Synchronous Generator can be either using permanent magnet or field-excitation coil as their main flux sources are located in rotor part. However, synchronous generator using field-excitation has advantages of variable flux control capabilities when compared to fix permanent magnet flux. In the given problem, investigate the synchronous generator with various field-excitation control configurations. The per phase equivalent circuit of synchronous generator is shown in figure 4. A 480- V (line-to-line), 50Hz, -connected, four-pole synchronous generator has the open-circuit characteristic shown in Figure 5. This generator has a synchronous reactance of 0. RN , an armature resistance of 0.015 . At full load, the machine supplies 1100+RN A at 0.8 PF lagging. Under full-load conditions, the friction and windage losses are 50 kW and the core losses are 30 kW. Ignore any field circuit losses. Answer the following questions

Figure 4

a. The design of the high-speed electrical machine is a multi-physical engineering problem in which electromagnetic, thermal and mechanical aspects must be considered at the same time, being equally important with respect to the final machine performance. In several application areas, there is a growing interest in high-speed electrical machines. Calculate the speed of rotation of this synchronous machine by using the given information? [3 marks]

HITEC UNIVERSITY Department of Electrical Engineering

b. If the generator is connected to a load and the load draws 1100+RN A at 0.8 PF leading, how much field current will be required to keep the terminal voltage equal to 480 V? [6 marks] c. How much power is the generator now supplying? How much power is supplied to the generator by the prime mover? What is this machine's overall efficiency at 0.8 PF lagging? [6 marks] d. Suppose that the generator is connected to a load drawing 1100+RN A at 0.8 PF lagging. How much field current would be required to keep the terminal voltage equal to 480 V? [6 marks] e. If the load changes and the field is left alone, what happens to the terminal voltage? Explain