BEE ASSIGNMENT-6

                                 Assignment-6(D.C. Motors)

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

         (B). the armature of a 6 – pole, 6 circuit DC shunt motor takes 300 A at speed of 400 rpm. The flux per pole 75 mWb. The number of armature turns is 500. The torque lost in windage, friction and iron losses can be assumed as 2.5 %. Calculate

          i) The torque developed by the armature

ii) The shaft torque.

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

          (B) A 200V DC shunt motor takes a total current of 100 A and runs at 750 rpm. The resistance of the armature winding and shunt field winding is 0.1 ohms and 40 ohms respectively. Find the torque developed by the armature.

  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 6 pole DC motor has a wave connected armature with 87 slots, each slot containing 6 conductors. The flux per pole is 20mwb and the armature has a resistance of 0.13ohm when the motor is connected to 240V supply and the armature draws a current of 80A driving a load of15KW.caluculate (i)speed  (ii)Armature torque and (iii)shaft torque

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

BEE ASSIGNMENT-5

                                                  BEE

                             ASSIGNMENT-5(UNIT-5: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). the armature of a 6-pole D.C. generator has a wave winding containing 664 conductors. Calculate the generated emf when the flux per pole is 0.06 weber

And the speed is 250 rpm. At what speed must the armature be driven to

Generate an emf of 250 V if the flux per pole is reduced to 0.058 weber?

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

                               (or)

 (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.

              (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 lap wound DC generator having 80 slots with 10 conductors per slot generates at no load emf of 400 V, when running at 1000 rpm. At what speed should it be rotated to generate a voltage of 220 V on open circuit.

       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

BEE ASSIGNMENT-4

                                                            ASSIGNMENT-4

                                                      Unit-4(TRANSFORMERS).

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

(B) Derive the induced emf equation of transformer

( C) A 220/110V,50Hz,1.5KVA transformer has primary and secondary winding resistance of 1ohm and 2 ohm respectively and reactance of 3ohm and 5ohm respectively. Find the total resistance, equilibrium reactance and impedance referred to primary and secondary

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

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

            ( c) 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 100W.

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)

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)  A100KVA lighting transformer has full load loss of 3 KW; the loss is being equally divided between iron and copper. During a day the transformer operates on full load for 3 hours, on half load for 4 hours, the output being negligible for the remaining day.Caluculate the all day efficiency

     5.  (a)A single phase transformer working at unity power factor has an efficiency of 90 % at both one half load and at the full load of 500 W. Determine the efficiency at 75 % of full load.

          (b) A 100 kVA, 1000/10000 V, 50 Hz, Single phase transformer has an iron loss of 1100 W. The copper loss with 5 A in the high voltage winding is 400 W. Calculate the efficiency at 25 %, 0.8 Power factor. The output terminal voltage being maintained at 10000 V.

        ( c)a 200/400V, 50 Hz1-phase  transformer on test gave the following readings,

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

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

Find the voltage regulation at 0.8 pf lagging at full load.

BEE ASSIGNMENT-3(Alternating quantities)

                                                          ASSIGNMENT-3

                                             Unit-3(ALTERNATING QUANTITIES).

1. (a).Define the following terms.

(A) Alternating quantity (B) Waveform (C) Frequency (D) Time period (E) Instantaneous value (F) Average value (Mean) (G) RMS value (H) Peak Value (Maximum value) (I) form factor

 (b) Derive the expression for root mean square value (Effective value or virtual value or RMS value) of an alternating sinusoidal voltage wave form v = v_m Sin θ. (Using mid ordinate method and Analytical method)

  (c)   Derive the expression for Average value (Mean value) of an alternating sinusoidal current i = i_m Sin θ

3. (A) explain Addition phasor using Parallelogram method and Method of components.

    (B) Explain A.C through pure inductor and Show that power dissipated by a pure inductor exited by a sinusoidal voltage source V = Vm Sinωt is Zero.

  ( c ) An alternating current is given by the equation i=100 Sin(314t) find (i) maximum value (ii)frequency   (iii) Time period  (iv) value of current after t=0.01 sec

4. (A) Explain Ac through RC series circuit with phasor diagrams.

    (B) Explain AC through RLC series circuit with Phasor diagrams and Explain Resonance in RLC series circuit.

    (C) A coil of resistance R and inductance L is connected across 100v 50Hz supply. The current through the coil is found to be 2A and the power dissipated is 100W.find R and L

****5. (A) A reactor having negligible resistance and an inductance of 0.1 H is connected in series with a resistor of 15 ohms. The circuit is connected across a 230 V, 50 Hz, Single phase AC supply. Find

i) Current flowing through the circuit

ii) Power factor of the circuit

            iii) Voltage across the reactor.

**** B) A capacitor of 100 μF is connected across 200 V, 50 Hz, Single phase supply. Calculate

i) The reactance of the capacitor

ii) RMS value of the current

iii) The maximum value of the current

**** 6. (A)Find the active and reactive components of the current taken by a series circuit Consisting of a coil of inductance 0.1 H and resistance 8 and a capacitor of 120 μF connected to a 240 V, 50 Hz supply?

             (B) A conductor carries a sinusoidal A.C peak value 12 Amps superimposed on an direct current of 12 Amps.. Find the RMS value of resultant current.