What is a Single-phase transformer: Construction and Its Working
The Single-phase transformer is a static electrical device used to change alternating voltage. The main structure of a single-phase transformer with two secondary and primary windings is converting the voltage of the AC system based on the principle of electromagnetic induction.
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The transformer is a device that converts magnetic energy into electrical energy. It consists of two electric coils called primary and secondary. The primary winding of a transformer receives electricity while the secondary coil is charged. A ferromagnetic circuit called a "core" is often used to wind these coils. Although the two windings are electrically isolated, they are magnetically linked.
Single-phase transformers use single-phase alternating current transformers, transformers based on voltage cycles that operate in a uniform time-phase.
A current flows through the transformer's primary winding creating a magnetic field, creating a voltage across the transformer's secondary winding. Based on the application types, single-phase transformers are used to increase or decrease the output voltage. This transformer is usually a high efficiency and low loss power transformer.
The alternating voltage source sends alternating current through the transformer primary winding. The alternating current creates an alternating electromagnetic field. The magnetic field line travels through the transformer iron core and includes the transformer secondary circuit. Thus the induced voltage in the secondary has the same frequency as the voltage on the primary. The induced voltage is determined using Faraday's Law.
f → frequency Hz
N → number of winding turns
Φ → flux density Wb
If the load is connected on the transformer's secondary side, current flows through the secondary winding. A single-phase transformer can act as a step-up transformer or step-down transformer.
The main parts of a transformer are the coil, core, and isolation. The windings should have a small resistance and are usually made of copper (rarely aluminum). They are wrapped around the core and must be isolated from it. Besides, the coils must be isolated from each other.
The transformer core is made of fragile, highly permeable steel plates. The coatings should be thin (0.25 mm to 0.5 mm) because of reduced power losses (known as eddy current losses). They must be isolated from each other, and usually, an insulating varnish is used for that purpose.
Transformer insulation can be supplied either dry or liquid-filled. Dry-type insulation is provided by synthetic resin, air, gas, or vacuum. It is only used for small-sized transformers (below 500 kVA).
Liquid insulation usually means using mineral oil. The oil has a long lifespan, good insulation properties, overload capacity, and transformer cooling. Oil insulation is always used for large transformers.
Single-phase transformers have two windings, one on the primary and the other on the secondary. They are mostly used in single-phase electrical systems. Three-phase system application means using three single-phase units connected in a three-phase system. This is a more expensive solution, and it is used in high voltage systems.
Video of Single-phase transformer:
a. Core-type transformers
In this type of construction, only half of the windings are cylindrically wound around each leg of the transformer to enhance magnetic coupling, as shown in the figure below. This type of construction ensures that magnetic field lines run through both coils simultaneously. The main disadvantage of core-type transformers is that the leakage flux occurs due to the current of a small proportion of the flux line from the outside of the core.
b. Shell type transformer
In this type of transformer construction, the primary and secondary windings are cylindrically placed on the median limb resulting in a cross-sectional area twice that of the outer limb. There are two closed magnetic lines in this structure, and the outer limb has a flux ɸ / 2 running through them. Shell-type transformers overcome leakage flux, reducing core loss, and increasing efficiency.
The advantages of three single-phase units are transportation, maintenance, and availability of backup equipment. Single-phase transformers are widely used in commercial low-voltage applications such as electronics. They act as a descending voltage transformer and reduce the home's voltage value to something appropriate for the electronic device supplied. On the secondary side, the rectifier is usually connected to convert the ac voltage to the direct voltage used in electronic applications.
The Single-phase transformers of MBT
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