These two types of transformers, step-up and step-down transformer, are used to step up the voltage from low value to high value according to the turns ratio of primary and secondary windings.
[This video can help you understand, although we will explain it later.]
Step-up Transformer
This transformer has less primary winding than secondary winding, so we find that the current that flows through primary winding is greater than secondary winding.
Considering the following variables:
According to this equation, a step-up transformer is;
(For an ideal transformer, that means no losses in power)
Such that :
So, Power in primary = Power in secondary (for an ideal transformer)
As example :
A single-phase ideal transformer of 100 watts with a primary winding of 5 turns and a secondary winding of 20 turns, and a primary voltage of 100 volts. How do you calculate the currents at primary and secondary sides and voltage at the secondary side? Here is the answer.
Solution:
Then
So
For an ideal transformer :
Power in primary = Power in secondary (for an ideal transformer)
So
According to this explanation, you must deduce that step-up transformers are present in power plants that operate megawatts of power. Also, in machines that require high voltage to work like X-ray and micro-wave.
Step Down Transformer
This transformer has greater primary winding than secondary winding. We find that the current that flows through the primary winding is less than the secondary winding. The primary voltage is higher than the secondary voltage, making step-up transformer the best in domestic consumption.
Now you may be asking, can we use the same transformer of step-up or step-down transformer at the same time? In other words, if I have a step-up transformer, can I use it as a step-down transformer and vice versa?
As we mentioned earlier, the transformer’s main task is stepping up or stepping down the voltage from the primary side to the secondary side, assuming that losses are eligible.
Any transformer designed as a step-up or step-down transformer has a primary and secondary winding designed to carry a specified current. So, if I have a step-up transformer of 1000 watt with this parameter:
So,
Then …. Ip = 10 amperes ( so we use wires for these winding with cross-section area withstand this current )
For
So
For an ideal transformer :
Power in primary = Power in secondary (for an ideal transformer)
So
So we use wires for these winding with cross-section areas withstand this current.
From the previous example, we conclude that if I use a step-up transformer as a step-down transformer, the secondary winding (now it primary) will burn because these winding are designed to withstand less current.
So, we can’t use a step-up transformer as a step-down transformer and vice versa.
Applications of a Step-up and Step-down Transformer
Step-up transformers are used at the power plant to decrease currents before the transmission process along transmission lines.
Step-down transformers are used at substations to decrease voltage to distribute to customers.
