Transformer Basics
Transformers are crucial electrical components that transfer electrical energy between different circuits.
They have made significant progress over the years, revolutionising the energy sector and facilitating the effective transmission and distribution of electricity.
The history of transformers, from their modest beginnings to present times, proves human ingenuity and the constant pursuit of innovation in the field of electrical engineering.
- A transformer only works with alternating current (AC), not with direct current (DC)!
- The AC supply is connected to the primary side --> the alternating current creates a alternating magnetic field --> the voltage induced by the magnetic field in the primary winding keep balance with the supply voltage (=induction law)
- Through the iron core the magnetic flux is conducted to the secondary side
- Now the secondary winding is also permeated with a changing magnetic field --> this induces an AC voltage in the secondary coil
- The induced voltage is the same in each turn / the induced voltage of both coils is proportional to the number of their turns = transformer ratio
[Translate to Spain:] Basic construction of a transformer
- Consists of two or more coils on a common iron core
- The core is built from a stack of individual sheets, with electrically insulation layers in between --> thus reducing eddy currents
- Primary winding = input winding --> voltage connection
- Secondary winding = output winding --> here is the electrical load connected
Different construction types
Shell type
Both windings are on the middle leg, either one above the other ore side by side.
Advantages:
- Higher efficiency
- More power
Disadvantages:
- Maintenance work is very hard
- Forced cooling indispensable
Core type
The middle leg is missing, the core forms the shape of a rectangle in side view. Usually, the windings are located separately on the two outer legs.
Advantages:
- Cheaper
- Easier maintenance
Disadvantages:
- Higher flux leakage
- Consists of only one coil which has one or more taps to draw the output voltage
- Primary coil and secondary coil are combined
- No galvanic separation
Advantages:
- Smaller construction with the same power
- More efficient compared to two windings transformer
Disadvantages:
- If a fault like a short circuit occurs on the primary side, this fault is also on the secondary side, because they are combined
Area of application:
Wherever deviating voltages have to be provided and galvanic isolation is not required.
In reality there is no loss-free transformer
- Losses due to resistances in the windings and parasitic capacitances
- Losses in the metal structure caused by scattering of the magnetic flux
- Eddy currents and magnetic reversal losses in the iron core
This results in energy losses.
The efficiency indicates the ratio of the power which leaves the transformer on the secondary side and the power which flows in on the primary side. That means how much energy gets "lost".
The higher the efficiency, the fewer the lossesand the more efficient the transformer works.
The efficiency can, because of the iron and copper losses never be 1. It is expressed in %.
Formula for calculation
Typical efficiency of different transfomers:
- Transformers with high rated power: 99%
- Small transformers: 80%
- Miniature transformers: 50%
The voltages, currents and the windings can be calculated with the formula below.
V = Voltage in Volt (V)
I = Current in Ampere (A)
N = Winding turn number
The ratio of the input and output voltage corresponds to the ratio of the winding turn numbers of the input and output sides.
V1 = input voltage; V2 = output voltage; I1 = current primary side; I2 = current secondary side; N1 = Number of windings primary side; N2 = Number of windings secondary side
