Low-voltage network

A low-voltage network or secondary network is a part of electric power distribution which carries electric energy from distribution transformers to electricity meters of end customers. Secondary networks are operated at a low voltage level, which is typically equal to the mains voltage of electric appliances. Most modern secondary networks are operated at AC rated voltage of 100–127 or 220–240 volts, at the frequency of 50 or 60 hertz (see mains electricity by country). Operating voltage, required number of phases (three-phase or single-phase) and required reliability dictate topology and configuration of the network. The simplest form are radial service drop lines from the transformer to the customer premises. Low-voltage radial feeders supply multiple customers. For increased reliability, so-called spot networks and grid networks provide supply of customers from multiple distribution transformers and supply paths. Electric wiring can be realized by overhead power lines, aerial or underground power cables, or their mixture. Electric power distribution systems are designed to serve their customers with reliable and high-quality power. The most common distribution system consists of simple radial circuits (feeders) that can be overhead, underground, or a combination. From the distribution substation, feeders carry the power to the end customers, forming the medium-voltage or primary network, operated at a medium voltage level, typically 5–35 kV. Feeders range in length from a few kilometers to several tens of kilometers. As they must supply all customers in the designated distribution area, they often curve and branch along the assigned corridors. A substation typically supplies 3–30 feeders. Distribution transformers or secondary transformers, placed along feeders, convert the voltage from the medium to a low voltage level, suitable for direct consumption by end customers (mains voltage). Typically, a rural primary feeder supplies up to 50 distribution transformers, spread over a wide region, but the figure significantly varies depending on configuration.