B2U3 Alternators, Controls, And Protective Devices Flashcards
What are the two distinct poles every magnet has?
(1) A North Pole.
(2) A south pole.
What are the magnetic lines of force?
Invisible lines of magnetic force that exist between the poles.
What materials make up one very good type of permanent magnet?
An alloy of aluminum, nickel, and cobalt.
What three things are required for the generation of AC?
(1) A magnetic field.
(2) Conductors.
(3) Relative motion.
What happens when the magnetic field is at 90 degrees during the generator of voltage?
The greatest number of magnetic lines of force cut the conductor causing the voltage to peak.
What happens as the rotation of the north pole of the magnet reaches 225 degrees?
The magnetic lines of force begin to cut the conductor again. This time the lines of force move in the opposite direction.
What is an exciter?
A device that provides the alternator electricity needed to produce the electricity you use to operate equipment.
What is the armature?
The rotating conductor of the exciter.
What is the rotor assembly?
A device that provides the magnetic field necessary to produce electricity.
What is the purpose of the interpoles?
They offer a slight magnetic force that aligns the main magnetic field so it remains most effective.
What is the biggest difference between the self-exciting and permanent magnetic voltage regulator?
The permanent magnetic voltage regulator uses a permanent magnet; the self-exciting voltage regulator uses a soft iron core.
Why do most exciters use soft iron cores?
Because they retain residual magnetism.
What happens if the voltage level of an alternator begins to drop?
The voltage regulator senses the lower than normal level and increases the current to the exciter field windings.
What happens if you turn the voltage adjustment down?
This lowers the reference voltage making the voltage regulator read the output voltage level as too high.
What is the output of a single set of stator coils on an alternator?
There will be a single output voltage induced by the magnetic field.
Since the alternator works over 360 degrees and there are three different phases, how far do they sit?
120 degrees apart.
Since there are three legs that all connect in the middle in a wye connected alternator, how many connection points are there?
Four
What is an indication of a shorted diode?
Low reading in both directions.
What is used to attach the leads to the diodes?
Soldering iron.
What is used to test the main rotor leads?
Multimeter set to ohms.
What do you attach the overhead hoist to when lifting the alternator assembly?
Lifting eye.
Why do you often use one voltmeter connected to a selector switch?
To avoid the expense of having a separate voltmeter for each phase of a three-phase alternator.
Why should you never open the secondary winding of a current transformer while the switchgear is energized?
Because of the very high buildup of voltage.
What is the change in the relationship of current and voltage in a purely resistive load?
Current and voltage are in phase, and the phase angle is 0.
What do switches provide for us?
On-off control of the circuit that the switch is associated with.
If your generator uses isolation dampeners, what do you inspect them for?
Cracking and deterioration.
What is the first step to replacing an exciter?
Tagging and removing the wiring from the rectifier assembly.
What will typically secure the adjustment knob?
A setscrew.
When does a magnetic-type circuit breaker respond to trip?
Instantaneously when an excess of current flows through the breaker.
What affects the strength of the magnetic force exerted on the armature?
(1) The number of wire windings.
(2) The size of the conductors.
(3) The amount of current applied.
What makes SSRs far more reliable than inductive relays?
They have no moving parts.
When selecting fuses, what must you consider as to which fuse to install?
Total current flow and voltage of the circuit.
What is the function of an arc chute that surrounds each set of arc (not main) contacts?
To extinguish or quench any arcing that takes place when the breaker opens or closes.
What does the closing assembly usually contain?
A closing coil or motor and a control switch.
What is the relay equipped with to align the coil and contact pins to the base?
Keyway
Where does a magnet have the greatest amount of magnetism?
a. In the center.
b. At the north pole.
c. At the south pole.
d. At each end of the magnet.
D. at the end of each magnet
What is the small amount of magnetism that remains in an item after removing the magnetic field?
a. Faint.
b. Residual.
c. Reluctant.
d. Specialized.
B. Residual
Which alternator component offers a slight magnetic force that aligns the main magnetic field so it remains most effective?
a. Rotor.
b. Interpoles.
c. Voltage regulator.
d. Damping windings.
B. Interpoles
Which alternator component helps the generator maintain a stable voltage under varying load conditions?
a. Rotor.
b. Interpoles.
c. Stator.
d. Damping windings.
D. Damping Windings
What type of cores do most exciters use that retain residual magnetism?
a. Galvanized.
b. Soft iron.
c. Mica.
d. Air.
B. Soft iron
What does a voltage regulator sense if it decreases the current to the exciter field windings causing the magnetic field to get weaker?
a. A drop in the load.
b. A drop in the current.
c. An increase in the frequency.
d. An increase in the voltage level.
D. An increase in the voltage level
Which type of alternator consists of a rotating magnetic field and a single set of stator coils?
a. Wye.
b. Delta.
c. Three phase.
d. Single phase.
D. Single Phase
Which alternator configuration has three legs that all connect in the middle?
a. Wye.
b. Beta.
c. Delta.
d. Gamma.
A. Wye.
What is the multiplier you use to determine the line voltage if you know the phase voltage?
a. .707.
b. 1.73.
c. 2.00.
d. 3.14.
B. 1.73
Which alternator configuration has no neutral that is common to all three phases?
a. Wye.
b. Beta.
c. Delta.
d. Gamma.
C. Delta
In a rotating rectifier test, what does it indicate if a diode has a low reading in both directions?
a. Open.
b. Closed.
c. Shorted.
d. Reversed.
C. Shorted
Which test instrument do you use when testing the main rotor leads?
a. Voltmeter.
b. Ammeter.
c. Ground tester.
d. Multimeter set to ohms.
D. Multimeter set to ohms.
Which component is used with a voltmeter for a three-phase alternator to save money?
a. Multi-tap transformers.
b. Multiple pointers.
c. Cheaper meters.
d. Selector switch.
D. Selector switch
Which meter indicates the true power load in an alternating current (AC) circuit?
a. Ammeter.
b. Voltmeter.
c. Wattmeter.
d. Power factor meter.
C. Wattmeter
On the power factor meter, what will an inductive load cause?
a. Current and voltage in phase.
b. Current to lead voltage.
c. Current to lag voltage.
d. Will have no effect.
C. current to lag voltage
What devices provide variable amounts of resistance to provide a circuit with different levels of output?
a. Rheostats.
b. Inductors.
c. Capacitors.
d. Selector switches.
A. Rheostats
When you inspect the voltage regulator vibration dampeners, look for
a. cracking and deterioration.
b. security and discoloration.
c. lubrication and dry rot.
d. staining and wear.
A. Cracking and deterioration
Where should you look for any signs of rubbing on an exciter?
a. At the diode ring.
b. Around the bearing.
c. Between the rotor and stator.
d. Where the shaft meets the diode.
C. Between the rotor and the stator
What color will a transformer turn if it gets too hot?
a. Bright red.
b. Dark gray or black.
c. Lighter than normal.
d. Shade of yellow or brown.
A. Bright Red.
Which type of circuit breaker responds instantaneously when an excess of current flows through the breaker?
a. Coil.
b. Heat.
c. Magnetic.
d. Secondary trip.
C. Magnetic
Which relay component provides a constant restraining force keeping the armature in the normal (deenergized) position?
a. Coil.
b. Spring.
c. Plunger.
d. Contact.
B. Spring
Which relay component is completely self-contained and has no moving parts?
a. Capacitive.
b. Solid-state.
c. Inductive.
d. Isolation.
B. Solid-state
The closing assembly of a circuit breaker usually consists of
a. arc chutes and a tripping coil.
b. advancing motor and distribution points.
c. closing coil or motor and a control switch.
d. closing transformer and adjustable resistors.
C. Closing coil or motor and a control switch.
Which ohmmeter reading indicates that a fuse is good and no further testing is necessary?
a. Zero.
b. Infinity.
c. Below 250 ohms.
d. Above 500 ohms.
A. Zero
