Power transformers are electrical components used in a variety of residential, commercial, and industrial applications to transfer energy between circuits with the help of electromagnetic induction. These equipment have a primary and secondary winding with varying magnetic fields that induce a varying electromotive force or voltage. Depending upon the application, power transformers can step up or step down the voltage level within the power network.
Power transformers in India are generally used where large amounts of electrical energy or voltage levels are required. They are widely used in power stations, transformer stations, industrial operations, auxiliary plants, reactors, etc. One of the major applications of power transformers is to raise the voltage of electricity before being transmitted across long distances through wires. It is this property that leads to economic transmission of power supply over long distances across the nation. Such transmission also reduces power loss to a great extent due to lower current. Depending upon the application to be used in, the type of power transformer is chosen. There is a long list of power transformer types that one can choose from, which includes step-up, step-down, high-voltage, low-voltage, current, isolation, dry-type, and oil-filled transformers.
Parts of a power transformer
Core
The most important part of a power transformer – the core – is used to support the windings within the transformer. It is generally a soft iron core that reduces eddy current loss and Hysteresis loss. Its dimension is directly proportional to copper loss, and is inversely proportional to iron loss. The core provides low reluctance path to the flow of magnetic flux.
Windings
As mentioned above, power transformers comprise of primary and secondary winding that are insulated from each other. They are comprised of several turns of copper coils bundled together, with each bundle connected in series to form a winding.
Conservator
This is a metallic air-tight cylindrical drum fitted above the transformer with a vent at the top that conserves the transformer oil. The normal oil level is approximately half of the conservator height so as to provide space for the oil to expand and contract as the temperature varies.
Breather
This is a cylindrical container filled with silica gel that absorbs the moisture from the atmospheric air within the transformer. With the temperature variations, moisture can arise, resulting in pressure changes, which is not controlled, can lead to internal faults. Thus, it is very important to keep the tank moisture-free, and this is where the breather helps.
Cooling tubes
As the name suggests, cooling tubes are used to cool the transformer oil. The oil is circulated through these tubes, either naturally or forcefully. In natural circulation, the rise in temperature oil raises the hot oil to the top and sinks the cold oil downward. And, in forced circulation, an external pump is used for the same.
Buchholz Relay
This is a protective container placed over the connecting pipe from main tank to the conservator tank. This device senses the faults occurring within the transformer, thus protecting it.
Tap changer
This is the equipment that balances the voltage variations. Off-load or on-load tap changers are used. In off-load tap changers, the transformer is required to be separated from the supply, which is not the case with on-load tap changers.
Explosion vent
This device, placed above the level of the conservatory tank, is used to expel the boiling oil in the transformer in case of heavy internal faults, to avoid transformer explosion.
Insulating materials
Insulating paper and cardboard are other important parts of a power transformer that isolate the winding's from each other, and from the transformer core too. Another insulating material is the transformer oil, into which the core and winding's are completely immersed.
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