects gain the benefit of quality from dedicated workshop conditions, as well as the cost benefits related to economies of scale in respect of sheet metal, structural steel and other components.”
When production is streamlined in this way, completion of the units is also quicker, he says, and will likely be accomplished by a smaller team than would be required to build brick-and-mortar structures on a distant site. He notes that the locations chosen for these renewable energy projects – especially for wind farms – are invariably in quite remote areas, making logistics challenging.
The usual inputs for on-site construction such as water, sand and aggregate are often difficult to find nearby and can be costly to transport. The best places to generate energy from wind turbines are often found in hilly or mountainous areas, and there is usually little infrastructure to support the early on-site operations.
“We have seen many of South Africa’s solar and wind power projects already incorporating a modular approach to inverters,” Claassen says. “As a supplier of modular substations, we also specialise in dry-type transformers which are well-suited to these applications.”
Positioning of the dry-type transformer in the E-House.
He highlights that dry-type transformers fit easily into compact modular substations along with the inverter, switchgear and ancillary equipment. And importantly, the design and operation of the transformers aligns closely with the sustainability philosophy that underpins the promotion of clean, renewable energy.
“It makes sense for renewable energy projects, which are leading the charge to supplement and over time replace fossil fuels, to employ technologies that do not rely on oil,” Claassen says. “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 there is no risk of oil contamination through leakage, and ensures higher levels of safety. The safety ranking of dry-type transformers allows them to be situated close to human traffic and even indoors – as the risk of fire or explosion is low.
With most renewable energy projects in South Africa and Africa being driven and funded by independent power producers (IPPs), the cost per kilowatt-hour is paramount to their success. They are generally selling their electricity at a pre-agreed price to a utility or customer, so they need to control their capital and operating expenditure carefully.
“The manufacture of substations in a modular format provides a saving on the upfront capital, and dry-type transformers require minimal maintenance, providing savings on the plant’s running costs,” he says. “In contrast, oil-cooled transformers need to be regularly inspected and the oil must be changed at intervals; on renewable projects where there could be 100 of these units to be maintained, there are substantial costs involved.”
Other important technical factors also play a role in making dry-type transformers the best choice for renewable power applications. Claassen explains that transformers need to be purpose-designed, and in the case of solar plants especially, high ambient temperatures need to be considered in the design. The cooling system must be capable of managing 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,” he says. “This includes naturally ventilated air, forced ventilated air or cooling strategies using heat exchangers based on either air or water.”
He adds 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 that transformers in a photovoltaic 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.”
Claassen emphasises that Trafo Power Systems has extensive in-house design experience to meet these requirements, and project management expertise in engaging effectively with clients, engineers and other stakeholders on each project.
“It is crucial that wherever substations and transformers are supplied to renewable energy projects, the designers have a thorough understanding of thermodynamics,” he says. “There is a considerable risk of poorly designed units overheating if they are operating outside of their design limits; the results can be catastrophic if all the project parameters are not fully considered.”
For more information visit: www.trafo.co.za
