Transformer structure and function summary of each component

The transformer is mainly composed of iron core, winding, fuel tank, oil pillow, insulating sleeve, tap changer and gas relay, etc. The functions of each part are as follows:

Iron core

The core is the magnetic circuit part of the transformer; In order to reduce the hysteresis and eddy current loss of the iron core under the action of alternating magnetic flux, the iron core is made of high-quality silicon steel sheets with a thickness of 0.35mm or thinner. At present, the cold-rolled grain with high permeability is widely used to replace the silicon steel sheet in order to reduce the volume and weight, and also save the wire and reduce the heat loss caused by the wire resistance.

The iron core consists of two parts: an iron core post and an iron yoke. The iron core column is coated with winding, and the iron yoke connects the iron core column to form a closed magnetic circuit. According to the arrangement of the winding in the iron core, the transformer is divided into iron core type and iron shell type (or referred to as core type and shell type) two kinds.

Single-phase two-core column. This kind of transformer has two core columns, and the upper and lower two iron yoke connect the core columns to form a closed magnetic circuit. Both core columns are fitted with high voltage and low voltage windings. Generally, the low voltage winding is placed on the inside, that is, near the core, and the high voltage winding is placed on the outside, so that it is easy to meet the insulation class requirements.

There are three phase core transformer three phase core column type and five phase core column type. Three phase five core column type (or three phase five column type), also known as three phase three core column side yoke type, it is in the three phase three core column (or three phase three column type) outside the plus two side yoke (no winding core), but the cross section and height of the upper and lower yoke is smaller than the ordinary three phase three column type. This reduces the height of the entire transformer.

Three phase three core column is the three phases of the three winding are placed on the three core column, the three core column is also by the upper and lower two iron yoke to connect the core column, forming a closed magnetic circuit. The windings are arranged in the same way as single-phase transformers. Three-phase five core column, compared with three-phase core, there are two more branch core columns on the left and right sides of the core column to become a choke. The windings of each voltage stage are respectively set on the middle three core columns according to the phase, and the side yoke has no winding, so that a three-phase five-core transformer is formed.

Because the phase flux of the three-phase five-column iron core can be closed by the side yoke, the three-phase magnetic circuit can be regarded as independent of each other, and unlike the common three-phase three-column transformer, the phase magnetic circuit is interrelated. Therefore, when there is an asymmetric load, the zero-sequence flux generated by the zero-sequence current of each phase can be closed by the side yoke, so the zero-sequence excitation impedance is equal to the symmetrical operation excitation impedance (positive sequence).

Medium and small capacity three-phase transformers are three-phase three-column. Large capacity three-phase transformer. Often limited by the height of transport, the three-phase five-column type is used.

The single-phase transformer with iron shell has a central core column and two branch core columns (also called side yoke), and the width of the central core column is the sum of the width of the two branch core columns. All the winding is placed on the central core column, and the two branch core columns are like "shells" around the outside of the winding, so it is called shell transformer. It is sometimes called a single-phase three-column transformer.

The iron shell three-phase transformer has an iron core that can be regarded as consisting of three independent single-phase shell transformers placed side by side.

The core transformer structure is relatively simple, the high voltage winding is far away from the iron core, and the insulation is easy to deal with. The structure of shell transformer is relatively strong, the manufacturing process is relatively complex, the distance between high voltage winding and iron core column is relatively close, and the insulation treatment is more difficult. Shell structure is easy to strengthen the mechanical support of the winding, so that it can withstand large electromagnetic force, especially suitable for transformers through high current. Shell construction is also used in large capacity Power Transformers.

In large capacity transformers, in order to make the heat emitted by the loss of the iron core can be fully taken away by the insulating oil during circulation, so as to achieve a good cooling effect, the cooling oil duct is usually provided in the iron core. The direction of the cooling oil passage can be made parallel or perpendicular to the plane of the silicon steel sheet.

winding

The arrangement of windings to each other on the core

The winding of a transformer, according to the arrangement of its high-voltage and low-voltage winding on the iron core, has two basic forms: concentric and overlapping. Concentric winding, high voltage winding and low voltage winding are made into a cylinder shape, but the diameter of the cylinder is different, and then the core is concentrically attached to the iron column. Overlapping winding, also known as pie winding, the high voltage winding and low voltage winding are divided into a number of wire cakes, along the height of the core column staggered. Overlapping winding is mostly used in shell transformers.

Core transformers generally use concentric winding. Usually, the low-voltage winding is assembled close to the iron core, and the high-voltage winding is set outside the low-voltage winding, and there is a certain insulation gap and heat dissipation oil channel between the low-voltage winding and the high-voltage winding as well as between the low-voltage winding and the iron core, and the insulated paper tube is separated.