Deemed University 2009 M.Tech Electrical & Electronics Engineering University: Lingayas University Term: I Title of the : Modeling and Analysis of Electrical Machine - Question Paper

Roll No. ..

 

Lingayas University, Faridabad

M.Tech (Electrical Engineering (Term I)

End Term Examination October, 2009

Course: Modeling and Analysis of Electrical Machine

Course Code: EL -501

[Time: 3 Hours] [Max. Marks: 100]

 

Before answering the question, candidate should ensure that they have been supplied the correct and complete question paper. No complaint in this regard, will be entertained after examination.

 

Note: Question No. 1 Part A is compulsory. Attempt any two questions from Part B and two questions from Part C. In all attempt five questions

 

SECTION A

Q-1 Part- A

(Choose the correct answer of the following multiple choice questions)

(i) Reluctance torque in rotating machines is present when

(a) air gap is not uniform

(b) reluctance seen by the stator mmf varies.

(c) reluctance seen by the rotor mmf varies.

(d) reluctance seen by the working mmf varies.

(ii) A pole-pitch in electrical machine is:

(a) = 180 elec (b) = 180 mech (c) > 180 elec (d) < 180 elec

(iii) The possible resistance of the shunt field winding of a dc machine is:

(a) 1 (b) 2 (c) 200 (d) 20

(iv) The induced emf (e) of a dc motor is:

(a) e = (b) e = _m (c) e = k _m

(d) e = k

(v) The armature inductance of dc machine is given by:

(a) - (b) L_a =
L_a = __________ ____________

2pf_s 2pf_s

(c) L_a = (d) None of these

L_a = ___________

2pf_s

(vi) The rotor current, I_rr is given by:

(a) I_rr = (b) I_rr =

(c) l_rr = (d) none of the above

(vii) In a stepping motor, the holding torque is the

(a) maximum load torque with phase-winding unexcited.

(b) Minimum load torque with phase-winding unexcited.

(c) minimum load torque with phase-winding excited.

(d) maximum load torque with phase-winding excited

(viii) In a 3-phase, 8/6 VRM, the total time taken for exciting the 3-phase windings is 30 msec. The rotor velocity in rpm is

(a) 250 (b) 333.33 (c) 500 (d) 111.11

(ix) A squirrel cage induction motor having a rated slip of 4% on fl has a starting torque as the full load torque. The starting current is

(a) equal to fl current (b) twice fl current (c) 4 times fl current (d) 5 times fl current

(x) For a bananced 3-phase machine, the power input is given by

(a) p_i = 3 (v_qs i_qs + v_dsi_ds) (b) p_i = 3/2 (v_qsi_qs+v_dsi_ds)

(c) p_i = 3/2 (v_qsi_qs + v_dsi_ds +2v₀i₀) (d) p_i = 3 (v_qsi_gs+ v_dsi_ds+ 2 v₀i₀

(1x10)

Part B

(a) Give the flow-chart for the computation of dc motor response. (5)

(b) Give the flow-chart for the dynamic simulation of the induction motor. (5)

Section B

Q-2. (a) Give the block diagram representation of the dc motor (10)

(b) A separately excited dc motor with R_a = 0.5, L_a = 0.003H, K_b = 0.8V|rad|sec is driving a load of J=0.0167 kg-m², B₁= 0.01N-m|rad|sec with a load torque of 100 N-m. Its armature is connected to a dc supply voltage of 220V and is given the rated field current. Find the speed of the motor. (6)

(c) Derive the expression for torque of a dc machine. (4)

Q-3. (a) How are noload test and blocked rotor test used for determining the induction motor parameters? Discuss. (5+5)

(b) Draw the flow chart for the steady state performance of the induction motor. (6)

(c) Discuss the operating characteristics of a 3-phase induction motor.

(4)

Q-4. (a) Derive the steady state equivalent circuit from the dynamic equations of the induction motor. (6)

(b) Derive the expression for electro magnetic Torque of induction motor in terms of current variables in arbitrary reference frames. (8)

(c) Discuss the power equivalence between 3- motor and 2machine to have meaningful interpretation in modeling, analysis and simulation. (6)

Section C

Q-5. (a) What are stationary reference frames and arbitrary reference frames. Explain with suitable diagrams. (10)

(b) Derive the expression for electromagnetic torque in terms of modified flux linkages and currents. (10)

Q-6. (a) Explain the concept of dynamic simulation and hence express the electromechanical equation in the form (10)

pw_rn = - -

(b) Derive the small signal dynamic equations for the voltages and torque for the induction motor. (10)

Q-7. (a) Draw the flow-chart for the computation of the transfer function and of frequency response and time response of induction motor (10)

(b) Derive the control principle of the induction machine (10)

Q-8. (a) Derive the normalized torque for induction motor as:

T_en = (7)

(b) Explain the working of a brushless dc motor. What are the advantages it offers over conventional dc motors. (5+3)

(c) Describe the operating principle of stepping motors. (5)