07a1ec07 Basic Electrical Engineering
Content
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 1
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆⋆⋆⋆⋆
1. (a) A coppe copperr wire of dia diamet meter er 1cm has re resi sist stanc ancee of 0.15 0.15Ω. Ω. It wa wass dra drawn wn und under er pressure so that its diameter was reduced to 50%. What is the new resistance of the wire? (b) (b) St Stat atee an and d ex expl plai ain n Far arad adaays la law w of elec electr trom omag agne neti ticc indu induct ctio ion. n.
[10+ [10+6] 6]
2. (a) Giv Givee a detail detailed ed comp comparis arison on of seri series es and par parall allel el cir circui cuit. t. (b) What are the applications applications,, merits and demerits of a series circuit? (c) What are the the aapp ppli licat catio ions ns and and aadv dvan antag tages es of a p para arall llel el circu circuit it??
[6+5 [6+5+5 +5]]
3. (a) In a para paralle llell magne magnetic tic circ circuit, uit, der deriv ivee the expres expressio sion n of tota totall mmf requi required. red. (b) An iron ring 100 sq.cm me mean an circumfere circumference nce and of cross sectiona sectionall area 5 sq.cm has a saw cut of 2mm length. It is wound with 500 turns of wire. If 0.5 mwb flux exists across the air gap, what will be the value of the exciting current? Take coefficien coefficientt of leak leakage=1.26 age=1.26 and relative permeabili permeability ty of iron = 5 00. [6+10] 4. (a) A coil of 20 ohms re resi sist stanc ancee has an in indu ducta ctance nce of 0.2 H and is connect connected ed in parallel with a 100 µF capacitor. Calculate the frequency at which the circuit will act as a non-inductive rsistance. Find also the value of that resistance at which the circuit will act as a non-inductive resistance. (b) An AC circu circuit it consis consists ts of tw twoo parall parallel el branc branches hes.. Bra Branc nch h 1 cons consist istss of a coil having R=20 Ω and L=0.1H. Branch 2 consists of a coil having resistor in series with 60 µF capacitor. Calculate i. The current in each branch ii. The line current iii. The power, when the circuit is connected to 230 V supply having a frequency of 50Hz. iv. Resistance v. Inductance of a single coil which will take the same current and power from the same supply. [8+8] 5. A 1 phase transformer has 500 turns on the primary and 40 turns on the secondary winding. windin g. The mean length of the magneti magneticc path on the core is 150 cm and the joints are equivalen equivalentt to an air gap of 0.1m 0.1mm. m. When the potenti potential al differe difference nce of 3000 3000V V is applied to the primary, the max flux density is 1.2 T. Calculate 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 1
(a) The cros crosss sectio sectional nal area of the core (b) No load secon secondary dary vo voltage ltage (c) The no load curren currentt drawn by the prima primary ry (d) Po Powe werr factor on no load give given n that amper amperee turn turnss p per er cm for a flux dens densit ity y of 1.2 T in the iron to be 5, the corresponding iron loss to be 2W/Kg at 50Hz and density of iron as 7.8 gm/cm 3 . [4+4+4+4] 6. (a) Deriv Derivee the express expression ion fo forr the aarmature rmature torque and sha shaft ft torq torque ue of a DC motor. (b) The armature of a 6 pole, DC shunt motor takes 300 A at the speed of 400 revolutions revo lutions per min minute. ute. The flux per pole is 75 mWb. The num number ber of armature turns tur ns is 500 500.. Th Thee tor torqu quee lo lost st in wind windage age,, frict frictio ion n and iro iron n loss losses es can be assumed a 2.5%. Calculate [6+10] i. Torque developed by the armature ii. Shaft torque iii. Shaft power in KW. 7. (a) Exp Explai lain n the revol revolvin vingg field type and the rev revolv olving ing arm armatur aturee type alternato alternators. rs. (b) A 6 pole DC generato generatorr is running aand nd producing a freq frequency uency of 60 Hz. Calculate the revolutions per minute of the generator. If the frequency is decreased to 20 Hz, how many number of poles will be required if the generator is to be run at the same speed. (c) Give Give the di diffe fferen rence ce bet betw ween a DC gen genera erator tor and and an alter alterna nator tor..
[6+6+ [6+6+4] 4]
8. What are the basic requiremen requirements ts of indicating instru instrument? ment? Briefly disc discuss uss them. [8+8] ⋆⋆⋆⋆⋆
2 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 2
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆ ⋆ ⋆ ⋆ ⋆
1. Fin Find d the curren currentt thro through ugh and the volt voltage age across all the elem elemen ents ts in the circui circuitt by applying Kirchoff ’s laws as shown in the figure 1. [16]
Figure 1 2. (a) Fin Find d the equiv equivale alent nt resi resistan stance ce betw between een the termi terminal nalss X and Y in the circ circuit uit as shown in the figure 2a.
Figure 2a (b) (b) Describe ribe in deta taiil the the step epss to app pplly Thev eveenin’ nin’ss theo eore rem m.
[12+ 2+44]
3. (a) Exp Explai lain n as ttoo wha whatt y you ou un unders derstand tand by: by: i. Static ii. Dynamic Dynamic induce inducemen mentt of ele electro ctromoti motive ve force. Illustr Illustrate ate by the help of simple sketches. (b) A coil of 100 turns is link linked ed by a mag magneti neticc flux of 20m 20mwb. wb. If this magn magneti eticc flux is reve reverse rsed d in a time of 2ms 2ms,, calc calcula ulate te the av averag eragee emf induced. induced. [6+ [6+10] 10] 4. Three impedances Z1=10+j31.4 Ω, Z2 = 6+j8 Ω, and Z3 = 3-j4 Ω are connected in parallel across a 200V AC supply. Calculate (a) Total admittanc admittance, e, conductance and susceptance of the whole circuit circuit.. 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 2
(b) Total current, power factor and power.
[8+8]
5. (a) Exp Explai lain n the princ principl iplee of work working ing of a singl singlee phase tra transfo nsformer rmer.. (b) Deriv Derivee from the first principles, the emf equation of a single phase transfor transformer. mer. [8+8] 6. (a) What is the fun function ction of a comm commutator utator in a DC m machi achine? ne? Discus Discusss with relev relevant ant figures. (b) Differe Differentiat ntiatee b betw etween een slip rings and commutator. (c) A 4 pole wa wave ve wou wound nd DC gene generato ratorr has 50 slo slots ts and 24 conduc conductors tors per slo slot. t. The flux per pole is 10 mWb. Determine the induced emf in the armature if it is rotating at a speed of 700rpm. [3+3+10] 7. (a) Giv Givee the differ difference ence bet betwe ween en an induc induction tion mo motor tor and a trans transform former. er. (b) A 12 pole, 3 phase alternator driven at 500 rpm supplies power to a 8 pole 3 phase induction motor. If slip of motor at full load is 3%, calculate the speed of the motor. (c) A 3 phase induction mo motor tor has starting torqu torquee of 100% and a maximum torq torque ue of 200 200% % of the ful fulll lo load ad tor torqu que. e. Fi Find nd slip slip at ma maxi ximu mum m tor torqu que. e. [4+ [4+6+ 6+6] 6] 8. (a) Giv Givee a comp comparis arison on of spri spring ng con control trol and gr grav avit ity y cont control. rol. (b) (b) Explain the erro errors rs occ occurri rring in a moving iron instr trum umen entt. ⋆ ⋆ ⋆ ⋆ ⋆
2 of 2
[8+ 8+88]
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 3
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆⋆⋆⋆⋆
1. (a) A 100W 100W,, 250V b bulb ulb is p put ut in se series ries w with ith a 40W 40W,, 250V bu bulb lb acr across oss a 500 500V V sup sup-ply.. What will be the power consumed by eac ply each h bulb? Will suc such h a comb combination ination work? (b) (b) State tate and explain Kirchoff’ off’ss curre rrent law and voltag agee law.
[10+ 0+66]
2. Determi Determine ne the p pow ower er loss in the 10Ω resistor by using Thev Thevenin’s enin’s theorem as show shown n in figure 2. [16]
Figure 2 3. Define the following: (a) Magn Magnetic etic fie field ld (b) Magnetic circui circuitt (c) Magn Magnetic etic flu flux x (d) Magnetic flu flux x densit density y (e) MMF (f) Rel Relucta uctance nce (g) Magnetic fi field eld stren strength gth (h) Permeability.
[16]
4. (a) A co coil il ooff power power fa factor ctor 0.9 iiss in seri series es w with ith a 120 µ F capacitor. When connected to a 50 Hz supply, the potential difference across the coil is equal to the potentiall difference across the capacitor. Find the resistance and inductance potentia inductance of the coil. (b) A metal filam filamen entt lamp rated 750 W, 110V is to be conn connecte ected d in seri series es with a capacitor across a 220V, 50Hz supply. Calculate i. The capacitance required 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 3
ii. The power factor.
[8+8]
5. The iron and full loa load d copper loss in a 40KVA 40KVA 1 phas phasee transfo transformer rmer are 450 W and 850 W respectively. Find (a) Effici Efficiency ency at full load when the power power factor of the load is 0.8 laggi lagging ng (b) The maxim maximum um efficienc efficiency y and (c) The load at which the maximum efficiency occurs.
[8+8]
6. What are the main part partss of a DC mac machin hine? e? Stat Statee the fun functio ction n of eac each h part with relevant figures. [6+10] 7. A 4-pole, 50 Hz, three phase induction motor has rotor resistance and reactance of 0.025 Ω and 0.02 Ω per phase respectively. Determine (a) The va value lue of speed at whi which ch the maxim maximum um torque occurs (b) The va value lue of the exter external nal rotor resi resistan stance ce per phas phasee to be ins inserte erted d to obtain 60% of the maximum torque at the starting. [16] 8. What do yo you u unde understa rstand nd by attraction attraction type and repu repulsi lsion on ty type pe ins instrum trumen ents? ts? Explain. [8+8] ⋆⋆⋆⋆⋆
2 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 4
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Six re resis sistors tors ar aree conne connected cted as ssho hown wn in figu figure re 1a. If a batte battery ry ha havin vingg an emf of 30V and an internal resistance of 2Ω is connected to terminals A and B. Find i. current from battery ii. potential difference across 10Ω and 12Ω.
Figure 1a (b) Fin Find d the effec effectiv tivee resi resista stance nce of the fol follo lowin wingg com combin binatio ation n of resi resistan stances ces and the voltage drop across each resistance when the applied voltage is 70V across P and Q as shown in figure 1b. [8+8]
Figure 1b 2. (a) Giv Givee a detail detailed ed comp comparis arison on of seri series es and par parall allel el cir circui cuit. t. (b) What are the applications applications,, merits and demerits of a series circuit? (c) What are the the aapp ppli licat catio ions ns and and aadv dvan antag tages es of a p para arall llel el circu circuit it?? 3. Define the following: (a) Magn Magnetic etic fie field ld (b) Magnetic circui circuitt 1 of 2
[6+5 [6+5+5 +5]]
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 4
(c) Magn Magnetic etic flu flux x (d) Magnetic flu flux x densit density y (e) MMF (f) Rel Relucta uctance nce (g) Magnetic fi field eld stren strength gth (h) Permeability.
[16]
4. (a) Exp Explai lain n the beha behavio viour ur of AC throug through h R-C ser series ies ci circui rcuit. t. (b) A resi resistor stor carries two alte alternat rnativ ivee curr curren ents ts havin havingg sam samee freq frequenc uency y and phas phasee and having the same peak value of 20A. One is sinusoidal and the other is rectangular in waveform. Find the RMS value of the resultant current.[6+10] 5. (a) A 3000/ 3000/300V 300V 1 phas phasee trans transform former er giv gives es 0.6A an and d 60W as amme ammeter ter and v volt olt-meterr read mete reading. ing. When supp supply ly is giv given en to the low volt voltage age windi winding, ng, the hig high h voltage winding is kept open. Find i. Power factor of no load current ii. Magnetizing current iii. Iron loss component. (b) Write a note on vario various us winding parameters of a transform transformer. er. (c) Define regulation stating an expression to obtain it.
[10+3+3]
6. (a) A short shun shuntt compound generator suppli supplied ed 7.5 K KW W at 230 V. The shun shuntt field, series field and armature resistances are 100 Ω, 0.3 Ω and 0.4 Ω respectively. Calculate the induced emf and the load resistance. (b) Write down the similaritie similaritiess and dissi dissimilari milarities ties between motors and generators. (c) Explai Explain n the mo motor torin ingg and gen gener erati ating ng act actio ions ns of a DC ma mach chin ine. e.
[6+ [6+5+ 5+5] 5]
7. A 3 phase, 50Hz induction motor has a starting torque which is 1.25 times full load torque and a maximum torque which is 2.5 times full load torque. Neglecting stator resistance and rotational losses and assuming rotor resistance, find (a) Sli Slip p at full load (b) Slip at maxi maximum mum torq torque ue (c) (c) Ro Roto torr cu curr rren entt at star starti ting ng in per per un unit it of full full loa oad d ro roto torr cu curr rren ent. t.
[16] [16]
8. (a) Differe Differentiat ntiatee betw between een mo moving ving coi coill and m movi oving ng iron iinstrume nstrument. nt. (b) Explain with neat sketch the air friction damping. ⋆ ⋆ ⋆ ⋆ ⋆
2 of 2
[8+8]
Code No: 07A 07A1EC 1EC07 07
Set No. 1
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆⋆⋆⋆⋆
1. (a) A coppe copperr wire of dia diamet meter er 1cm has re resi sist stanc ancee of 0.15 0.15Ω. Ω. It wa wass dra drawn wn und under er pressure so that its diameter was reduced to 50%. What is the new resistance of the wire? (b) (b) St Stat atee an and d ex expl plai ain n Far arad adaays la law w of elec electr trom omag agne neti ticc indu induct ctio ion. n.
[10+ [10+6] 6]
2. (a) Giv Givee a detail detailed ed comp comparis arison on of seri series es and par parall allel el cir circui cuit. t. (b) What are the applications applications,, merits and demerits of a series circuit? (c) What are the the aapp ppli licat catio ions ns and and aadv dvan antag tages es of a p para arall llel el circu circuit it??
[6+5 [6+5+5 +5]]
3. (a) In a para paralle llell magne magnetic tic circ circuit, uit, der deriv ivee the expres expressio sion n of tota totall mmf requi required. red. (b) An iron ring 100 sq.cm me mean an circumfere circumference nce and of cross sectiona sectionall area 5 sq.cm has a saw cut of 2mm length. It is wound with 500 turns of wire. If 0.5 mwb flux exists across the air gap, what will be the value of the exciting current? Take coefficien coefficientt of leak leakage=1.26 age=1.26 and relative permeabili permeability ty of iron = 5 00. [6+10] 4. (a) A coil of 20 ohms re resi sist stanc ancee has an in indu ducta ctance nce of 0.2 H and is connect connected ed in parallel with a 100 µF capacitor. Calculate the frequency at which the circuit will act as a non-inductive rsistance. Find also the value of that resistance at which the circuit will act as a non-inductive resistance. (b) An AC circu circuit it consis consists ts of tw twoo parall parallel el branc branches hes.. Bra Branc nch h 1 cons consist istss of a coil having R=20 Ω and L=0.1H. Branch 2 consists of a coil having resistor in series with 60 µF capacitor. Calculate i. The current in each branch ii. The line current iii. The power, when the circuit is connected to 230 V supply having a frequency of 50Hz. iv. Resistance v. Inductance of a single coil which will take the same current and power from the same supply. [8+8] 5. A 1 phase transformer has 500 turns on the primary and 40 turns on the secondary winding. windin g. The mean length of the magneti magneticc path on the core is 150 cm and the joints are equivalen equivalentt to an air gap of 0.1m 0.1mm. m. When the potenti potential al differe difference nce of 3000 3000V V is applied to the primary, the max flux density is 1.2 T. Calculate 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 1
(a) The cros crosss sectio sectional nal area of the core (b) No load secon secondary dary vo voltage ltage (c) The no load curren currentt drawn by the prima primary ry (d) Po Powe werr factor on no load give given n that amper amperee turn turnss p per er cm for a flux dens densit ity y of 1.2 T in the iron to be 5, the corresponding iron loss to be 2W/Kg at 50Hz and density of iron as 7.8 gm/cm 3 . [4+4+4+4] 6. (a) Deriv Derivee the express expression ion fo forr the aarmature rmature torque and sha shaft ft torq torque ue of a DC motor. (b) The armature of a 6 pole, DC shunt motor takes 300 A at the speed of 400 revolutions revo lutions per min minute. ute. The flux per pole is 75 mWb. The num number ber of armature turns tur ns is 500 500.. Th Thee tor torqu quee lo lost st in wind windage age,, frict frictio ion n and iro iron n loss losses es can be assumed a 2.5%. Calculate [6+10] i. Torque developed by the armature ii. Shaft torque iii. Shaft power in KW. 7. (a) Exp Explai lain n the revol revolvin vingg field type and the rev revolv olving ing arm armatur aturee type alternato alternators. rs. (b) A 6 pole DC generato generatorr is running aand nd producing a freq frequency uency of 60 Hz. Calculate the revolutions per minute of the generator. If the frequency is decreased to 20 Hz, how many number of poles will be required if the generator is to be run at the same speed. (c) Give Give the di diffe fferen rence ce bet betw ween a DC gen genera erator tor and and an alter alterna nator tor..
[6+6+ [6+6+4] 4]
8. What are the basic requiremen requirements ts of indicating instru instrument? ment? Briefly disc discuss uss them. [8+8] ⋆⋆⋆⋆⋆
2 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 2
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆ ⋆ ⋆ ⋆ ⋆
1. Fin Find d the curren currentt thro through ugh and the volt voltage age across all the elem elemen ents ts in the circui circuitt by applying Kirchoff ’s laws as shown in the figure 1. [16]
Figure 1 2. (a) Fin Find d the equiv equivale alent nt resi resistan stance ce betw between een the termi terminal nalss X and Y in the circ circuit uit as shown in the figure 2a.
Figure 2a (b) (b) Describe ribe in deta taiil the the step epss to app pplly Thev eveenin’ nin’ss theo eore rem m.
[12+ 2+44]
3. (a) Exp Explai lain n as ttoo wha whatt y you ou un unders derstand tand by: by: i. Static ii. Dynamic Dynamic induce inducemen mentt of ele electro ctromoti motive ve force. Illustr Illustrate ate by the help of simple sketches. (b) A coil of 100 turns is link linked ed by a mag magneti neticc flux of 20m 20mwb. wb. If this magn magneti eticc flux is reve reverse rsed d in a time of 2ms 2ms,, calc calcula ulate te the av averag eragee emf induced. induced. [6+ [6+10] 10] 4. Three impedances Z1=10+j31.4 Ω, Z2 = 6+j8 Ω, and Z3 = 3-j4 Ω are connected in parallel across a 200V AC supply. Calculate (a) Total admittanc admittance, e, conductance and susceptance of the whole circuit circuit.. 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 2
(b) Total current, power factor and power.
[8+8]
5. (a) Exp Explai lain n the princ principl iplee of work working ing of a singl singlee phase tra transfo nsformer rmer.. (b) Deriv Derivee from the first principles, the emf equation of a single phase transfor transformer. mer. [8+8] 6. (a) What is the fun function ction of a comm commutator utator in a DC m machi achine? ne? Discus Discusss with relev relevant ant figures. (b) Differe Differentiat ntiatee b betw etween een slip rings and commutator. (c) A 4 pole wa wave ve wou wound nd DC gene generato ratorr has 50 slo slots ts and 24 conduc conductors tors per slo slot. t. The flux per pole is 10 mWb. Determine the induced emf in the armature if it is rotating at a speed of 700rpm. [3+3+10] 7. (a) Giv Givee the differ difference ence bet betwe ween en an induc induction tion mo motor tor and a trans transform former. er. (b) A 12 pole, 3 phase alternator driven at 500 rpm supplies power to a 8 pole 3 phase induction motor. If slip of motor at full load is 3%, calculate the speed of the motor. (c) A 3 phase induction mo motor tor has starting torqu torquee of 100% and a maximum torq torque ue of 200 200% % of the ful fulll lo load ad tor torqu que. e. Fi Find nd slip slip at ma maxi ximu mum m tor torqu que. e. [4+ [4+6+ 6+6] 6] 8. (a) Giv Givee a comp comparis arison on of spri spring ng con control trol and gr grav avit ity y cont control. rol. (b) (b) Explain the erro errors rs occ occurri rring in a moving iron instr trum umen entt. ⋆ ⋆ ⋆ ⋆ ⋆
2 of 2
[8+ 8+88]
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 3
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆⋆⋆⋆⋆
1. (a) A 100W 100W,, 250V b bulb ulb is p put ut in se series ries w with ith a 40W 40W,, 250V bu bulb lb acr across oss a 500 500V V sup sup-ply.. What will be the power consumed by eac ply each h bulb? Will suc such h a comb combination ination work? (b) (b) State tate and explain Kirchoff’ off’ss curre rrent law and voltag agee law.
[10+ 0+66]
2. Determi Determine ne the p pow ower er loss in the 10Ω resistor by using Thev Thevenin’s enin’s theorem as show shown n in figure 2. [16]
Figure 2 3. Define the following: (a) Magn Magnetic etic fie field ld (b) Magnetic circui circuitt (c) Magn Magnetic etic flu flux x (d) Magnetic flu flux x densit density y (e) MMF (f) Rel Relucta uctance nce (g) Magnetic fi field eld stren strength gth (h) Permeability.
[16]
4. (a) A co coil il ooff power power fa factor ctor 0.9 iiss in seri series es w with ith a 120 µ F capacitor. When connected to a 50 Hz supply, the potential difference across the coil is equal to the potentiall difference across the capacitor. Find the resistance and inductance potentia inductance of the coil. (b) A metal filam filamen entt lamp rated 750 W, 110V is to be conn connecte ected d in seri series es with a capacitor across a 220V, 50Hz supply. Calculate i. The capacitance required 1 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 3
ii. The power factor.
[8+8]
5. The iron and full loa load d copper loss in a 40KVA 40KVA 1 phas phasee transfo transformer rmer are 450 W and 850 W respectively. Find (a) Effici Efficiency ency at full load when the power power factor of the load is 0.8 laggi lagging ng (b) The maxim maximum um efficienc efficiency y and (c) The load at which the maximum efficiency occurs.
[8+8]
6. What are the main part partss of a DC mac machin hine? e? Stat Statee the fun functio ction n of eac each h part with relevant figures. [6+10] 7. A 4-pole, 50 Hz, three phase induction motor has rotor resistance and reactance of 0.025 Ω and 0.02 Ω per phase respectively. Determine (a) The va value lue of speed at whi which ch the maxim maximum um torque occurs (b) The va value lue of the exter external nal rotor resi resistan stance ce per phas phasee to be ins inserte erted d to obtain 60% of the maximum torque at the starting. [16] 8. What do yo you u unde understa rstand nd by attraction attraction type and repu repulsi lsion on ty type pe ins instrum trumen ents? ts? Explain. [8+8] ⋆⋆⋆⋆⋆
2 of 2
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 4
I B.T B.Tec ech h Sup Suppli plimen mentar tary y Examin Examinati ations ons,, Aug Aug/Se /Sep p 200 2008 8 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours
Answer any FIVE Questions All Questions carry equal marks
Max Marks: 80
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Six re resis sistors tors ar aree conne connected cted as ssho hown wn in figu figure re 1a. If a batte battery ry ha havin vingg an emf of 30V and an internal resistance of 2Ω is connected to terminals A and B. Find i. current from battery ii. potential difference across 10Ω and 12Ω.
Figure 1a (b) Fin Find d the effec effectiv tivee resi resista stance nce of the fol follo lowin wingg com combin binatio ation n of resi resistan stances ces and the voltage drop across each resistance when the applied voltage is 70V across P and Q as shown in figure 1b. [8+8]
Figure 1b 2. (a) Giv Givee a detail detailed ed comp comparis arison on of seri series es and par parall allel el cir circui cuit. t. (b) What are the applications applications,, merits and demerits of a series circuit? (c) What are the the aapp ppli licat catio ions ns and and aadv dvan antag tages es of a p para arall llel el circu circuit it?? 3. Define the following: (a) Magn Magnetic etic fie field ld (b) Magnetic circui circuitt 1 of 2
[6+5 [6+5+5 +5]]
www jntuworld om
Code No: 07A 07A1EC 1EC07 07
Set No. 4
(c) Magn Magnetic etic flu flux x (d) Magnetic flu flux x densit density y (e) MMF (f) Rel Relucta uctance nce (g) Magnetic fi field eld stren strength gth (h) Permeability.
[16]
4. (a) Exp Explai lain n the beha behavio viour ur of AC throug through h R-C ser series ies ci circui rcuit. t. (b) A resi resistor stor carries two alte alternat rnativ ivee curr curren ents ts havin havingg sam samee freq frequenc uency y and phas phasee and having the same peak value of 20A. One is sinusoidal and the other is rectangular in waveform. Find the RMS value of the resultant current.[6+10] 5. (a) A 3000/ 3000/300V 300V 1 phas phasee trans transform former er giv gives es 0.6A an and d 60W as amme ammeter ter and v volt olt-meterr read mete reading. ing. When supp supply ly is giv given en to the low volt voltage age windi winding, ng, the hig high h voltage winding is kept open. Find i. Power factor of no load current ii. Magnetizing current iii. Iron loss component. (b) Write a note on vario various us winding parameters of a transform transformer. er. (c) Define regulation stating an expression to obtain it.
[10+3+3]
6. (a) A short shun shuntt compound generator suppli supplied ed 7.5 K KW W at 230 V. The shun shuntt field, series field and armature resistances are 100 Ω, 0.3 Ω and 0.4 Ω respectively. Calculate the induced emf and the load resistance. (b) Write down the similaritie similaritiess and dissi dissimilari milarities ties between motors and generators. (c) Explai Explain n the mo motor torin ingg and gen gener erati ating ng act actio ions ns of a DC ma mach chin ine. e.
[6+ [6+5+ 5+5] 5]
7. A 3 phase, 50Hz induction motor has a starting torque which is 1.25 times full load torque and a maximum torque which is 2.5 times full load torque. Neglecting stator resistance and rotational losses and assuming rotor resistance, find (a) Sli Slip p at full load (b) Slip at maxi maximum mum torq torque ue (c) (c) Ro Roto torr cu curr rren entt at star starti ting ng in per per un unit it of full full loa oad d ro roto torr cu curr rren ent. t.
[16] [16]
8. (a) Differe Differentiat ntiatee betw between een mo moving ving coi coill and m movi oving ng iron iinstrume nstrument. nt. (b) Explain with neat sketch the air friction damping. ⋆ ⋆ ⋆ ⋆ ⋆
2 of 2
[8+8]
