1 Flashcards
What holds the electron in orbit around the nucleus?
A force of attraction
Potential difference will exist between two points in the circuit that have a?
Difference in charge
to produce a Voltage chemically, the two metals need to be made of?
Dissimilar metals
Name 3 requirements needed to produce voltage by induction
1: Electrical conductor
2: Magnetic field
3: Relative movement
What are the lines of force that pass through a space surrounding a magnet called?
lines of magnetic flux
3 materials that mixed with steel, will produce stronger magnets
Aluminium,nickel, cobalt
What is produced around a conductor when a current is passed through it?
lines of magnetic flux
There are 3 requirements needed for magnetism to produce voltage by induction, they are?
Conductor
Magnetic field
Relative movement
What direction does AC travel through a conductor?
both ways
List 2 advantages of AC over DC
Wiring & equipment can be lighter.
Easier to transform
The level to which the voltage or current rises to is called?
amplitude
How are AC cycles per second expressed?
Hertz
What are the values of the ships main electrical supplies?
450v 60hz 3 phase
What is the frequency equation?
time(seconds)= 1/frequency
List 4 advantages of an AC motor
less maintenance
more efficient
cheaper
more compact
What is the main disadvantage of AC?
difficult to vary speed
List the 2 main components of an AC motor
stator
rotor
What causes movement in a 3 phase induction motor?
the rotating magnetic field produced by the stator
What is the most common AC motor used in the navy?
squirrel cage
List the components of a Squirrel cage
Non drive end bearing
Copper end ring
Copper bars
Drive end bearing
How does the rotating magnetic field from the stator cause the rotor to rotate?
the rotating field induces a current
this current causes a magnetic field
the interaction between the two magnetic fields causes the rotor to ‘follow’ the rotating field
What will happen if a running 3 phase AC motor were to lose 1 phase of input?
reduced speed
increased noise/ vibration
overheat
What is Back EMF?
Movement of the conductor causes it to cut the magnetic field of the magnet meaning an EMF is induced into the conductor.
The induced EMF will be opposite in polarity to tue EMF applied to the conductor.
What position must the carbon brushes be fixed and why?
The magnetic neutral axis (MNA)
to ensure no back EMF in the coil when the gap of the split ring passes the brush so there is no sparking.
What are Inter-Poles and what do they do?
Poles similar to the main poles but smaller situated between the main poles and wound in series with the armature to offset varying current.
What is the name given to materials in a solar panel?
semi conductor
What’s the difference between Volts, Watts And Current?
Volts measure the electrical potential difference
current is measure the flow of electrons
watts measure the rate at which electrical energy is used volts x current
What is Torque?
amount of turning moment exerted upon what is being turned
What is an armature?
coils of wire which carries the alternating current
What is magnetic flux?
lines of force around a magnet
What is the Magnetic Neutral Axis (MNA)?
magnetic position centred in the magnetic feild between the opposite feild windings. can be charged by distortion.
What is Field winding?
the insulated current-carrying coils on a field magnet that produce the magnetic field
What is Lamination for?
improves efficiency
Name the 3 classifications of DC motors.
series shunt compound
What is a secondary cell?
can be re charged
What is an electrolyte?
fluid carrying a electric charge
What is the difference between magnetic flux and magnetic field?
magnetic flux is a measurement of magnetic field passing through
What is an advantage of DC over AC?
more efficient
Define power?
the rate of doing work
The amount of torque produced by a motor depends on?
strength of magnetic field
magnitude of armature current
Electric power depends on?
voltage and current
1 horsepower = ?
746 W
Earth faults can be caused by?
low resistance between conductor and earth
Dampness
insulation becoming hard or brittle with age or heat
accidental damage
A transformer consists of 2 coils close together but insulated from one another. What are they called?
shell
The 3 sets of windings of a 3-phase motor are usually connected in 2 which ways?
star or delta
Describe the Compound wound motor.
combination of series and shunt motor
series field winding’s connected in series with the amarture + shunt feild parallel.
Good torque and regulated speed
Name the 2 neutral axis associated with DC motors
Geometric + magnetic
Why wont DC current work with transformers?
no change to the magnetic field
