What is Transformer Retrofilling?

Retrofilling is the process of replacing the existing insulating fluid (e.g. mineral oil) in an operational transformer with new fluid. Doing so effectively upgrades the transformer. When retrofilling also involves the use of an advanced fluid such as synthetic ester fluid or natural ester fluid, it then delivers further demonstrable benefits.


Benefits of retrofilling

Customers usually retrofill transformers with MIDEL ester fluids to improve service life, reduce environmental hazards or increase fire safety. The process is very simple because the thermal expansion characteristics, cooling performance and electrical properties are comparable to those of mineral oil. Additionally, the materials used in the standard mineral oil-filled transformers are generally compatible with MIDEL fluids.


Reasons for Retrofilling with a MIDEL ester fluid

The unique capabilities of MIDEL ester fluids and their high performance in transformers means advantageous financial outcomes can be achieved by retrofilling mineral oil-filled transformers. MIDEL ester fluids can deliver significant cost savings and operational benefits without sacrificing reliability. Here are some examples:

It makes financial sense

Get all the benefits of MIDEL without investing in a new transformer.

Remove fire risk

The high fire point of MIDEL fluids eliminates the possibility of transformer fire, thereby protecting lives and property plus reinforcing business continuity.

Avoid risk of environmental contamination

MIDEL fluids are readily biodegradable, unlike mineral oil which is both toxic and non-biodegradable. Using MIDEL reduces the risk of environmental damage to the environment in case of either minor leak or catastrophic failure of the transformer.

Demonstrate Corporate Social Responsibility

Retrofilling your transformer with MIDEL shows a commitment to your employees, customers and environment without needing to invest in a new transformer.

Recommended by insurance companies

Insurance companies, such as FM Global, acknowledge that all transformers are at risk of failure which can result in fire or environmental damage, and can adversely affect business continuity. They regularly advise their clients to retrofill mineral oil transformers with MIDEL fluids.

Increase transformer life, delay transformer replacement

Using MIDEL will extend transformer life and delay investment in a new replacement transformer. The superior water tolerance properties of MIDEL significantly increase the life of solid insulation, thereby extending the life of the transformer. MIDEL has also been successfully used to enable wet transformers to be brought back into service.


Read more on the benefits of alternative fluids such as ester for fire safety, the environment and moisture tolerance.

Cut operating expenses

Maintenance of mineral oil transformers can be costly – consider oil filtration operations and maintenance of fire suppression systems. Using MIDEL can help reduce maintenance OpEx requirements. MIDEL is also much more tolerant of moisture ingress than mineral oil. For areas prone to wet conditions, retrofilling transformers with MIDEL fluids can lead to increased asset reliability.

Reduce substation footprint

FM Global guidelines mean MIDEL transformers require significantly less space compared to mineral oil transformers. Using MIDEL enables more than one transformer to be installed in the same footprint required for mineral oil – a compelling solution if new capacity is needed in an existing substation.

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Retrofilling transformers with ester fluids


Transformer Retrofill Case Studies

There are many cases of MIDEL fluids delivering measurable gains in retrofill applications. Some involve transformers that were retrofilled decades ago and were monitored for long periods to validate the benefits. Take a look at these latest case studies.


Guidelines for retrofilling transformers

We have comprehensive guidelines to assist in the transformer retrofill process with MIDEL ester fluids - for power transformers, distribution transformers. We can also discuss material compatibility and general storage and handling guides. Get in touch with our transformer team for more information.


Retrofilling transformers?

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Transformer Ester Fluids