TRANS ACTIONS OF SECTION G. 479 



developed by the writer of this paper. In the latter type of gear two magnetic 

 clutches are employed, these being fitted at opposite ends of the motor ; and, as 

 no gearing is kept continuously in motion, the wear and tear, as well as the cur- 

 rent required, are reduced to a minimum. The clutches prevent the shock of the 

 sea being transmitted to the electrical system, and as they have considerable 

 flywheel effect, the current taken by the motor does not fluctuate widely under 

 normal conditions, and the steering gear may therefore be supplied from the 

 ship's lighting generator. To economise power it is advantageous to arrange the 

 gear so that greater leverage is obtained when the rudder is hard over than when 

 amidships, and by doubling the leverage in this manner a saving of 30 per cent, 

 may be made in the motor power. Drawings were shown of a steering gear 

 suitable for an ll-^-inch rudder-post, and of a smaller gear of the same type, 

 built by Messrs. Brown Brothers & Co., Ltd., of Rosebank, Edinburgh, suitable 

 for a 7-inch post. When tested against an artificial hydraulic load the latter 

 gear developed a torque of 50 foot-tons at the rudder-post and showed an 

 efficiency of over 50 per cent, at half load. It was found capable of moving the 

 tiller through 70° in 25 seconds and responded to motions of the hand-wheel 

 equivalent to 1° of helm. 



3. The Single-phase Repulsion Motor. 

 By Thomas F. Wall, M.Sc, M.Eng., Assoc.M.Inst.C.E. 



The single-phase repulsion motor partakes partly of the nature of a trans- 

 former and partly of the nature of a synchronous machine, and this dual effect 

 gives rise to certain difficulties of treatment which are further complicated by 

 the fact that the flux distribution in the air gap is not sinusoidal. 



In the first part of the paper expressions were deduced for the following 

 quantities (the flux distribution in the air gap being taken as triangular or 

 trapezoidal as the case may be) : — 



1. The E.M.F. induced in the stator winding due to an alternating current 

 in that winding. 



2. The E.M.F. induced in the rotor winding due to an alternating current in 

 the stator winding. 



3. The E.M.F. induced in the rotor winding when rotating in the field due to 

 an alternating current in the stator winding. 



4. The E.M.F. induced in the stator winding due to an alternating current in 

 the rotor winding. 



5. The E.M.F. induced in the rotor winding due to an alternating current in 

 that winding. 



Curves were given which have been deduced from the expressions for Nos. 

 2, 3, and 4, and which enable the values of these E.M.F.s to be rapidly deter- 

 mined for any value of the displacement of the rotor brushes from the stator axis. 



In the second part of the paper the above results were employed in develop- 

 ing the theory of the repulsion motor. The theory cannot be explained in a few 

 words, but it results in the establishment of a series of simultaneous equations, 

 the solutions of which give expressions for the speed, stator current, power 

 factor, and power of the motor. It was shown that, if the vector of the applied 

 pressure be drawn in the direction of the ordinate axis, the extremity of the 

 current vector moves over the circumference of a circle which passes through 

 the origin, and that diameter which passes through the origin is inclined to the 

 abscissa axis at a certain angle, the magnitude of which depends upon the resist- 

 ance and the leakage reactance of the rotor winding. The torque and power of 

 the motor are respectively represented by the distance of the extremity of the 

 current vector from certain lines. The speed is given by the intercept of the 

 current vector on a line drawn at 90° to that diameter of the circle which passes 

 through the origin. 



In the third part of the paper the results of some tests on a 6-b.h.p. motor 

 were given, and the agreement of the values of the stator current, the power 

 factor, and the speed as deduced from the theory, and the values determined 

 from the test was shown in the form of curves. The curves have been plotted 

 with the speeds as abscissae. 



