AC Machines Flashcards
To adjust the power of the alternators, adjust the ____________.
A. power factor
B. governor
C. field current
D. frequency
Governor
What kind of load of an alternator has for a negative voltage regulation?
A. resistive
B. inductive
C. Inductive and resistive
D. Capacitive
capacitive
For two alternators operating in parallel, if the load shared by one of them is to be increased, its field excitation is
A. to be strengthened keeping input torque the same
B. to be weakened keeping input torque the same
C. to be kept constant but input torque should be increased
D. to be kept constant but input torque should be decreased
to be kept constant but input torque should be increased
What is the formula for the synchronous speed of a motor?
A. Ns = 120P/f
B. Ns = 120fP
C. Ns = 120f/P
D. Ns = 60f/P
Ns = 120f/P
What affects the speed of a rotating field?
A. torque and frequency
B. torque and no. of poles
C. frequency and number of poles
D. frequency and horsepower
frequency and number of poles
If the speed of an induction motor increases, what happens to the rotor frequency?
A. Increases
B. Decreases
C. does not change
D. frequency has no relation to the speed
Decreases
When the frequency of a synchronous motor increases, what happens to its speed?
A. Decreases
B. Increases
C. remains the same
D. none of these
Increases
Which of the following is NOT a reason why single-phase induction motor run?
A. two windings are displaced from each other
B. hysteresis
C. one of the current is made out of phase between the lines
D. shaded poles
Hysteresis
What is the main reason that alternating current replaced DC for general used?
A. AC voltages conveniently transformed
B. AC generators do not need slip rings
C. AC minimizes magnetic fields
D. A given AC current does not heat a power line as much as the same as DC current.
AC voltages conveniently transformed
Which of the following is not a basic element of transformer?
A. core
B. Primary winding
C. secondary winding
D. mutual flux
Mutual flux
Which of the following transformer has only one winding?
A. current
B. distribution
C. autotransformer
D. power
autotransformer
What type of transformer bank is used to convert 2-phase to 3-phase power?
A. open-delta
B. scott-T
C. wye-delta
D. delta-wye
scott-T
Transformers are used to change the value of the following EXCEPT:
A. alternating current
B. alternating voltage
C. power
D. resistance
power
Which is not a characteristic of an ideal transformer?
A. finite permeability
B. infinite permeability
C. no losses
D. no leakage flux
finite permeability
Ideal transformer assumptions do NOT include _____________
A. zero resistance of the winding
B. zero reactance of the winding
C. no saturation of the core
D. no leakage flux
zero reactance of the winding
Open circuit test on transformers is conducted to determine
A. hysteresis loss
B. copper loss
C. core loss
D. eddy current loss
core loss
Copper loss of a transformer are determined by means of a/an ___________ test.
A. open-circuit
B. polarity
C. short-circuit
D. inductive-circuit
short-circuit
To protect the Δ-Δ power transformer against fault, the CT will have
A. Δ-Δ connection
B. Δ-Y connection
C. Y-Δ connection
D. Y-Y connection
Y-Y connection
An excellent indicator of the condition of the oil in the power transformer is obtained by dividing the IFT (interfacial tension) by the NN (neutralization number). This ratio is known as the _____________.
A. Neutralization Number
B. Myers Index Number
C. Polarization Index Number
D. Transformer turn ratio
Myers Index Number
The starting / in rush current of the transformer is generally _______ times of its full load current.
A. 12
B. 20
C. 10
D. 6
10
