Special transformers - industrial dry-type transformers designed specifically for electrical networks and energy consumers, which are characterized by special conditions - for example, increased load or special operating conditions. Such transformers are intended mainly for industrial enterprises, since they protect industrial electrical appliances and direct current. Transformers of a special type allow you to reduce the ripple of the electric current, adjust the frequency of the current and change the number of phases.
Types of transformers
Special group of transformers include:
- High frequency.
- Welding transformers.
- Autotransformers and many others designed for a narrow range of applications.
Special isolating transformers widelyare used in areas requiring additional safety measures when working with power tools. They are used in medical equipment where direct contact with the human body is required.
In order to ensure electrical safety, two windings of an identical design are placed on a common magnetic circuit, which allows you to get the same voltage at the output as at the input.
On the body of the device in the event of a breakdown of the wire insulation, a potential is formed that can hit a person and cause electrical injury. Optimum use of the power supply of electrical equipment is possible with the galvanic separation of the circuit, while at the same time it excludes the possibility of electrical injury in the event of a breakdown of the secondary insulation circuit to the case.
High frequency transformers
Special-purpose transformers that differ from conventional equipment in the material of which the magnetic circuit is made, which allows high-frequency signals to be transmitted without distortion.
Designed to match the resistance in the electronic circuit. Matching special transformers are widely used in audio amplifiers and antenna devices.
Welding-type transformers are used in industrial enterprises, while enjoying considerable popularity among radio amateurs.
The primary winding is formed with a large number of turns, thanks to which processing is carried outelectrical energy with an input voltage of 220 or 380 volts. The number of turns in the secondary winding is less, but the current flowing through it is high and can reach thousands of amperes.
Transformers for electric arc welding
A step-down single-phase special transformer capable of converting the mains voltage of 220 or 380 V to the 60-70 V required for burning an electric arc. Since the resistance of the electric arc is minimal, the operation of the welding inverter is carried out in conditions as close as possible to a short circuit. In this regard, a moving core choke is connected in series to the secondary circuit of the transformer to limit the current. The value of the welding current and the inductive resistance of the inductor can be adjusted by changing the value of the air gap in the magnetic circuit.
Moving core transformer
A special transformer, the core of which consists of two parts - movable and fixed, and the movable with the secondary winding is located inside the fixed with the primary winding. The primary winding of such a transformer is made of two coils connected in opposite directions. Connecting such a transformer to the circuit simultaneously with a booster transformer allows you to adjust the secondary direction.
Transformers for rectifiers
The secondary circuit of such transformers includes valves, thanks to which the alternating current is converted intothrobbing. The dimensions and weight of special transformers for rectifier installations are much larger than those of similar devices of identical output power, but there is a sinusoidal current in their windings. This is explained by the fact that in transformers connected to rectifier circuits, the useful power depends on the component of the secondary current, and the heating of the windings depends on the total primary and secondary currents with higher harmonics.
Network, or primary, winding of three-phase rectifier transformers is connected in a "triangle" or "star", and the secondary - valve - is connected in such a way that single- and three-phase current is converted into multi-phase with the number of phases required for a particular circuit transformations. The greater the number of phases, the lower the ripple of the rectified voltage. Single-phase current rectifiers installed on electric locomotives operate on two-phase circuits, on traction substations - six-phase and twelve-phase.
A transformer whose operation mode depends on a change in the bias of the shunts and has three combined windings, one of which is powered by direct current. The output voltage of the transformer changes with a change in the DC bias circuit.
Designed to transform voltage pulses while maintaining their shape unchanged. The windings of pulse transformers of a special type are made with a few layers in order to reducehysteresis distortion, parasitic capacitances, eddy currents and leakage inductances. The cores are made of permalloy or electrical cold rolled steel.
Transformers designed to convert a sinusoidal voltage into a peak voltage required to open thyratrons, controlled valves - thyristors and similar equipment. Peak transformers are two-winding transformers with linear active or inductive resistance in the primary winding circuit and a highly saturated magnetic circuit. Due to this structure, an EMF is induced on the secondary winding in the form of short-term pulses, while the moments of current passage through zero correspond to the maxima of the pulses.
Electromagnetic static equipment used in electrical circuits due to its inductance. The reactor, or choke, is a coil with a ferromagnetic core. Depending on the purpose and mode of operation, transformers are divided into several types:
- Smoothing. Designed to smooth out rectified current ripples and are used in traction motor circuits of electric trains and electric locomotives.
- Transitional. Switch the terminals of the transformer.
- Current-limiting. Reduce short circuit currents.
- Dividing. Equally distribute load currents between valves connected in parallel.
- Interference suppression. Eliminate interferencearising from the operation of apparatus, equipment and electrical machines.
- Inductive shunts. They distribute current between the windings of operating traction motors and resistors connected in parallel to them during transients.
The types of special transformers listed above are among the most popular and commonly encountered.