Fig. 1,414.—Section of armature and field showing strengthening effect of armature reaction when the current leads the pressure. If the circuit contain an excess of capacity the current will lead the pressure, so that when the coil is in the position of zero induction, as shown, the current will have come to rest and reversed. Accordingly, lines of force (indicated by the dotted lines) are set up by the current flowing through the coil and which are in the same direction as the lines of force of the field, thus strengthening the latter.
Ques. What would be the effect if the current lead the pressure?
Ans. It would tend to strengthen the field as shown in fig. 1,414.
The value of the armature ampere turns which tend to distort and to diminish or augment the effect of the ampere turns on the field magnet is sometimes calculated as follows:
| .707 × I × T × P | ||
| A | = | |
| s |
in which
- A = armature ampere turns;
- I = current per phase;
- T = turns per pole per phase;
- P = number of phases;
- s = product of the distribution and pitch factors of the winding.
This value of ampere turns, combined at the proper phase angle with the field ampere turns gives the value of the ampere turns available for producing useful flux.
