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                         All the best for BEE exam.Follow the instructions given on the last day for the Exam.

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BEE 5,6,7,8 assignments

                                        Assignment-5

                            UNIT-4(a):D.C. Generators

1.      (A) Explain in detail, the principle of a single loop DC generator.

                                  (OR)

      Explain the principle of operation of DC generator.

 (B). A 4-pole generator having wave wound armature winding has 48 slots, each slot contains 20 conductors. What will be the voltage generated in the machine when driven at 1500 r.p.m? Assume the flux per pole is 7.0 mWb.

2.      (A). Explain briefly various types of generators.

                               (Or)

Explain different types of excitations in D.C. Generators

                               (Or)

Explain how will you classify DC generators in detail and also explain the types of DC generators

 (B) Write the applications of D.C generators.

 (C). A 6 – pole, Lap wound armature has 840 conductors and flux per pole of 0.018 Wb.   Calculate the emf generated when the machine is running at 600 rpm.

3.      (A) Draw a detail sketch of a DC machine and identify the different parts. Briefly explain the function of each major part.

                                        (or)

List out the main parts of a DC machine and explain with help of neat sketch.

                                        (or)

     Explain the construction of D.C.Generator

                                        

              (B) A 4 – pole DC shunt generator with lap connected armature supplies a load of 100 A at 200 V. The armature resistance 0.1 ohms and the shunt field resistance is 80 ohms find the i) Total armature current ii) Current per armature path iii) Emf generated.

         4. (A). Explain the losses that occur in a DC machine.(or) explain the total losses in D.C. Generator (or)Explain the total losses in D.C. Motor and explain how to reduce them

    (B) A 4 pole D.C. shunt generator with wave wound armature has 45 slots each having 15 conductors. The armature resistance is 0.5 Ω and the shunt field resistance is 200 Ω.

The flux per pole is 30 m Wb. If a load of 15 Ω resistance is connected across the

Armature terminals. Calculate the voltage across the load when the generator is driven

at 1200 r.p.m. (ans 781.9)

       5. (A). Derive from first principle an expression for the induced EMF in the armature of the dc Machine.  (Or)  Derive the emf equation of D.C. Generator.

     (B) A dynamo has a rated armature current at 250A.what is the current per path of the armature if the armature winding is lap or wave connected? The machine has 12 poles.

6. (A) Discuss in detail the process of voltage build up in a dc generator and explain about causes for failure of voltage build up process in d.c generator.

  (B) A separately exicted D.C generator ,when running at 1000RPM supplied 200A at 125V.what will be the load current when the speed drops to 800RPM if “If” is unchanged? Given that the armature resistance=Ra=0.04Ω and brush drop=2V

                                                                       Assignment-6

                                                           UNIT-4B:D.C.MOTORS

1.     (A).Explain the principle of operation of DC motors.

             (B). A 220V series motor runs at 800RPM, when taking a current of 15A the motor has Ra=0.3ohm and R_f=0.2ohm.find the resistance to be connected in series with the armature. If it has to take the same current at the same voltage at 600 RPM.assume flux is proportional to current.

 2. (A) Derive the torque equation of a DC motor.

     (B) A 250 V. D.C shunt motor takes a line current of 20 A. Resistance of shunt field winding is 200ohms and resistance of the armature is 0.3ohms. Find the armature current and the back e.m.f.

  3. (A) what is the significance of back emf generated in a DC machine hence explain the principle of operation of a DC motor.      

                                                   (or)

          Explain how back emf makes d.c motor self regulating.

       (B) A 100V series motor takes 45 A when running at 750 rpm. Its armature resistance is 0.22 ohms, while the series field resistance is 0.13 ohms. Iron and frictional losses amounts to 750 W.Find the shaft power.

4. (A) Draw the power flow diagram of a DC shunt motor and also explain the following terms

 i. Electrical Efficiency,

ii. Mechanical Efficiency and

iii. Commercial Efficiency.

  (B) A 220 V D.C shunt motor runs at 500 r.p.m when the armature current is 50 A. Calculate the speed if the torque is doubled. The armature resistance of the motor is 0.2 Ω

5. (A) Write the applications of Dc motors.

   (B) A 460V D.C series motor runs at 1000RPM taking a current of 40A.caluculate the speed and percentage change in torque if the load is reduced so that the motor is taking 30A.total resistance of the armature and field circuits is 0.8Ω.Assume ‘Ø’ is proportional to filed current.

6. (A) Explain the losses in D.C. Motor  (b) What happens if D.C series motor is started on no load?(C) why series motors are applicable for traction applications

                                                                 Assignment-7

      UNIT4C:A.C.MACHINES (3 PHASE INDUCTION MOTOR)

1. (A) Explain the principle of operation of a 3 phase induction motor.

    (B) . Three phase induction motor is wound for 4 – poles and is supplied from a 50 Hz supply. Calculate

                      i) The synchronous speed

                     ii) The speed of the motor when the slip is 3 %

          iii) The rotor frequency.

*****2. (A) Explain with the help of diagrams how a rotating magnetic field is produced in a 3 phase induction motor. (Or) Explain why 3-phase induction motor is self stating induction motor.

(Or)   A rotating magnetic field is produced in the air gap of a 3-phase induction motor when a balanced supply is given to the stator. Justify the statement with necessary mathematical equations and phasor diagrams.

      (B).power input to a three phase induction motor is 75kw.the stator losses total 1.5kw.find the total mechanical power developed and the rotor copper losses per phase if the motor is running at a slip of 3%.

3. How the induction motors are classified? Explain the types of induction motors in detail.
4. (A) Explain why a 3-phase induction motor cannot develop torque when running at synchronous speed.
   (B) Explain why induction motor is called rotating transformer
   (C).  A 3 phase 4 pole 50 Hz induction motor at stand still has 180v induced across its star connected terminals. The rotor resistance and stand still reactance per phase are 0.6ohm and 0.4ohm respectively. Calculate the speed when the rotor is drawing a current of 6A at a particular load. Also calculate the speed at which the torque is maximum and the corresponding value of the rotor.

5. (A) Derive the condition for maximum torque under running condition of 3-phase induction Motor
      (B) a three phase induction motor has starting torque of 100% and a maximum torque of 200% of the full load torque. Find the slip at maximum torque.

6.  (a) Explain the effect of slip on the rotor circuit.
     (b)  A 6 pole induction motor is fed by 3-phase supply and running with a full load slip of 3% .find the full load slip of 3 phase induction motor and also the frequency of rotor emf.

                                                                    Assignment-8                      

                                                      UNIT-5: BASIC INSTRUMENTS

1.     (A) explain the classification instruments

(B)Explain the operating principles of Electrical instruments

2.     Explain the essentials of indicating instruments.

3.     (a) Compare spring control with gravity control

(b) Explain about damping curves.

4.     (a)Explain the construction and operation of Permanent Magnet Moving Coil instruments with a neat diagram.

(b) Explain PMMC ammeters and voltmeters.

             (c) a moving coil voltmeter with a resistance of 20Ω gives a full scale deflection  of 120°

When a potential difference of 100mV is applied across the moving coil. The moving coil has dimensions of 30mm×25mm and is wound with 100turns.the control spring constant is 0.375×10^-6  Nm/deg.find the flux density in the air gap  .find  also the diameter of copper wire of coil winding if 30 percent of instrument resistance is due to coil winding. The specific resistance for copper =1.7×10^-8 ohm-meter.

      5. (a) Prove that deflecting torque is Proportional to the Square of the current in

Attraction type MI instruments.(General torque equation of MI instruments)

          (b) Explain the construction and operation of Moving iron attraction type instruments with  a Neat diagram.

         (c) The inductance of a moving iron instrument is given by L=(10+5ⱷ-ⱷ²) µh where “ⱷ” is the deflection in radian from zero position. The spring constant is 12×10^-6 nm/rad. Estimate the deflection for a current of 5A.

       6. (a) Explain the construction and operation of Moving iron Repulsion type instruments with  a Neat diagram.

           (b) Explain advantages and disadvantages and errors in MI instruments.

        

ASSIGNMENTS SUBMISSION

1.All CSE second year students are instructed to submit  all assignments,observation,record on or before 08-OCT-2014.

2.write the part b(EDC related experiments) of EE Lab on or before 08-OCT-2014.

Solutions to few assignment problems

                                        Solutions to few assignment problems.

Assignment 4(Transformers)

                                                   

                                                            ASSIGNMENT-4

                                                      UNIT-3: Transformers

1.(A) Explain the working principle of 1-Ø (Single phase) Transformer and what happens If DC supply is given to transformer? Give the applications of transformer.

  (B) Derive the induced emf equation of transformer

  (C) The maximum flux density in the core of 250/3000V, 50Hz, single phase transformer is 1.2 web/m² .if the emf/turn is 8v determine the primary and secondary turns and the area of the core.

[Ans: 32, 375, 0.02m2]

     2.    (A) Explain the losses that occur in Transformers

     (B)Derive the maximum efficiency condition and expression for load KVA corresponding to Maximum efficiency

      (c).A 3000/300V 1-phase transformer gives 0.6A and 60W as ammeter and wattmeter reading, when supply is given to the low voltage winding, the high voltage winding is kept open. Find (i) power factor of no load current (ii) Magnetizing current (iii) Iron loss component

[Ans: 0.333 lagging, 0, 05656A, 0.02A]

    3.      (A) Draw the phasor diagram of Transformer under no load.(IDEAL T/F AND PRACTICAL T/F)

       (B) Draw the phasor diagram of transformer on load (consider resistance and leakage reactance)

        ( c ). A 250 KVA single phase transformer has iron loss of 1.8KW.The full load copper loss is 2000watts.caluculate (i) Efficiency at full load.  (ii) KVA supplied at maximum efficiency.(iii)Maximum efficiency at 0.8 lagging power factor.

[Ans:98.135%,237.1708KVA,98.137%]

    4.      (A) Define efficiency and regulation of a Transformer. Explain how will you pre - determine the efficiency and regulation with neat circuit diagrams.

                                        (OR)

          Explain OC and SC tests on single phase transformer to determine regulation and efficiency

 (B) Explain why the transformer is rated in KVA instead of KW.

  ( C) a 200/400V, 50 Hz 1-phase  transformer has the following test data.

OC Test (LV):200V, 0.7A, 70w on LV side.

SC Test (Hv); 15V, 10A, 80W on HV side.

Calculate the secondary voltage when delivering 5KW at 0.8 lag v1=200v.

     5.   (A) Explain the construction of transformer.  

          

        ( B) The required no load voltage ratio in a 150 KVA, 50Hz single phase transformer is 5000/250V.find the efficiency at half rated KVA, Unity power factor and also efficiency at full load 0.8 PF lagging if the full load copper losses are 1800watt, core losses are 1500W.

[Ans:97.46%,97.33%]

  

ASSIGNMENT-3-Alternating quantities

ASSIGNMENT-3(Alternating quantities)

Assignment -2 (UNIT-1.b Network analysis )

                        Assignment -2  (UNIT-1.b  Network analysis )

              

                                                       

                                                            

BEE unit 1 (a ) assignment

                                                      BEE

                  

Note: write the below guidelines in the first page of the Assignment note book

Guidelines for writing assignment:

1. Read the entire unit thoroughly before writing the assignment

2. Don’t copy the assignment from the others.

3. Write the assignment in separate note book (do not write in papers, do not write in class work)

4. During the evaluation of the assignment questions will be asked from the corresponding unit.

5. Strictly instructed to submit the assignment on or before scheduled time. Assignments will not be accepted after schedule time.

6. during the evolution of the assignment approach towards the concept, practical understanding of the concept, documentation skills, presentation skills, problem solving skills are checked. Assignment will be evaluated for 10 marks.

                ASSIGNMENT-1 (unit-1(a): Introduction to electrical engineering)

NOTE:  Submit the assignment on or before 09-09-2013

1. (a) write about electrical engineering concepts that you come across in your daily life(not more than two pages)

   (b) A copper wire is stretched so that its length is increased by 0.1%. What is the percentage change in its resistance? 

 (Ans: 0.2%)

2. (a) Explain the characteristics of resistor, inductor, capacitor.

    (b) A length of wire has a resistance of 4.5 ohms. Find the resistance of another wire of the same material three times long and twice the cross-sectional area (ans: 6.75 ohm)

     (c) Explain about self inductance and mutual inductance.

3. (a) State and explain ohm’s law and discuss where it fails.

   (b) An electric radiator is required to dissipate 1KW when connected to a 230V supply. If the coils of the radiator are of wire 0.5mm in diameter having resistivity of 60µΩ-cm, caluculate the necessary length of the wire

(Ans: 1730.2cm)

4. (a) Explain Laws of resistance  (or)  explain the different factors on which the resistance is dependent

   (b) Three resistances of 5 ohms, 10 ohms and 15 ohms are connected in parallel. If the current in 10 ohms resistance is 3 A, What is the current in other resistors and total current? Also determine the voltage applied to the circuit

(Ans: 6A, 2A, 11A, 30V)

5. (a)  state and explain Kirchhoff’s laws.

    (b ) Two coils connected in parallel across 100v Dc supply, takes 10A current from the supply. Power dissipated in one coil is 600W.find

(a)  What is the resistance of the coil (ans: 16.667ohm)

(b)  What is the current flowing through that coil(ans:6A)

(c)  What is the current in the other coil(4A)

(d)  What is the resistance of the other coil(25ohm)

  

6. (a) write a short notes on

    (1) Conductors (2) insulators (3) semiconductors

     (b) What is the voltage across X and Y in the circuit shown in below figure.