These two windings are magnetically coupled and electrically isolated. But the transformer in which a part of windings is common to both primary and secondary is called Autotransformer. The input to the transformer is constant but the output can be varied by varying the tapings. The autotransformer is both the most simple and the most fascinating of the connections involving two windings.
Uses and styles[ edit ] The Autotransformer motor starting apparatus is relatively simple compared to solid-state variable frequency drives. Since it does not contain any power electronics devices, the output waveform is a sine wave with no additional harmonic distortion or switching waveforms.
No special shielding or cable length limitations are created. Cooling requirements are similar to those of a transformer or switchgear. The write application of autotransformer starter provides the maximum torque with a minimum of line current.
Transformer manufacturers, switchgear manufacture and a European design organization could not give a clear reason for the failures. The transient is of a very short duration, less than 5 microseconds and occurs when the motor current from the secondary of the autotransformer is forced to the line voltage.
Figure 5 Michael Faraday D. S, in published a paper on his discovery of electromagnetic induction which is the time rate of change of the magnetic flux with a coil induces a voltage in that coil, the amplitude of the induced voltage is proportional to the velocity of flux linkages with the coil.
The uncontrolled timing of the changeover allows the peak motor current to be switched at any point on the wave. Figure 5 shows the changeover at 90 degrees. This is a worst-case scenario, peak current at changeover, creates a very high and fast transient. The central switch circuit prevents voltage escalation, as discussed above.
It is therefore desirable to control the point on the wave at which to switch, the ideal point is when the motor amperes to the lowest value in all the active windings of the autotransformer.
A 3-coil autotransformer requires a 3 pole switch to control 3 phase voltages, an examination of figure 9 shows three sine waves displaced at degree intervals.
There appears there is no real point on the cycle where all three phases can be switched simultaneously at any equal low motor amperage without resorting to complex staggered switching methods. Figure 11 shows the motor current curves for a 2-coil autotransformer.
Line 2 is not switched. This topology is suitable for controlled switching. An inspection of the sine curves shows that at 30 degrees and degrees, both motor currents are at the same value and are in the same phase quadrant.
Therefore the magnetic core flux in first leg of the transformer is the same as the magnetic core flux in the third leg, the centre leg has no windings and its magnetic flux is of no interest.
At 30 degrees the amplitude of the motor currents supplied by the autotransformer are only half the peak motor current that occurs at 90 degrees.
The central switch therefore prevents any step-up autotransformer connection and a practicable means of controlling the switching transient to a lower value than the star connected switch.Modern Protection of Three-Phase and Spare Transformer Banks Michael Thompson, Faridul Katha Basha, and Craig Holt autotransformer application.
The figure shows switches for reconfiguring the bank.
In many applications, removable This allows us to write the ATB equations for. Other Uses and application of Transformer: It step up the level of voltage at generation side before transmission and distribution. in distribution side, for commercial or domestic use of electricity, transformer step down (decries) the level of voltage for example form 11kV to V single phase and V three phase.
Autotransformer (Auto-Transformer) is an electrical transformer in which there is one winding, a portion of which is common to both the primary and the secondary circuits. An autotransformer uses common winding and offer no interference or disturbance isolation.
Figure Autotransformer - Physical Arrangement The primary and secondary windings of a two winding transformer have Figure Kirchoﬀ’s Law Application to auto transformer As mentioned earlier the magnetizing current can be neglected, for simplicity.
Writing An autotransformer has a single winding with two end terminals, and one or more terminals at intermediate tap points, or it is a transformer in which the primary and secondary coils have part of, or all of their turns in common.
An Auto-transformer (sometimes called auto-step down transformer) is an electrical transformer with only one winding. The " auto " (Greek for "self") prefix refers to the single coil acting alone and not to any kind of automatic mechanism.