REVA INSTITUTE OF TECHNOLOGY AND MANAGEMENT, BANGALOREELECTRICAL AND ELECTRONICS ENGINEERING DEPT.TUTORIAL ON UNIT-3: Three Phase AC Cir!i"s (Common to I Semester-A,B,C,D,E,F,G,H-sections)O#$e"i%e "&'e (!es"i)*s-Ch))se "he )rre" a*s+er1. In double notation, te s!mbol "ab re#resents---A. $e %olta&e o' terminal (b) *it res#ect to tat o' terminal (a)B. $e %olta&e o' terminal (a) *it res#ect to tat o' terminal (b)C. te %olta&e di''erence bet*een terminals (a) and (b)D. te %olta&e di''erence bet*een terminals (b) and (a)+. In a tree #ase, star connected s!stem, te tree #ase %olta&es are 1,,00", 1,, 1200"and 1,, 2400". $en te tree line %olta&es must be---A. 1-..+ 00", 1-..+ 1200" and 1-..+ 2400"B. 1-..+ 300", 1-..+ 1500" and 1-..+ 2700"C. 1-..+ 300", 1-..+ 900" and 1-..+ 1500"D. /-.- 00", /-.- 1200" and /-.- 2400".. In a balanced . #ase star connected load, te tree #ase currents are 1,-.,,A, 1,-1/,,A and1,0,,A. $en te tree line currents must be1A. 1-..+ 300", 1-..+ 1500" and 1-..+ 900"B. 1-..+ 00", 1-..+ 1200" and 1-..+ 1200"C. 1, 00", 1, 1200" and 1, 1200"D. 1, 300", 1, 1500" and 1, 2700"2. A . #ase, 2 *ire s!stem su##lies #o*er to a balanced star connected load. $e current in eac #ase is1/A. $e current in te neutral *ire *ill be--- A. 1/A B. .,A C. 2/A D. ,/. $e se3uence 45B denotes tat---A. te em' o' #ase 4 la&s tat o' #ase B b! 1+,, B. te em' o' #ase 4 la&s tat o' #ase 5 b! 1+,,C. te em' o' #ase 4 leadstat o' #ase 5 b! 1+,,D. te em' o' #ase B leadstat o' #ase 4 b! 1+,,6. Ina . #ase#o*ermeasurementb! t*o *attmetermetod,bot*attmeters readtesame %alue.$e#o*er 'actor o' te load must be---A. 1 B. ,.-,- la&&in& C. ,.-,- leadin& D. 7ero-. In a . #ase #o*er measurement b! t*o *attmeter metod, te readin& o' one o' te *attmeters *as 7ero.$e #o*er 'actor o' te load must be----A. 1 B. ,.8 C. ,./ ,8. Ina.#ase#o*ermeasurementb!t*o*attmetermetod, tereadin&o'oneo'te*attmeters*asne&ati%e. $e #o*er 'actor o' te load must be ---A. 9,./ B. :,./ C. ;,./ D. .F. la&&in&. Find te line currents and te current in eac #ase o' te load. Bat is te loadim#edance #er #aseE GAnsF +-.1-A, 1/.68A,(+,..1CI1/.+.)H2 $ree identical coils a%in& resistance o' 1/and inductance o' ,.,.H are connected in delta across .#ase2,,",/,H7su##l!.Calculate(i)>asecurrent(ii)@inecurrent (iii)#o*erconsumed. GAnsF (i)++./-A (ii) .0.1A (iii) ++0+..++BH/ A balanced . #ase star connected load dra*s #o*er 'rom 22," su##l!. $e t*o *attmeters connectedindicate B1;/JB and B+;1.+JB.Calculate#o*er,>.F.andcurrentintecircuit. GAnsF6.+JB,,.68/,11.88AH6 $*o Battmeters connected to measure #o*er in a . #ase circuit read /JB and 1JB, te latter readin&bein&obtaineda'terre%ersin&current coil connections. Calculate>.F.o'teloadandtetotal #o*erconsumed. GAnsF ,../0,2,,,BH- >o*er is measured in a . #ase balanced load usin& t*o *attmeters. $e line %olta&e is 2,,". $e load andits >.F. is so adIusted tat te line current is al*a!s 1,A. Find te readin& o' te *attmeters *en te >.F. is(i) unit! (ii) ,.866 (iii) ,./ and (i%) 7ero. GAnsF (i) .262.1B,.262.1B (ii) 2,,,B, +,,,B (iii) .262.1B (i%)+,,,B, -+,,,BH8 Estimate te >.F. in eac o' te 'ollo*in& cases o' t*o *attmeter metod o' measurin& . #ase #o*er. (i)Battmeter readin&s are e3ual (ii) *attmeter readin&s are e3ual and o##osite (iii) *attmeter readin&s are inte ratio 1F+ (i%) one *attmeter reads 7ero. GAnsF (i) 1 (ii) , (iii) ,.866 (i%) ,./H