33.3 : 二次配電

Secondary distribution delivers electricity at customer utilization voltages from distribution transformers to customer premises, with voltage levels varying for residential, commercial, or industrial applications.

There are four general types of secondary systems.

Individual distribution transformers serve single customers, especially those with large loads or low-voltage issues. Although costlier, they eliminate the need for secondary mains.

A common secondary main system connects a primary feeder to multiple customers using distribution transformers, efficiently handling load changes without significant voltage drops and often featuring isolated sections for safety.

Secondary networks, typically found in high-density urban areas, are powered by multiple primary feeders through network transformers, ensuring operation even if two feeders fail.

Parallel paths to loads minimize customer outages.

Spot networks, ideal for high-rise buildings or malls, provide high reliability and can handle large loads because they are powered by multiple feeders.

Network protectors automatically disconnect transformers during faults or power-flow reversal, ensuring uninterrupted customer service.