Fig. 1,552.—Radial diagram of three phase wave winding with star connection.
Ques. In a three phase star connected alternator what is the value of the current in each line?
Ans. The same as the current in each phase winding.
Figs. 1,553 and 1,554.—Gramme ring armatures showing three phase star and mesh connections, respectively, with direction of currents in the coils. In the figures, the coils A, B, C, are spaced at equidistant positions on the ring core. The arrow heads represent the directions of the induced pressures or currents for the position shown, the rotation being clockwise. In coil A the pressure is increasing, in coil B it is diminishing, but is in the same direction as in A, whereas in coil C it is also diminishing, but is in the opposite direction to what it is in coils A and B. As the rings rotate the three coils have similar alternations of pressure induced in them, but differ in phase. If a, b and c be joined to collector rings three phase currents can be supplied to the outer circuits. In fig. 1,553 at the instant represented a and b are giving their current to their lines, while c is receiving from its line a current equal to the sum of a and b. In fig. 1,554, at the instant represented, the currents sent out from a will be equal to the sum of the currents in x and y, and intermediate between them in phase. The current from b will be equal to the difference of the currents in z and y, and of intermediate phase, while similarly the current received by c will be equal to the sum of the currents in x and z.
Ques. What is the value of the total output in watts of a star connected alternator?
Ans. It is equal to the sum of the outputs of each of the three phases. When working on a non-inductive load, the total output of a star connected alternator is equal to √3 multiplied by the product of the line current and line voltage.
Ques. What is the value of the line voltage in a three phase delta connected alternator?