Power Transformer Construction and Operation

A transformer is electrical equipment or device that converts voltage from one voltage level to another while ideally retaining input and output power the same. There are various types of transformers depending on the basis of classification. To broad classification is on construction and purpose or use. On the basis of purpose, we have; power transformer, distribution transformer, instrument transformer, isolation transformer to mention a few. In this article, we will discuss on the power transformer.

power transformer application, Construction and Operation
Power Transformer

What is a Power Transformer?

A power transformer is designed to convert power from one voltage level to another. It’s usually used in power transmission from the generation station to the distribution station. One power transformer sits at generation substation it steps up the voltage of input power from the generator and its output is connected to the transmission line. On the far end of the transmission line –near the load center- a step-down power transformer lowers the voltage and output are fed to the distribution circuit.

Further classification of a Power transformer is based on two parameters i.e the input and output voltage rating and the power rating. Simply stated, these transformers are used in power transmission circuits.

Construction and Operation

The functionality of every device owes to how it is constructed. Transformers work on the principle of magnetic induction. Two circuits are magnetically connected but electrically separate. Two winding are magnetically connected by a magnetic core. When the primary winding is connected primary circuit and powered, power is induced secondary winding. This is the principle behind the use of this transformer. The ratio of primary and secondary turns gives the voltage transformation.

A step-up machine will have more turn in the secondary side than primary and vice versa is true. Because of the high voltage rating (in Kilovolts) there is high insulation of live parts. The transformer can be in a single-phase or three phases, however, due to the efficiency of the three-phase machine in large power, they are mostly in three phases. Further components may be incorporated for efficiency such as cooling mechanisms. This transformer is usually ground-mounted and of outdoor installation.

To transmit large power at this voltage will mean a large current in the transmission. This will require large conductors to be employed and at the same time heavy transmission losses. Given power equal product of voltage and current and losses in conductor equal product of current squared and resistance, we can therefore lower current by raising the voltage at constant power. At generation, step-up transformer raises the voltage and lowers current for transmission. On the distribution station, it steps down the transmission voltage for distribution. Small current in transmission will allow the use of small conductors to transmit large power. This has three major advantages;

  • Low current power transmission which reduces power losses and heating of conducting.
  • Improved voltage regulation by reducing voltage drop along with transmission.
  • Small conductors being able to carry large amounts of power.


The device works optimally near full load. This is partly because the load does not vary much owing to the fact that it serves a large pool of consumers. It’s online 24 hours a day 7 days of the week, only at maintenance is the load transferred to other transformers. Today a load of a single machine can go up to several thousands of megawatts. 

Power Transformer Applications

  • The step-up voltage at the generation station for transmission at low current.
  • Step down high transmission voltage at the distribution station for supply to consumers.


Power transformation has been extension been used since their invention in the 1880s. They were a solution to the problem of power transmission where generation station and load center were far apart. Today power is conveniently transmitted at a minimal loss at thousands of kilometers to consumers. As countries and regions construct an interconnected network of power transmission, this machine sits to be the enabler of the project. The article was a summarized overview, for in-depth knowledge the reader is advised to read relevant books.

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