Energy Conversion II

Daffodil International University Department of Electrical and Electronic Engineering Faculty of Engineering Mid Term Examination, Fall – 2026 Course Code: 0713-223 Course Title: Energy Conversion II Section: A, B, C, D, E, F, G Level-Term: L2-T2 Teacher's Initial: NR, RS, RIR Full Marks: 25 Exam Date: October 28, 2026 Time: 1.5 Hours Notes: Answer all the questions below. The second right most column indicates the course outcomes (COs) with respective Bloom's level and the right most column indicates the allocated marks. Q1. Illustrate and briefly explain the brushless excitation system working principle of a synchronous generator incorporating a pilot exciter with a neat, labeled diagram. | CO-1 C(2) | 5 Q2. Analyze the effect of excitation changes on a synchronous generator while delivering constant power outputs using phasor diagram. | CO-2 C(4) | 5 Q3. A 100 kVA, 3000 V, 50 Hz, 3-phase star-connected alternator has an armature resistance of 0.2 Ω per phase. A field current of 40 A produces a short-circuit current of 200 A and an open-circuit line voltage of 1040 V. Analyze how the power factor affects the voltage regulation by determining the full-load voltage regulations and drawing the corresponding phasor diagrams of the alternator at 0.8 power factor lagging and 0.8 power factor leading. | CO-2 C(4) | 5 Q4. A 480-V, 50-Hz, Y -connected, six-pole synchronous generator has a per-phase synchronous reactance of 1.0 Ω. Its full-load armature current is 60 A at 0.8 PF lagging. This generator has friction and windage losses of 1.5 kW and core losses of 1.0 kW at 60 Hz at full load. The armature resistance is negligible and the field current has been adjusted so that the terminal voltage is 480 V at no load. (i) Determine the speed of rotation of this generator. (ii) Evaluate the terminal voltage of this generator if it is loaded with the rated current at 0.8 PF leading. (iii) Calculate the efficiency of the generator when it is operating at the rated current and 0.8 pf leading. (iv) Calculate the shaft must be supplied by the prime mover at full load and induced counter torque? (v) Determine the voltage regulation at 0.8 pf leading. | CO-3 C(5) | 5 Q5. Two synchronous generators are operating in parallel supplying a total load of 2.5 MW at 0.8 power factor lagging. Generator 1 has a no-load frequency of 61.5 Hz and a slope of 1 MW/Hz, while Generator 2 has a no-load frequency of 61.0 Hz and a slope of 1 MW/Hz. After steady-state operation, an additional 1 MW load is connected and the governor set point of Generator 2 is increased by 0.5 Hz. Evaluate the system frequency and the generator powers before and after the change in system condition. | CO-3 C(5) | 5 [Figure: Diagram of Generator 1 and Generator 2 connected in parallel supplying Loads] Fig. 1