Transformer Basic Knowledge


This paper introduces the basic knowledge of transformers, including the classification of transformers, transformer rated parameters, typical transformer structure and component functions.

Key words: transformer, load, no-load, equivalent circuit.

I. Introduction

Transformers are well known. We use a variety of transformers in our lives, ranging from boost transformers, step-down transformers used in power transmission to power transformers used in household appliances. But we do not know that transformers are divided into many types in various ways, and each has its own characteristics. This paper mainly focuses on the types of transformers and tells about transformers. Basic knowledge.

Definition of transformer

Transformer is a device of static motor which converts the electric energy of one voltage into that of another voltage.

Classification of Transformers

1. Use classification: (1) power transformer, power system transmission; (2) electric furnace transformer, power supply for steelmaking furnace; (3) rectifier transformer, large electrolytic plating, DC electric locomotive power supply; (4) instrument transformer, control transformer; (5) radio transformer, only transmission signal.

2. Classification of pressure swing modes:

(1) Boost transformer - transformer with higher voltage; (2) Boost transformer - transformer with lower voltage; (3) Special transformer, such as high voltage transformer for test, transformer for electric furnace, transformer for welding, transformer in thyristor circuit, voltage transformer and current transformer for measuring instrument, etc.

3. Classification of coil number

(1) Double-winding transformer, there are two windings in the core, one is primary winding and the other is secondary winding; (2) autotransformer, the combination of primary winding and secondary winding is one; (3) three-winding transformer, three windings connected with three different voltage lines; (4) multi-winding transformer, such as split transformer.


(1) oil-immersed transformer; (2) dry-type transformer.

5. Phase Number Classification

(1) Single-phase transformer; (2) Three-phase transformer.

Introduction of typical transformer-power transformer structure and components

The main structural components of oil-immersed transformer are core, winding, oil tank, insulating bushing, etc.

1, iron core

It consists of core pillar and yoke. The core pillar is used to set windings. The yoke connects the core pillar to form a closed magnetic circuit. In order to reduce core loss, the core is made up of 0.30-0.50 mm thick silicon steel sheets and coated with insulating paint to avoid short circuit between the sheets. In large power transformers, cold-rolled silicon steel sheets are often used to improve permeability and reduce core loss. In order to reduce joint clearance and excitation current, coiled core made of cold-rolled silicon steel sheets is sometimes used.

2, winding

Definition: The circuit part of a transformer is wound with an insulated flat or round wire wrapped in paper or yarn. Primary winding - winding of input electric energy, secondary winding - winding of output electric energy. Similarities and Differences: Primary and secondary windings have different turns, voltage and current. The winding with higher voltage is called high voltage winding, and the winding with lower voltage is called low voltage winding. From the relative position of high and low voltage windings, transformer windings can be divided into concentric and overlapping types.

3, fuel tank

The body of the oil-immersed transformer is immersed in the oil tank of the transformer oil. Oil is both a cooling medium and an insulating medium. There are cooling tubes (radiator or cooler) on the side wall of the tank, mechanical support, cooling and heat dissipation.

4. Insulation bushing

Leading the high and low voltage lead of the coil to the outside of the box is the insulation of the lead to the ground, which plays a fixed role. (Porcelain), the casing shape is usually made into umbrella shape, the higher the voltage, the more series.

VI. Rating of Transformers

1. rated capacity SN: rated apparent power

Double-winding transformer, primary and secondary rated capacity S1N = S2N; three-winding transformer three-side capacity is not necessarily equal. Three-phase transformer refers to the total capacity of three-phase, unit: VA, KVA, MVA. Small power transformers with capacity below 630KA, medium power transformers with capacity between 800 and 6300KA, large power transformers with capacity between 8000 and 63000KA, and super large power transformers with capacity above 90000KA.

2. Nominal Voltage UN: Nominal Voltage U1N on Primary Side and Nominal Voltage U2N on Secondary Side. The rated voltage refers to the line voltage. U2N: No-load voltage of the secondary side when the primary side is applied with rated voltage U1N in units of V and KV.

3. Nominal current IN: Nominal current I1N in primary side and Nominal current I2N in secondary side. Rated current refers to line current, unit A.

4. Rated frequency fN: China's regulation is 50HZ.

Each transformer has a nameplate marked with model, rating and other data to facilitate users to understand the operation performance of the transformer.

Six, conclusion

This paper mainly describes some basic knowledge of transformer from the aspects of classification, basic principle and main parameters of transformer. It is hoped that it will be helpful for friends engaged in electrical work to understand transformer.