Understanding Distribution Transformers and Power Transformers: Differences and Classifications

What is a Distribution Transformer?

Distribution transformers are fundamental components of electrical power systems, playing a critical role in the conversion and transmission of alternating current (AC) voltage and current, in accordance with the principles of electromagnetic induction. These static electrical devices are the backbone of distribution networks on a global scale.

In some regions of China, transformers with voltage ratings below 35 kV (most commonly 10 kV and below) are commonly referred to as "distribution transformers." They are typically found in substations, where they facilitate the transformation of AC voltage and current, enabling the efficient distribution of electrical energy within the grid.

In China, transformers are typically categorized based on their voltage levels, including Ultra-High Voltage (750 kV and above), Extra-High Voltage (500 kV), 220-110 kV, and 35 kV and below. Distribution transformers, specifically engineered for voltage levels between 10-35 kV and capacities up to 6300 kVA, directly supply power to end-users within distribution networks.

Key Differences Between Distribution Transformers and Power Transformers

Distribution transformers primarily serve the crucial function of delivering electricity directly to end-users within distribution networks. In China, they typically operate at lower voltage levels, up to 66 kV, with low-voltage outputs ranging from 380/220V, 3 kV, 6 kV, and 10 kV. In contrast, power transformers are designed to transfer electrical energy between grids operating at different voltage levels. For instance, they connect regional substations operating at 500 kV and 220 kV, facilitating the exchange of power between these grids. Power transformers are characterized by their high capacity and do not participate in the direct supply of power to end-users.

Energy-efficient distribution transformers encompass oil-immersed transformers and amorphous alloy transformers. Oil-immersed distribution transformers are categorized based on their loss performance into S9, S11, and S13 series. Among these, the S11 series transformers exhibit a 20% reduction in no-load losses compared to the S9 series, while the S13 series transformers further reduce no-load losses by 25% compared to the S11 series.

How Are Distribution Transformers Classified?

Distribution transformers can be classified based on several criteria:

Based on Phase: Distribution transformers can be categorized into single-phase transformers (used for single-phase loads and forming three-phase transformer banks) and three-phase transformers (employed for voltage up- or down-transformation within three-phase systems).

Based on Cooling Method: They are further classified into dry-type transformers (cooled by natural air convection, commonly used for small-capacity applications such as local lighting and electronic circuits) and oil-immersed transformers (relying on oil as the cooling medium).

Based on Purpose: Distribution transformers can serve different purposes, including electrical power transformers (for voltage transformation within transmission and distribution systems), instrument transformers (such as voltage and current transformers used for metering and relay protection), and special transformers (including electric furnace transformers, rectifier transformers, and regulating transformers).

Based on Winding Configuration: They may be classified as two-winding transformers (connecting two voltage levels within the power system), three-winding transformers (typically used in regional substations, connecting three different voltage levels), and autotransformers (connecting power systems with varying voltage levels or functioning as conventional step-up or step-down transformers).

Based on Core Type: Distribution transformers can be categorized as core-type transformers (suitable for high-voltage power applications) and shell-type transformers (special transformers designed for high-current applications, such as electric furnace transformers, welding transformers, and power supply transformers for electronic instruments like TVs and radios).