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9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes !"#$%& '($)*%%+# !,-./Bar CodeInstructions:1. The exam time is two hours.2. Answer all the questions.3. The exam consists of Three questions in 9 pages including this page.4. Electronic calculators are allowed.5. Clearly show all steps used in your solutions.Please, do not write anything on this page Question 1 2 345 Total Mark Mark Out of 10 10 101010 40

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesQuestion # 1Choose the correct answer1. If the turns ratio of a single phase transformer is 2:1 then, the per-unit impedance ofthe transformer referred to the primary will bea) 4 times the per-unit impedance referred to the secondary.b) 2 times the per-unit impedance referred to the secondaryc) 1/4 times the per-unit impedance referred to the secondary.d) Same as the per-unit impedance referred to the secondary.2. A 3 – phase ∆ – Y transformer has primary to secondary turns ratio of 4, If theprimary line voltage is 69.282 kV then, the secondary line voltage isa) 11 kV.b) 17.32 kV.c) 10 kV.d) 13.8 kV.3. The induced emf of a synchronous generator supplying a capacitive load isa) higher than the terminal voltage.b) lower than the terminal voltage.c) may be higher than terminal voltage or lower than terminal voltage.d) equal to the terminal voltage.4. Increasing the field current of a synchronous generator at no load leads toa) Increasing the stator line current.b) Increasing the terminal voltage of the generator.c) Decreasing the armature line current.d) Decreasing the magnetic flux in the stator core.5. Increasing the speed of a synchronous generator at no load leads toa) Increasing the stator line current.b) Increasing the terminal voltage of the generator.c) Decreasing the armature line current.d) Decreasing the magnetic flux in the stator core.6. Transformers are located in distribution substations toa) Step down the voltage.b) Step up the voltage.c) Step up or step down the voltage as necessary.d) To increase the system efficiency.

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes7. The main reason of using extra high voltage for transmission losses isa) The cheap cost of this transmission system.b) The high safety level of this transmission system.c) To be able to use bare conductors.d) To minimize the transmission losses.8. The line voltage of a three phase system is the same as the phase voltage, thena) The line current and the phase current are the same.b) The phase current is larger than the line current.c) The line current is larger than the phase current.d) The three phase system is Y connected.9. An 80% power factor meansa) That the active power is 80 % of the reactive power.b) That the reactive power is 80 % of the active power.c) That the active power is 80 % of the apparent power.d) That the active power is 80 % of the apparent power.10. The maximum output power of a synchronous generator occurs when the phase shiftbetween the terminal voltage and the induced voltage isa) 0 degrees.b) 45 degrees.c) 90 degrees.d) 180 degrees.

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesQuestion # 2The data of all the components of the electric power system shown in Figure 1, are asfollows:Generator G: 30 KVA, 11 KV, Xg = 1 p.u. and Rg = 0.5 p.u.Transformer T1: 40 KVA, 13.8 kV /220kV 3-phase, with X T1 = 0.2 p.u and negligibleresistance.Transmission line T.L.: 75 km with Z Line = 0.05 + j 0.01 ohm /kmTransformer T2: 50 KVA, 200 kV / 20kV 3-phase, with X T2 = 0.2 p.u and negligibleresistance.Load A: constant impedance load where Z A = 100 + j 20 ohmsLoad B: 20 kVA at 0.8 power factor leading.Figure 2a) Draw the per phase equivalent circuit of the power system. [ 4 Marks ]b) Choose a base of 40 kVA , 12kV at the generator bus and calculate the per unit value ofthe equivalent circuit parameters. [ 8 Marks ]c) If the generator voltage is kept constant at 11kV, find the voltage of load bus and thencalculate the overall power loss of the system. [ 4 Marks ]

Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes/9

Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes/9

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesQuestion # 3a) A 4-pole 220V, 10 kVA synchronous generator is running at 1800 rpm a. If the maximum flux perpole is 0.01 Weber and the armature has 100 turns per phase, neglecting the armature resistance andassuming that the synchronous reactance is 1 Ω , calculate ,a) The generator induced voltage.b) How much power (active and reactive) can be delivered by this generator at rated terminal voltageand 0.8 power factor lagging? What is the power angle in this case.

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesb) A 100-kVA, 400/2000 V, single-phase transformer has the following parametersR 1 = 0.01Ω R 2 = 0.25 ΩX1 = 0.03 Ω X2 = 0.75 ΩThe transformer supplies a load of 80 kVA at 2000 V and 0.85 PF leadinga) Calculate the primary voltage and current using the simplest equivalent circuit.b) Find also the voltage regulation (V.R.) and efficiency for the transformer.

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesQuestion # 4a) A three phase 25kVA, 380V, Y connected synchronous generator has a rated phasecurrent of --------------------- A.b) A single phase 20kVA, 220/110V transformer is loaded with a 10 ohm resistor on thesecondary side. The 10 ohm resistor referred to the primary side has a value of ------------- Ohm.c) A 10kVA, 0.8 power factor lagging load has a reactive power of ------------- VAR.d) A 6-pole, 50 HZ, 20KVA, 33kV synchronous generator is running at a speed of ------------- r/m.e) A single phase transformer draws 1.5 A at 0.9 pf. Lagging from a 220 V supply at noload. Using the approximate circuit of the transformer, the iron losses of thetransformer is ------------ Watt and the Magnetizing reactance is ----------- Ohm.f) The rms phase voltage of a three phase 50Hz synchronous generator at no load is444V. If the number of turns per phase is 100, then the magnetic flux per pole is ------------ Wb.g) A 3-phase synchronous generator has a synchronous reactance of 2 Ω and negligibleresistance. The no load phase voltage of the machine is 230V. The power angle of themachine is ---------------- 0 when the machine supplies a 3kW load at 220V.h) A 440/110 V single phase transformer supplies a load at the secondary side at ratedvoltage. If the voltage regulation is 3% then the primary voltage of the transformer is--------------- V.i) A single phase transformer supplies an inductive load. If the core losses of thetransformer are 1% of the output power and the copper losses of the transformer are3% of the output power, then the transformer efficiency is ------------------.j) A 3-phase Y connected synchronous generator has a synchronous reactance of2 Ω and negligible resistance. If the machine supplies a load of 10kVA, 0.85 p.f.leading at 230V, then the induced voltage per phase of the armature windings isleading the terminal voltage by an angle of ------------- 0

9Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutesQuestion # 5For the system shown in Figure 3, assume that the p.u. reactances of all the systemcomponents are as follows,Generators: X g1 = X g2 = X g3 = 0.5 p.u.Transformers X T1 = X T2 = X T3 = 0.2 p.u.Transmission Lines X L1 = X L2 = X L3 = 0.1 p.u.a) Formulate the admittance matrix of the system.b) Consider that G 1 is the system slack bus; G 2 is PV bus with p =1 p.u. and V= 1 p.u.;bus 4 is supplying a 3 phase load with apparent power of 0.8+j0.5 p.u., write downthe load flow equations for the system using the Gaussian formulation.c) Write down 2 iterations of the Guess-Siedel solution using your own initialconditions.Figure 3

Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes/9

Midterm Exam Distributed Power Systems(ELCT908) Time allowed : 120 minutes/9