Transformers are devices that transfer power from one circuit to another, following the principle of electrical induction. Step-up devices raise voltage, typically before transmitting electricity over distribution grids. In contrast, step-down models reduce voltage levels near the point of power usage.

Frequent applications include manufacturing production lines, pumping stations, windmills, power generation units and electric machinery in commercial establishments.

How do transformers change the voltage?

Transformers contain coils of conductive copper wire wound together to transfer the energy between physically separate circuits. They function with alternating current (AC), characteristically used in most devices, from industrial machinery to domestic appliances.

When the AC supply voltage fluctuates in the primary coil, it affects the secondary coil. Although electrically insulated, this second winding is physically close. The induced current or electromotive force (EMF) follows the principles of Faraday’s Law of electromagnetic induction.

If the secondary winding has more turns of wire than the primary coil, the device will step the voltage down. Conversely, suppose the secondary coil has fewer windings than the primary. In that case, it steps up the voltage, also in a direct ratio.

The two coils and circuits are electrically isolated, except in the case of autotransformers*.

Why wrap coil windings around a core?

winding machinery

When a transformer assembly uses only air as insulation, the electrical energy transfer between the two windings is relatively inefficient. As a result, losses through heat and hysteresis (please see below) are significant.

Transformers usually feature primary and secondary windings of insulated wire wrapped around a conductive core. This design increases transformer efficiency and reduces energy loss. In particular, iron cores have low electrical reluctance, resulting in less resistance.

To produce large transformers, we use purpose-designed automatic winding machinery.

What are eddy currents and hysteresis?

Eddy currents arise in iron cores due to the magnetic field interacting with the ferrous conductor. These energy losses dissipate as heat. Thankfully, it is possible to minimize them with lamination, i.e., stacked, insulated electric plates instead of a solid iron block. Shell transformers feature these laminated cores.

Hysteresis depends on flux density and the AC frequency. To help visualize hysteresis, consider the analogy of pushing a physical object away and pulling it back.

Similarly, AC voltages appear as sine waves on oscilloscopes. With the opposing cycles, transformers lose a little energy with every change of electron flow and — consequently — magnetic field.

European AC mains supplies are at a frequency of 50 Hertz, i.e., 50 cycles per second.

What are the different types of transformers?

In certain industrial and medical applications, cooling is essential to ensure the stability of internal electronics and electric machinery.

  • Self-cooled oil-filled transformers are typical up to 3.0 MVA, where ambient airflow is sufficient for cooling.
  • Air-cooled (air blast) types use fans or blowers to carry heat away from the windings and the core.
  • Water-cooled oil-filled designs feature heat exchangers and water circulation to cool the heat-conductive oil of the core assembly. Thus, temperature conditions within the assembly remain within the designed operating range.

Step-up transformers are sometimes necessary for heavy machinery in factories and industrial applications. Let us consider the engineering power equation, W=VxI. High voltage (V) enables the delivery of more power (in Watts) without raising the current (I, in Amperes). Consequently, there is less risk of overheating the conductors or supply cabling.

Summary of transformer characteristics

Regardless of type, transformers share the following features:

  • The primary and secondary coils are electrically isolated; power transfers through the induced magnetic flux.
  • Moving parts are unnecessary to transfer energy by induction, so there are no losses due to friction.
  • The AC input and output frequency are the same. In other words, transformers change voltage – but not frequency.
  • Some electrical losses arise due to heat generated by current circulating in the windings. Known as copper losses, the dissipated energy is not excessive. Nonetheless, it is the most significant type of attenuation.
  • Due to lags between magnetic fields and electrical flux alternations, core energy losses arise from eddy currents and hysteresis.

Most transformers output 94 to 98 per cent of their input power at full load.


Successful Coil Winding Takes Precision and Control

Tuboly-Astronic offers three decades of experience and expertise to clients in the engineering, manufacturing and medical sectors. Our goal is to equip clients with reliable, high-quality components for maximum efficiency. For further details, please see here. Alternatively, to discuss your equipment and service requirements, we invite you to contact us today.