AP ECET EEE 2019-7

1. Free running and coasting periods are generally long in case of

A. City service
B. sub urban service
C. main line service
D. outer Suburban service

Answer : main line service
Explanation:-

2. In an induction motor under running condition, the rotor reactance per phase is_______________its standstill phase reactane

A. s times
B. equal to
C. 1/s times
D. (1-s) times

Answer : s times
Explanation:-

3. AC voltage regulators are widely used in_____

A. traction drives
B. fan drives
C. synchronous motor drives
D. slip power recovery scheme of slip ring induction motor

Answer : fan drives
Explanation:-

4. A lap wound DC machine has 400 conductors and 8 poles. The voltage induced per conductor is 2v. The machine generates a voltage of

A. 100V
B. 200V
C. 400V
D. 800V

Answer : 100V
Explanation:-
Given Conductors=400, poles=8, Voltage induced per conductor=2v
For a lap wound DC machine the number of parallel paths is equal to Number of poles
A=P=8
The Generated voltage=(voltage induced in 400 conductors)/A
Vg=(400*2)/8
Vg=800/8=100 V

5. The maximum possible speed at which an alternator can be driven to generate 50Hz and 4000V is_______

A. 400 rpm
B. 3600 rpm
C. 3000 rpm
D. 1500 rpm

Answer : 3000 rpm
Explanation:-
Given 50Hz
Speed is inversly proportional to Number of Poles
For a max speed we use min poles, so we Consider 2 poles
N=120f/P=(120*50)/2=60*50=3000 rpm

6. The DC series motor is most suitable for traction services but more practically for urban/Suburban services because___

A. DC series motors are suitable for regenerative breaking
B. DC series motors are capable of withstanding rapid fluctuations in supply voltage
C. DC series motors are capable of developing high torque at start
D. DC series motors are capable of withstanding temporary interruption of supply without undue rush of current

Answer : DC series motors are capable of developing high torque at start
Explanation:-

7. The short circuit characteristics of an alternator is___

A. Always linear
B. Always non linear
C. Always triangular
D. Always circular

Answer : Always linear
Explanation:-

8. The form factor of sinusoidal alternating current is_________

A. 1
B. 0
C. 1.11
D. 1.15

Answer : 1.11
Explanation:-
The form factor is defined as the ratio of Rms value to the Average value
for a sinusoidal alternating current the form factor = 1.11

9. The earth wire should be

A. good conductor of electricity
B. mechanically strong
C. good conductor and mechanically strong
D. mechanically strong but bad conductor of electricity

Answer : good conductor and mechanically strong
Explanation:-

10. In order to reduce the hysterisis loss

A. core may be laminated
B. silicon steel may be used as the core material
C. core may be constructed with any permanent magnet material such as Alnico
D. core may be impregnated with varnish

Answer : silicon steel may be used as the core material
Explanation:-