Electrical Transformer, How it works ?
Transformers are capable of receiving AC power at one voltage and delivering it at another voltage. In this article, we will go through the working and construction of a 3 phase transformer by starting from its simplest form. We will also understand what is power transformer and how it is constructed.
Why Transformers are used ?
Transformers are ubiquitous devices. They are used to either step-up the A.C voltage or to step-down it. But, why should we do this voltage transformation ?. It is a science fact that a stepped-up voltage is associated with a reduced current. A reduced current leads to low eddy current energy loss. In this way, transformers help achieve better transmission efficiency while transferring the power over longer distances.Transformers help in step-up or step-down the voltage; this in turn increases the transmission efficiency After the electrical power has transmitted to the desired spot, the voltage can be reduced to the desired level, using a step-down transformer.
The Basic Working Principle
The basic working principle of a transformer is simple, electromagnetic induction. According to this principle, a varying magnetic flux associated with a loop will induce an electromotive force across it. Such a fluctuating magnetic field can easily be produced by a coil and an alternating E.M.F (EP) system. A current carrying conductor produces a magnetic field around it. The magnetic field produced by a coil. With the fluctuating nature of the alternating current, the magnetic field associated with the coil will also fluctuate.This magnetic flux can be effectively linked to a secondary winding with the help of a core. This fluctuating magnetic field will induce an E.M.F in the secondary coils due to electromagnetic induction. The induced E.M.F is denoted by ES.AC current in a coil produces a fluctuating magnetic field; this magnetic field can effectively linked to a secondary coil with the help of a coreSince the turns are arranged in a series, the net E.M.F induced across the winding will be sum of the individual E.M.Fs (eS) induced in each turn. Nsrepresents, number of turns at the secondary winding.Since the same magnetic flux is passing through the primary and secondary coils, the EMF per turn for both the primary and secondary coils will be the same.The E.M.F per turn for the primary coil is related to the applied input voltage as shown.By rearraging the above equations, it can be established that, the induced E.M.F at the secondary coil is expressed as follows.This simply means that with fewer turns in the secondary than in primary, one can lower the voltage. Such transformers are known as step-down transformers. For the reverse case, one can increase the voltage (step-up transformer).But since energy is conserved, the primary and secondary currents have to obey the following relationship.
3 Phase Transformer
Three phase transformers use 3 such single-phase transformers.
Transformers are capable of receiving AC power at one voltage and delivering it at another voltage. In this article, we will go through the working and construction of a 3 phase transformer by starting from its simplest form. We will also understand what is power transformer and how it is constructed.
Why Transformers are used ?
Transformers are ubiquitous devices. They are used to either step-up the A.C voltage or to step-down it. But, why should we do this voltage transformation ?. It is a science fact that a stepped-up voltage is associated with a reduced current. A reduced current leads to low eddy current energy loss. In this way, transformers help achieve better transmission efficiency while transferring the power over longer distances.Transformers help in step-up or step-down the voltage; this in turn increases the transmission efficiency After the electrical power has transmitted to the desired spot, the voltage can be reduced to the desired level, using a step-down transformer.
The Basic Working Principle
The basic working principle of a transformer is simple, electromagnetic induction. According to this principle, a varying magnetic flux associated with a loop will induce an electromotive force across it. Such a fluctuating magnetic field can easily be produced by a coil and an alternating E.M.F (EP) system. A current carrying conductor produces a magnetic field around it. The magnetic field produced by a coil. With the fluctuating nature of the alternating current, the magnetic field associated with the coil will also fluctuate.This magnetic flux can be effectively linked to a secondary winding with the help of a core. This fluctuating magnetic field will induce an E.M.F in the secondary coils due to electromagnetic induction. The induced E.M.F is denoted by ES.AC current in a coil produces a fluctuating magnetic field; this magnetic field can effectively linked to a secondary coil with the help of a coreSince the turns are arranged in a series, the net E.M.F induced across the winding will be sum of the individual E.M.Fs (eS) induced in each turn. Nsrepresents, number of turns at the secondary winding.Since the same magnetic flux is passing through the primary and secondary coils, the EMF per turn for both the primary and secondary coils will be the same.The E.M.F per turn for the primary coil is related to the applied input voltage as shown.By rearraging the above equations, it can be established that, the induced E.M.F at the secondary coil is expressed as follows.This simply means that with fewer turns in the secondary than in primary, one can lower the voltage. Such transformers are known as step-down transformers. For the reverse case, one can increase the voltage (step-up transformer).But since energy is conserved, the primary and secondary currents have to obey the following relationship.
3 Phase Transformer
Three phase transformers use 3 such single-phase transformers.
A 3 phase transformer can be considerred as three independent single phase transformers.
independent 3 phase transformer will require a huge amount of core material and results in a bulky design. As a result practical 3 phase transformers use a slightly different coil configuration. To make it more economical the design is used. Here, the primary and secondary coils sit concentrically. Three such concentric pairs are used in 3 phase transformer.
HV and LV windings are placed concentrically in 3 phase transformers.
The concentric windings are made to sit on three transformer core limbs . We will learn more about the core constriction in the coming sessions.
Power Transformer - Construction Features
The transformers which are used in high voltage applications are referred as 'Power Transformers'. They handle voltage in the range of 33 to 400 kV. The winding of a power transformer is quite different from that of a low voltage transformer (Distribution Transformer). We will explore the construction and connection details of the power transformer .
Power Transformer - Construction Features
The transformers which are used in high voltage applications are referred as 'Power Transformers'. They handle voltage in the range of 33 to 400 kV. The winding of a power transformer is quite different from that of a low voltage transformer (Distribution Transformer). We will explore the construction and connection details of the power transformer .
Winding Connection
The low-voltage windings of a power transformer are connected in a delta configuration and the high-voltage windings are connected in a star configuration.The low voltage winding is connected in a Delta configurationThe delta connection in low voltage windings result in 3 terminals to connect the electrical power. This is marked as 'R','Y' and 'B' . The high voltage windings are connected in a Star configurationOn the contrary, the star connection in high voltage transformer results in 4 terminals to connect the electric power.This is marked as 'r','y','b' and 'n' .. Thus, if you tap the electrical power between any pair of the phase wires the voltage further rises to root 3 times. This voltage is known as 'line voltage'. This also means that, from a 3 phase step-up transformer we can draw 4 output wires; 3 phase power wires and one neutral. If you draw power between a neutral and phase wire, that is know as 'phase voltage'.High voltage insulated bushings are required to bring out the electrical energy. It is clear that, the bushings at the high voltage side are quite bigger compared to the low voltage bushings. Insulated bushings are required for smooth transfer of electrical power
The Core Construction
The core of the transformer is made of thin, insulted, steel laminations. Such steel laminations are stacked together to form 3 phase limbs. The purpose of thin laminations is to reduce energy loss due to eddy current formation. The separated out layer blocks in the first part is a stacked layer of much thinner steel laminations. The thickness of each steel laminations varies from 0.25 - 0.5 mm. The core is made of thin insulated steel laminations; Such laminations are stacked together to form 3 phase limbs. The low voltage windings usually sit near the core. If HV windings were placed near to the cored, due to the winding's high voltage, a huge amount of insulation material would be required between the winding and core. Thus by placing the LV winding near to the core, we can save a good amount of insulation material.The output voltage of a transformer will undergo minor fluctuations due to the reasons like load variation and change in power input supply. A tapping mechanism in the secondary coil helps in regulating the output voltage to the specified limit. The tapping mechanism simply changes the number of active coils in the transformer action, thus controls the output voltage. Since more number of turns are there in the HV windings, voltage fine tuning can be more accurately controlled by providing the tapping on the HV side. This is another reason why HV windings are not placed near to the core. If they were placed near to the core, movement of tapping mechanism would have been more difficult, causing the tapping design more complex.
