What distinguishes primary distribution from secondary distribution in power systems?

The distinction between primary distribution and secondary distribution in power systems is primarily based on the voltage level at which electricity is transmitted and the role that each distribution level serves within the overall electrical grid.

Primary distribution is responsible for carrying high voltage electricity, typically ranging from about 4 kV to 69 kV, from substations to different distribution points closer to the end users. This high voltage is beneficial because it minimizes losses due to resistance in the wires when transporting electricity over distances. Therefore, option A accurately describes the function of primary distribution by emphasizing its role in carrying high-voltage power from substations.

In contrast, secondary distribution operates at lower voltage levels, usually less than 1 kV. It typically involves the last step in the delivery of electricity, where power is distributed from primary distribution lines to the final users, such as residential buildings and small businesses. This explains why other options do not fit: secondary distribution does not transmit power over long distances or generate power at substations; instead, it focuses on delivering that power directly to consumers at a utilization voltage.