• It is conventional that the current indicated by is positive when it is flowing inwards in the conductors r, y & b and outwards in r1, y1, and b1.
  • The current indicated by "Dots" are considered negative and flowing outwards.
  • The current in the three phases are represented by the curves in figure.
  • You can observe that the current in phase R is at maximum positivee value at instant a.
  • At the same instant, the currents are  negative in phases Y and B, and their magnitudes are half of maximum value.
  • These currents produce magnetic fluxes. They are represented by the dotted lines as shown.
  • The resultant flux axis is indicated by the flashing arrow NS.
  • After some milliseconds the R phase current reaches the instant b. Now, both the currents in phrases R and B will be 0.866 times the maximum value.
  • The distribution of magnetic flux due to these current is shown.
  • The axis of the magnetic field as no in line with a coin y and y1.
  • It would be observed that the line of magnetic field has turned clockwise by 30 degree from that of the instant with maximum current in the first figure.
  • At instant c the current in phase B attains its maximum negative value.
  • The current in R and Y are now both positive but their magnitudes are being has the maximum value.
  • The magnetic flux is produced by these currents are shown.
  • The axis of this flux could be seen displaced clockwise by another 30 degree compared with the previous instant discussed. 
  • so for every interval of time corresponding to any angle along the horizontal Axis axis of the magnetic flux moves forward by the same angle in space.
  • This means that the flux rotates through one revolution in one cycle,This is a synchronous speed of a two pole motor.
  • Therefore it is seen that the magnetic flux is rotating at synchronous speed inherently in a three phase induction motor.

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