BASIC ELECTRICAL ENGINEERING


UTTARAKHAND TECH. UNIVERSITY
B.TECH FIRST YEAR, 2012
 BASIC ELECTRICAL ENGINEERING


Time :- 3 hrs}
Total marks : 100]
Q1:- Attempt any four parts of the following :

  1. he Norton's and Thevenin's theorem. Also discuss about the duality of Norton's and Thevenin's Theorem.
  2. Use Nodal Analysis to find out the current in 4Ω. Resistor of Fig.1
    fig. 1.
      
  3. Apply Norton's theorem to calculate current following through 10Ω. Resistor of Fig.2
    fig 2. 
  4. Using Delta-Star Transformation Theorem calculate current from the supply voltage 130 V shown in Fig.3.
    fig 3.
     
  5. Distinguish the difference between following :
    (a) Active and Passive elements
    (b) Ideal voltage and Current source.
  6. State and proof the maximum power transfer theorem.
Q2:- Attempt any four parts of the following :
  1. Calculate the r.m.s value, the form factor and the peak factor of a periodic voltage having following values for the equal time interval changing suddenly from one value to the next.
    0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, -5, -10V etc.
    What would be the r.m.s. value of sine wave having same peak value ?
  2. Explain the nature of power factor in two watt-meter method of three phase power when :
    (a) the two readings are equal and positive
    (b) the two readings are equal but opposite in sign and
    (c) one of the watt-meter reads zero
  3. A capacitor of 25 mF is connected in series with a variable resistor. The circuit is connected across 50 Hz mains. Find the value of the resistor for a particular condition when the voltage across the capacitor is half the supply voltage.
  4. Explain relative permeability. Calculate the mmf required to produce a flux of 0.015 Wb across an air gap 2.5 mm long an effective area of 200 cm2.
  5. An alternating current of peak value 45 A has the following wave forms in turn :
    (a) Sinusoidal
    (b) Full wave rectified sinusoidal
    (c) Rectangular and
    (d) Triangular
    Show the above wave forms and calculate average and r.m.s. value.
  6. An iron ring of mean circumference 1.2m is uniformly wound with 400 turns of wire. When a current of 1.5 Amp is passed through the coil, a flux density of 1.25 Wb/ m2 is produced in the iron. Find the relative permeability of iron under these conditions.
Q3:- Attempt any two of the following :
  1. Explain the following :
    (a) Defecting Torque
    (b) Controlling Torque
    (c) Damping Torque
    Discuss the principle of operation and construction of PMMC type measuring instrument.
  2. A single phase energy meter hours a constant of 1200 rev/kWh, When a load of 200 W is connected the disc rotate at 4.2 rev/min if the load is on for 10 hours, how many units are recorded as an error ? Also find percentage error.
  3. Explain how does the input current adjust to meet out the new conditions, when the load current in the transformer increases ?
    Calculate the efficiency at half and full a 100 k VA transformer for p.f. of
    (a) unity
    (b) 0.8 The copper loss is 1000W at full load and iron loss is 1000W.
Q4:- Attempt any two parts of the following :
  1. Three impedance each having a resistance of 20Ω and an inductive reactance of 18Ω are connected in star across a 400V, three phase supply. Calculate
    (a) the line current,
    (b) the power factor,
    (c) total power in kW.
  2. Explain principle of operation of a DC generator. Also derive the E.M.F equation for DC generator. Also derive the E.M.F equation for DC generator.
  3. A shunt generator has a full load current of 196A at 220V. The stray losses are 720 W and the shunt field resistance is 55 Ω . If it has a full load efficiency of 85%, find the armature resistance. Also, find the load current corresponding to maximum efficiency.
Q5:- Attempt any two of the following :
  1. Explain the method of starting of 3 phase synchronous motor. Also discuss its application.
  2. What do you mean by "slip" ? A three phase, 50 Hz, pole induction motor has a slip of 2% at on load and 4% at full load. Determine
    (a) synchronous speed
    (b) no load speed
    (c) full load speed
    (d) frequency of rotor current at stand still,
    (e) frequency of rotor current at full load.
  3. Write short technical note on any two of the following :
    (a) Slip-Torque characteristics of 3 phase induction motor.
    (b) Construction and working of single phase capacitor start induction motor.
    (c) Basic elements of power system with help of single line diagram.
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