TRANSFORMER
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 (electro motive 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.
TRANSFORMER AND ITS TYPES |
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
- 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
- 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:
Transformers can be classified according to the insulating/cooling fluid in:
- Oil-filled transformers
- Gas-filled transformers (mainly with SF6)
- Dry-type 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
- Reactors
- Distribution transformers
- Reactors
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.
General manufacturing process of transformer:
The process of manufacturing an transformer is as
follows
1.
Winding
2.
Core building
3.
Assembly
4.
Oven
5.
Tanking
6.
Testing
Dispatch
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