Electrical Machines Which of the following bearings and their uses are correct ball bearings → small machines both A and B roller bearings → large machines neither 1 nor 2 ball bearings → small machines both A and B roller bearings → large machines neither 1 nor 2 ANSWER DOWNLOAD EXAMIANS APP
Electrical Machines The direction of generated emf in the armature coil of a DC machine is 1. the same as that of the current in a generator 2. the same as that of the current in a motor 3. opposite to that of the current in a generator 4. opposite to that of the current in a motor From these, the correct answer is 2, 3 1, 4 2, 4 1, 3 2, 3 1, 4 2, 4 1, 3 ANSWER DOWNLOAD EXAMIANS APP
Electrical Machines Unbalance 3 - Φ stator currents cause All of these double frequency currents in the rotor. vibrations. heating of rotor. All of these double frequency currents in the rotor. vibrations. heating of rotor. ANSWER DOWNLOAD EXAMIANS APP
Electrical Machines How can the synchronous speed of a 3 - Φ IM be varied? Both (A) and (B). By varying supply voltage. By varying number of poles. By varying the supply frequency. Both (A) and (B). By varying supply voltage. By varying number of poles. By varying the supply frequency. ANSWER DOWNLOAD EXAMIANS APP
Electrical Machines In a 3 - Φ IM with line frequency f1 and winding factor kw1 and kw2 for stator and rotor respectively the ratio of per phase stator winding emf E1 to per phase rotor winding emf E2 at standstill is given by E1 / E2 = N1kw1 / N2kw2. E1 / E2 = N1 / N2. E1 / E2 = f1kw1 / f2kw2. E1 / E2 = 1. E1 / E2 = N1kw1 / N2kw2. E1 / E2 = N1 / N2. E1 / E2 = f1kw1 / f2kw2. E1 / E2 = 1. ANSWER DOWNLOAD EXAMIANS APP
Electrical Machines If the field of a dc shunt motor gets opened while the motor is running, then the armature will oscillate about original speed as the mean speed armature current will drop motor will become slow. motor will attain dangerously high speed armature will oscillate about original speed as the mean speed armature current will drop motor will become slow. motor will attain dangerously high speed ANSWER DOWNLOAD EXAMIANS APP
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