Partial preview of the text
Download ECEN 226 ASSIGNMENT. and more Lecture notes Engineering in PDF only on Docsity!
ELE TRIcAe PRI e1 PLES LCEN Q1G AssiGWuMENT ATrE™ Pr Aer Questions oe A) Stete Thevenins We on . i tas Methods of ae é fons, Kev chhofefts and supe 0 Site Ff telving For clvvents pion f Peeutlee i alan | § ane heuzls & fe ( [2 marks) QUESTION TWO (8 marks) » (a) Define the following terms as applied to circuit elements. (i) Resistance (R) (2 marks) (ii) | Capacitance (C) (2 marks) (iii) Inductance (L) (2 marks) (iv) | Resonance (2 marks) (b) () @ Show their unit of measurements. Derive an expression for equivalent capacitance of three capacitors connected in series. (3 marks) The equivalent or total capacitance of the circuit below Fig 2(c) is given as Cy = 15pF. Calculate the value of the unknown capacitor C. 15uF 10uF —l —I 5SaF __} j. ve [Jett Cc SaF < Vv Fig. 2(c) (3 marks) A pure inductance of 318mH is connected in series with a pure resistance of 752. The circuit is supplied from a 50Hz source and the voltage across 75Q resistor is found to be 150V. Calculate: (i) The supply voltage (2 marks) (ii) The phase angle (2 marks) And draw the phasor diagram. (2 marks) ICEN 206 QUESTION THREE (a) Define the terms as applied to ac circuits. (60) Impedance (Z) (2 marks) (ii) | Admittance (A) (2 marks) (iii) | Conductance (G) (1 mark) (iv) Susceptance (B) (1 mark) Show how they relate to each other. (b) The impedance of an R-L.C series circuit is given by Z= JR? +(X,-X- y Explain what each term represents and hence describe the three cases when X, > Xe Xe > X, (3 marks) X, =X, (c) A coil of p.f 0.8 is connected in series with a 110yF capacitor. The supply frequency is 50Hz. The p.d across the coil is found to be equal to the p.d across the capacitor. Calculate @ the resistance (2 marks) and (ii) the inductance of the coil (2 marks) (d) Two impedances z; = (10 + j5)Q and z = (25 —j10)Q are connected in parallel to a 100V, 50Hz supply Find (6) current in each branch (2 marks) (ii) Tine current (2 marks) (iii) circuit p.f (1 mark) (iv) power taken by the circuit. (2 marks) UESTION FOUR (a) Explain the following terminologies in d.c networks. (i) Active element (2 marks) (ii) Passive element (2 marks) (iii) Loop (1 mark) (iv) The converse of Thevenin’s theorem.(2 marks) (b) State (i) Superposition theorem. (2 marks) (3 marks) (ii) | Thevenin’s theorem. Page 4 of 7 ICEN 206 QUESTION FIVE (a) Describe how 3-phase voltages are generated in a 3-phase circuit. *(3 marks) (b) State four reasons why three phase power system is preferred over single phase system. (4 marks) (c) Ina balanced 3 phase-star and delta connections what is the relationship between * (i) Line and phase voltages Gi) Line and phase currents (iii) Power (4 marks) (d) The load to a3 phase supply comprises three similar coils connected in star. The line currents are 25A and the kVA and the kW inputs are 20 and 11 respectively. Find (i) phase and line voltages (ii) ~~ the KVAR input. (iii) resistance and inductance of each coil. (4 marks) e A3 phase 10kW induction motor has a p.f of 0.5 lagging. P . A bank of capacitors is connected in delta across the supply terminals and p.f raised to 0.9 lagging. Determine the kVAR ratings of the capacitors connected in each phase. (5 marks) UESTION SIX (a) Describe with the aid ofa diagram the operation of a single phase Transformer. (4 marks) (b) Explain ina Transformer the use of (i) Silica gel (1 mark) (ii) Transformer oil (2 marks) (iii) Laminations in the core (1 mark) (c) List the industrial applications of a Transformer. (3 marks) . ; 2 marks) e (i an ideal transformer. ; ( / ik a voltage transformation ratio (K). (3 marks) Page 6 of 7 
