A Complete Guide to Power Transformer Basics: Classification & Nomenclature

Power transformers are the core equipment of power transmission and distribution systems, with diverse types tailored to different application scenarios, voltage levels, and operating conditions. This guide systematically explains the classification of power transformers by purpose, winding configuration, structure, cooling method, and the meaning of transformer model nomenclature, providing a professional reference for global buyers, engineers, and power system operators.

1. Classification by Application

Transformers are categorized based on their core function in the power system:

Step-Up Transformer: Used in power plants to boost voltage for long-distance power transmission.

Step-Down Transformer: Used in utility substations to reduce high grid voltage for distribution.

Distribution Transformer: Used to deliver power directly to end-users (residential, commercial, industrial).

Station Service Transformer (Power Plant): Supplies auxiliary power for the internal operation of power plants.

Station Service Transformer (Substation): Provides auxiliary power for the internal operation of substations.

Converter Transformer: Used in HVDC (High-Voltage Direct Current) transmission systems, with one side connected to AC power and the other to converter valves.

Rectifier Transformer: Used in thermal power plants to supply power for electrostatic precipitators (ESP).

2. Classification by Winding Configuration

Transformers are grouped by the number and structure of their windings:

Double-Winding Transformer: The most common type, used for step-up, step-down, and station service applications.

Three-Winding Transformer: Used for step-down, interconnection, and other applications requiring three voltage levels.

Autotransformer: Used for step-down, interconnection, and voltage regulation in power grids.

Split-Winding Transformer: Available in axial-split and radial-split designs, mainly used for station service and backup power applications.

3. Classification by Structure

Transformers are classified by their phase and assembly structure:

Single-Phase Transformer: Used for high-voltage transformers in the 330~1000kV range.

Three-Phase Transformer: The standard type for power distribution, used for transformers in the 10~500kV range.

Modular/Combination Transformer: The transformer is split into multiple components for transportation, then assembled on-site, ideal for remote areas with limited transportation access.

4. Classification by Cooling Method

Cooling method is a key factor determining transformer application and performance:

Oil-Immersed Transformer: The most widely used type, suitable for transformers in the 10~1000kV range, with mineral oil as the cooling and insulating medium.

Dry-Type Transformer: Air-cooled, non-flammable, suitable for indoor applications in the 10~110kV range, ideal for commercial buildings and urban substations.

SF6 Gas-Insulated Transformer: Currently used for 110kV transformers, with sulfur hexafluoride gas as the insulating and cooling medium, suitable for special environments.

5. Power Transformer Model Nomenclature

The model of a power transformer is a standardized code that defines its core parameters, structure, and features. Below is the meaning of common letters in Chinese transformer models, widely used in global trade for Chinese-manufactured transformers:

5.1 Meaning of Letters in Transformer Models

表格

Note: Copper windings and double-winding designs do not require additional symbols in the model.

5.2 Example of Model Interpretation

For example, the model SCB10-1000/10 can be interpreted as:

S: Three-phase

C: Epoxy resin cast dry-type

B: Foil winding

10: Design series

1000: Rated capacity 1000kVA

10: Rated voltage 10kV

Why This Guide Matters for Your Business

For global buyers, power system integrators, and electrical contractors, mastering transformer classification and nomenclature ensures:

Correct selection of transformers for specific power grid and application requirements

Accurate communication with manufacturers and suppliers

Compliance with international electrical standards (IEC, ANSI)

Reliable operation and maintenance of power distribution systems

Cost-effective procurement of transformers for power plants, substations, and industrial projects

Whether you are sourcing step-up transformers for power plants, distribution transformers for commercial buildings, or special transformers for industrial applications, this guide provides the foundational knowledge to make informed purchasing decisions.