December 15, 2006

Readers talk back and Correction (Nov/Dec 2006)

Fireproofing switchyards

From an insurance carrier's perspective, we fully condone the use of on-line condition monitoring for large, critical transformers ("Monitoring key gases in insulating oil keeps transformers healthy," POWER, October 2006). However, another issue that the transformer failure and subsequent fire at Arizona Public Service's West Wing Substation in 2004 highlights is the need for adequate passive fire protection for transformers.

 

Although condition monitoring of this transformer may have helped prevent its failure, sudden and unforeseen transformer failures can still occur for various reasons. In addition, the consequential damage caused by the fire following this failure could have been significantly reduced if the transformer had [included a] fire wall separation, oil containment bundling [berms], and/or adequate spatial separation—as recommended by NFPA 850, "recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations."

Although this code is primarily intended for power stations and high-voltage DC facilities, the recommendations relating to transformer passive protection are equally relevant for transmission and distribution substations. While this passive protection would not have prevented the loss of the transformer which failed, it would have kept the fire from spreading to adjacent transformers.

Finally, had there been a spare single-phase transformer on site, the resulting business interruption would have been reduced to several days. Arizona Public Service should consider itself fortunate that a spare was able to be acquired from another site. Had that not been the case, the business interruption would likely have been much longer; it typically takes nine to 12 months to replace a large transformer.

—Daniel Cole, Manager, Energy & Utility, Australia & New Zealand, ACE Insurance Ltd.

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