Electric Transmission and Distribution
Posted under Industry, Power Source
While the generation side of electric power systems usually receives the most attention, the shift toward utility restructuring, along with the emergence of distributed generation systems, is causing renewed interest in the transmission and distribution (T&D) side of the business.
Below chart shows the relative capital expenditures on T&D over time compared with generation by U.S. investor-owned utilities. The most striking feature of the graph is the extraordinary period of power plant construction that lasted
from the early 1970s through the mid-1980s, driven largely by huge spending for nuclear power stations.
Except for that anomalous period, T&D construction has generally cost utilities more than they have spent on generation. In the latter half of the 1990s, T&D expenditures were roughly double that of generation, with most of that being spent on the distribution portion of T&D.
The utility grid system starts with transmission lines that carry large blocks of power, at voltages ranging from 161 kV to 765 kV, over relatively long distances from central generating stations toward major load centers. Lower voltage sub-transmission lines may carry it to distribution substations located closer to the loads. At substations, the voltage is lowered once again, to typically 4.16 to 24.94 kV and sent out over distribution feeders to customers.
Notice the combination of switches, circuit breakers, and fuses that protect key components and which allow different segments of the system to be isolated for maintenance or during emergency faults (short circuits) that may occur in the
system.