TVA Sequoyah replaces ITE HK breakers
TVA's Sequoyah Nuclear Facility was originally built with 16kV switchgear cubicles utilizing Type HK air magnetic breakers originally manufactured by ITE. Typical problems associated with air magnetic breakers such as numerous parts and scarce and costly availability of renewal parts led TVA to investigate modernizing the switchgear with roll-in replacement vacuum circuit breakers.
In 1998, TVA decided to replace their existing line up with vacuum bottle technology. TVA said, "We decided to work with the Siemens-Wiley team to have replacement breakers qualified for nuclear safety related application. The low maintenance requirements of Siemens' AH operator were appealing to us as was Wiley's reputation in certifying the Siemens' operator was a nuclear compliant component in the original ITE HK cubicles."
Availability and cost of replacement parts led them to consider alternatives that would give them a long term solution that would reduce their maintenance requirements.
Since the Siemens AH operator has a recommended major maintenance interval of 10 years or 10,000 operations, it was a good fit to ease some of the costs associated with maintaining old gear. But beyond the operator, several challenging cubicle interface issues needed to be qualified before Wiley Testing could certify the breaker qualified for 1E nuclear applications. Since vacuum circuit breakers operate at about 10 times the "linear velocity" of air magnetic designs, the resultant force applied on MOC linkages is proportional to the square of the velocity (100 times greater). Translated, the replacement circuit breaker's existing MOC linkages need to be buffered / dampened in order to prevent the existing cubicle's MOC linkages from being damaged.