Learning about self-excited and separate shunt generators

In summary, a self-excited generator cannot build up an output voltage if it has lost all of its residual magnetism. In older vehicles with generators, the main charging current passed through the commutator and brushes, and the generator needed to be polarized after servicing in order to regain its residual magnetism. On self-excited motors/generators, the residual magnetism can be restored by flashing the field with a DC voltage. This should be done with all other circuits off and the armature disconnected. On separately excited motors, there should not be a problem as there is a separate exciter generator.
  • #1
vptran84
46
0
hi,

I'm currently learning about self-excited and separate shunt generators, and I'm having a hard time comprehending the residual magnetism.

i was just wondering if a generator have lost all of its residual magnetism, can it still build up an output voltage? can someone explain this to me if they have time?

Also how would you get a generator to work after it has lost all of its residual magnetism?

any help would be greatly appreciated.
 
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  • #2
A self excited generator cannot work if it has lost all of its residual magnetism. Older vehicles had generators instead of alternators. They had a commutator and brushes instead of diodes. The main charging current in modern alternators does not go through the slip-rings and brushes, it comes from the stator which is wound and arranged to provide 3 phases to the diodes. In generators however the main charging current passed through the commutator and brushes. Typically if the generator was serviced in some way it was 'polarized'. This simply meant passing current through some part of the generator to create residual magnetism. I imagine the field coil. I own an older military suplus 120 Vac generator that is self-exciting. It always come up to voltage but sometimes it takes a couple of seconds. It has a set of slip rings that the main current passes through as well as a commutator that rectifies the voltage coming off of the armarature to power up the field coils.
 
  • #3
On self excited DC motors/generators that lose their residual magnitism. You can use a technique called 'Flashing the field' aka, applying a DC voltage to the field and it should come up.

If it builds up in the wrong direction then it can be reversed. This should be done with all other circuits off and the Armature disconnected.

On Separately excited DC motors it should not be a problem because there is a separate exciter generator or known as an MG set.
 

1. What is a self-excited generator?

A self-excited generator is a type of electrical generator that uses the principle of electromagnetic induction to convert mechanical energy into electrical energy. It is called "self-excited" because it does not require an external power source to start producing electricity.

2. How does a self-excited generator work?

A self-excited generator consists of a stator (stationary part) and a rotor (rotating part). When the rotor spins, it creates a rotating magnetic field which cuts through the windings of the stator, inducing an electrical current. This current then passes through the rotor windings and creates a magnetic field that reinforces the initial magnetic field, resulting in a self-sustaining cycle of electricity production.

3. What is a separate shunt generator?

A separate shunt generator is a type of self-excited generator that uses a shunt field winding in addition to the main field winding. The shunt winding creates a magnetic field that is parallel to the main field, providing a more stable output voltage and better voltage regulation.

4. How does a separate shunt generator differ from a compound generator?

Both a separate shunt generator and a compound generator use a shunt winding, but in a compound generator, the shunt winding is connected in series with the main field winding. This results in a more complex magnetic field and better voltage regulation, but it also requires more maintenance and control.

5. What are the advantages of using a self-excited and separate shunt generator?

The main advantage of using a self-excited and separate shunt generator is its ability to maintain a constant voltage output even under varying load conditions. This makes it suitable for applications that require a stable power supply, such as in hospitals, data centers, and sensitive electronic equipment. Additionally, these types of generators are relatively simple and cost-effective to operate and maintain.

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