Electricity + Control February 2018

TRANSFORMERS + SUBSTATIONS

Transformer Technology: Liquid-Filled vs. Dry-Type

Information provided by Cooper Power

Dry-type transformer technology has been traditionally specified for in and near building applications to minimise the impact of environmentally detrimental fluids and accompanying fire safety issues, while sacrificing environmental issues of en- ergy efficiency, sound level, and ease of recycling.

T his application diverges from this historical trend and utilises liquid-filled transformers with an environmentally preferred fluid that maximises performance in all of these areas. Use of less-flammable dielectric fluids and installation guidelines according to a listing body such as FM Global or Underwriters Laboratories will result in a certified installation that optimises the many advantages of the liquid-filled transformers. Purchases of transformers are often based on the first cost (without any consideration of long- term economics) when transformer evaluation and purchase decisions are not made by the end-user. This is particularly true when agents or electrical contractors make purchase decisions on the ba- sis of temperature rise and low first cost for C&I Commercial and Industrial) end-users buying dry- type, pad-mounted transformers. These agents or contractors may have little incentive to take into consideration any economic factors other than the transformer’s first cost. End-user concerns about higher first costs discourage OEMs and contrac- tors from offering or recommending the more ex- pensive, efficient options to customer who do not specifically request them [1]. Because air is the basic cooling and insulat- ing system for dry-type transformers, all dry-type transformers will be larger than liquid-immersed units for the same voltage and capacity (kilovolt/ kilovolt-ampere) rating. When operating at the same flux and current density, more material for core and coil implies higher losses and higher costs. These trade-offs are inherent in the design of dry-type units, but dry-type transformers have traditionally offered certain fire-resistant, environ- mental, and application advantages for industrial

and commercial situations. Recent advances in liquid-filled units are reducing some of these (dry- type) advantages. [1] Recent advances Developments in less-flammable transformer flu- ids have overcome the previous mineral oil-filled fire safety issues. Less-flammable fluid-filled transformers now have a 30+year, 350 000 unit installation record of no reported fires – a fire safety record that dry-type and cast-coil trans- formers cannot claim. Since the 1996 Oak Ridge National Laboratory citations, transformer fluid developments have also overcome the previous liquid-filled environmental issues. High fire point natural ester fluids are renewable, biodegradable, non-toxic, non-bio-accumulating, non-carcinogen- ic, and recyclable. With these new fire safety and environmental advances in dielectric fluids, all of the other envi- ronmental performance advantages of liquid-filled transformers can now be exploited, including: • Greater energy efficiency • Lower sound level • Smaller footprint • Much longer operating life, ease of maintaina- bility and repairability • Ease of recycling 1 Feature: Liquid-filled transformers have higher standard energy efficiency. Energy/environmental benefit: Less transform- er-related energy usage and air conditioning ener- gy use. When purchased on the basis of lowest first cost, dry type transformers typically have significantly higher

Take Note!

Liquid-filled transform- ers have higher standard energy efficiency and a smaller footprint. Liquid-filled transform- ers have a lower op- erating sound level, a superior operating life, maintainability and re- pairability. Liquid-filled transform- ers allow easier core/ coil reclamation.

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Natural-ester fluid-filled transformers contribute to affordable, sustainable engineering

& building practices.

32 Electricity + Control

FEBRUARY 2018