TRANSFORMER AND ITS TYPES: Transformer is a static device which converts electrical power from one circuit to another without changing its frequency. It Step up (or Step down) the level of AC Voltage and Current.
Transformer works on the principle of mutual induction of two coils or Faraday Law’s Of Electromagnetic induction. When current in the primary coil is changed the flux linked to the secondary coil also changes.
Hence an EMF (electromotive force) is induced in the secondary coil due to Faraday law’s of electromagnetic induction.
The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism), and, second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil.
Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.
Classification of Transformer
As mentioned above, transformers perform a very simple function and they can have many applications. Transformers are used in every power plant, all grid substations, buildings, in the industry, the underground installations, wind turbines, on platforms, marine vessels, under the sea, etc.
Due to peculiarities of all these applications, many different types of transformers have been developed in the course of history. To simplify the overview of many transformer types, it is useful to have some kind of systematic classification.
However, this is not easy to do because there are many ways of doing it. The transformer types could be classified according to their power rating, voltage, current, weight, type of cooling etc., but such approach would have a limited applicability.
Probably the simplest and the clearest transformer classification is according to the number of phases in:
– Single-phase transformers
– three-phase transformers
In a three-phase system, the single-phase units are used in a bank of three transformers linked together. A single three-phase transformer costs approximately 15% less and occupies less space than one unit of three single-phase transformers within the same tank.
However, due to limitations during the manufacturing and mainly transportation, particularly of large units, the transformers sometimes must be produced as single-phase transformers. Another reason for using a single-phase unit rather than a three-phase unit, is the possibility of having a fourth identical unit as a spare.
Despite its simplicity and clarity, this type of classification does not overly help in classification of the whole transformers family.
Classification according to basic technology of a transformer design and manufacturing is also often used. There are two main technologies for designing and manufacturing the transformers:
– Core type
– Shell type
In a shell-formed transformer, the primary and secondary windings are quite “flat” and are positioned on one leg surrounded by the core.
In a core-formed transformer, cylindrical windings are like “coils” and cover the core legs. However, this classification is also limited in the large portfolio of either of those two transformer types.
Transformers can be classified according to the insulating/cooling fluid in:
– Oil-filled transformers
– Gas-filled transformers (mainly with SF6)
– Dry-type transformers
In oil-filled transformer is immersed in oil and the heat generated in the cores and the windings is passed on to oil by conduction.
Oil in contact with the surface of windings and core gets heated up and moves towards the top and is replaced by the cool oil from the bottom.
The heated oil transfers its heat to the transformer tank through convection and which in turn transfers the heat to the surrounding air by convection and radiation.
As the dry-type, and particularly gas-filled/insulated transformers have limited applications in a large power system, this classification is also not perfect.
Despite not being a perfect one, perhaps the most practical classification used by the industry is the one according to the transformer application. According to this approach, transformers can be roughly classified as:
– Power transformers
– Distribution transformers
This classification could, however, raise some questions. There are no obvious technical reasons for classifying a transformer as a distribution transformer rather than a power transformer but it is widely used in practice, and it is helpful.
The term “distribution transformer” is somewhat used in the IEC 60076, while it is commonly used in IEEE C57. Some companies define distribution transformers as the power transformers below 10 MVA. The 2.5 or 5 MVA limits are also used elsewhere instead of 10 MVA.
TRANSFORMER AND ITS TYPES
Types of Transformers
Based on above classification, ‘the transformers are as following types’.
1 Oil cooled Transformer
2 Dry-type Transformer
3 Power Transformer
4 Furnace Transformer
5 Converter Transformer
6 Regulating Transformer
7 Distribution Transformer
8 Pad-Mounted Transformer
9 Multi-Phase Transformer
1 Specialized transformer
Depending on the requirement, specification, working conditions, area of working etc., an specific transformer is selected for the above types of transformers.
The general manufacturing process of the transformer
The process of manufacturing a transformer is as follows
2. Core building