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Auto transformer
- 2. INDEX ABOUT AUTO TRANSFORMER A BRIEF DIFFERENCE BETWEEN AUTO TRANSFORMER AND THE CONVENTIONAL ONE EQUIVALENT CIRCUIT DIAGRAM PHASOR DIAGRAMS PROS AND CONS APPLICATIONS
- 3. AUTO TRANSFORMER • Auto transformer is kind of electrical primary and secondary same common single So basically it’s a one transformer. • This single winding is tapped various points along its to provide a percentage of primary voltage supply its secondary load.
- 4. • Autotransformers are often used to step up or step down voltages in the 110-115-120 V range and voltages in the 220- 230-240 V range - for example, providing 110 V or 120 V (with taps) from 230 V input, allowing equipment designed for 100 or 120 V to be used with a 230 V supply.
- 5. AUTO TRANSFORMER Only one winding Self induction Power transfer, partly by process of transformation, and partly by the direct current Better voltage regulation Non-electrically insulated windings Higher efficiency Less leakage flux, resistance, impedance, losses and cost Variable output voltage CONVENTIONAL TRANSFORMER Two windings Mutual induction Power transfer through electrical transformation, due to which power losses occur Lower than auto transformer Electrically insulated windings Lower when compared to auto transformer More when compared to auto transformer Fixed output voltage DIFFERENCE BETWEEN AUTO TRANSFORMER AND A TRANSFORMER
- 8. PROs For transformation ratio = 2, the size of the auto transformer would be approximately 50% of the corresponding size of two winding transformer. For transformation ratio say 20 however the size would be 95 %. The saving in cost of the material is of course not in the same proportion. The saving of cost is appreciable when the ratio of transformer is low, that is lower than 2. Thus auto transformer is smaller in size and cheaper. An auto transformer has higher efficiency than two winding transformer. This is because of less ohmic loss and core loss due to reduction of transformer material. Auto transformer has better voltage regulation as voltage drop in resistance and reactance of the single winding is less.
- 9. CONS: Because of electrical conductivity of the primary and secondary windings the lower voltage circuit is liable to be impressed upon by higher voltage. To avoid breakdown in the lower voltage circuit, it becomes necessary to design the low voltage circuit to withstand higher voltage. The leakage flux between the primary and secondary windings is small and hence the impedance is low. This results into severer short circuit currents under fault conditions. The connections on primary and secondary sides have necessarily needs to be same, except when using interconnected starring connections. This introduces complications due to changing primary and secondary phase angle particularly in the case of delta/delta connection. Because of common neutral in a star/star connected auto transformer it is not possible to earth neutral of one side only. Both their sides should have their neutrality either earth or isolated. It is more difficult to maintain the electromagnetic balance of the winding when voltage adjustment tappings are provided. It should be known that the provision of tapping on an auto transformer increases considerably the frame size of the transformer. If the range of tapping is very large, the advantages gained in initial cost is lost to a great event.
- 10. APPLICATIONS: Compensating voltage drops by boosting supply voltage in distribution systems. Auto transformers with a number of tapping are used for starting induction and synchronous motors. Auto transformer is used as variac in laboratory or where continuous variable over broad ranges are required. required.