Transformer and Alternator Question Bank PDF

Government Polytechnic, Ranchi Transformer and Alternator (Question Bank) 1. Define Permeability? What do you mean by Absolute permeability and Relative permeability? 2. State the relationship between Flux, MMF and Reluctance? 3. Derive the relationship between cur...

Government Polytechnic, Ranchi Transformer and Alternator (Question Bank) 1. Define Permeability? What do you mean by Absolute permeability and Relative permeability? 2. State the relationship between Flux, MMF and Reluctance? 3. Derive the relationship between current and power in a pure resistive, inductive and capacitive circuit. 4. Derive the expression of A.C circuit containing R-L,R-C,R-L-C in series and parallel. 5. Define series resonance? State the properties of series resonance properties. 6. Explain the working principle, construction and working of Transformer. 7. Explain the working principle, construction and working of Alternator. 8. Explain Operation of a transformer on No-load and On-load with a vector diagram. 9. Draw equivalent Circuit of transformer. 10. Compare the salient pole and non salient pole alternator. 11. Explain Full pitch Armature windings and Fractional pitch Armature windings. 12. Derive the EMF equation of an 3 phase alternator. 13. Explain armature reaction in an alternator with sketches. Discuss effects of P.F of load on armature reaction. 14. Explain O.C & S.C. tests on an alternator with circuit. 15. Define Voltage regulation. Explain method for voltage regulation in alternator. 16. What is Hunting and its prevention in alternators? 17. Briefly explain the maintenance of transformer yearly or half yearly basis. 18. What is the effect of change in excitation? Explain briefly. 19. Give a brief introduction of Vector Grouping and its types. 20. Explain working principle, construction and connection type of three-phase transformers. 21. What are the necessity and conditions for parallel operation of transformer. 22. What is voltage regulation and efficiency in the transformer. 23. A star connected,3 phase is rated at 3000kva,15000v R a 3ohm/phase and XS=10ohm/phase.Calculate the percent regulation of Ra load of 1200Kw at 0.8 lagging PF. 24. A 3phase star connected alternator is rated at 1500Kva,14000V.The armature effective resistance and synchronous reactance are 1.6ohm and 30 ohm respectively per phase. Calculate percent regulation for a load of 120kW at power factor of: (i)0.8 leading (ii) unity (iii)0.8 lagging. 25. A single-phase transformer has 500 turns on the primary and 40 turns on the secondary winding. The mean length of the magnetic path in the iron core is 150 cm and the joints are equivalent to an air-gap of 0.1 mm. When a p.d. of 3,000 V is applied to the primary, maximum flux density is 1.2 Wb/m2. Calculate (a) the cross- sectional area of the core (b) no-load secondary voltage (c) the no-load current drawn by the primary (d) power factor on no-load. Given that AT/cm for a flux density of 1.2 Wb/m2 in iron to be 5, the corresponding iron loss to be 2 watt/kg at 50 Hz and the density of iron as 7.8 gram/cm3. 26. Calculate the percentage voltage drop for a transformer with a percentage resistance of 2.5% and a percentage reactance of 5% of rating 500 kVA when it is delivering 400 kVA at 0.8 p.f. lagging 27. In a 25-kVA, 2000/200 V, single-phase transformer, the iron and full-load copper losses are 350 and 400 W respectively. Calculate the efficiency at unity power factor on (i) full load (ii) half full-load. 28. A 25 kVA, single-phase transformer has 250 turns on the primary and 40 turns on the secondary winding. The primary is connected to 1500-volt, 50 Hz mains. Calculate (i) Primary and Secondary currents on full-load, (ii) Secondary e.m.f., (iii) maximum flux in the core. 29. A 25-kVA transformer has 500 turns on the primary and 50 turns on the secondary winding. The primary is connected to 3000-V, 50-Hz supply. Find the full-load primary and secondary currents, the secondary e.m.f. and the maximum flux in the core. Neglect leakage drops and no-load primary current. 30. The maximum flux density in the core of a 250/3000-volts, 50-Hz single-phase transformer is 1.2 Wb/m2. If the e.m.f. per turn is 8 volt, determine (i) primary and secondary turns (ii) area of the core.