Because many transformers are exposed to dust and high operating temperatures, over time they incur such problems as clogged air inlets, clogged cooling ducts, and deterioration of winding insulation, all of which can degrade capacity. If a transformer is operating under such conditions – particularly operating at or above its rated load – unexpected outages can occur.
Among the more catastrophic of those events are explosions, fires and meltdowns that result in immediate outages.
Often, this can be due to end of life cycles for high-voltage transformers that stem from transient overvoltage switching surges or surges due to degraded insulation of coil windings.
“Insulation breakdown often results due to high heat, which is one of the biggest enemies of power transformers, as well as over voltage and high current loads above the rated values,” says Alan Ober, Vice President Engineering and Manufacturing at ELSCO (Cincinnati, OH). “Over a 20-year period insulation can deteriorate to the point that it leads to tracking, flashover to ground of the winding turns, and resulting short circuits.”
Such was the case at Avista Corporation’s Kettle Falls Generating Station in northeastern Washington State. The Kettle Falls 60 MW station utilizes a variety of wet-type transformers for its power transmission functions, but also uses four dry-type transformers to run motors for pumps, evaporators, etc.
It is these four transformers, enclosed in a dedicated room with switchgear that came into question in 2015 during the station’s annual preventive maintenance outage. The insulation of the four transformers, each 35 years old, had already deteriorated to a concerning degree.
The power station decided to replace two of the units immediately and two the next year. Yet, there were concerns about being able to find a replacement manufacturer who could provide the Kettle Falls facility with units that were essentially identical with their aging ones, that would drop right into the same footprint and also hook up to the switchgear via the same connections, without requiring significant modifications.
For this, the company turned to Electric Service Company (ELSCO), a company that was founded in 1912 and provides quality new, repaired and rebuilt transformers, including both liquid-filled and dry-type models.
The Kettle Falls station team selected ELSCO, in part, because of its abilities to design and build replacement transformers for older or outdated units.
Nathan Sarber, General Forman of the Kettle Falls facility explains that not only was matching a tight transformer footprint a challenge, but also getting the replacement units in place was a strenuous task.
“These are 10,000-lb. transformers that are located in a room inside of a building, so we had to make sure we dealt with a transformer manufacturer who would be able to help us with the footprint, installation and connection requirements,” he says.
Sarber worked directly with ELSCO’s Ober to ensure that the dimensions of the new units would not only meet the existing transformer specs, but would also facilitate the installation requirements of fitting through the transformer room and having compatibility with the existing switchgear connections.
For more information, visit: www.electricservice.com.