Transformers are essential in electrical power transfer from higher power rating to lower rating or vice versa. Thus, it is wise to learn about the parts of a transformer.
Transformers can be divided into step-up transformers and step-down transformers. We will not learn about them at the moment, let us spare them for another time. Now we will learn about the important parts of a transformer.
Parts of a Transformer
A transformer is built from many different parts with their specific functions to make sure it works very well. If we have learned or read about a transformer we will remember that a transformer is built from: core, primary winding, and secondary winding. They are not wrong but it is not completely true.
The terms of core, primary winding, and secondary winding will always be used when we try to do mathematical analysis. When it comes to “physically built from”, there will be more than them.
Below are the parts of a transformer and their functions:
Frame made from insulated material like cellulose paper (wood). We use this to place the laminated sheet.
We place several iron plates to make a laminated and insulated iron core above the insulated frame. This stacked iron plate is the magnetic circuit and able to reduce the iron losses and eddy current losses.
We assembly the laminated sheets in series to make the laminated core. The thickness needs to be calculated thoroughly. The core is the part where we place the copper windings. It is usually made from iron to reduce current loss and Hysteresis loss. The iron material has low reluctance against the flow of magnetic flux. From the mathematical analysis, the core’s diameter is proportional to copper loss and inversely proportional to iron loss.
Limb is used to place the windings.
Windings can be made from copper wire formed in a coil and bundled together. The bundle is connected to each other to form a winding. Windings will be divided into primary winding and secondary winding.
The primary winding is connected to the supply circuit (input) while the secondary winding is connected to the load circuit (output). It is also different between high voltage winding and low voltage winding. We place the primary windings and secondary windings on the limbs and separate each other using insulating sheets.
The insulating sheets will protect the windings from each other along with the core. The windings are made from copper wire formed in a coil. The copper itself has high conductivity and ductility. High conductivity means less needed copper and losses. High ductility means easier bending for conductors to become a tight winding around the core and reduces the needed copper and winding volume.
The tank will protect all the parts inside it, the cores and windings from the atmospheric effect. The windings will be placed inside it.
Conservator is usually made from metallic material with the shape of a drum and placed on top of a transformer. It is half-filled with oil for expansion and contraction when temperature changing happens. Conservator in the transformer contains the insulation oil. It has a level indicator and silica gel to absorb water content. Oil in the transformer covers all parts of a transformer, thus high voltage and low voltage coils are immersed in oil.
There are two types of insulation: solid (cellulose paper) and liquid (oil).The purpose of insulation is to prevent contact between coils which can cause short-circuit and faulty, along with spark. Conservator is mounted on the top of a transformer.
This oil is mainly used for cooling and insulating purposes. What parts of a transformer which need to be cooled down and insulated? Of course the core and coils. This oil usually contains hydrocarbon mineral oils.
Breathers or silica gel breathers are commonly used or even mostly used to fit inside the conservator of the oil filled transformers. Silica gel breather is used to absorb the moisture in the air sucked in by the transformer during the transformer breathing activity.
The moisture sucked in inside the transformer can cause faulty because the insulation is affected. The silica crystals absorb the moisture inside the air when it passes through the silica gel.
The Buchholz Relay is used to sense the faulty in the transformer. This part is installed between the transformer tank and conservator. This is the type of gas actuated relay and able to detect faults at an earlier stage than any other protection types.
Explosion vent is installed above the conservator tank. It is used to expel boiling hot oil from the transformer when internal faults occured to prevent the transformer from exploding.
The name already implies its function as a part of a transformer. What does a cooling tube cool? The cooling tube cools the transformer oil used in the conservator. The cooling protocol is divided into natural and forced. The natural cooling will make the cold oil move down when the hot oil moves up. For the forced cooling we will use an eternal pump.
Tap changer is used for changing transformation ratio to produce secondary operating voltage which is better than changing the primary operating voltage. It is essential for the power grid to meet the quality of service voltage by changing the transformation ratio so it can produce desired output voltage.
When the tap changer is used it will be either on-load or off-load. For an on-load changer we don’t need to disconnect the transformer from the input while for the off-load changer we need to disconnect the transformer from the input.
Low and High Voltage Bushing
Bushing is used as an insulation between generated voltage from windings inside the transformer to deliver it to the power grid. This will minimize the contact risk with the atmosphere and cause a short circuit. Bushing is usually made from ceramic. Bushing also gives insulation between conductor and earthed tank.
Pictures source: (YT) LearnEngg: Construction of three phase transformer