Teshmont was retained as a sub-consultant to Amec Foster Wheeler for the BC Hydro Merritt Area 138 kV Transmission Project. Teshmont’s first task was to perform an assessment for upgrading the existing 69 kV transmission line to 138 kV, from Highland station to Merritt station, and for two new alternative 138 kV transmission lines (Highland-Merritt and Nicola–Merritt).
The new Merritt station was to be located close to the existing station, so that construction could take place without interruption to the existing 69 kV supply, and only minimal outages would occur when the changeover to the new station occurred. An additional constraint of upgrading the existing transmission line to 138 kV was to keep the design within the existing Right-of-Way, to eliminate the long process of acquiring a new Right-of-Way.
The project was divided in two stages:
The initial assessment for the project included preparation of preliminary routes and plan and profile drawings for the three transmission line alternatives. Preliminary layout and bus work design were developed for a new station at Merritt for three 138 kV transmission lines in a ring-bus configuration, which included three 138/25 kV power transformers.
Preliminary alternatives of modifications to the stations were prepared to terminate the new or upgraded transmission lines. Live-line work was taken into account as the existing 69 kV supply must be maintained until all components are ready for 138 kV operation.
A cost estimate for the transmission lines and stations alternatives was then prepared.
The second stage of the work included developing considerations for upgrading the Merritt 69 kV Substation to 138 kV. This stage also included preliminary design of a 69 kV switchyard with three transmission-line connection points, two 138/69 kV power transformers, and 25 kV gas insulated switchgear (GIS) to connect to the existing distribution system; within a constrained available station site.
Additional EMF studies were performed for a critical section of the transmission line in Merritt city. A detailed project plan was developed which included project schedule, and risk management.
A more detailed cost estimate was prepared for the preferred alternative selected by BC Hydro.