The choice of the suitable transformer depends on various factors:

Context of use

Due to the insulating material used (resin vs oil), resin transformers are particularly suitable for environments with high risk of fire or pollution, such as shopping centers, hospitals, chemical industries, and marine applications. Oil-filled transformers are preferred in applications with high voltage and strategic contexts, even outdoors, where high reliability and durability over time are required.

Voltage at play

Oil-filled transformers reach higher powers (production and energy transmission), while resin transformers are used up to voltages of 36 kV for powers of 30 MVA (distribution). Air-cooled transformers usually stop at 20 kV.

Logistic constraints

Thanks to their reduced weight and compact dimensions, resin transformers are easy to transport and install, even in confined spaces. In these contexts, dry-type transformers avoid the double handling of the insulating fluid and the apparatus. Oil-filled transformers can be installed outdoors, while resin transformers require a cabinet or cells to protect them from the weather.

Costs

The cost of the asset, with the same installed power, is essentially comparable between the two technologies. Analyzing the total cost over the life cycle, there is a misconception that oil-filled transformers represent a higher expense due to checks and maintenance, while, with a closer analysis, it should be considered that resin transformers require constant maintenance of the cabinet housing them, since a “dirty” environment significantly affects their operation and consequently the failure rate of the asset. Speaking of costs, there are certainly differences related to installation and mandatory fire safety measures, which are considerably more stringent in the case of oil-filled transformers.

Sustainability

This area is becoming increasingly important in adopting one technological solution over another. Typically, resin transformers are considered a more environmentally friendly choice due to the absence of oil (a potential contaminant of groundwater in case of spills); however, it should be noted that there is an environmentally sustainable alternative, namely natural vegetable fluids (natural esters). Natural esters are almost completely biodegradable and, having a very high flash point, are an extraordinary response to the risk of fire.

Expanding the concept of sustainability beyond environmental aspects, we must mention the end-of-life phase of the asset. We could say that the disposal and replacement phase is simpler for resin transformers, which, however, have a significantly shorter overall lifespan compared to oil-filled transformers.

Monitoring/Maintainability

Here lies one of the main differences between the two types of transformers. Oil-filled transformers allow monitoring through fluid analysis in the laboratory and, for the most important and strategic machines, there are also devices capable of online monitoring of key parameters. Those in resin do not require maintenance, except for the cabinet housing them, and do not allow monitoring of their health status. The absence of maintenance of resin transformers is often seen positively due to a reduction in total operating costs. However, if we connect it to a higher failure rate and the inability to monitor their health status, the main weakness of resin transformers emerges: absence of alert/alarm signals that can improve efficiency in managing the asset and productivity.