Complete Story

Rubber for Transformer Seals

Paul Smith, American Biltrite

For many years the transmitting of electric power over high voltage wires has been the “staple” of North America. Coal fired power-generating plants; nuclear plants and hydroelectric power producers ship high voltage out through grids that break down the energy flow into useable voltages at homes and factories everywhere.

Transformers all over the earth do the lowering of the voltage, and in North American alone, more than 2 billion transformers exist on poles everywhere and to that number are added larger versions of transformers on pads near larger industrial sites or outside communities. Some of these transformers are obvious as they simply hang on poles. Many others are fenced away from easy access for safety.

Companies like Westinghouse, General Electric, and Edison manufacture transformers. An ingredient inside each is oil that is used to cool the container and make the power fluctuation safe. These oils are volatile and harmful if leaked into the environment. Consequently seals and gaskets are used to keep the fluids contained safely inside the container of the transformer. In recent years the oils have been improved to last longer, provide higher viscosity, and last longer and be more effective in the applications they were designed to control.

In the early history of sealing oils in transformers, a blend of cork and rubber polymers was developed as the sealing solution. Many seals were designed to last for long lengths of time and in practical use, the seal is not generally inspected prior to its failure. The “brown outs” in the East in recent years were exacerbated by seal failure.

Although not definitely proven, many criticisms of cork and rubber seal failures have been made. A direct result to curtail many leaks has been many transformers being converted to Nitrile rubber compounds used in the gasketing applications of sealing rather than the cork blends. The chosen Nitrile blends are high quality and generally about 70 durometer in hardness. The advantage of Nitrile without cork is that the Nitrile product retains more resilience over it’s sealing life than when it’s a blend with cork that takes compression sets after installation and looses its sealability. Often the cork portion dries out and hardens, weakening the seal and its effectiveness, particularly where large ambient temperature fluctuations are experienced and transformers are buffeted by high winds that contribute to vibration of attachments bolted to the transformer.

Recent improvements in Nitrile compounding have demonstrated that using a product called Transeal (by American-Biltrite, Inc.) provides both features and benefits in transformer sealing. Transeal is made in 65 durometer and 70 durometer and had additives in the chemistry that resist the effects of swell from immersion in the new oils being used today. Many of these oils are hyper active on rubber-like compounds, particularly the commercial grade quality available from import grade products sold at low prices.

Converters catering to the manufacture, repair and maintenance of transformers have learned quality comes at a price and avoid the commercial grades entirely.

For more information, contact your ISD Distributor located near you, or contact customer service at American-Biltrite, Inc. 888-275-7075.

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