Transformers play a significant role in electrical engineering, performing the functions of transformation, isolation, measurement and protection. One of the most common tasks of devices of this type is the regulation of individual current parameters. In particular, voltage transformers (VT) convert the performance of the primary power grid to optimal values, from the point of view of consumers.
Overall design of equipment
The technical basis of the transformer is formed by an electromagnetic filling that provides the functional processes of the device. The dimensions of the equipment may vary depending on the requirements for the power load in the circuit. In a typical design, the transformer has current input and output devices, and the main working elements perform voltage conversion tasks. A set of insulators, fuses and a relay protection device are responsible for ensuring the reliability and safety of technological processes. In the design of a modern low voltage transformersensors for recording individual operating parameters are also provided, the indicators of which are sent to the control panel and become the basis for commands to the regulatory authorities. The operation of electrical components in itself requires power supply, therefore, in some modifications, converters are supplemented with autonomous power sources - generators, accumulators or batteries.
Transformer Cores
The key working elements of VT are the so-called cores (magnetic cores) and windings. The first are of two types - rod and armor. For most low-frequency transformers up to 50 Hz, rod cores are used. In the manufacture of the magnetic circuit, special metals are used, the characteristics of which determine the working properties of the structure, for example, the performance and magnitude of the no-load current. The core of a voltage transformer is formed by thin sheets of alloy, insulated between layers of varnish and oxide. The degree of influence of eddy currents of the magnetic circuit will depend on the quality of this insulation. There is also a special kind of typesetting cores, which form structures of arbitrary section, but close to a square shape. This configuration allows you to create universal magnetic circuits, but they also have weaknesses. So, there is a need for a tight tightening of metal plastics, since the smallest gaps reduce the filling factor of the coil working area.
Voltage transformer windings
Usually two windings are used - primary and secondary. They are isolated both from each other and from the core. The first level of winding is distinguished by a large number of turns made with a thin wire. This allows it to serve high voltage networks (up to 6000-10,000 V) required for basic conversion needs. The secondary winding is designed for parallel supply of measuring instruments, relay devices and other auxiliary electrical equipment. When connecting the winding of voltage transformers, it is important to consider the markings on the output terminals. For example, power direction relays, multimeters, ammeters, wattmeters and various meters are connected to the coils through the beginning of the primary winding (designation A), the end line (X), the beginning of the secondary winding (a) and its end (x). An additional winding with special prefixes in the designation can also be used.
Mounting fittings and grounding facilities
The list of additional elements and functional devices may vary depending on the type and characteristics of the transformer. For example, oil structures with a primary voltage indicator of up to 10 kV or more are provided with fittings for filling, draining and sampling technical lubricants. For oil, a tank is also provided with nozzles and regulators that control the smooth supply of fluid to the target areas. Typical fitting kits most often include brackets with bolts, spigots, relay components, electrical cardboard gaskets, flange elements, etc. As for grounding, thentransformers with a voltage on the primary winding up to 660 V are provided with clamps with threaded fastening of bolts, studs and screws of size M6. If the voltage indicator is higher than 660 V, then the grounding fitting will have to have hardware connections of the format not less than M8.
The principle of operation of TH
The main functions and processes of electromagnetic induction are performed by a complex that includes a metal core with a set of transformer plates, primary and secondary windings. The quality of the device will depend on the accuracy of the basic calculation of the amplitude and the angle of the current. Mutual induction between several windings is responsible for the transformation in an electromagnetic field. Alternating current in a 220 V voltage transformer is constantly changing, passing through a single winding. According to Faraday's law, an electromotive force is induced once per second. In a closed winding system, the default current will flow through the circuit and close to the metal core. The lower the load on the secondary winding of the transformer, the closer the actual conversion factor to the nominal value. Working with connecting the secondary winding to measuring devices will especially depend on the degree of conversion, since the smallest load fluctuations will affect the accuracy of the measurements entered into the instrument circuit.
Types of transformers
Today, the following types of TN are most common:
- Cascade transformer - a device in which the primary winding is divided into several successive sections, and equalizing and connecting windings are responsible for transferring power between them.
- Grounded VT - single-phase designs, in which one end of the primary winding is tightly grounded. It can also be three-phase voltage transformers with a grounded neutral from the primary winding.
- Unearthed VT - a device with full winding insulation with adjacent fittings.
- Two-winding VT - transformers with one secondary winding.
- Three-winding VTs are transformers that, in addition to the primary winding, also have a main and additional secondary windings.
- Capacitive VT - designs characterized by the presence of capacitive separators.
Features of electronic VTs
According to the main metrological indicators, this type of transformers differs little from electrical devices. This is due to the fact that in both cases the traditional conversion channel is used. The main features of electronic transformers are the absence of high-voltage insulation, which ultimately contributes to a higher technical and economic effect from the operation of the equipment. In high-voltage networks with a primary voltage of a voltage transformer up to 660 V, the converter is connected to the central network in a galvanic way. Information about the measured current is transmitted at a high potential, as is the case with an analog-to-digital converter with an optical output. Howeverthe dimensions and weight of electronic models are so small that they make it possible to install transformer units in the infrastructure of high-voltage wire buses even without connecting additional insulators and mounting hardware.
Transformer Specifications
The main technical and operational value is the voltage potential. On the primary winding, it can reach 100 kV, but for the most part this applies to large-sized industrial stations containing several converting modules. As a rule, no more than 10 kV is supported on the primary winding. A voltage transformer for single-phase networks with a grounded neutral works at 100 V at all. As for the secondary winding, its nominal voltage indicators are 24-45 V on average. Again, low energy metering devices are serviced on these circuits, which do not require a high power load. However, the secondary windings sometimes have high potentials of more than 100 V in three-phase networks. Also, in assessing the characteristics of a transformer, it is important to take into account the accuracy class - these are values from 0, 1 to 3, which determine the degree of deviation in the conversion of target electrical indicators.
Ferroresonance effect
Electromagnetic devices are often subjected to various kinds of negative influences and damage associated with violations in the insulation. One of the most common winding destruction processes is ferroresonance disturbance. It causes mechanical damage and overheating.windings. The main reason for this phenomenon is called the nonlinearity of the inductance, which occurs in situations of unstable response of the magnetic circuit to the surrounding magnetic field. To protect the voltage transformer from ferroresonant effects, external measures are possible, including the inclusion of additional capacitances and resistors to the switched device. In electronic systems, the possibility of inductive non-linearity can also be minimized by programming equipment shutdown sequences.
Use of equipment
The operation of transformer devices that convert voltage is governed by the rules for the use of electrical engineering. Taking into account the optimal operating values, specialists introduce substations into the supply infrastructure of the target facility. The main functions of the systems allow serving buildings and enterprises with powerful power plants, and the secondary voltage of the transformer up to 100 V controls the load for less demanding consumers such as meters and metrological devices. Depending on the technical and structural parameters, HP can be used in industry, in the construction industry and in households. In each case, the transformers provide electrical power control by adjusting the input power ratings to match the rated requirements of the particular site.
Conclusion
Electromagnetic transformers provide a rather old, but in demand to this daythe principle of power regulation in electrical circuits. The obsolescence of this equipment is associated with both the design of the equipment and its functionality. Nevertheless, this does not prevent the use of current and voltage transformers for critical power management tasks in large enterprises. In addition, it cannot be said that converters of this type are not subject to improvements at all. Although the basic principles of operation and even the technical implementation as a whole remain the same, engineers have recently been actively working on protection and control systems. As a result, this affects the safety, reliability and accuracy of the transformers.
