480 V, 200 kVA, 08 PF lagging, 60 Hz two pole Y connectedsynchronous generator has a synchronous reactance of 0.25 Ω and anarmature resistance of 0.03 Ω. At 60 Hz, its friction and windagelosses are 6 kW, and its core losses are 4 kW. The field circuithas a dc voltage of 200 V, and the maximum IF is 10 A. Theresistance of the field circuit is adjustable over the range from20 to 200 Ω. The OCC of the generator is shown in figure
a. How much the field current is required to make VT equal to480 V when the generator is running at no load? [4.55 A]
b. What the internal generated voltage of this machine atrated conditions? [322 @ 7.8°]
c. How much the field current is required to make VT equal to480 V when the generator is running at rated conditions? [558V]
d. How much power and torque must the generator’s prime moverbe capable of supplying? [175.2 kW, 465 Nm]
e. Assume that the field current of the generator is adjustedto achieve rated voltage (480 V) at full load conditions in each ofthe questions below.
1. What is the efficiency of the generator at rated load?[91.3%]
2. What is the voltage regulation of the generator if it isloaded to rated kilovoltamperes with 0.8-PF lagging loads?[16.2%]
3. What is the voltage regulation of the generator if it isloaded to rated kilovoltamperes with 0.8-PF leading loads?[-9.0%]
4. What is the voltage regulation of the generator if it isloaded to rated kilovoltamperes with unity power-factor loads?[5.1%]
f. Assume that the field current of the generator in Problem5-2 has been adjusted so that it supplies rated voltage when loadedwith rated current at unity power factor. (You may ignore theeffects of RA when answering these questions.)
1. What is the torque angle δ of the generator when supplyingrated current at unity power factor? [12°]
2. What is the maximum power that this generator can deliverto a unity power factor load when the field current is adjusted tothe current value? [941 kW]
3. When this generator is running at full load with unitypower factor, how close is it to the static stability limit of themachine? [196 kW]
4. Plot the torque angle δ as a function of the power suppliedby the generator for these conditions.
3. A 3-phase 50-Hz star-connected 2000-kVA, 2300 V
