torques usually present in salient pole machines? This second harmonic component of torque, especially under line-toline fault conditions, can constitute an appreciable percentage of the total torque. This is pointed out by Concordia (see reference 14 of the paper, p. 140).We feel that a more standard nomenclature might have been followed for distinction between the so-called d-c currents and the various fundamental frequency currents and their symmetrical components.The paper might have mentioned the maximum radial sole plate forces due to short-circuiting of one-half of the field poles. Our water-wheel generator foundations are always designed to meet the forces resulting from this eventuality.Mr. Ruskin's paper should stimulate a great deal of interest in the subject of generator sole plate reaction. It appears to be particularly valuable in providing the utilities with a practical method of evaluating these forces as given by the manufacturers, and in drawing attention to the magnitude of forces which may be developed by faulty single-and 3-phase synchronizing.Vernon W. Ruskin: The simplified equations include the effect of that part of the second harmonic torque, which is caused by the interaction of the rotating field due to the negative-sequence armature currents with the fundamental component of the rotor field. The simplified equations do not include that part of the second harmonic torque due to saliency, which is the reluctance torque due to the trapped armature flux in a salient pole machine.5 For a lineto-line short circuit this part of the torque can be taken care of by the K factor developed in Appendix I.As to forces due to short circuit of onehalf of the field poles, this event requires two simultaneous grounds in the rotor circuit, so that one-half of the rotor periphery is dead while the remainder is still energized. While such an o^currence is very uncommon, there have been isolated cases of trouble from this cause. The discussers ivisehy-design generator foundations to take care of this eventuality.
