What is the rated voltage of electrical equipment? How are they defined?

A: Electrical equipment is a general term for equipment such as generators, transformers, power lines, and circuit breakers in a power system. The rated voltage of electrical equipment is one of the most important technical data points for electrical products. In particular, the long-term continuous operating voltage of high-voltage electrical equipment is a series of voltage levels stipulated by the state based on the needs of national economic development, considering economic and technological rationality and the level of electromechanical manufacturing, according to the maximum economic effect produced during long-term normal operation. These voltage levels are mainly divided into the following categories.

(1) Rated voltage of power grid and electrical equipment. Generators and power grids supply power to electrical equipment during operation. Due to voltage losses in transmission lines, the voltage at the beginning of the line will be higher than the voltage at the end, resulting in different voltage experiences for loads distributed along the line. Since the rated voltage of electrical equipment cannot be manufactured according to varying line voltages but must be standardized according to regulations, it can only strive to approximate the actual operating voltage. Generally, the arithmetic mean of the voltage at the beginning and end of the transmission line is defined as the rated voltage of the power grid, which is also the rated voltage of all electrical equipment connected to that power grid.

(2) Rated voltage of the generator. Due to voltage loss in the power grid, the operating voltage of electrical equipment also has deviations related to its own characteristics. The allowable deviation range is generally no more than ±5%, that is, the voltage on the bus at the beginning of the power grid is 5% higher than the rated voltage. Therefore, the rated voltage of the generator should be equal to the bus voltage and should be 5% higher than the rated voltage of the power grid to meet the requirements of system voltage quality.

(3) Rated voltage of the transformer. The rated voltage of the transformer should be consistent with the definition rules of the rated voltage of the generator and the power grid. Since the secondary rated voltage of transformers manufactured in my country refers to the no-load state, the voltage drop of the winding itself is about 5% when operating at full load. Therefore, for transformers of all voltage levels, the rated voltage of the primary low-voltage side is equal to the rated voltage of the generator, and the rated voltage of the secondary high-voltage side should be 10% higher than the rated voltage of the power grid. In this way, when operating under rated load, it can be ensured that the voltage at the beginning of the line (busbar) is about 5% higher than the rated voltage of the power grid. For step-down transformers, the rated voltage of the primary high-voltage side is equal to the rated voltage of the power grid; for the secondary low-voltage side, when its voltage level is low, the rated voltage is 5% higher than the rated voltage of the power grid, and when its voltage level is high, the rated voltage should be 10% higher than the rated voltage of the power grid.