Tunnel and vertical shafts
Transmitting power at transmission voltages often means the step-up transformers within hydroelectric applications are located near the generator—while the transmission system is most accessible at a higher elevation.
The utilization of CGIT bus from Avail High Voltage Bus System for vertical shaft applications offers the following advantages relative to conventional technologies:
- SF6 bus is enclosed and grounded. Therefore, clearances can be smaller, reducing the required shaft size. Additionally, dead-front construction eliminates high voltage safety hazards.
- SF6 is an inert gas and will not burn. Therefore, the risk of fire is mitigated.
- Since SF6 is a gas, the pressure head is very low; typically about 10psi per 1000 feet of vertical head.
- The design of SF6 bus enclosures poses little risk of stretching or mechanical damage. Since the joints offer the same mechanical strength as the balance of the bus system, no elaborate support methods are required.
- The CGIT bus system is designed and tested for a reliable operating life of 50 years.
Project Profile: Revelstoke Hydroelectric Project, British Columbia, Canada
An example of CGIT’s application in hydroelectric projects is British Columbia Hydro’s Revelstoke Project. This plant included gas insulated switchgear in the underground powerhouse and connection circuits installed in an inclined tunnel to a gas insulated substation where the output of the facility connects to the transmission grid. It was determined that CGIT provided the best solution for the connections between gas insulated switchgear substations.
Within the Revelstoke powerhouse, there are gas insulated breaker/grounding switch sets at each GSU transformer output, and a dual set of 500kV GIS connecting the generator transformers output into two main feeder circuits. At the substation building end, another set of 500kV GIS modules connects the feeders to the outgoing overhead lines; a separate 230kV GIS receives incoming power for internal plant service.
The high current rating of CGIT bus, combined with the switching configuration, enables the full output of the power plant to be transmitted through either one of the two feeder circuits. This provides 100 percent redundancy for plant operation. This redundancy could not be achieved using conventional cable systems. CGIT bus allowed a compact installation along the walls of the tunnel, and because of its fully grounded enclosure, it permitted the use of the tunnel as the main access route to the powerhouse.
Another CGIT bus circuit, located outside the substation building, connects the incoming 230kV transmission lines to the 230kV GIS substations.