Transformer installations - converters of electrical energy. They are used in most electrical appliances, power grids, automation devices, household appliances and communication devices. The principle of operation of transformers is based on Faraday's law of electromagnetic induction.
Content
- Transformer device
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Types of converters
- Operating modes of transformer devices
- Equipment selection criteria
Transformer device
Structurally, the transformer consists of one or more insulated windings that are wound on a ferromagnetic core. In the simplest scheme, these are the primary and secondary windings. Voltage is applied to the primary, and removed from the secondary. Under the influence of alternating current, which is supplied to the primary winding, a sinusoidal magnetic flux F. is formed in the magnetic circuit. Penetrating the windings, it induces in the primary winding the electromotive force of self-induction (EMF), and in the secondary - the EMF of induction.
Both of these electromotive forces are induced by the magnetic flux Ф, therefore, the EMF (E) is the same in each turn. The turns are connected in series, so the EMF of the primary winding will be E1 = E · w1. For the secondary, this is the ratio: E2 = E · w2, where w1, w2 is the number of turns.
When the secondary winding is open, the current does not flow in it, and the voltage at the ends is equal to the EMF, U2 = E2. With a small current in the primary winding, the losses will be insignificant and U1 ≈ E1. Replace E1 and E2, and then the voltage ratio will be expressed by some constant K, called the transformation ratio, U1 / U2 = E1 / E2 = w1 / w2 = K.
Types of converters
Purpose and principle of operation transformer consists in the ability to increase and decrease the voltage, change the number of phases, convert the frequency. Depending on the functions performed, transformers are divided into the following types:
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Power transformer installations. Generators in power plants produce high voltage power of 6-24 kV. To avoid large losses in power lines, it is required to increase the voltage to 750 kV. To distribute energy between end users, it is necessary to lower the voltage to 380 V. Power transformers perform these voltage conversion tasks. - Current transformer installations. They are used for measurements in electrical circuits. The primary winding is connected to the circuit in which the current is to be measured, and the secondary is used to connect the measuring instruments. In the secondary winding, a current flows proportional to the primary current.
- Voltage transformer installations. Converts high voltage to low voltage.
Welding transformer installations. They are used in welding units. They convert high voltage to low voltage, while the current rises to thousands of amperes.
- Autotransformers. Both windings are connected, there is a magnetic and electrical connection.
- Pulse transformer installations. Serve for converting impulse signals.
By the number of windings, they are distinguished:
- Double-winding installations.
- Three-winding installations.
- Multiphase transformer installations.
By design, transformers are dry and oil-filled. Heat losses occur during the operation of transformer installations. For low-power units, they are small, air cooling is used there. These are dry transformers. Oil immersed transformers are more powerful and require liquid cooling. To do this, they are placed in tanks with transformer oil, which contributes to more complete cooling and improves insulation. Oil units are designed to operate at voltages above 6 thous. V.
Operating modes of transformer devices
All devices can be idle, under load and short circuit. Idling is a working condition in which there is no load, the secondary winding is open. In this mode, the following are calculated:
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Transformation ratios. - Resistance of the magnetization branch. For this, a voltmeter is connected to the secondary winding. The resistance should be such that the current is minimal.
- Power factor.
- A short circuit is an operating condition under which the ends of the secondary winding are connected. When the unit is operating, a short circuit is an emergency mode. Primary and secondary currents increase tens of times. To prevent an accident, protection mechanisms are activated.
The short-circuit voltage is determined under test conditions. This is the passport characteristic of the unit. To determine the characteristics, the ends of the secondary winding are connected, and the voltage on the primary is reduced to such that the current does not exceed the nominal values.
In such tests, together with the no-load tests, the efficiency of the installations is determined.
Equipment selection criteria
When purchasing transformer equipment, it is necessary to consider its main parameters:
- Voltage.
- Transformation ratio.
- Angular error for current transformers.
The operating conditions are also taken into account. The area of application, load and short-circuit voltage are very important for the selection. It is especially necessary to operate the equipment correctly. There are standards for the start-up, commissioning and use of units. The main point is the maintenance of the installations, in which the resistance on the windings and the current should be checked.
The oil level and the cleanliness of the insulation should be checked periodically. If all the requirements of the regulations for the installation and maintenance of the units are met, the safety of operation and the warranty period of the devices will be ensured.
