Step-up transformer: design features of devices capable of increasing and decreasing voltage

The transformer converts power in networks and installations designed to receive and work with electricity. A step-up transformer is a static unit powered by a voltage source to transform high power into low power. It is used to isolate logic protection circuits and measuring lines from high voltage.

Transformer concept

An electromagnetic device with two or more windings coupled by induction on a magnetic circuit is called a transformer. It is designed to vary AC voltage while maintaining frequency and is used in the production, transmission and reception of electrical power.

The voltage boosting unit contains a wire coil surrounded by magnetic lines located on a core to conduct flux. The core material is ferromagnetic alloys. The unit operates with high power, its use is due to different indicators of the voltages of city lines (about 6.2 kV), consumer circuit (0.4 kV) and the power required for the operation of electrical appliances and machines (from single readings to several hundreds of kilovolts).

Application in networks

The devices are installed in electrical lines and power supplies of consumer points. In accordance with the Joule-Lenz law, as the current increases, heat is released, which heats the wire. To transmit energy over long linear distances, the voltage is increased, and the currents are reduced. When supplied to the consumer, the power is reduced, since for safety reasons it would be necessary to use massive insulation.

At the beginning of the chain, a step-up transformer is installed, and at the receiving point, the indicators are lowered. Such combinations are used repeatedly throughout the power transmission line, achieving favorable conditions for the transportation of electricity and creating acceptable values ​​for the consumer.

Due to the presence of three phases in the network, three-phase units are used to transform energy. Sometimes a group is used in which the devices are combined into a star model, while they have a common conducting rod.

Although the efficiency of high-power units reaches almost one hundred percent, a lot of heat is still generated. A typical 1 GW power plant transformer produces several megawatts. To reduce this phenomenon, a refrigeration system has been developed in the form of a tank with non-combustible liquid or transformer oil and a strong air heat distribution device. Cooling is often water, the dry principle is used at low power.

Magnetic system

A magnetic circuit is a complex of plates or other elements made of electrical steel, composed in a selected geometric configuration. The structure contains the fields of the unit. The assembled magnetic core together with the nodes and connecting elements forms the transformer skeleton. The part on which the windings are wound is a rod. The area of ​​the system intended for closing the circuit and not carrying the loop turns is called the yoke. The arrangement of the rods in space serves to divide the system into the following types:

• flat design, in which all cores are located on a single surface;
• spatial method - longitudinal rods or cores and yokes are in different planes;
• symmetrical order - rods of the same length and shape are located so that their spatial arrangement is the same for all elements and cores;
• asymmetrical action involves rods of different types and sizes, located differently from similar parts.

Unit windings

The winding consists of individual turns, which are conductors, or a set of such transmitters (strands of several wires). The turnover once bypasses the rod, the current of which, together with the currents of other cores and systems, reproduces the magnetic field. The result is an electromotive force (EMF).

The winding is an ordered set of turns. It forms a chain in which the forces induced in revolutions are added. The winding of a three-phase unit consists of several combined windings of three phases with the same voltage.

Step-down and step-up transformer rods are made in a square configuration for the best use of space (increasing the filling factor in the rod window). If it is required to increase the cross-section of the core, then it is divided into several conductors. This is used to reduce eddy currents in the sheath. A square conductor is called a conductor. According to the functioning of the windings, they are divided into several types:

• main - the coils, designed to receive or remove the converted or transformed AC energy;
• regulating - those that provide outputs for changing the voltage conversion ratio with a small winding current and a small normalization range;
• auxiliary turns provide power for their own needs, while using a low power, much less than the same rated value of the step-up transformer.

The core is insulated with a layer of paper or enamel varnish. Two parallel protected wires, located side by side, are fenced off with a common paper wrapper and are called a transposed cable. Its separate form is a continuous continuation, which is formed when the vein of one layer moves to the next layer with the same pitch in a single insulation. The paper protection is made of thin strips 2-4 cm wide, applied around the cable. To obtain the required layer of a given thickness, the paper is applied in several layers. Depending on the design, the winding is:

1. Private. The turns on the core are laid in the direction of the axis along the entire length of the wrapping. Subsequent turns are placed tightly to one another, without allowing a gap between them.
2. Screw. It is one of the options for multi-layer application. A distance is left between each turn.
3. Disk. A number of drives are sequentially combined. In them, the revolutions are placed in a radial direction in a spiral shape. On the primary layer, the wrapping is carried out inward, and on the adjacent circles it is done outward.
4. Foil. Instead of a rectangular cable, copper or aluminum plates are used. They are wide, with a thickness ranging from 0.1 to 2.5 mm.

Cooling tank

It is a container for oil and at the same time protects the active components of the unit from overheating. In the design, it plays the role of a support for additional and control devices. Before filling, air is removed from the tank, which destroys the insulation and reduces its protective properties. Because of this, the tank operates at low atmospheric pressure.

To reduce the noise from the operation of the transformer, the sound frequencies reproduced by the rod of the unit must match, and similar indicators of the resonance of structural elements. To discharge when the volume of liquid in the tank increases from heating, a separately located expansion tank is installed.

Raising the power ratings increases the speed of movement of electrons outside and inside the transformer, which destroys the structure. The scattering magnetic current in the tank acts similarly. Liners are used from a material that is not subject to magnetization. They are positioned around high flow insulators to reduce the risk of overheating. The interior of the tank is made so that it does not allow the magnetic flux to pass through the tank barriers. Material with low resistance to magnetism absorbs the flow before it penetrates the outer walls.

The number of semicircles almost corresponds to the number of wrapping revolutions. With increasing turns, more arcs are made, but there is no strict proportionality. Near the exit, the beginning of the windings (on two and more coils) is indicated by a bold point. They put the designations of the instantly occurring EMF, they are usually the same at the outputs.

This approach is used when showing the intermediateness of aggregates in converting chains to outline synchronicity or antiphase. The designation is also relevant for several coils, if polarity is required for their effective operation. The absence of an explicit designation of the wraps suggests that they go in one direction, that is, the end of the previous one corresponds to the beginning of the next one.

Features of operation

To determine the service life, the concept of economic and technical service life is used. The economic segment ends when the price of power transformation with the help of the required transformer exceeds the unit cost of the same services in the corresponding market niche. The technical service life is terminated with the failure of a large number of elements that require major overhaul of the unit.

Parallel use

This regulation is applied due to the fact that at a low load, the power reduction unit allows significant losses at idle. To remedy the situation, it is replaced by a group of low-power devices, which, if necessary, are turned off one by one. Requirements for such a connection:

• units with equal angular error between the secondary and primary voltage indicators are allowed for parallel use;
• equally polar poles from low and high power regions are connected in parallel;
• the devices to be combined must show a similar voltage transfer ratio;
• short-circuit resistance should differ in the direction of decrease or increase by no more than 10%;
• the power ratio of the transformers involved should not exceed 1: 3.

The units included in the group are used with the same technical parameters.

Frequency and power regulation

In cases of equal voltage on the primary windings, units with a certain frequency can be operated with increased network indicators with the recommended replacement of attachments. At a frequency less than the nominal, the induction increases the values ​​in the magnetic drive, which leads to a surge in the current during idle operation and a change in its type.

Voltage regulation of the transformer is used in the network due to the fact that the normal operation of consumers is possible only with the power of certain parameters and minimum deviations from them.

Isolation and overvoltage

Specialists carry out regular tests and repairs of the protective layer of the transformer, as it loses its properties from high temperatures. This applies to the aggregate oil in the cooling tank and the isolation of active elements. After checking, the information on the state of the protective materials is entered into the unit's passport.

Sometimes the devices operate in high power conditions. Overvoltage is classified into two types:

• the short-term effect of a strong factor lasts from one second to 2-4 hours;
• transient overvoltage lasts from 2-5 nanoseconds to 3-5 milliseconds, it is oscillatory or non-oscillatory, but always has the same direction.

Sometimes both types of overvoltage are combined during an overload. The reasons for their occurrence can be lightning discharges, while the current pulse rate depends on the distance between the transformer and the impact site. The second reason is the changes in the operating conditions formed within the system. They consist in breakdowns, conduction disturbances, short circuits, fires, frequent connections and disconnections.

During quality control in the factory, the units are checked and reported on the possibility of uninterrupted operation in accordance with the standards.