How to calculate new current and terminal voltage?, Electrical Engineering

Q. Series generator having a combined armature and field resistance of 0.4? is running at 1000 r.p.m. and delivering 5.5kw at terminal voltage of 110 V. If the speed is raised to 1500 rpm and load is adjusted to 10 kw. Find the new current and terminal voltage. Assume that machine is working on the straight line portion of the magnetization characteristics.

Sol.    Given        P1 = 5.5kw

 

                            V1 = 110V

 

        Thus load current P1/V1 = 5500/110 = 50A

 

        Now generated voltage will be  (when N1 = 1000rpm)

 

                             Eg1 = V1 + I1 (ra + rsc) = 110 + 50 × 0.4

 

      Let at 1500 rpm, current supplied by generator at terminal voltage V2 is I2

 

                                       V2 = P2/I2 = 10000/I2

 

            Generated voltage Eg2 = V2+ I2(ra + rsc) =10000/I2 + 0.4I2

 

            As          Eg

 

             or          Eg2/Eg1 = Φ21 × N2/N1 = N2/N1  × I2/I1

 

             or          10000/I2 + 0.41/130 = 1500/1000 × I2/50

 

             or          10000 + 0.4 I22 = 3.9 I22

 

             or           3.5 I22 = 10000

 

             thus        I2 = 53.45 A

 

             and         V2 = 10000/53.45 = 187.14

Posted Date: 7/23/2012 1:41:00 AM | Location : United States







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