Classification of Power Transformers and Their Unique Roles in the Power Grid

Classification by Voltage Level

• Low-Voltage Transformers: Usually refer to transformers with a voltage level below 1 kV. These transformers are commonly found at the user end, such as in the workshops of some factories and the distribution rooms of residential communities. Their main function is to further reduce the slightly higher voltage to a voltage value suitable for the direct use of various electrical equipment. For example, they can supply voltages of 380V and 220V to motors, lighting equipment, and household appliances, ensuring that these devices can operate safely and stably to meet the daily production and living electricity needs of people.
• Medium-Voltage Transformers: The voltage level is generally between 1 kV and 35 kV. They are widely used in urban distribution grids. They can receive the medium-voltage electrical energy transmitted from the upstream substations and then adjust the voltage appropriately according to the electricity load conditions in different areas before distributing it to smaller power supply units such as various blocks and communities. They play a connecting role in voltage adaptation, enabling electrical energy to be smoothly transmitted to various electricity consumption points and ensuring the reliability and stability of regional power supply.
• High-Voltage Transformers: Their voltage level is 35 kV or above and they are an important part of long-distance power transmission. For example, high-voltage transformers with voltage levels of 110 kV, 220 kV or even higher can significantly increase the voltage of the electrical energy generated by power plants. This is because when transmitting electrical energy over long distances, according to the principle of electrical energy transmission, increasing the voltage level can effectively reduce the current on the transmission lines, thereby reducing the energy loss during the transmission process and ensuring that electrical energy can be efficiently transmitted to distant substations or areas with concentrated electricity consumption, realizing large-scale cross-regional allocation of electrical energy.
• Ultra-High-Voltage Transformers: The voltage level reaches 500 kV or above and they are mostly used in large-scale long-distance and large-capacity power transmission projects between regions, even across provinces or countries. For example, in China's ultra-high-voltage power transmission network, a large number of ultra-high-voltage transformers are used. They have extremely high insulation performance and powerful electrical energy conversion capabilities, enabling them to boost electrical energy to an extremely high voltage level, allowing electrical energy to be transmitted over extremely long distances. This greatly expands the transmission range of electrical energy, transporting power resources from energy-rich areas to energy-deficient areas with high electricity demand, optimizing the allocation of power resources across the country and even on a larger scale.

Classification by Number of Phases

• Single-Phase Transformers: Single-phase transformers are mainly used in power supply scenarios where single-phase loads account for a large proportion or where the requirement for three-phase balance is not high. For example, in some rural areas, for the scattered residential electricity consumption where most of the electrical equipment are single-phase lighting fixtures and small household appliances, single-phase transformers can directly supply appropriate single-phase voltages to these devices, reducing the power loss and equipment cost during the process of converting three-phase to single-phase. Meanwhile, in some special single-phase experimental circuits or small single-phase power supply systems, single-phase transformers also play a role in accurately providing single-phase voltages to meet specific electricity consumption requirements.
• Three-Phase Transformers: Three-phase transformers are the most widely used type in modern power systems. In industrial production, the vast majority of motors and large mechanical equipment are three-phase loads. Three-phase transformers can provide symmetrical and stable three-phase voltages for these devices, ensuring the normal operation of the equipment and improving production efficiency. Moreover, on the main transmission and distribution lines, three-phase transformers can simultaneously transmit three-phase electrical energy. Compared with single-phase transmission, they have higher power transmission efficiency and better balance and can carry larger power loads. They are the core equipment for ensuring the stable operation of the entire power grid and the large-scale transmission and distribution of electrical energy.

Classification by Winding Connection Method

• Star-Connected Transformers (Y Connection): In three-phase power systems, star-connected transformers play an important role. Their neutral point can be grounded, and this grounding method helps to stabilize the potential of the power grid and improve the safety of the power grid operation. In the distribution grid, star-connected transformers can conveniently lead out the neutral wire to provide users with phase voltages (such as the common 220V) and line voltages (such as 380V), meeting the voltage requirements of different types of electrical equipment. Moreover, in high-voltage power transmission systems, star-connected transformers, while performing voltage transformation, also facilitate the accurate operation of the relay protection devices in the system, enabling rapid detection and isolation of power grid faults and ensuring the reliable operation of the power grid.
• Delta-Connected Transformers (Δ Connection): Delta-connected transformers can provide stable line voltages for three-phase loads. One of their most significant features is that they can eliminate the influence of the third harmonic current on the power grid. In some industrial occasions with high requirements for power quality, such as precision electronics manufacturing factories, using delta-connected transformers can effectively reduce harmonic interference, ensuring that stable and pure three-phase power supplies are provided for production equipment and improving the production quality of products. Meanwhile, in three-phase transmission lines, delta-connected transformers used in combination with star-connected transformers can flexibly realize the conversion between different voltage levels and the rational distribution of electrical energy, optimizing the voltage level structure and the electrical energy transmission and distribution system of the entire power grid.