Efficiency, Rating and application of Dynamos

Efficiency, Rating and application of Dynamos

1) A 50 KW gnerator has a efficiency of 91 percent at full load.Calculate the input in kilowatts and the power loss.

Given:
Pl=150 Watts
Efficiency=91% at full load

Required:

Calculate the input Power in Kilowatts and Power loss.

Solution:

Efficiency=(Power out/Power In) 100%

Pin=164.835KW


2) A 15HP motor operates at an efficiency of 87.5 % at full load. If the stray Power loss is approximately one forth of the total loss, calculate the copperloss.

Power Input=[(15 hp)(746)]/0.875
Power Input=12789 Watts

Power Total=Power Input-Power out

Power Total=12789-11190 Watts

stray Power loss = (1/4) Power Total

stray Power loss =(1/4) 1599

stray Power loss =399.75 watts

Power copper loss=Power Total -stray Power loss =1599-399.75=1200 watts


3. The rotational loss in a generator was found to be 780 watts when the generated emf was 132 volts .Determine the rotational loss for generated voltages 138and 126 Volts.

stray Power loss =EgIa
Ia=780/132=5.9 A



At Eg= 138 Volts

stray Power loss =(138)(5.9) =815.5 watts


At Eg= 126 Volts

stray Power loss =(126)(5.9)=743.4 watts

5. The output torque of a motor is 69.2 lb-ft when it operates at 950 rpm.Calculate the losses in the machine and its efficiency whenthe power input is 10900 Watts.

Horsepower=[(2)(Pi )(RPM) (T)]/33000

Horsepower=[(2)(Pi )(950) (69.2)]/33000=12.5HP

Power Input=[(12.5 hp)(746)]=9325 Watts

Power losses=Power Input-Power out =10990-9325=1575 Watts

Efficiency=(Power out/Power In) 100%

Efficiency=(9325/10900) 100% =85.6%