Transformers: device and principles of operation, purpose and scope of the device

The name "transformer" comes from the Latin word "transformare", which means "to transform, transform". This is precisely its essence - the transformation by magnetic induction of alternating current of one voltage into alternating current of another voltage, but of a similar frequency. The main purpose of the transformer is to use a variety of devices in power grids and power supplies.

Device and principle of operation

A transformer is a device for converting alternating current and voltagewith no moving parts.

The device of transformers consists of one or more isolated wire, sometimes tape coils (windings), which are covered by a single magnetic flux. The coils are usually wound on a core (magnetic circuit). It is usually made from a ferromagnetic material.

The figure schematically shows the principle of operation of the transformer.

The figure shows that the primary winding is connected to the AC source, and the other (secondary) to the load. In the turns of the primary winding, an alternating current flows, its value I1. And both coils are surrounded by a magnetic flux Ф, which produces an electromotive force in them.

If the secondary winding is without load, then this mode of operation of the converter is called "idle". When the secondary coil is loaded, a current I2 is generated in the secondary coil under the action of the electromotive force.

The output voltage in this case depends directly on how many turns on the coils, and the current strength depends on the diameter (section) of the wire. In other words, if both coils have the same number of turns, then the output voltage will be equal to the input voltage. And if you wind 2 times as many turns on the secondary coil, then the voltage at the output will be 2 times higher than the input.

The final current also depends on the diameter of the winding wire. For example, with a large load and a small diameter of the wire, overheating of the winding, violation of the integrity of the insulation and even complete failure of the transformer can occur.

To avoid such situations, tables have been drawn up for calculating the converter and choosing the wire diameter for a given output voltage.

Classification by type

It is customary to classify transformers according to several criteria: by purpose, by method of installation, by type of insulation, by voltage used, etc. Let's consider the most common types of devices.

Power converters

This type of devices is used to supply and receive electrical energy on power lines and from power lines with voltages up to 1150 kW. Hence the name - power. These devices operate at low frequencies - on the order of 50-60 Hz. Their design features are that they can contain several windings, which are located on an armored core made of electrical steel. Moreover, the low voltage coils can be powered in parallel.

Such a device is called a split-winding transformer. Typically, power transformers are placed in a tank with transformer oil, and the most powerful units are cooled by an active system. For installation at substations and power plants, three-phase devices with a capacity of up to 4 thousand. kVA. They are most widespread, since losses in them are reduced by 15% compared to single-phase ones.

Autotransformers (LATR)

This is a special kind of low frequency device. In it, the secondary winding is simultaneously part of the primary and vice versa. That is, the coils are connected not only magnetically, but also electrically. Different voltages are obtained from one windingif several conclusions are drawn. Due to the use of fewer wires, a reduction in the cost of the device is achieved. However, there is no galvanic isolation of the windings, and this is already a significant drawback.

Autotransformers have found application in high-voltage networks and in automatic control installations, for starting AC motors. It is advisable to use them at low transformation ratios. LATR is used for voltage regulation in laboratory conditions.

Current transformers

In such devices, the primary winding is connected directly to the current source, and the secondary winding is connected to devices with a small internal resistance. These can be protective or measuring devices. The most common type of current transformer is the measuring one.

It consists of a core made of laminated silicon cold-rolled electrical steel with one or more separate secondary windings wound around it. While the primary can be just a bus or a wire with a measured current passed through the window of the magnetic circuit. For example, clamp meters function according to this principle. The main characteristic of the transformer current is the transformation ratio.

Such converters are safe and therefore have found application in current measurement and in relay protection circuits.

Pulse converters

In the modern world, impulse systems have almost completely replaced heavy low-frequency transformers. Typically, a pulse device is made on a ferrite core of various shapes and sizes:

• ring;
• kernel;
• cup;
• in the form of the letter W;
• U-shaped.

The superiority of such devices is beyond doubt - they are capable of operating at frequencies up to 500 kHz and more.

Since this is a high-frequency device, its size decreases significantly with increasing frequency. A smaller amount of wire is consumed per winding, and to obtain high-frequency current in the first circuit, it is enough only to connect a field-effect or bipolar transistor.

There are many more types of transformers: isolation, matching, peak transformers, double choke, etc. All of them are widely used in modern industry.

Scope of devices

Today, perhaps, it is difficult to imagine the field of science and technology, where transformers are not used. They are widely used for the following purposes:

1. For transmission and distribution of electricity.
2. To create a valid valve switching circuit. It is used in converting devices with simultaneous matching of input and output voltage.
3. In production: in welding, for supplying electrothermal installations, etc. The power of such devices sometimes reaches tens of thousands of kVA and voltages up to 10 kV, and the operating range is 50 Hz.
4. Low-power and low-voltage converters are used for radio and television equipment, communication devices, household appliances, for voltage matching, etc.
5. When electrical measuring instruments and relays are included in high voltage electrical circuits in order to expand the measurement ranges and ensure electrical safety.

Based on the variety of devices and types of transformer purposes, it can be argued that today they are irreplaceabledevices used almost universally, thanks to which stability and achieving the voltage values ​​required by the consumer for both civil networks and enterprise networks industry.