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Power Engineering 4a - Unit 8 โ Electro
technology Questions and Answers
Graded A+
When using Fleming's Left Hand Rule, the index finger represents
A) generator action flux direction.
B) motor action motion direction.
C) generator conductor motion direction.
D) motor action flux direction.
E) motor action direction of current flow. โโD
A basic law of electricity is, unlike charges attract each other and like charges
A) impact each other.
B) hold each other.
C) attract each other.
D) are neutralized.
E) repel each other. โโE
Some of the hazards of electrical transformer cooling oil can be compensated for by adding
A) chelates.
B) anti-foaming substances.
C) chlorinated hydrocarbons.
D) Freon.
E) organic compounds. โโC
Synchronous motors are used to
A) improve electrical system power factor.
B) bring up alternators to synchronous speed.
C) reduce the power factor for a power system.
D) eliminate the need for a DC power source.
E) drive a steam turbine. โโA
A kilowatt-hour meter has a small motor which
A) turns at a constant speed.
B) slows down as power consumption increases.
C) has a speed proportional to power consumption.
D) moves the meter demand pointer.
B) Reduce the voltage to zero first and then open the circuit breaker
C) Reduce the alternator current first to zero and then open the main disconnecting switch.
D) Reduce the current first and then reduce the voltage of the alternator
E) Reduce the speed of the alternator first and then open the circuit breaker. โโC
The use of electronic switches can result in excessively high transformer voltages due to a phenomena called
A) capacitive reactance.
B) inductive reactance.
C) phase lag.
D) reactive voltage loss.
E) harmonic distortion. โโE
A simple step-up transformer has a primary winding of 400 turns and a secondary winding of 1800 turns. If the primary voltage is 440 volts, the voltage at the terminals of the secondary winding will be
A) 880 V.
B) 1636 V.
C) 1800 V.
D) 1980 V.
E) 2000 V. โโD
A megohmmeter measures
A) amperage.
B) megawatts of power.
C) resistance.
D) voltage drop.
E) current flow. โโC
The following materials have HIGH reluctance (select 3 correct answers):
A) iron
B) glass
C) steel
D) air
E) oil โโB, D, E
The connection provided on DC motors to supply the armature with power
E) magnetic flux density. โโC
The brushes used to transfer power from armature are made up of carbon because
A) It has high coefficient of friction and is good conductor of electricity
B) It has low coefficient of friction and bad conductor of electricity
C) It has low coefficient of friction and is good conductor of electricity
D) It is good conductor of electricity and easy to replace
E) It does not wear out easily โโC
Current flow direction and intensity will
A) affect magnetic field direction and intensity.
B) affect the voltage.
C) affect the resistance of a circuit.
D) not affect electromagnetic field direction.
E) not affect electromagnetic field intensity. โโA
The most common measurement made with a meter is
A) amperage.
B) wattage.
C) resistance.
D) voltage.
E) capacitance. โโD
The black demand pointer of a power meter
A) moves the red pointer.
B) always reads the current demand.
C) resets automatically.
D) indicates the amperage being drawn.
E) must be manually reset. โโE
In an electrical distribution system, if one source is lost, power can still be maintained to the switchboard main bus by means of
A) a transformer tap.
B) a bus duct.
C) a cable tap.
D) a fusible panelboard.
A wire 90 m in length and 3 mm in diameter has a resistance of 150 ohms. Calculate the resistance of a wire of the same material 200 m long and 5 mm in diameter.
A) 300 ohms
B) 200 ohms
C) 120 ohms
D) 90 ohms
E) 24.3 ohms โโC
The field strength of an alternator can be adjusted by varying the strength of the DC current supplied to the
A) stator windings.
B) rotating field.
C) alternator frame.
D) rotating stator.
E) commutator โโB
Two resistors with resistance values of 10 ohm and 20 ohm, respectively, are connected in series to a battery. If the current flowing through the circuit is 5 A, the supplied voltage is
A) 150 V
B) 33.3 V
C) 16.67 V
D) 5 V
E) 3.33 V โโA
Electrical transformer cooling oil has
A) a high specific heat.
B) a poor insulating characteristic compared to air.
C) conducts electricity which requires wire to be insulated.
D) to flow at low temperatures.
E) a low safety hazard concern. โโA
The battery of an electrical circuit
A) gives a load to the circuit.
B) withholds neutrons from the circuit.
C) supplies electromotive force.
D) is the driving force of AC current.
E) all of the above. โโC
E) Produce high starting torque โโA
The total current supplied to a parallel electrical circuit is
A) equal to the product of the branch currents.
B) inversely proportional to the sum of the resistances.
C) directly proportional to the sum of the resistances.
D) inversely proportional to the sum of the branch currents.
E) equal to the sum of the branch currents. โโE
If a conductor is moved across a stationary magnetic field, it forms what is known as
A) motor action.
B) electromagnetism.
C) generator action.
D) transformer action.
E) conduction. โโC
A commutator is used in conjunction with
A) a kilowatt-hour meter.
B) an AC generator.
C) a transformer set.
D) an AC rheostat.
E) a DC generator. โโE
The utilization voltage refers to the nominal voltage minus approximately
a) 10%
b) 7.5%
c) 4%
d) 1.5%
e) 0%. โโC
Auto-transformers:
Select one:
a. Have an equal ratio of transformation
b. Have large ratios of transformation
c. Use more copper
d. Can use less copper โโD
b. conductance
c. voltage drop
d. insulation โโA
The stator of an alternator is built of _____ mounted in a frame.
Select one:
a. Non-metallic materials
b. Armature conductors
c. Carbon ring
d. laminated steel sheets
e. Copper alloys โโD
A shunt type DC generator produces _____ voltage:
Select one:
a. Alternating.
b. Very low.
c. Nearly constant.
d. Very high. โโC
The voltage required to be supplied to a 12 kW motor drawing 24 A is:
Select one:
a. 5 kV
b. 50 kV
c. 2 kV
d. 500 V โโD
Shunt wound DC motors are used where speed must remain constant regardless of load, such as on:
Select one:
a. Traction engines
b. Lathes
c. Elevators
d. Automobile starters โโB
The three main types of DC generators:
Select one:
Low voltage systems may have an actual voltage variation of plus or minus:
Select one:
a. 0.
b. 0.
c. 0.
d. 0.1 โโA
Neglecting the efficiency of a 15 kW motor connected to a 400 V supply, the amperage will be _____ A.
Select one:
a. 26.
b. 37.
c. 0.
d. 3.75 โโB
If a conductor is held stationary and a magnetic field is moved across it, it behaves according to:
Select one:
a. Motor action
b. Electromagnetism
c. Generator action
d. Transformer action โโC
An electrical distribution system is composed of service, feeders and:
Select one:
a. Trunk circuits
b. Branch circuits
c. Primary circuits
d. Secondary circuits โโB
The voltage required to force a current of 15 A through a resistance of 5? will be _____ V.
Select one:
a. 3
b. 7.
c. 33
d. 75 โโD
