Electrical Machines - I Mid - II, November - 2014

1.The value of the diverter resistance is of the order ____
  • 025Ω
  • 100Ω
  • 0.1Ω
  • 1000Ω
Answer: C
2.A d.c. machine has maximum efficiency near ____
  • Half full-load
  • Full-load
  • 3/4 full-load
  • Twice the Full-load
Answer: B
3.The most economical method of finding no-load losses of a large d.c. machine is
  • winburne’s test
  • Hopkinson’s test
  • Retardation test
  • Brake test
Answer: A
4.The d.c. generator that has the poorest voltage regulation is_____
  • Shunt generator
  • Over-compounded generator
  • Under-compounded generator
  • series generator
Answer: D
5.A shunt generator gives its greatest voltage at ______
  • No-load
  • Full-load
  • half full-load
  • 3/4 full-loads
Answer: A
6.To increase the speed beyond the rated speed in a dc shunt motor the method used is
  • armature resistance
  • armature voltage
  • filed control
  • all the above
Answer: C
7.The value of back e.m.f in a d.c. motor is maximum at _____
  • Full-load
  • No-load
  • half full-load
  • 3/4 full-load
Answer: C
8.One of the main advantage of Swinburne’s test
  • is that applicable for both shunt and compound
  • very economical
  • ignores any change in iron losses
  • needs one of the running test
Answer: B
9.Shaft torque of a d.c. motor is less than armature torque because of
  • cu losses
  • mechanical losses
  • iron losses
  • rotational losses
Answer: D
10.Motor starters are essential for ______
  • Accelerating the motor
  • Starting the motor
  • avoiding excessive starting current
  • preventing fuse blowing
Answer: C
11.When two dc machines are connected back to back it is called as _________testing.
Answer: regenerative
12.The O.C.C. of a d.c. generator is also called its ___________characteristic.
Answer: no-load or magnetizing characteristics
13.No load test that can be performed on a motor (or) generator is ________test.
Answer: swinburne’s
14.Hopkinson’s test can be used to determine ________________.
Answer: temp rise
15.The armature copper losses in a d.c. machine are about _________%of total full load losses.
Answer: 20-30%
16.Maximum efficiency occurs at _________________.
Answer: cu losses = iron losses
17.The difference between no-load and full-load speed of a d.c . shunt motor is of the order of __%.
Answer: 2-5% of the no load
18.D.C. series motors are used in those applications is _____________is required.
Answer: traction
19.Cumulatively compounded motors application is ___________________.
Answer: rolling mill
20.The mechanical power developed in a d.c. motor is maximum when back e.m.f. is equal to ________ the applied voltage.
Answer: half of the applied voltage