With minimal levels of maintenance needed, dry-type transformers offer reliable performance over lengthy lifespans, with few of the risks and hazards associated with oil cooled transformers. 

According to David Claassen, Managing Director of dry-type transformer specialist Trafo Power Solutions, the fact that these units are air cooled means much of the limited servicing required relates involves maintaining clear air channels, which can be compromised by the accumulation of dust layers.

“To allow for the transformer to cool effectively, it is important to regularly check that there is not an excessive build-up of dust on or around the transformer,” Claassen explains. “Depending on the ambient conditions, dust can build up in these confined spaces and start to impede the free flow of air.”

Dust accumulation can be easily addressed by using a leaf blower or similar appliance to remove the dust from the transformer. This method quickly disperses the dust, leaving the surfaces clean and allowing for more efficient heat transfer. 

He highlights that a regular maintenance schedule is especially vital in applications such as coal mines, where there are often high dust levels. Where dust layers prevent adequate cooling, the transformer could run at temperatures higher than its design parameters. This, in turn, degrades the insulation material faster and could significantly reduce the unit’s lifespan. Even in the event that a completely sealed enclosure is used (≥ IP55), it is possible for dust to enter the enclosure while the doors are opened or in cases where the doors are left open accidently. 

“It is also important to check that the temperature probes are measuring accurately,” he notes. “This, of course, ensures that any unexpected temperature rise will trigger the necessary alarm, and that the feed-in circuit breaker to the transformer is tripped in the event of overheating.”

Terminals on the transformer should be checked, as it is possible for these connections to loosen due to vibrations or other factors. This is a simple process of checking the torque on these connection points, as any looseness could lead to partial discharge, heat build-up and further damage.

To guide the customer in their maintenance planning, Trafo Power Solutions provides a maintenance manual with each installation. This details the required frequency of service interventions, which in a clean indoor environment is usually only once a year. Under dusty conditions that might be encountered outdoors, the maintenance should normally be conducted every six months.

“Beyond our standard requirements, we also provide our customers with site-specific servicing guidelines that suit their application and environment,” says Claassen. “Indeed, we can provide the actual maintenance service should the customer require – ensuring that they have access to a detailed log of results and recommended interventions.”

He explains that, while the maintenance tasks are generally straightforward, the transformer does need to be de-energised by a qualified technician before this work is conducted. This ensures the necessary compliance to regulations relating to medium voltage equipment, including procedures for lock-out and isolation. 

“A key advantage of dry-type transformers is that this maintenance is relatively quick and simple compared to oil cooled transformers,” he notes. “A key difference in the servicing of these two technologies is that conventional oil cooled transformers require oil samples to be regularly taken and sent away for testing and analysis. This is a costly and time consuming addition to their total cost of ownership.”

Rather like a vehicle, the total cost of running and maintaining a transformer over its lifespan will be considerably higher than its purchase price; these other cost factors therefore deserve close consideration before any purchasing decision is made. 

“The rated power of a transformer is usually among the key determinants of its capital cost, but there are various design differences which will also come into play,” says David Claassen, Managing Director of Trafo Power Solutions. 

To help the purchaser to effectively assess the capital cost, transformer manufacturers need to provide a detailed data sheet indicating required parameters such as losses, windings material and environmental conditions to name a few. . 

“The next main area of costs is operational – in other words, the running and maintenance costs,” explains Claassen. “Running cost is essentially the cost of electricity, measured in kWh. These costs are affected by the efficiency of the transformer. All transformers have both no-load losses and load losses. The monthly cost of electricity for low loss transformers is lower than that of those with higher losses. However, the capital cost of a low loss transformer will be higher due to the design requirements to meet lower losses.” 

Turning to the maintenance costs, he points out that these vary considerably between oil cooled transformers and dry-type transformers – the latter being cooled by air. Oil samples from oil type transformers need to be regularly taken and analysed as this provides valuable insight into the condition of the unit and any possible areas of underperformance.

“These oil checks are similar to taking a blood sample, as the analysis allows the owner to predict the necessary steps to keep the transformer in optimal condition,” he says. “In dry-type transformers, the absence of oil as a coolant significantly reduces the maintenance cost.”

Other important maintenance tasks include testing of a transformer’s instrumentation such as temperature and pressure gauges, as well as relays. Dry-type transformers will tend to have less instrumentation, with a focus on temperature variation and surge protection. On all types of transformers, it is vital to regularly test that the probes are accurately measuring the unit’s temperature. Another basic check is the torque measurement on the termination points. 

“The next big cost factor to consider is the installation cost of the transformer,” he says. “There are regulations that govern where and how transformers are installed, depending on their characteristics – such as their fire hazard level and their potential danger to the environment.”

Oil cooled transformers are, generally speaking, classified as hazardous in terms of their fire risk, so must be located at a safe distance from human activity. Systems need to be in place to both detect and suppress a fire in the transformer, should this occur. There is also a requirement for containment of oil, in case of a leak or rupture – to avoid environmental damage. 

The inherent safety of dry-type transformers means that they can be installed indoors without this added infrastructure. Rated as Class F1 for fire safety, this dry-type technology can even be safely installed in confined spaces. Where an outdoor location is required, a concrete plinth is usually sufficient as a base. 

“When considering the total cost of ownership – in other words, the capital cost plus operational cost plus installation cost – there is a compelling argument in favour of dry-type transformers, particularly for applications of 5MVA and below up to a voltage level of 33kV,” Claassen says. “This argument becomes stronger with the number of transformers present on a single site.”

On a large mining or industrial site, which may have dozens if not hundreds of transformers, it reduces the cost and workload substantially if they are low maintenance dry-type units. As these operations look to become safer and more streamlined, there are great opportunities offered by dry-type transformers, he says. 

As the price of electricity continues to rise, there is also a focus on reducing the energy losses incurred by transformers. This, he explains, highlights why transformer suppliers must be able to quantify the predicted losses over time. 

“By specifying a lower-loss design, a purchaser could calculate whether it is worth spending more upfront on the capital cost, in order to save on losses over the 20 to 30 year lifespan of the transformer,” he concludes. 

The upgrade of a data centre in Nigeria has called for a custom-engineered dry-type transformer solution that can deal with, among other challenges, high level of voltage fluctuations.

According to Trafo Power Solutions Managing Director David Claassen, the contract followed successful past engagements with an existing data centre customer – who is now involved in Africa’s most populous state.

“In the context of an unstable power supply, this application required an unusual but effective solution,” says Claassen. “The challenge is that the voltage of the electrical supply in this area often fluctuates between plus and minus 10% of nominal voltage, so we designed our transformers to include an automatic on-load tap changer (OLTC).”

Further to this, the high level of total harmonic distortion, related to data centres, necessitated the need to design the transformer according to K-factor 13 to ensure maximum reliability and to compensate for the additional heat caused by these harmonics, as well as the associated voltage distortion.

The OLTC is installed on the transformer feet and fully integrated by Trafo Power Solutions. When there are fluctuations in voltage – up or down – this is sensed automatically and the secondary voltage of the transformer is adjusted accordingly by the OLTC, which ensures a stable secondary voltage reaches the data centre’s critical equipment. This specific design will allow the transformer to correct up to 10% under-voltage and up to 10% over-voltage in the power supply in four equal steps.

“It is important to realise that this level of fluctuation – if not corrected – would be extremely detrimental to electrical infrastructure,” Claassen continues. “In fact, some equipment would experience catastrophic failure under these conditions.”

Included in the project scope was also the control and protection of both the transformer and tap changer – as well as an automatic voltage regulator – making up a complete solution for the customer. The transformer supplied by Trafo Power Solutions is a 2,000 kVA unit which will step down the incoming voltage from 11 kV to 400 V. The company is also responsible for commissioning the solution on site.

“Cooling will be achieved in an air natural (AN) configuration, but fans have been included on the transformers to allow them to carry a 25% higher load, if necessary,” says Claassen. “The cooling aspect of the design is important in this context, as the higher harmonics can also lead to raised temperatures in the transformer.”

Trafo Power Solutions includes an electrostatic shield between the primary and secondary windings in this type of design to arrest any stray current that could be caused by the harmonic distortion. He highlights that there is no room for downtime in the data centre industry, so transformer design must be exacting and the manufacturing must be to the highest industry standards.

“A critical measure of any data centre is its level of uptime, so the customer needs stable voltage to underpin the reliability of all its infrastructure,” he says.

Claassen adds the company also offers modular solutions for data centres, an approach with particular benefits as customers can build up their medium voltage infrastructure gradually as their business grows. This facilitates a smooth and cost effective ramp up of operations, with the modular approach allowing the addition of new capacity without disruption.

With its experience in Africa and its agility in executing projects rapidly, Trafo Power Solutions is supplying three mini-substations and two transformers to a copper-zinc mine in the Democratic Republic of Congo.

David Claassen, Managing Director of Trafo Power Solutions, says the pressure was on from early in the planning stages to ensure this critical equipment would be available on time – to facilitate the continued  mine expansion. From the date of the contract award, the company will deliver the units to the mine site within just four months – despite most of South African industry taking an annual December break.

“We have conducted projects previously with the end-client and the engineering, procurement and construction (EPC) contractor, so have a good understanding of their requirements,” explains Claassen. “This experience – combined with our history in the DRC and in the mining sector – gave us the edge in expediting the whole process.”

The order was for two 2000 kVA transformers to step down the electricity supply from 6,6 kV to 550V, as well as three dry-type miniature substations. Two of the mini-substations are rated 315 kVA and 6,6 kV to 400 V, while the third is a 630 kVA unit which also steps down from 6,6 kV to 400 V.

“This equipment is an important part of the mine’s electrical infrastructure upgrade,” he says. “Of particular interest were the dry-type mini-substations, which were quite unique in certain respects.”

As a specialist in dry-type transformer applications, Trafo Power Solutions designed the mini-substations in an IP54 configuration – ensuring that the units are completely sealed from dust and water. This level of insulation usually requires a forced air solution to ensure adequate air movement for cooling.

“For this application, the requirement was for natural air cooling – so the installation would not include external fans and related control instrumentation,” he says. “This option enhances simplicity and further reduces any chance of ancillary equipment needing attention.”

The design of the enclosure and the transformer therefore took account of this configuration, allowing enough natural cooling despite the high ambient daytime temperatures in the region. Another demanding aspect of the contract was that the two 2000 kVA transformers are to replace units in the mine’s existing substation. This required innovative design to ensure that the new equipment fits into the available space.

“Our replacement units have a higher power rating than the ones they will replace, so the design was customised to ensure the mine does not have to re-engineer the space,” says Claassen. “This highlights our flexibility in designing solutions to optimise ease of installation.”

Delivery to site will take place after a factory acceptance test (FAT) has been conducted. While the functional commissioning of the units is not part of Trafo Power Solutions’ scope of supply on this contract, the company offers a standard commissioning and assistance service. This is part of its value-add to any of its contracts.

“The rapid pace of this project indicates a growing trend not only in mining but in other sectors, towards fast tracking new developments and expansions,” he notes. “Clients are expecting their supply partners to deliver on shorter timelines, so one of our key strategies is to learn from each project and apply those lessons going forward.”

This keeps Trafo Power Solutions at the forefront of efficient project execution, focusing actively on quality and communication. This ensures first-time accuracy and customised designs, so that no time is lost by unnecessarily revisiting aspects of the project as it progresses.

“Our non-corporate approach means that we can take decisions and act quickly on matters commercial and technical,” says Claassen. “Our proven skill is in achieving these goals without compromising on quality.”

Data centres are experiencing significant growth in South Africa as the digital revolution continues to gain momentum. To keep up with the demand, these facilities must have the flexibility to expand rapidly when needed, as must the substations that provide them with power.

David Claassen, Managing Director of Trafo Power Solutions, says that modular substations have emerged as a perfect solution for accommodating the expansion of data centres over time. “Typically, data centres start with large structures that are only partially equipped with servers and related equipment, usually about 30% to 40%. The strategy is often to set up a cost effective facility to serve the initial customer base and expand the infrastructure as this base grows,” he says. “Modular substations offer the advantage of scalability, allowing data centres to start with the required number of substations and add more as demand increases.”

Data centres operate around the clock, demanding reliable and uninterrupted power. They employ backup systems like diesel generators and uninterruptible power supplies (UPS) to ensure continuous operation. These backup systems can also be scaled up by adding additional units as needed.

Claassens says speed is of the essence in planning, constructing and expanding data centers since earlier operation means quicker revenue generation. “Modular substations are the preferred choice due to their quick design and construction capabilities, with the repetitive nature of manufacturing facilitating rapid production, and economies of scale in material requirements.”

Dry-type transformers and medium voltage switchgear are typically provided in data centre substation solutions provided by Trafo Power Solutions. These units step down incoming medium voltage power for low voltage servers and ancillary equipment on racks with the substations designed to seamlessly interface with other aspects of the data centre including low voltage distribution, medium voltage switchgear, UPS systems, and the overall control and monitoring system.

Efficiency is crucial for data centre success, as these facilities consume substantial electrical power. Trafo Power Solutions contributes to efficiency by designing and manufacturing energy efficient dry-type transformers with some of the lowest losses globally. These air-cooled transformers require minimal maintenance compared to conventional oil-filled transformers, reducing operational costs and minimising downtime.

Trafo Power Solutions has been involved in various data centre projects, ranging from 1 MW to 60 MW, supplying up to 20 modules for each project. They have also been involved in a  data centre project in the Netherlands, where they are supplying three 22,5 MVA, 50 kV/13.8 kV dry-type transformers being used in the intake substation, demonstrating their expertise in delivering customised solutions to meet unique project requirements.

As the demand for raw material continues to surge, the spotlight has turned to the mining sector, bringing both greenfield and brownfield mining projects into focus. Ensuring these ventures are efficiently executed without compromising on time or budget necessitates a tailored strategy. Often, this means relying on the expertise of an Engineering, Procurement, and Construction Management (EPCM) contractor.

David Claassen, Managing Director of Trafo Power Solutions, firmly believes in the importance of partnering with adept EPCM professionals and says the key to successful partnerships lies in comprehending the EPCM domain. Established in 2017, Trafo Power Solutions specialises in dry-type transformers and has established robust collaborations with EPCM contractors globally, especially across South Africa, Africa, Australia, and Canada.

According to Claassen, Trafo Power Solutions’ consistent successes hinge on several principles, which include understanding project complexities, fostering effective communication, flexibility in adjusting to evolving project scopes, access to proven technology and products, and delivering timely results.

“It’s vital to understand that each project has its uniqueness, and our team successfully navigates this by adopting an “understanding strategy”, emphasising the importance of collaboration to manage the complexities,” he says. “Our deep comprehension of the project process helps us pinpoint and provide the most suitable solution tailored to customer needs.”

EPCM contractors handle intricate tasks such as detailed engineering and design. Trafo Power Solutions contributes by suggesting alternate solutions, ensuring efficient procurement, avoiding redundancy and ensuring the best outcomes for every project.

Communication is the cornerstone of successful project execution. With various EPCM entities employing different communication tools and software, Trafo Power Solutions prides itself on its adaptability. “Our flexibility allows us to mesh with any project team, irrespective of their chosen software,” Claassen notes. He emphasises that this adaptability optimises project management processes, contributing to each project’s success.

Integrity and collaboration remain at the core of Trafo Power Solutions’ operations. Their dedication to understanding project requirements and prompt responses ensures minimal risks and streamlined operations. As Claassen aptly puts it, “The collective goal of stakeholders is the successful execution of a project.”

“Trafo Power Solutions, in partnership with TMC Transformers from Italy, offers top-tier dry-type transformers, emphasising quality and reliability. As the world shifts towards rapid infrastructural developments, such collaborations and expertise will only become more invaluable,” Claassen concludes.

Trafo Power Solutions has supplied 40 dry-type mini-substations, as well as seven standalone ring main units, to one of the Africa’s largest and fastest growing copper operations, situated in the Democratic Republic of Congo. 

“We are immensely proud to be involved in this mega project,” says David Claassen, Managing Director at Trafo Power Solutions. “Considerable design work and planning went into this contract, with very demanding lead times to keep up with the mine’s rapid expansion.”

The mini-substations include units of between 630 kVA and 1,600 kVA capacity with primary voltages of 11 kV and 33 kV. The secondary voltage configurations are 400 V, 690 V and 1,000 V – and some units have dual-ratio secondaries. Protection against the ingress of water and dust was also designed into the units, with an IP54 ingress protection rating.

Fully designed and manufactured in South Africa, the mini-substations were completed in a streamlined production process that facilitated a fast track delivery in batches of five to six units every 10 days. After the manufacturing and assembly process, each unit went through a programme of intensive testing before it was ready for dispatch.

“The units are designed to be as compact as possible,” he explains. “While many will be used for surface infrastructure, the design had to ensure that they could be used underground, where space is limited.”

The underground environment is governed by stringent safety regulations and standards, making the dry-type transformer an ideal choice. This technology uses air rather than oil to cool the windings, making it safer with less risk of fire, explosion or environmental contamination through leakage. The windings in dry-type transformers are also encapsulated with cast resin, protecting them against humidity levels up to 95%.

Undertaking both the electrical and mechanical design, Trafo Power Solutions has ensured a limited footprint through the use of air-to-air heat exchangers. Air is channelled through the transformer windings and flows over the aluminium tubes of the heat exchanger, while a fan blows air through the tubes to cool the air on their outer surface. 

“The substation design also includes arc protection, which will shut the unit down in the event of an arc occurring – before any further damage can be caused,” he says. Each mini-substation is equipped with a control system that will allow the protection functions to be monitored remotely.

The contract was conducted through a leading South African engineering, procurement and construction management (EPCM) firm, and Trafo Power Solutions ensured that all units were delivered by the end of 2023. 

“Our early engagement with the EPCM was important on this project, as it allowed our team to understand the project requirements and develop a cost effective solution,” Claassen says. During this process, all documentation was strictly managed within an online system, including designs, specifications and test certificates – to which the EPCM and end-client had easy access. In this way, designs could be uploaded, shared and signed off using this platform, further streamlining activities for the fast pace of the project. 

“The ring main units are fully motorised and controlled externally by remote pendant switching,” he says. “This enhances safety and ease of management, so that personnel seldom have to open the panel doors which requires the necessary safety equipment and protocols.”

The transformers are rated for Class H insulation – for temperatures up to 180 degrees – while the dual-voltage boards are sizeable for a relatively complex voltage distribution system on each mini-substation. 

“The detailed design and variety of solutions within the complete contract package really highlights the technical capability of the Trafo Power Solutions team,” says Claassen. “This can be seen in the mini-substation from the medium voltage side and its control and protection functionality, through to the low voltage distribution and the customised transformer design for these applications.”

He emphasises that the standard attributes of dry-type transformers allow them to operate reliably with very little maintenance. With air rather than oil for cooling, for instance, they do not require any regular oil testing or oil changing. 

The robust nature of dry-type transformers makes them well-suited for mining applications, whether surface or underground. Claassen notes that Trafo Power Solutions’ extensive experience in Africa reflects that dry-type technology is becoming more popular in the mining sector. The reasons for this trend include their inherent safety, their reliability and their ability to operate without much maintenance.

The growing renewable energy generation sector in Africa is realising the value of modular substations in solar and wind projects, as well as the suitability of dry-type transformers in these installations. 

According to David Claassen, Managing Director of Trafo Power Solutions, solar photovoltaic 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 renewable 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 frequently to be 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 this modular approach to inverters,” he says. “As a supplier of modular substations, we also specialise in dry-type transformers which are well-suited to these applications.”

He highlights that dry-type transformers fit easily into compact modular substations along with the inverter, switchgear and ancillary equipment. Perhaps most importantly, the design and operation of these transformers aligns closely with the sustainability philosophy that underpins the promotion of clean, renewable energy. 

“It makes sense for renewable energy projects, who are leading the charge to supplement and eventually replace fossil fuels, to employ technologies that do not rely on oil,” explains Claassen. “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 much 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. 

With most of these renewable energy projects 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 carefully control their capital and operating expenditure. 

“While the manufacture of substations in a modular format saves them 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 other important technical reasons why dry-type transformers are the best choice for renewal power applications. Claassen explains that it is vital for transformers to be purpose-designed, and in the case of solar plants especially, there are high ambient temperatures 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 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 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.”

He emphasises that Trafo Power Systems has extensive in-house design experience to meet these requirements, and project management expertise for engaging effectively with clients, engineers and other stakeholders on each project. 

“In summary, it is crucial that wherever substations and transformers are supplied to renewable energy projects, the designers have a thorough understanding of thermodynamics,” says Claassen. “There is a considerable risk of poorly designed units overheating due to operating outside of their design limits; if all the project parameters are not fully considered, the results can be catastrophic.”

It has been five years since Trafo Power Solutions supplied Alphamin’s Bisie tin mine in the Democratic Republic of Congo with two dry-type transformers; they have performed so well that another three of these modular substations equipped with dry-type transformers will soon be on their way, to keep up with the mine’s expansion.

“This latest order is testament to the operational performance of our dry-type transformers at Bisie mine over the past five years,” says David Claassen, Managing Director of Trafo Power Solutions. “There were numerous challenges that our design had to accommodate, not least of which is a very arduous section of road in the journey to the mine.”

The mine’s location in the Walikale Territory of DRC is remote, being about 180 km north west of Goma, and more than 30 km from the national route linking Walikale with Kisangani. Like the initial order, the three 3000 kVA, 400 V/11 kV substations will be supplied in standard six metre containers to facilitate transportation. However, specialised steel bracing is required – to withstand the challenging road conditions, especially over the last part the journey.

“These conditions make the road almost impassable by any vehicle other than a six-wheeled Unimog,” says Claassen. “There is intense vibration and tilting of the cargo on these trailers, so our design and bracing is done with this in mind.”

He notes that the mine had considerable foresight in specifying the first dry-type transformers, especially given the relative novelty of this option at the time. At that stage, it tended to be standard practice to use oil-filled transformers for this type of application. Apart from the logistics, the substation solution also had to withstand the equatorial climate and frequent lightning strikes.

“The region where the mine is located is ranked in the top five most vulnerable to lightning strikes, so there is a high risk of damage to equipment related to electrical surge,” he says. “We therefore designed robust surge protection solutions on both the medium voltage and low voltage sides of the substations, and for the transformers.”

Given the warm climate, Trafo Power Solutions designed a fully redundant N+2 cooling system for the transformers; this means that each transformer is cooled by two fans, with another two fans on standby. Among the advantages of dry-type transformers in this climate is that the MV winding is completely cast in resin, so is highly resistant to humidity.