Jaypee Institute of Information Technology (JIIT) 2008 B.E Test 3 : Electrical Machines
37-
Roii No
JAYPEE UNIVERSITY OF INFORMATION TECHNOLOGY Waknaghat. Distc. SOLAN (HP>- 173 215 TeM-3.2008
Subject : Electrical Machines and Instruments Code : 07B3IEC103
Branches : ECE/CE Mil 30
Sem : III Time : 1 h 30 min.
1. (ar) Derive the emf equation for a DC generator. Hie induced emf in a dc generator
running at 600 rpm is 230 V. Determine the $pccd a: which the induccd cmf is 220 V. assuming the flux to be constant. (1 -* 2 * 3)
(6) Explain the term critical field resistance"* of a dc shunt gcncrwor with reference to its relevant characteristic. (2)
2. (a) Explain how the torque is produced in a dc motor r id derive its formula. A 4.
pole. Iap*connccted dc scncs motor, with $64 condi ton. takes u cancel of 100 A at 440 V. The antutuie resistance and the series-field resistance ore 0.16 Cl and 0.04 ft, respectively. The flux per pole is 100 mWb. Calculate (0 the speed, and (jf| the gross torque developed by the armnturc. (1 + 1 +1 *3)
(b> Explain why the induced emf in a dc motor is called back or counter etnf. (2)
3. (a) A 230-V, 50-H7- split-phase induction motor has the mam-winding resistance of
I Cl aad inductive reactance of 10 O. and the auxiliary-winding resistance of 20
II and inductive reactancc of S fi. Determine the value of capacitance to be connected in series .\ith the auxiliary winding to obtain maximum starting torque. (3|
(A) Draw the schematic diagram or a single-phase, permanent-capacitor induction motor. (2>
4. (a) Draw a diagram of a VR stepper motor with 6 poles on its stator and 4 teeth on its
rotor. and make its corresponding truth table for 2-phase ON mode. (2 + I *3) <6) Calculate' the pulse rate required to obtain rotor speed of 2400 rpm for a stepper motor having a resolution of 200 steps/rev. (2|
5. ta) Draw the equivalent circuit per pha.se of a synchronous generator and the phasor
diagram for the lagging power factor <1 + 23)
A 4-pole induction motor is fed from 50-H? supply If the frequency of rotor cmf at full-load is 3 Hz, find the full-load slip. (2)
6. itf) In a SO-kVA, I l-kV'400-V, single-phase transformer, the iron and coppcr
losses are 500 W and 600 \V, respectively under rated conditions Calculate (f) the cfficicncy at unity power factor at full load. 00 the load tor maximum efficiency, and {Hi) the iron and copper losses for this load. <1 + 1 + 13)
(6) What is the role of damping torque in analog type indicating instruments? A moving coil instrument gives a full-scale Jcflcction of 10 mA when (he potential difference across its terminals is 1 V Calculate the s*rics resistance to measure 1 (H) V on full scalc (I + 1 2)
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| Earning: Approval pending. |
