Complex, record-time, emergency transformer replacement ensures Nalcor’s power supply commitments

2016-03-17 - Process and safety excellence, and record speed, were at the heart of the replacement plan executed by the ABB’s Transformer Service team (TRES) for Nalcor Energy following a transformer failure at the remote Churchill Falls generating station in Canada.

Churchill Falls hosts one of the world's largest hydropower plants. The 5,428 megawatt (MW) generating station is operated by utility Nalcor Energy and owned by the province of Newfoundland and Labrador.

Commissioned in the early 1970s, the power plant’s 11 turbines provide clean, renewable energy to millions of consumers throughout North America. In 2011, Nalcor Energy awarded ABB a contract to supply, install, and service the replacement units for most of the site’s aging transformers, including nine underground generator step-up (GSU) transformers.

Fast response to guarantee operational efficiency
GSUs are critical links between a power station and the transmission network; continuously operating, often at full load, and built to withstand frequent thermal loading. From November to April, the Churchill Falls power plant operates at maximum generating capacity, but on October 4, 2015, one of the underground GSUs failed.

ABB deployed a team of service technicians to Churchill Falls the next day to commence emergency replacement of the failed unit, and harnessed its operational expertise to review scheduling and free-up resources that would allow a second crew to support a 24/7 emergency operation.

The failure jeopardized Nalcor Energy’s power supply commitments. To prevent this from happening, ABB’s service transformer team undertook the challenge to replace the GSU by November 1st, which meant a change-out window of approximately 25 days.

The old transformer is dismantled in the tunnel so that it can be hauled above ground.

Replacement in record-time
Past replacements ordinarily take more than eight weeks to complete, and the Churchill Falls environment provided a host of challenges. For example, the failed unit was in a cavern 1,000 feet below ground only accessible via a 1.6-km long, 8-percent grade tunnel just big enough to accommodate its large dimensions. The very tight space underground requires specialized equipment and pin-point accuracy in terms of logistics and planning.

Daily consultations with Nalcor Energy were crucial to the project’s success. Potential project and safety concerns were mapped out before each work shift, and detailed mitigation plans were developed including coordination of materials needed in this remote area.

On the plus side, Nalcor had proactively procured a spare GSU transformer from the ABB’s high voltage transformer factory in Varennes, Quebec. This enabled the service team to immediately initiate the replacement strategy. Process and safety excellence, and speedy completion were at the heart of the replacement plan, as the ABB TRES team worked around the clock to complete the job. The result was that just 22 days after the failure a new GSU was in place, energized and fully functional.

ABB TRES provides a full range of transformer services including on-line monitoring, technical assistance, on-site repair, condition assessment; innovative solutions meeting environmental conditions, diagnostic and testing, training courses, engineering and consulting services.

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