Nominal voltage of distribution networks

According to GOST 21128-83, the nominal voltages of a three-phase AC network up to 1000 V are 40, 220, 380 and 660 V. Accordingly, the phase voltages are 23, 127, 220 and 380 V. Line-to-line network voltages are higher than 1000 V in accordance with GOST 721 -77 are equal to 3, 6, 10 and 20 kV.

The rated voltages of the primary windings of the transformers are equal to the rated voltages of the network or the rated voltages of the generators to whose busbars they are connected. The nominal voltage of the secondary windings of the transformer transformers is 5% higher than the nominal voltage of the network.

The selection of the nominal voltage of the power supply systems is based on a technical and economic comparison of the options for power supply schemes, in the preparation of which they seek to minimize the number of energy transformations.

Distribution networks with a voltage of up to 1000 V are currently implemented, as a rule, three-phase with solid neutral grounding with a voltage of 380/220 V.

Voltage 660 V is used in industrial networks with long and branched lines (coal, oil and chemical industries), the presence of electric motors of receivers for a given voltage, if it is necessary to reduce the short-circuit currents on the side of the secondary voltage of powerful substations ( 1000 kVA and above).

The 6 kV voltage is mainly used in urban and industrial networks. Its use in industrial networks is due to the presence in the enterprise of electrical receivers or power plants with a generator voltage of 6 kV. The use of 6 kV voltage in urban networks (up to 60% of all networks) developed historically due to the fact that the distribution lines were connected to the buses of the corresponding voltage of the generator of urban power plants.

Currently, the existing city networks with a voltage of 6 kV during reconstruction are transferred to 10 kV, and the new ones are designed exclusively for 10 kV. The nominal voltage of 10 kV is widely used in urban, rural and industrial networks (for internal distribution of electricity).

The voltage of 20 kV is mainly used in rural electricity grids, and in industrial networks — for powering individual remote sites (quarries, mines, etc.).