Three phase transformers is often used for power distribution systems, it is made of three sets of primary and secondary windings, each set wound around one leg of an iron core assembly, essentially it looks like three single phase transformers sharing a joined core as shown down below. or it can be formed by by connecting together three single-phase transformers, thereby forming a so-called three phase transformer bank.
The principle of operation is exactly the same as single phase the core of the transformer works to direct the path of the oscillated magnetic field between the primary and secondary coils to prevent wasted energy, once the magnetic field reaches the secondary coil, it forces electrons with in it to move, creating an electric current via electromotive force.
The combinations of the three windings may be with the primary delta-connected and the secondary star-connected, or star-delta, star-star or delta-delta, depending on the transformers use.
Components of three phase transformer:
Core#
the core of the transformer is made of thin insulated steel laminations, they are stack together to reduce energy loss due to eddy current formation.
Windings and insulations#
Insulations are used between the high voltage and low voltage windings to prevent the short circuit.
Tank or Box#
it is used to protect the core and windings from external environment.
Terminals and Bushings#
for connecting incoming and outgoing cables, terminals are mounted upon bushings and connected to the ends of windings
Bushings are insulators that form a barrier between the terminals and the tank.
Oil conservator#
there is transformer oil inside the tank used to provide better heat dissipation as well as more insulations between conducting parts. the oil expands and contracts with temperature variations, the
oil conservator provides adequate space for oil expansion. it is connected to the tank through a pipe. a level indicator is fitted to the conservator to indicate the oil level inside.
Breather#
it is used to remove moisture from the air in the transformer oil, as the air flows in and out of the conservator removes the moisture before entering the conservator.
Radiators and fans#
they are mounted on the transformer tank for cooling purpose.
Explosion vent#
it acts as an emergency exit for oil and gases inside the transformer. it is a metallic pipe with a diaphragm at the end, when failure occurs, the diaphragm ruptures at a relatively low pressure to release the forces out to the atmosphere.
Tap changers#
they are used to adjust the secondary voltage of transformer, they are designed to change the turn ratio of the transformer as required, some of them can be changed online and offline.
Buchholz relay#
when faults accrues inside the transformer like short circuit which leads to high temperature, the high temperature will transfer the gas into carbon monoxide , methane , the Buchholz relay senses these gases and activates trip and alarm circuits.
