Transformers are used to transfer electrical energy from one circuit to another through electromagnetic induction. They are used either to step up or step down voltage levels. A transformer is made of several different parts that function in their own different ways to enhance the overall functioning of a transformer. These include core, windings, insulating materials, transformer oil, tap changer, conservator, breather, cooling tubes, Buchholz Relay and explosion vent. The core, windings, insulating materials and transformer oil are seen in almost every transformer, while the other components are seen in transformers that are more than 50 KVA.
The core of the transformer is used to support the windings. It is made of soft iron to reduce eddy current loss and Hysteresis loss, and provides low reluctance path to the flow of magnetic flux. The diameter of a transformer’s core is directly proportional to copper loss and inversely proportional to iron loss.
Windings consist of several copper coil turns bundled together, each bundle connected to form a complete winding. Windings can be based either on the input-output supply or on the voltage range. Windings that are based on supply are classified into primary and secondary windings, meaning the windings to which the input and output voltage is applied respectively. On the other hand, windings based on voltage range can be classified into high voltage and low voltage windings.
Insulating materials like papers and card boards are used to isolate primary and secondary windings from each other as well as the transformer core. These windings are made of copper due to high conductivity and ductility. High conductivity minimizes the amount of copper needed and minimizes losses. Moreover, high ductility results in easy bending of conductors into tight winding around the core that also minimizes the amount of copper and volume of winding.
The transformer oil insulates as well as cools the core and coil assembly. The core and windings of the transformer must be completely immersed in the oil that normally contains hydrocarbon mineral oils.
The conservator is an airtight metallic cylindrical drum fitted above the transformer that conserves the transformer oil. It is vented at the top and is filled only half with the oil to allow expansion and contraction during temperature variations. However the main tank of the transformer with which the conservator is connected is completely filled with the oil through a pipeline.
The breather is a cylindrical container filled with silica gel, which is used to keep the air that enters the tank moisture-free. This is because the insulating oil when reacts with moisture can affect the insulation and cause internal faults, which is why it is a must to keep the air free from moisture. In the breather, when the air passes through the silica gel, the moisture contents are absorbed by the silica crystals.
To balance voltage variations within the transformer, tap changers are used. There are two types of tap changers – on load and off load. In on load tap changers, tapping can be changed without isolating transformer from the supply, while in off load, the transformer needs to be disconnected from the supply.
As the name suggests, cooling tubes are used to cool the transformer oil. The circulation of oil within the transformer may be natural or forced. In the case of natural circulation, when the oil temperature rises, the hot oil naturally moves to the top and cold oil moves down, while in case of forced circulation, an eternal pump is used.
Placed over the connecting pipe that runs from the main tank to conservator tank the Buchholz Relay senses the faults occurring within the transformer. It operates by the gases emitted due to decomposition of transformer oil during internal faults. Thus, this device is used to sense and in turn protect the transformer from internal faults.
The boiling hot oil from the transformer is expelled during internal faults through the explosion vent to avoid explosion of the transformer. This is generally placed above the level of the conservatory tank.