ELECTRICAL POWER TRANSMISSION & DISTRIBUTION - page 8

• Due to a large transmission distance, the lower cost of DC overhead lines or underground cables compensates the additional expense of HVDC terminals.

• The economically justified power transfer is lower than the AC capacity needed to connect two systems in a stable manner.

• The characteristics of the two connected systems are incompatible, e.g. due to differences in frequency .

• The damping capability of the HVDC is valuable for maintaining a stable AC transfer.

When SF6-­‐Gas Insulated Substations (GIS) are useful

Adoption of GIS is necessary in areas where the cost of land is high, the environment is harsh, severe contamination problems exist, or where there is no space for conventional stations.

They occupy about one eighth of the space of open-­‐air stations, but may even be cost-­‐competitive where space limitation is not a problem. GIS should be regarded as a mature technology that has been successfully applied up to 500 kV.

ELC fully participated in the design, construction supervision and commissioning stages for the world first 500 kV GIS installed on Itaipù power plant (Brazil).

First in the world with 500kV GIS: ELC fully participated in the de s ig n, cons truction s upe rv is ion a nd commissioning stages for the world first 500 kV GIS installed on Itaipù power plant (Brazil).

Substations

Fiber optic control leads, successfully applied in substations, offer an excellent way to reduce or eliminate interference problems and the need for shielding.

Protection Relay application remains one of the most sophisticated aspects of system engineering.