3.17: AC Generators

Question 1

463. Which type of alternator is aircraft system?
     (a) Induction type alternator.
     (b) Rotating field type alternator,
     (c) Rotating armature type alternator.

Answer 1

(b) Rotating field type alternator,

Question 2

464. An AC Generators output is rated :
     (a) In kWatts with a Power Factor
     (b) In KVA with a Power Factor
     (c) As a Power Factor only

Answer 2

(b) In KVA with a Power Factor

Question 3

465. With a rotating field type alternator the slip rings carry the:
     (a) Field current.
     (b) a.c. output current.
     (c) rectified a.c. output current.

Answer 3

(a) Field current.

Question 4

466. An alternator has two pairs of rotating poles, if the output frequency is 400 Hz, the
     rotational speed is:
     (a) 120rpm.
     (b) 12000rpm.
     (c) 2000rpm.

Answer 4

(b) 12000rpm.

F = (N*P)/120

where F is frequency in Hertz (Hz), N is the number of poles total (not pairs of poles) and N is the speed of rotation in RPM
(400*120)/4 = 12,000 rpm

Question 5

467. The Synchronous Speed of the rotating magnetic field in a generator is given by
     which formula:
     (a) Ns = 60 X f X p
     (b) Ns = 60 / f X p
     (c) Ns = 60 X f / p

Answer 5

(c) Ns = 60 X f / p

Note: Formula is F = (NP)/120
This is where P is total poles, however is use pairs of poles then formula is F = (NP)/60

Question 6

468. A resistive load on an alternator will
     (a) reduce the output frequency.
     (b) increase the output frequency.
     (c) decrease the output voltage.

Answer 6

(c) decrease the output voltage.

Question 7

469. An inductive load on an alternator will
     (a) reduce the terminal voltage.
     (b) increase the terminal voltage.
     (c) reduce the output frequency

Answer 7

(a) reduce the terminal voltage.

Question 8

470. If the line voltage of a three phase star connected system is 300 V. The phase
     voltage will be:
     (a) 500.5 V
     (b) 173.4 V
     (c) 140.5 V

Answer 8

(b) 173.4 V

Star wound: Line to line voltage = Phase x 1.73

Question 9

What are the formulas for the below: (Line to line vs phase)
Star wound
Delta wound

Answer 9

Star Wound:

Delta Wound:

Question 10

471. In a three phase balance system:
     (a) each phase is the same
     (b) each phase is different
     (c) one phase is different from the other two

Answer 10

(a) each phase is the same

Question 11

472. The output winding of a three phase brushless alternator, are wound in which
     formation?
     (a) Star
     (b) Delta
     (c) Star-Delta

Answer 11

(a) Star

Question 12

473. The brushless Alternator uses diodes mounted in the
     (a) Stator
     (b) Rotor
     (c) Terminal Connection Box

Answer 12

(b) Rotor

Question 13

What is the most common type of aircraft alternator?

Answer 13

Question 14

Generator output is what unit?

Answer 14

Question 15

In a Rotating field type alternator, what carries the field current?

Answer 15

Note: The field current is the current supplied to the field windings of a generator or motor to establish the magnetic field for its operation

Question 16

What is the formula for Synchronous speed ? (pairs of poles)

Answer 16

Question 17

What is the effect of an inductive load on an alternator?

Answer 17

Question 18

A Three phase balance system means what? (in terms of phase)

Answer 18

Question 19

What way (Star/Delta) is the output winding of a three phase brushless alternator wound?

Answer 19

Question 20

Brushless alternator uses diodes mounted where?

Answer 20

Question 21

46. Why are two-phase ac servomotors made long and narrow?
    (a) to make it take less current rom the supply
    (b) to increase the starting torque and lower the inertia
    (c) to reverse its direction of rotation

Answer 21

(b) to increase the starting torque and lower the inertia