Explain with the neat circuit diagram only the scott connection scheme for conversion of three phase supply to two phase supply. Name one application of the same.

Explain with the neat circuit diagram only the scott connection scheme for conversion of three phase supply to two phase supply. Name one application of the same.
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1 Answer

Answer :

Three-phase to Two-phase Transformation (Scott Connection of Transformers):

image

Working:

i) Scott connection can be used for three-phase to two-phase conversion using two single-phase transformers.

ii) Scott connection for three-phase to two-phase conversion is as shown in figure.

iii) Point 'O' is exactly at midpoint of winding connected between phases Y & B.

iv) The no. of turns of primary winding will be √3/2 N1 for Teaser and N1 for main transformer. The no. of secondary turns for both the transformers are N2.

v) When three-phase supply is given to primary, two-phase emfsare induced in secondary windings as per turns ratio & mutual induction action.

vi) It is seen that the voltage appearing across the primary of main transformer is V1M = VL i.e line voltage. The voltage induced in secondary of main transformer is V2M which is related to V1M by turns ratio N1:N2.

vii) From phasor diagram it is clear that the voltage appearing across the primary of Teaser transformer corresponds to phasor RO which is √3/2 times the line voltage VL. Due to this limitation, the turns selected for primary of Teaser transformer are not N1 but √3/2 N1 . This makes the volts per turn in teaser transformer same as that in main transformer and results in voltage induced in secondary of teaser transformer same as that in main transformer, i.e V2T = V2M. As seen from the phasor diagram, the output voltages to the two loads are identical. 


Applications: 

i) The Scott-T connection is used in an electric furnace installation where it is desired to operate two single-phase loads together and draw the balanced load from the three-phase supply. 

ii) It is used to supply the single phase loads such as electric train which are so scheduled as to keep the load on the three phase system balanced as nearly as possible. 

iii) The Scott-T connection is used to link a 3-phase system with a two–phase system with the flow of power in either direction. 

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