In this article, we will discuss why a step up transformer is used to transmit electrical energy. A Step-up transformer increases the voltage in its secondary when voltage is fed to its primary without changing the frequency and power. The power at primary and secondary remains the same. The step-up transformer increases the secondary voltage, and in the same proportion to the increased voltage, it decreases the secondary current. Thus, the power remains the same.
How does a step-up transformer increase the AC Voltage?
The voltage induced in the primary and secondary depends on the number of turns used in the primary and secondary. The voltage induced is directly proportional to the number of turns.
In a step-up transformer, the secondary voltage is more than the primary voltage. (E2>E1). It is possible when the number of turns in the secondary is more than the number of turns in the primary. Thus, in a step-up transformer,
N2 > N1
Applications of a step-up transformer
A step-up transformer is used to boost voltage at the generation end and transmit electrical energy over a long distance. The following advantages are achieved when the power is transferred at a high voltage through the transmission line.
a. Reduced line losses
The current gets reduced in the same proportion as the increased voltage. For example, if the voltage is 3 times increased, the current will be 1/3 rd times the current at a lower voltage to deliver the same power. The line loss is proportional to the square of the current. In this case, the line loss will be 1/9th of the line losses with lower voltage transmission. If generation power 5MW is to be delivered at 11 kV voltage at unity power factor, then the current is equal to;
If the same power is to be delivered at 33 kV, then the current is equal to
Thus, the current at 33 kV is 1/3 rd of the current at 11 kV.
The line loss is equal to;
Thus, by increasing transmission voltage 3 times, the line losses become 1/9th.
b. Reduced Voltage drop
The voltage drop in the transmission line at 11 kV,262 amperes, is,
The voltage drop in the transmission line at 33 kV,87 ampere is;
Reduction in Voltage drop
c. Improved Voltage Regulation
The decrease in a voltage drop at a higher voltage causes less difference between the sending and receiving end voltage. Thus, voltage regulation at higher voltages is better.
A Step-up transformer is also used in X-ray machines and electrostatic precipitators(ESP).
Step-down Transformer
A Step-up transformer decreases the voltage in its secondary when voltage is fed to its primary without changing the frequency and power. The power at primary and secondary remains the same. The step-down transformer decreases the secondary voltage in the same proportion of the decreased primary voltage, and it increases the secondary current. Thus, the power remains the same.
In a step-down transformer, the secondary voltage is less than the primary voltage (E2<E1). It is possible when the number of turns in the secondary is less than in the primary. Thus, in a step-down transformer,
N2< N1
A step-down transformer utilizes the power at an equipment-rated voltage level. It is used for distribution and isolation purposes.
Author: Satyadeo Vyas