Question

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Q2. (a) Fig Q2) shows a separately excited DC generator with compensating windings, and rated at 430V, 400A and 1800rpm. The field winding has NF1000 turns and resistance R-200. Adjustable resistance Rad 0-300 is included in the field circuit to enable the field current to be controlled. The generator magnetising characteristic at 1800rpm is shown in Fig. Q2(i) Rad-0-3002 R,-0.050 Rf-202 V-430V NF1000 turns 500 L 400 300 200 E 100 4 Field Current (A) Fig. Q2 () separately excited DC generator ii) magnetising characteristic at 1800rpm (0) f Radj 630 and the generator is driven at 1600rpm, what is the field (i) If a 1 load is connected across the output terminals, what is the teminal (ii) What field current is required to restore the terminal voltage to the no-load current and the no-load terminal voltage? voltage? value of part (), and what value of Rad is required to accomplish this? (b) A second separately excited DC generator has the same electrical parameters as the generator in part (a) first but does not have compensating windings. The full-load demagnetising armature reaction is equivalent to 500 Ampere-turns (0) With Rad 630 and the generator is driven at 1600rpm, what is the no-load teminal voltage? (i) What would be the output terminal voltage if 364A were drawn from the armature at 1600rpm?

Answer 1

しげn (') From given parameteTs - 130 8ろ 5 18 A ieid currentIç . 63 +2 C From mag gneftising chaTac tevistics , for Tf 5 -1g A niernat jenerated emf is approximately 125 v but it s or 18OO pm Speed- 160口 tS Connec fed 97778 ろヌマ·マ8 35 9.79 A

Hence the terminat vottage (359. 7 X1 as , Nore: Effect。f amnatu'e reaction is ign compeniatin winolings are canceltinq out fhe To Ystoe the terminal vottage to the no toad vatue of part (i) VT37778 TfAmature current 377.78 A Geneτα ted emf , Ea-can be calc ut ated 39 6-67 V To find out the necessary fietd curent, fvom given etising chaacteisHc we wi nave to find outEcovre sponding20 0 pm 600V 446. 25 V Arroximate field current vequired 58A Approximate retd current reguired 5.8 A Desired Rad t accomplish his- A20 5- 8 54. 14

(i) in -the second case, when he'e ,台 uncin the mo- oadrminal Vitage fRad632 and Spred 1600 Because at η。 toad conditiore is no ama ture curent hence no am a ture Teaction So, as calculated from a.(, o ad lerminat voltae i's same as tiう Given fu(1 load dernaan eti sing A.R. mm f- 500 A-ㄱ mm FE AR mmf at3 64 E 500 X 6 demaq netisin 6 455 A-T turns If こ5.130 ienerated emf wil redure accoramgly 4725 518O 344 6 Y Terminal Yotage

oo5 L/ 326.9 y.