How to calculate the bus - bar voltage and kilowatt output., Electrical Engineering

Q. Two shunt wound generators running in parallel supply a total load current of 4000 A. Each generator has an armature resistance of 0.02? and a field of 40?. The fiels are excited so that the emf induced in one generator is 480 V and in another 490 V, find the bus - bar voltage and kilowatt output of each machine.


Sol.            V = bus bar voltage


                  I1 = current output of generator 1


                  I2 = current output of generator 2


             I1 + I2 =  4000

               Ish = V/Rsh


       Bus - bar voltage


       In each machine


       Bus bar voltage + voltage


       Drop in armature = EMF generated


       for  generated 1, E1 = V + Ia1 Ra


                 480 = V + (I1 + V/40) × 0.02


               (Ia1 = I1 + Ish)


      for  generated 2 490 =  V + (I2 + V/40) × 0.02


      Subtrating both with each other we get,


            0.0212 - 0.0211 = 10


  or      I2 - I1 = 500


  or      (4000 - I1) - I1 = 500


             I1 = 1750A and I2 = 4000 - 1750 = 2250A


Now          480 = V + (I1 + V/40) × 0.02    or      490 =  V + (I2 + V/40) × 0.02


                On solving V = 444.8 volts


           Kilowatt output


               kW output of gen. 1, VI1/1000 = 444.8 × 1750/1000 = 778.4kW


               kW output of gen. 2, VI1/1000 = 444.8 × 2250/1000 = 1001kW 

Posted Date: 7/23/2012 1:54:07 AM | Location : United States

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