Helms Rotors Project
What makes it interesting?
One Million Pounds. That’s what the rotor for a single Helms 404 Mw Unit weighs. When VoithSiemens notified PG&E that a similar type of unit in Austria had experienced a catastrophic failure, we took notice. The disaster in Austria occurred when a magnetic pole mounting structure failed, stopping the unit in less than one rotation. After evaluating the risk of failure on the Helms Units, PG&E took action. When they inspected the rotors on all three Helms units, some cracking was found that could lead to this same type of failure.
How HCSS Software assisted with this project
The GC Hydro Construction Crew’s implemented HeavyJob during this project to help improve time cards, material, and cost tracking. Using HeavyJob has allowed us to better manage GC crews. Additionally, it has allowed our Project Engineering, Project Management, and Outage Management teams to better manage their projects and get real-time cost.
The Helms Rotors Project was an immediate repair to the large rotors on 3 Helms Units near Fresno, Ca. Repairs included grinding out the cracks and in one case, indexing the 20 7.5-ton poles to new positions on the rim that had not experienced any stress or cracking. The units were then returned to service with a Justification for Continued Operation (JCO) that set a number of start-stop cycles before the rotor must be permanently decommissioned. PG&E also initiated a massive project to replace all three rotors, the successful contractor being Alstom Power, a multi-billion-dollar, world-wide, French-owned consortium.
The first replacement effort kicked off in Fall 2014 with the delivery of the 50-ton hub that forms the core of the rotor, also known as the spider. Around this hub, 4,500 laminations have been placed, each weighing 150 pounds. Each lamination makes up a 60-degree circumference, six being required to form one layer about 1/8-inchÂ thick. The 750 layers of laminations are held together by 240 through bolts, torqued to hold the laminations in compression. The whole stack of laminations, once completed, was then heated to expand the inside diameter of the rim, allowing keys to be placed in grooves in the spider and the back of the rim. As the rim cooled it shrank, creating compression on the keys, fixing the 325-ton rim to the spider. The new Brazilian manufactured poles were installed, and the rotor was nearing completion.