In the United States, electricity might have to travel over very long distances from the power stations to reach the urban or industrial load centers. For this reason, some utilities invest in extra high voltage transmission networks.
American Electric Power (AEP) is one of America's largest utilities, and one of the few in North America to use extra high voltage 765 kV transmission lines. This high-voltage system, which delivers power to the heavily industrialized eastern United States, requires rigorous specifications and oversight to ensure the grid's ongoing stability and reliability.
To help meet these unique protection and control requirements, AEP selected three of ABB's 800 kV SF6 current transformers (CT) plus a spare - the first order for these devices in the USA.
Safety and reliability concerns at high voltage levels led AEP to specify the use of a gas-filled insulating medium in the measuring devices installed at the substation. The inherently safe nature of a gas-insulated design, which uses polymer insulators, rupture disk construction and alarm indicators to monitor gas pressure levels, made it the obvious choice to ensure safe, reliable operation at high voltages.
The large core capacity of ABB's TG 800 top core CT design is an excellent solution for the four core, 3000 ampere primary, 50 kA short circuit requirement. ABB's current transformers also have a safe failure mode in the event of an unexpected high voltage transient.
The units were shipped from the factory in Italy to AEP. An ABB technical expert from the technical lead center also was sent to oversee the installation and all three transformers are now in service.