MR. SACHS:-Mr. President, I do not think Mr. Lamb's motor ever takes any notion to run off the track, and I think that is rather one of the features that militates against it from the simple fact that it is mighty difficult to take it off the track. In taking off a motor from the track, in case it should be absolutely essential to do so, say for instance through accident at some intermediate points between terminals, it would be necessary to take off the pulling sheave. That pulling sheave encircles the elliptically grooved wheel say two or three times. That means so much slack cable. There must be some point where you will probably get enough slack cable to make it necessary to stop taking the motors off the line. But I should not think it would be essential at all to take any motors off the line on a system of that kind, for the simple reason that if a motor should break down, the motor going in the opposite direction would push that broken down motor back to the point it came from, and the next motor coming along would pull the waiting boat ahead. So I think there is no difficulty there. MR. PAUL G. BURTON:-I would like to ask Mr. Lamb a question about the wear of this cable in the sheaves. The method, as I understand it, is simply to make two or three bights right around the sheave in much the same manner as they are using throughout the city in these hoisting engines-what is commonly called a niggerhead" in the trade. As far as I can discover, and I have had a little oversight of machinery-there is a good deal of wear even where there is simply a rolling friction In this the cable enters on one side of an elliptical surface and goes out on the other. Consequently there must be a grinding all the time, and I would like to know what effect that has in the way of wear on the sleeve and on the cable. It seems to me it must be much more considerable than is claimed MR. LAMB:-That depends on the difference in hardness which you would have between the cable and the face of this elliptically grooved sheave. You do not of course intend to build a sheave as hard as you would have the cable and expect the cable to last longer, because the face of this sheave is made so that you can remove the part that wears very easily and put another one on. It is inexpensive. But they have a very fair life and they are much larger than the winch-head that you referred to, and the bight of the rope is different. In one case you have a large circumference; in the other you have only 12 inches diameter. It in consequence would wear much harder. The actual distance of play is not very much, and the groove is very slight because it is paying in all the time just about evenly except when it is going around a curve. The two rollers in front and in the back, guide the rope and keep it in the right place on the sheave. On the other hand, when you have got a drum that is winding up a rope and it is elliptical in its groove, it pays off and winds down the cable a long distance on the drum. We only have in one case two coils of rope on, (three coils at the most), and they are guided, and there is very little play upon the sheaves. MR. SACHS-I would like to have Mr. Lamb answer this question that I asked some time ago that is, whether it is not a fact that one of the difficulties with this rope-hauling method is that the motor acts in a very fantastic and cranky fashion; that it takes sudden notions to stop and sudden notions to go ahead, and all that sort of thing. The motor may slacken its speed and the boat may be retarded slightly. That may mean an increase of speed or it may mean a stopping of the motor. In either case it must mean the attention of the attendant on the boat at once. I would like to know if there is not some system that Mr. Lamb has devised to obviate these objections, and if they are not real. MR. LAMB:-There would not be any reason for a motor stopping or not stopping except the loss of voltage. In the case of logging I never knew that to happen. On some of the Erie traction experimental trips it did happen. Our line was connected with a street trolley line and our voltage went from nothing to 500 volts. Sometimes the motor would stop, sometimes go slow, sometimes go fast. But there is nothing in the design of the motor that would give grounds for thinking it would go faster than at other times. It MR. SACHS: It was not a question of design of motor. was a question of whether the regulating rope, the rope that you have connected from the operating controller and switch, unless you employ the rheostat for both functions, does not slacken as it certainly would. For instance, we will consider the boat and the motor propeller being propelled at a certain rate, and that suddenly you meet a curve in the line, or something of that sort, and a heavy load is put on the motor in addition to what is already carried. That would mean a slow down, especially where have not particularly excellent distribution. That slowing down must certainly mean that your rope is going to slacken and it certainly needs but very little slack in the rope to bring the rheostat back to the stop position;-at least so I should presume. MR. LAMB-What would make the motor stop, would it not be the pull of the boat, the extra heavy pull? MR. SACHS-I know-but your boat is moving forward. Its momentum is carrying it ahead at about the same speed as the motor previously pulled it. Now the motor gradually slacks up -it meets a curve-it has got to go up a steep incline, or there is some difficulty in the propelling machinery, and it slows down. That means that the boat is carried ahead and will be carried ahead for a few moments. But the motor is gradually slowing; that means that the rheostat is going back to where it started, and it means that the man has got to come forward and pull it. MR. LAMB:-That would not be the condition in practice. There is nothing on the line of the cableway that would stop that motor from its speed except the pull, and when the pull ceases, then you want your motor to stop, and that is the only time that the controlling rope is slack. MR. SACHS-If you are going to build a motor to overcome any possible obstruction and any possible curve at the maximum load that the motor is going to pull, you are going to have a pretty big motor. The question of weight has to be considered in the construction of carriages. THE PRESIDENT:-I think it is rather late to take up that question of the relative efficiency of hauling and propulsion. [Adjourned]. Associate Members elected by the Executive Committee, November 30th, 1897. Name. BRACKETT, BYRON B. Address. Instructor Electrical Engineering, Schenectady, N. Y. BURROUGHS, HARRIS S. 1416 Pacific Street, DE LEW, M. A. HENDERSON, ALEX. Brooklyn, Electrical and Mechanical En MOLE, HARVEY EDWARD Ass't in Engineering Dept J. G. PECKHAM, W. C. SPENCER, PAUL Prof. of Physics, Adelphi College, Ass't Engineer, Stanley Electric & VENABLE, WM. MAYO Electrical Inspector, Cincinnati WILLIS, EDWARD J. Total 9. Supt. Richmond Traction Co.. Richmond, Va. Endorsed by. F. B. Crocker. T. A. W. Shock. J. G. White. Wm. S. Barstow. Wm. E. Geyer. John A. Cabot. E. W. Trafford. A. M. Schoen Herbert Lloyd. American Institute of Electrical Engineers, SPARKING, ITS CAUSE AND EFFECTS. BY THORBURN REID. Present theories in regard to the operation of commutation and the nature of sparking, show considerable progress beyond those of a few years ago. The most important step forward was taken when the reactance of the coil under commutation was recognized as the greatest obstacle to perfect commutation, and the duty of overcoming this reactance was assigned to the E. M. F. set up by the cutting of the lines from the field by the coil under commutation. It was also recognized that this must be limited by the available reversal E. M. F. This was a long step forward, but it stopped just short of a complete explanation of the phenomena involved. This failure was due to an erroneous idea, which has fastened itself on the theory from the start, that injurious sparking was due to the cur rent sparking across the gap between the brush and the receding segment, by reason either of incomplete reversal of the current, or of over-reversal. I shall attempt to show in what follows, that sparking from either of these causes may be harmless, and that the real injury is done before the segment leaves the brush. Taking first the simplest case of commutation, that of a coil of n turns with its ends connected to adjacent commutator segments, we may state the operation of perfect commutation thus: First, consider a coil which is approaching a brush through which the current is entering the armature from the outside cirquit. The brush covers the segment connected to one end of this coil, and half of the brush current is passing through the coil from segment 3 to segment 2 (Fig. 1), the other half from segment 3 to segment 4. Second, consider this coil receding from the brush, which now covers segment 2, as shown in Fig. 5. Half of the brush current is now passing through the coil from segment 2 to segment 1, the other half passing through the next adjacent coil from segment 2 to segment 3. The current in the coil 3-2 now has the same value under the conditions shown in Fig. 5, as it had before in Fig. 1, but its direction of flow through the coil has been reversed. Between these two positions of the coil with reference to the brush, the whole operation of commutation has taken place, requiring generally but a very small fraction of a second. Fig. 2 shows the first operation in commutation. The two ends of the coil are now connected through the brush, and the current passing around the left hand circuit of the armature has two possible paths, the one through segment 2, the other through segment 3. The amount of current which will flow from the brush direct to segment 2 depends on the difference of potential between the brush and segment 2, and on the resistance of contact area of segment 2. Since the difference of potential of any two points in a circuit is the same through whatever path the current flows, this D. p. is equal to the algebraic sum of the potentials reckoned from the point of contact of the brush with segment 2 to the point of contact of the brush with segment 3, across this contact |