Hazardous materials


FOCUS


are readily biodegradable and non toxic, which means that if a transformer is damaged and begins to leak, the chemistry of the esters ensures that it poses no harm to the environment. Another vital benefit is that they help


to prolong the life of transformers: a high moisture tolerance allows esters to absorb more water than mineral oil. Because of their high moisture saturation level, water migrates from the cellulose into the ester, thereby drying the paper in the transformer and reducing the rate at which it degrades. This not only extends the lifetime of the transformer, but also allows it to run at a higher temperature, increasing the available power output.


Retrofilling transformers


One way of preventing fire is to install new transformers with ester fluids rather than mineral oils. However, there is also substantial potential to retrofill existing transformers by removing the mineral oil in the transformer and replacing it with ester fluid. If a transformer is approaching the end


of its life cycle, this will not undo the damage to the degraded paper within, but replacing the mineral oil with ester fluids will delay the replacement of the transformer. Naturally, the earlier the retrofilling is undertaken, the longer this is delayed.


So long as the mineral oil is fully emptied


from the transformer by hosing down the sump of remnant material, the transformer will be left with around just 3% mineral oil, substantially reducing the fire risk. For distribution transformers up to 66kV without an on load tap changer (OLTC), no design changes are necessary, although if fitted with an OLTC or at higher voltages, further assessment of the transformer may be needed.


Change afoot?


While it is difficult to argue against the high performance, environmental and fire safety benefits of ester fluids, the fact remains that the dielectric fluid market is still dominated by mineral oils. Despite posing a potential fire risk,


mineral oils continue to benefit from their own ubiquity and therefore it is going to take a wholesale change in mentality from what is a traditionally conservative industry to embrace the alternative. The problem of transformer fire risk is not


going away. However, an increased uptake of ester fluids by utilities and transformer original equipment manufacturers could provide a safe and cost effective solution


Barry Menzies is managing director of Midel Dielectric Fluids Global. For more information, view page 5


www.frmjournal.com APRIL 2018 31


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