General Knowledge 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
Cobalt
Nickel
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 ( it alternates)
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?
3 Phase
450 V
60 Hertz
What is the frequency equation?
Time (Seconds) = I divided Frequency
List 4 advantages of an AC motor
- Less maintenance
- More efficient
- Cheaper
- More compact
What is the main disadvantage of AC?
It’s 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 generated 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
- The 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?
- Keep running
- Lose power
- Vibrate
- Create excessive noise
- Heat up
What is Back EMF?
It is opposite in polarity to the EMF that is being applied to the conductor
What position must the carbon brushes be fixed and why?
- MNA (Magnetic neutral axis)
- To stop sparking of the brushes
What are Inter-Poles and what do they do?
- They assist in giving sparkless commutation, by neutralising the effect of armature reaction.
- They are poles similar to the main poles but smaller
What is the name given to materials in a solar panel?
Semiconductors
What’s the difference between Volts, Watts And Current?
- Voltage (Volts) is like water pressure in a pipe, i.e. How hard is the electricity pushing?
- Current (Amps) is like the volume of water flowing in a pipe i.e. How much water is flowing?
- Power (Watts) is the product of the two, when you multiply Voltage by Current you get Power.
What is Torque?
a force that tends to cause rotation.
What is an armature?
a device through which electric current is passed for generating torque (rotor).
What is magnetic flux?
Magnetic flux is a measurement of the total magnetic field which passes through a given area
What is the Magnetic Neutral Axis (MNA)?
The axis on which there is no Flux generated in the armature conductors. Because they move parallel to the main field flux lines.
What is Field winding?
Where the main field flux is produced
What are interpoles?
Interpoles are designed in DC motors To counter act armature reaction, they are smaller than the main poles
What is Lamination for?
to improve efficiency of transformer
What is torque?
Rotational forces
Name the 3 classifications of DC motors.
- Series
- Shunt
- Compound
What is a secondary cell?
An electric cell that can be recharged and can be used to store chemical energy
What is an electrolyte?
A liquid that can conduct electricity using a chemical reaction
What is the difference between magnetic flux and magnetic field?
- Magnetic field describes a region where a magnetic force can be felt.
- Magnetic flux describes how much magnetic field passes through an area
What is an advantage of DC over AC?
Better speed control
The amount of torque produced by a motor depends on?
- Strength of magnetic field
- Size of the armature current
Define power?
The rate of doing work
Electric power depends on?
- The number of electrons to be moved
- The speed in which the are made to travel
1 horsepower =?
746 watts
Earth faults can be caused by?
- Dampness
- Old, brittle insulation
- Accidental damage
A transformer consists of 2 coils close together but insulated from one another. What are they called?
Primary and secondary windings
What is the equation for transformers?
Output V= No. secondary turns / No. primary turns x input V
What is the purpose of a HF (High frequency) Generator?
To give voltage to the AVR
The 3 sets of windings of a 3-phase motor are usually connected in 2 which ways?
- Star
- Delta
Describe the Compound wound motor.
A combination of series and shunt.
Has the best of both motors.
Name the 2 neutral axis associated with DC motors
- Geometric neutral axis
- Magnetic neutral axis
what is another term for Commutator?
Split ring
What is the difference between Split ring & Slip ring?
The slip ring is a closed circle (used in AC motors)
The Split ring is divided (used in DC motors)
Why wont DC current work with transformers?
because there is no change in the magnetic field
