Thursday, 2 January 2020

Power Transformer: Introduction, Construction, Working principle, Types, Losses

Power Transformer


A transformer transforms electrical energy from a certain voltage and current levels to another voltage and current levels keeping the frequency of supply  same.
The generation of energy is available in abundance far away from the load center and the energy so generated at economical voltage level can be transmitted at economical voltage level using transformer and the electric energy. 


Construction of transformer
Construction of transformer


  • The core gives support to the winding in the transformer. 
  • It also provides a low reluctance path to the flow of magnetic flux. 
  • It is made of laminated soft iron core to reduce eddy current loss and Hysteresis loss. 
  • The composition of a transformer core depends on such as factors voltage, current, and frequency. 


  • Mainly transformer is of two windings Primary winding and secondary winding and the magnetic core are three important parts of the transformer. These are insulated from each other.
  • The main flux  induced in the primary winding of the transformer this flux passes through the low reluctance path of magnetic core and linked with the secondary winding of transformer.
  • There are two types of windings core type and shell type.

Insulating material

  • Insulating paper and cardboard are used in transformers to isolate primary and secondary winding from each other and from the transformer core.
  • Transformer oil is also insulating material.
  • Transformer oil performs two important roles: in addition to insulating function, it can also cool the core and coil assembly.


  • The conservator conserves the transformer oil. It is an airtight, metallic, cylindrical drum that and fitted above the transformer. 
  • The conservator tank is vented to the atmosphere at the top, and the normal oil level is approximately in the middle of the conservator to allow the oil to expand and contract as the temperature varies. 
  • The conservator is connected to main tank inside the transformer, which is completely filled with transformer oil through a pipeline.


  • Moisturizing level is controlled by the breather in transformer.
  • The transformer's breather is a cylindrical container and it is filled with silica gel. When the atmospheric air passes through the silica gel of the breather, the air's moisture is absorbed by the silica crystals. 
  • The breather acts like an air filter for the transformer and controls the moisture level inside a transformer. It is connected to the end of breather pipe.

Tap changer:

  • The output voltage of transformers vary according to its input voltage and the load. During loaded conditions, the voltage on the output terminal decreases, whereas during off-load conditions the output voltage increases. 
  • Tap changers are used in order to balance the voltage variations, . 
  • Tap changers can be either on-load tap changers or off-load tap changers. 

Buchholz relay:

  • The Buchholz Relay is a protective device container housed over the connecting pipe from the main tank to the conservator tank.
  • The faults occurring inside the transformer then it is used to sense that fault.
  • It is a simple relay that is operated by the gases emitted during the decomposition of transformer oil during internal faults. 
  • It helps in sensing and protecting the transformer from internal faults.

Working principle of Transformer

  • 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. Consequently an EMF 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 (electromagnetic induction). 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.
Working principle of transformer
Working principle of transformer 

Types of transformer 

Types of Transformers based on its Phases
  • Single Phase Transformer
  • Three Phase Transformer

Types of Transformers based on its Core Design
  • Core Type Transformer
  • Shell Type Transformer
  • Berry Type Transformer
Types of Transformers based on its Core
  • Air core Transformer
  • Ferromagnetic/Iron Core Transformer

Types of  Instrument Transformer
  • Current Transformer
  • Potential Transformer
  • Constant Current Transformer
  • Rotating Core Transformer or Induction regulator
  • Autotransformer

Losses in transformer

Copper losses 
These losses occur in the windings of the transformer when heat is dissipated due to the current passing through the windings and the internal resistance offered by the windings.

Iron losses 
These losses occur in the core of the transformer and are generated due to the variations in the flux. These losses depend upon the magnetic properties of the materials which are present in the core.
It has two types:

  1. Eddy current losses 
  2. Hysteresis losses


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