A transformer is an electrical device that can transfer and convert electrical energy from one or more electrical circuits to another, through a magnetic coupling and based on the principle of electromagnetic-induction. Transformers are widely used, both in the field of electric power and electronics. The use of a transformer in the power system allows the selection of an appropriate, and economical voltage for each need, for example the need for high voltage in long-distance electrical power delivery
The main part
A. Iron core
The iron core serves to facilitate the path of flux, which is generated by an electric current passing through the coil. Made of thin insulated iron plates, to reduce heat (as iron losses) caused by "Eddy Current".
B. Transformer coil
Several windings of insulated wire form a coil. The coils are insulated both against the iron core and against other coils with solid insulation such as cardboard, pertinax and others.
Generally, in transformers there are primary and secondary coils. When the primary coil is connected to an alternating voltage / current, then the coil arises a flux which induces a voltage, if the secondary circuit is closed (load circuit), current will flow in this coil. So the coil as a means of transforming voltage and current. The transformer has two types of coils, namely:
- Core Type
In a core type transformer, the coil surrounds the core and the construction of the core is in the form of the letter L or the letter U. The shape of the winding can be seen in (Figure 3.3).
Figure 3.Core Type Coils
- Shell Type
In a shell type transformer, the coil or winding of the transformer is surrounded by a core and the core construction is in the form of the letter E, letter I, and letter F. The shape of the winding can be seen in (Figure 3.4).
Figure 4. Shell Type Coil
C. Tertiary Coils
Tertiary coils are needed to obtain tertiary voltages or for other purposes. For both purposes, the tertiary coil is always delta connected. Tertiary coils are often used also for connecting auxiliary equipment such as synchrone capacitors, shunt capacitors and shunt reactors, however not all power transformers have tertiary coils.
D. Transformer Oil
Most of the coil-coil power transformers and their core are immersed in transformer oil, especially large-capacity power transformers, because transformer oil has properties as a heat transfer medium (circulated) and also acts as insulation (high breakdown voltage) so that it functions as a cooling and insulation media. For this reason, transformer oil must meet the following requirements:
- High insulation strength
- A good heat transfer has a small density, so that the particles in the oil can settle quickly
- Lower viscosity for easier circulation and better cooling ability
- High flash point, non-volatile which could be harmful
- Does not damage solid insulating materials
- Stable chemical properties.
E. Bushing
The connection between the transformer coil to the external network is through a bushing, which is a conductor covered by an insulator, which also functions as an insulator between the conductor and the transformer tank. based on the construction there are 2 types of bushings, namely:
solid bushing
Capacitance-graded bushing
Figure 5. Bushing
F. Tanks and Conservators
In general, the parts of the transformer that are immersed in transformer oil are (placed) in the tank. To accommodate the expansion of transformer oil, the tank is equipped with a conservator. The tank is grounded to discharge current due to magnetic field induction.
Figure 6. conservator
2. Auxiliary equipment
A. Cooler
In the iron core and the coils there will be heat due to iron losses and copper losses. If the heat causes an excessive temperature rise, it will damage the insulation inside the transformer, then to reduce the excessive temperature rise, the transformer needs to be equipped with a cooling system to channel heat out of the transformer.
The media used in the cooling system can be: air / gas, oil and water. Pengalirannya (circulation) can be by:
Natural (natural)
Pressure / force (forced).
In the natural way (natural), the flow of the media as a result of the difference in media temperature and to accelerate the heat transfer from the medium to the outside air, a wider field of heat transfer between the media (oil-air / gas) is required, by equipping the transformer with fins. fins (radiators). If a faster heat distribution is desired, this natural method can be equipped with equipment to accelerate the circulation of the cooling media with oil, air and water circulation pumps. This method is called Forced cooling.
B. Tap Changer (change tap)
Tap Changer is a transformer ratio changer to get the desired secondary operating voltage from changing primary / network voltages. Tap changer can be done either under load conditions, also called on load tap changer. At PT. Indonesia Power tap changer of this type is in the Service Transformer Unit (UST) and at the Station Service Transformer (SST) or it can also be operated in a loadless state, also known as an off load tap changer. for this type only in generator transformers.
C. Respiratory apparatus
Due to the influence of ups and downs of transformer loads
o and the temperature of the outside air, then the oil temperature will vary according to these conditions. When the oil temperature is high, the oil will expand and force the air above the oil surface out of the tank, on the other hand, when the oil temperature drops, the oil shrinks, so the outside air will enter the tank.
The two processes above are called transformer breathing. The surface of the transformer oil will always come into contact with outside air which reduces the value of the transformer oil breakdown voltage, so to prevent this, the end of the outer air connecting pipe is equipped with a tube filled with crystals of hygroscopic substances.
D. Indicators
To supervise during the operation of the transformer, it is necessary to have indicators on the transformer as follows :
- Oil temperature indicator
- Oil level indicator
- Cooling system indicator
- Tap position indicator
Figure 7. Temperature Indicator
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