322 



PRINCIPLES OF ELECTRICAL DESIGN 



the remedy consists in providing ammortisseur or damper 

 windings on the pole faces, as mentioned in Art. 94, Chap. XIII. 

 A simple form of damper is illustrated in Fig. 134, where a num- 

 ber of copper rods through the pole face and on each side of 



FIG. 134. Short-circuited damping bars in pole face of single-phase alternator. 



the pole shoe are short-circuited at both ends by heavy bands 

 of copper. Any tendency to sudden or periodic changes of flux 

 through any portion of the pole face is checked to a very great 

 extent by the heavy currents that a small change of flux will 

 establish in the short-circuited rods. 



114. Design Sheets for Alternating-current Generator. 



SPECIFICATION 



Output, k. v.a 8,000 



Number of phases 3 



Terminal voltage 6,600 



Power factor of load 0.8 



Frequency 60 



Type of drive Steam turbine 



Speed, r.p.m 1,800 



Inherent regulation Within 25 per cent, rise when full 



load is thrown off. 



Exciting voltage 130 



Permissible temperature rise after 6 hr. full-load run 



(by thermometer) 45C. 



Ventilating fan Independently driven (not part 



of generator). 



GENERAL OUTLINE OF PROCEDURE 

 (a) .Design armature. 

 (6) Design pole faces. 



(c) Draw flux distribution curves. Obtain wave shapes and form factors. 



(d) Complete field system. Open-circuit saturation curve. Regulation, and short-circuit 

 current. 



(e) Efficiency. 



