Moccasin Powerhouse and Generator Step-Up Transformer Rehabilitation

The two Moccasin Powerhouse generators were completed in 1969 and generate a combined maximum output of 110 megawatts.  Both generator units have exceeded their life expectancy and are in need of repair in order to continue operating reliably.  The objective of this project is to replace stator cores and coils.  The scope of work also includes rehabilitation of the rotor field poles with new pole cores and re-insulated field coils, replacement of the rotor pole/rim tail connection system with a new T-tail connection system, and supply of a new rotor rim for each generator following inspection and testing.  

The project will also involve replacement of two generator step-up transformers (GSUs) with new oil containment barriers, and remaining plant work including: replacing 480V switchgear, 13.8kV switchgear, motor control centers, main control boards, protective relays, and cooling water piping.

Construction Milestones:

• Moccasin Powerhouse GSU Transformers Replacement – HH-1003 – Construction NTP 06/07/21, Final Construction Completion 05/23/23
• Moccasin Powerhouse Generator Rewind – DB-121R2 – Construction NTP 08/08/22, Final Construction Completion 06/27/24
• Moccasin Powerhouse Systems Upgrade – Construction NTP 10/02/24, Final Construction Completion 06/07/27
   

The project is part of a larger Hetchy Capital Improvement Program (HCIP), a multi-year capital program to upgrade or improve water conveyance, water storage, and power generation facilities in the Sierra Nevada portion of the Hetch Hetchy Regional Water System.