07 Voltage Levels in the Distribution Electric System

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According to Circular 39/2015/TT-BCT, the distribution power system is a power system consisting of a distribution grid and power plants connected to the distribution grid. In which, the nominal voltage levels in the distribution power system are specified as 110 kV, 35 kV, 22 kV, 15 kV, 10 kV, 06 kV, and 0.4 kV.

Additionally, the Circular also specifies that the voltage level is one of the nominal voltage values used in the power system, including:

- Low voltage is a nominal voltage level up to 01 kV;- Medium voltage is a nominal voltage level over 01 kV up to 35 kV;- High voltage is a nominal voltage level over 35 kV up to 220 kV;- Ultra-high voltage is a nominal voltage level over 220 kV.

Under normal operational policies, the operational voltage allowed at the connection point may fluctuate compared to the nominal voltage as follows:

- At the connection point with electrical customers: ± 05 %;- At the connection point with the power plant: + 10% and - 05 %;- In cases where the power plant and electrical customers are connected to the same busbar on the distribution grid, the voltage at the connection point is decided by the electricity distribution unit managing the operational grid, ensuring compliance with the technical requirements of the distribution power grid and maintaining the voltage quality for electrical customers.

Note:

- In the event of isolated incidents or during the recovery of stable operations after an incident, the allowed voltage fluctuation at the connection point with the electrical customers directly affected by the incident is within + 05 % and - 10 % compared to the nominal voltage.

- In the event of severe transmission system incidents or incident recovery, the allowed voltage fluctuation is within ± 10 % compared to the nominal voltage.

If electrical customers using the distribution grid require a higher voltage quality than the regulations, they may negotiate with the electricity distribution unit or the distribution and retail sales unit.

For more details, refer to Circular 39/2015/TT-BCT, effective from January 18, 2016.

Le Hai

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