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Worked Examples, Chapter 6 Worked Example 1 Q A 4-pole d.c. shunt generator has an armature resistance of 0.018 . The armature is lap-wound with 520 conductors. When driven at 750 rev/min the machine produces a total armature current of 400 A at a terminal voltage of 200 V. Calculate the useful flux/pole. A p 2; a 4; Ra 0.018 ; z 520; n 750 12.5 rev/s 60 I a 400 A; V 200 V E V I aRa volt 200 ( 400 0.018 ) E 207.2 V 2 pzn volt E a Ea 207.2 4 so, weber 2 pzn 4 520 12.5 31.9 mWb Ans Worked Example 2 Q A short-shunt compound generator has armature, shunt field and series field resistances of 0.5 100 , and 0.3 respectively. When supplying a load of 8 kW at a terminal voltage of 250 V the input power supplied by the driving motor is 10.4 kW. Calculate (a) the generated emf, (b) the efficiency, (c) the iron, friction and windage loss, and (d) the total fixed losses. A Ra 0.5 ; Rf 100 ; RSe 0.3 ; Po 8000 W; V 250 V; Pi 10 400 W RSe Ia Ra IL 0.3 Ω 0.5 Ω If Pi E Rf 100 Ω V 250 V 80 kW Po 10.4 kW (a) IL PO 8000 amp 32 A VL 250 Vf V I LRSe volt 250 (32 0.3) Vf 259.6 V If 259.6 Vf amp 2.6 A 100 Rf I a I L I f amp 32 2.6 34.6 A E Vf I aRa volt 259.6 (34.6 0.5) E 276.9 V Ans 167 168 Supplementary Worked Examples (b) Po 8 100% 100% Pi 10 .4 76.92% Ans (c) From the power flow diagram PFe Pi E I a watt 10 400 (276.9 34.6 ) PFe 819.26 W Ans (d) total fixed losses PFe I f2Rf watt 819.26 (2.6 100 ) total fix ed losses 1.08 kW Ans