2010-05-18 - The 3 x 1155 MW Browns Ferry Nuclear Power Plant owned by TVA (The Tennessee Valley Authority) and located in the state of Alabama in USA has been in operation since 1974. With the objective of improving the plant’s reliability and performance and widening the site’s safety margin TVA has replaced its existing air blast generator circuit breakers (GCBs) with ABB’s new SF6 GCBs.
ABB’s GCB HEC-7C
The new GCB type HEC-7C uses SF6 gas as an interrupting medium and is rated to extinguish 200,000 amperes of short circuit current at 25,000 volts. It requires minimum maintenance and has low operation costs thereby improving performance and reliability of operation. Moreover the air-blast circuit breakers required multiple support systems including the high maintenance and problematic water cooling system and a complicated air supply system which are not required by the GCBs, thus creating a win – win scenario for TVA.
ABB's HEC-7C Generator Circuit Breaker at Brown Ferry Nuclear Power Plant.
Project execution under demanding conditions
The manufacturing and project execution was closely collaborated between ABB’s GCB factory in Switzerland and the project team in USA with the first of the three installations completed in spring 2009 and the second in spring 2010. The replacement of the existing air-blast breaker with the new GCB installation performed over 4 weeks working in 24 hour shifts required specialized expertise and use of state of the art equipment.
The job presented multiple challenges amongst which was installing a breaker within a confined space with minimal clearances due to the existing structures. The existing isolated phase bus sections were cut back and modified to interface with the new bus sections and transition pieces. A work platform specifically designed to fit within the confined work area was raised in the space vacated by the former air blast breaker and the multiple support systems to carry out the new GCB installation.
Integrity and safety
A battery of various tests (example Hi-Pot and megger) was performed on the newly installed equipment to verify integrity of the complete installation. This proved most beneficial as results identified damaged support insulators of an IPB conductor which were suitably replaced.
Safety was a major priority throughout the project. New safety rails and access walk ways were installed at major locations to improve accessibility to equipment.