AC Generators

Question 1

What things are required to produce an EMF by induction?

Answer 1

An electrical conductor
Relative movement
A magnetic field

Question 2

What is the most common type of generator used today?

Answer 2

Brushless generator

Question 3

What does the generated EMF output depend on?

Answer 3

The speed at which the lines of flux pass the conductor.
(Frequency)
The amount of lines of flux cutting across the conductor.
(Voltage)

Question 4

What is fitted to the AC generator to make it turn?

Answer 4

Prime mover

Diesel engine and gas turbine unit

Question 5

How is the HF Generator turned, what is its output and where is it fed to?

Answer 5

Belt driven
115V - 1 phase - 1600Hz
Fed to the Automatic Voltage regulator (AVR)

Question 6

What sort of current is fed into the Exciter Stator?

Answer 6

DC

Question 7

What is the purpose of the Rectifier assembly?

Answer 7

To convert the AC input from the Exciter Rotor into a DC output to the main AC Generator Rotor

Question 8

How can the voltage generated by an AC generator be altered?

Answer 8

The generated voltage can only be altered by increasing or decreasing the strength of the magnetic field

Question 9

If the magnetic field around the AC Generator Rotor is stable (made from a DC supply), how does the Generator produce an AC output?

Answer 9

As the AC Generator Rotor is turned by the Prime Mover the stable magnetic field rotates too. As this rotating magnetic field cuts through the Stator windings it produces the AC output voltage

Question 10

What is the output from Generators fitted to HM Ships and how does the AVR know what’s being produced?

Answer 10

450V - 60Hz - 3 phase

The AVR takes a sample using a sensing line

Question 11

What the difference between AC Generators and AC Motors?

Answer 11

Generators turn mechanical movement into electrical energy, motors turn electrical energy into mechanical movement.

Question 12

What are the components of a single loop generator?

Answer 12

Poles
Carbon brush
Slip ring
Load
Wire loop/armature

Question 13

How is current created in a single loop generator?

Answer 13

As the loop rotates an EMF is generated (induced in to the loop), and if it is connected to an external circuit, a current will flow around the loop and the external circuit.

Question 14

What are the 6 components of the brushless generator?

Answer 14

Prime mover
High frequency generator
Automatic voltage regulator
Exciter
Rectifier assembly
Main generator

Question 15

What does the prime mover do?

Answer 15

The item which drives the rotor of the exciter, the generator and the HF generator.

Question 16

What does the high frequency generator do?

Answer 16

Supplies voltage to the windings of the AC exciter via the automatic voltage regulator (AVR).

Question 17

What does the automatic voltage regulator do?

Answer 17

Supplies a DC to the AC exciter and maintains the generator output at 450 V.

Question 18

What does the AC exciter do?

Answer 18

The rotor of the AC exciter cuts the magnetic field of the set up by the HF generator/AVR, this gives an AC output which is fed to the rectifier assembly.

Question 19

What does the rectifier assembly do?

Answer 19

It converts the AC excited output into DC which is then fed to the rotor of the main generator.

Question 20

What does the main generator do?

Answer 20

The rotor of the generator sets up a rotating magnetic field which cuts across the stationary windings of the stator, this produces the final AC of 450 V, 60Hz, 3 phase output.