A transformer is a static, passive electrical device that transfers the electrical energy galvanically between two or more circuits.
The changing current in a coil produces a changing magnetic flux in the same coil, which in turn induces a varying emf (electromotive force) across another winding, wounded on the same core.
This electrical energy is transferred between the two coils magnetically without being electrically connected. The transformers are rated in VA, KVA or MVA .
Transformers are used to either step up or step down the alternating voltage.
The transformers may be step up transformers or step-down transformers depending upon the primary and secondary windings.
A step up transformer is a transformer that step ups the voltage from the primary winding to the secondary winding while keeping the power same in both the windings at the rated frequency.
Where are the Step up Transformers used?
The step up transformers are generally used in generating stations and other power transmission applications. The primary windings of the power transformers at the power generating stations are supplied with the lower voltage to give a higher voltage at the other end of the transmission lines.
The step up transformers are constructed of windings, core, enclosure, and other accessories.
The core of the transformer is constructed from a highly permeable material. Laminations of thin silicon steel are assembled and tightly clamped to form the core.
This core is designed to allow magnetic flux to flow through them quickly with minimum losses.
The core material has a higher permeability than the surrounding air. This high permeability of the core material makes the magnetic field lines restricted in the core material and thus increases the efficiency of the transformer by reducing the losses of the transformer.
The magnetic cores though are advantageous in permitting the magnetic flux flow across them but also leads to core losses such as eddy current losses due to hysteresis. Therefore, low coercivity and hysteresis materials are preferred for making magnetic cores, like silicon steel or ferrite.
The core of transformers is laminated to keep the eddy currents at a minimal low to prevent the heating of the core. The electrical energy got wasted in heating the core and thus decreased the efficiency of the transformer.
The windings of the transformers are meant to carry currents and are wounded over the core. These windings are insulated and are designed to keep the transformer cool and to withstand the operational and test conditions. The windings are of copper or aluminium.
The primary windings comprise of thick wire with a smaller number of turns on the core, while the secondary windings comprise of thin wires with a large number of turns. The primary windings are designed to carry low voltage at a higher current, whereas the secondary windings are designed to carry higher voltages at a lower current. The power across both the windings, however, remains the same at any point of time;
The copper windings, though expensive, bear higher mechanical strength and carries 1.6 times higher current than the aluminium windings. Silver bearing copper windings have greater strength and is required where higher extreme forces are there. These copper wounded transformers are preferred where the smaller ratings of the transformers or the compact transformers are required.
The aluminium windings are lighter as well as less expensive, though a large cross-section of aluminium is required as they carry less current than copper. These windings are preferred where the price is the criteria, and space is not an issue. They are generally preferred to transfer higher kVA rating power to large distances.