Self-excited DC generator load end.

Silhorn · 27th March 2012, 9:50 PM

Hello,
I am doing a electromagnetism subject for a TAFE course and i am having a bit of trouble understanding DC generators.

I have a question,

For a Self-excited DC generator, what is connected to the load end since it is self-excited?

BeanerSA · 27th March 2012, 9:51 PM

I'm not quite sure what you are asking?

SLATYE · 27th March 2012, 9:58 PM

This may seem like a ridiculous answer, but "the load" sounds about right to me.

It's a generator. It's meant to drive a load. Presumably that load gets connected to the aptly named "load end".

Symon · 27th March 2012, 10:00 PM

The armature.

BeanerSA · 27th March 2012, 10:06 PM

Quote:

Originally Posted by SLATYE

This may seem like a ridiculous answer, but "the load" sounds about right to me.

It's a generator. It's meant to drive a load. Presumably that load gets connected to the aptly named "load end".

Well, that's what I thought, but I wondered if I was missing something. Aaaah, DC machines. My bread and butter for many years.

Silhorn · 27th March 2012, 10:21 PM

Sorry i should of explained more.

From what i understand.

A generator usually has an electromagnet for the main field and also electromagnets for the armatures.

If i am correct, the load terminals are the terminal connected to the main field and the output terminals are the ones connected to the armatures.

For a separately excited generator an external source such as a battery must be connected to the load end to start the generator and power the main field.

For a self excited generator an external supply is not need because residual magnetism is used to start the generator, so what is there anything that is connected to the load terminals?

Or am i misunderstanding something?

schnappy · 27th March 2012, 10:27 PM

This batter you're connecting... are you sure you're not confused with a DC motor? A generator is just a wire moving in a magnetic field, which produces a potential difference between the ends of that wire.

rainwulf · 27th March 2012, 10:42 PM

A regulator is connected from the output of the armatures back to the field coil to control the DC excitation.

Its called an exciter.
In some cases it disconnects the load until the residual magnetism has built up enough voltage to run the field safely to "Boot" up the generator.

Symon · 27th March 2012, 10:46 PM

Quote:

Originally Posted by Silhorn

Sorry i should of explained more.

From what i understand.

A generator usually has an electromagnet for the main field and also electromagnets for the armatures.

If i am correct, the load terminals are the terminal connected to the main field and the output terminals are the ones connected to the armatures.

For a separately excited generator an external source such as a battery must be connected to the load end to start the generator and power the main field.

For a self excited generator an external supply is not need because residual magnetism is used to start the generator, so what is there anything that is connected to the load terminals?

Or am i misunderstanding something?

I think you basically are correct, but I think your terminology is a little off. I'm assuming you are talking about a drawing that shows a resistor connected across the main field terminals? That actually isn't a 'load' per se, it is a variable resistor that is used to adjust the excitation current into the main winding.

The 'load' (ie, what is being powered by the generator) is connected directly to the armature for a shunt connected generator, and is connected across the series winding and armature for a series connected generator.

paulvk · 27th March 2012, 11:09 PM

I love how words mean diffrent things to diffrent trades a generator could be an alternator, a dc generator which would have a commutator or even a radio transmitter.

Silhorn · 28th March 2012, 6:05 PM

Ah i just read the replies and went over my subject book and think i understand everything now.

So please correct me if i am wrong, i want to know if this is correct.

A separately excited generator needs to have an external source to power the main fields.
So a separately excited motor has physically 2 sets of terminals, one which is connected to the main field windings and two which connects to the armature windings. A supply source is connected to the first set of terminals to power the main field.

When a torque is applied to the shaft of the generator current is produced in the armature because of induction so the armature terminals are the output terminals. The main field terminals are called the load terminals?

In a self-excited generator both armature and main field windings are connected to the same terminals in either series or parallel or both depending if shunt, series or compounded. When a torque is applied to the shaft these terminals output current.
So in a self-excited generator there are only one set of terminals? These are called the load terminals?

McDaddy_ · 28th March 2012, 6:36 PM

Physically, the DC Motor and Generator can be identical. The difference being that the generator is connected to a prime mover (mech to elec conversion) and the motor is connected to an electrical power source (elec to mech conversion).

For the different types of DC Generators, they can physically be the same machine but in different wiring configurations, assuming the armature and field windings are brought out to terminals.

DC Separately Excited Generator

Shaft is connected to a prime mover.
Field winding is connected to a separate DC power supply or battery.
Armature (or power) winding is connected to the load - the electrical equipment you want to power.

http://imgur.com/NIlmR

DC Self Excited Generator

Shaft is connected to a prime mover.
Field winding is connected to the armature terminals.
Residual magnetism provides initial flux.
Armature (or power) winding is connected to the load - the electrical equipment you want to power.

http://imgur.com/2HOVH

Symon · 28th March 2012, 11:36 PM

Quote:

Originally Posted by Silhorn

When a torque is applied to the shaft of the generator current is produced in the armature because of induction so the armature terminals are the output terminals. The main field terminals are called the load terminals?

In a self-excited generator both armature and main field windings are connected to the same terminals in either series or parallel or both depending if shunt, series or compounded. When a torque is applied to the shaft these terminals output current.
So in a self-excited generator there are only one set of terminals? These are called the load terminals?

Field terminals are usually marked as F1 and F2, or just simply 'field'. As McDaddy mentions, DC motors and DC generators are pretty much the same, except one is driven, and the other drives.

On small motors/generators that have permanent magnet stators, you would only have two terminals.

With the larger motors and generators, you would have two sets of terminals - field (F1, F2) and armature (A1, A2).

Silhorn · 29th March 2012, 5:51 PM

So for the larger machines that have 2 sets of terminals is that for both self and separately excited machines?

rainwulf · 29th March 2012, 11:12 PM

well.. no.
If they have a field terminal, they will need external excitation.

27th March 2012, 9:50 PM	#1
Silhorn Member Join Date: May 2008 Posts: 206	Self-excited DC generator load end. Hello, I am doing a electromagnetism subject for a TAFE course and i am having a bit of trouble understanding DC generators. I have a question, For a Self-excited DC generator, what is connected to the load end since it is self-excited?

27th March 2012, 9:58 PM	#3
SLATYE SLATYE, not SLAYTE Join Date: Nov 2002 Location: Canberra Posts: 25,832	This may seem like a ridiculous answer, but "the load" sounds about right to me. It's a generator. It's meant to drive a load. Presumably that load gets connected to the aptly named "load end". __________________ Main system: Phenom II X4 920 \| 8GB (4x 2GB) DDR2-800 \| Gigabyte M57SLI-S4 v2.0 \| Leadtek Geforce 9600GSO 384MB \| Enermax Modu82+ 525W \| 1TB Hitachi HDD \| 3.5" + 5.25" FDD Laptop: Compal EL80 \| C2D T7200 \| 320GB Fujistu HDD \| 2GB DDR2-667 \| GF Go 7600

27th March 2012, 10:00 PM	#4
Symon (Plugging your Socket) Join Date: Apr 2002 Location: Brisbane QLD Posts: 2,835	The armature. __________________ DISCLAIMER - The mindless babble of this post does not constitute professional advice. I will not be held responsible if you choose to act on this advice. Unless I tell you to eat jellybeans, everyone likes jellybeans OCAU's self-appointed electrical safety expert - Founder of the bakasan Technical College - enrollments welcome. -- My Web Server in a Box

27th March 2012, 10:42 PM	#8
rainwulf Member Join Date: Jan 2002 Location: bris.qld.aus Posts: 2,679	A regulator is connected from the output of the armatures back to the field coil to control the DC excitation. Its called an exciter. In some cases it disconnects the load until the residual magnetism has built up enough voltage to run the field safely to "Boot" up the generator. __________________ derp

28th March 2012, 6:36 PM	#12
McDaddy_ Member Join Date: Sep 2001 Location: Newcastle Posts: 612	Physically, the DC Motor and Generator can be identical. The difference being that the generator is connected to a prime mover (mech to elec conversion) and the motor is connected to an electrical power source (elec to mech conversion). For the different types of DC Generators, they can physically be the same machine but in different wiring configurations, assuming the armature and field windings are brought out to terminals. DC Separately Excited Generator Shaft is connected to a prime mover. Field winding is connected to a separate DC power supply or battery. Armature (or power) winding is connected to the load - the electrical equipment you want to power. http://imgur.com/NIlmR DC Self Excited Generator Shaft is connected to a prime mover. Field winding is connected to the armature terminals. Residual magnetism provides initial flux. Armature (or power) winding is connected to the load - the electrical equipment you want to power. http://imgur.com/2HOVH __________________ "True ignorance is not the absence of knowledge, but the refusal to acquire it." - Sir Karl Raimund Popper Last edited by McDaddy_; 28th March 2012 at 7:04 PM.

27th March 2012, 9:51 PM	#2
BeanerSA Member Join Date: Aug 2009 Location: Gateway to the Barossa Posts: 3,096	I'm not quite sure what you are asking?

27th March 2012, 10:21 PM	#6
Silhorn Member Join Date: May 2008 Posts: 206	Sorry i should of explained more. From what i understand. A generator usually has an electromagnet for the main field and also electromagnets for the armatures. If i am correct, the load terminals are the terminal connected to the main field and the output terminals are the ones connected to the armatures. For a separately excited generator an external source such as a battery must be connected to the load end to start the generator and power the main field. For a self excited generator an external supply is not need because residual magnetism is used to start the generator, so what is there anything that is connected to the load terminals? Or am i misunderstanding something?

27th March 2012, 10:27 PM	#7
schnappy Member Join Date: Apr 2008 Location: 3124 Posts: 612	This batter you're connecting... are you sure you're not confused with a DC motor? A generator is just a wire moving in a magnetic field, which produces a potential difference between the ends of that wire.

27th March 2012, 11:09 PM	#10
paulvk Member Join Date: Mar 2010 Posts: 698	I love how words mean diffrent things to diffrent trades a generator could be an alternator, a dc generator which would have a commutator or even a radio transmitter.

28th March 2012, 6:05 PM	#11
Silhorn Member Join Date: May 2008 Posts: 206	Ah i just read the replies and went over my subject book and think i understand everything now. So please correct me if i am wrong, i want to know if this is correct. A separately excited generator needs to have an external source to power the main fields. So a separately excited motor has physically 2 sets of terminals, one which is connected to the main field windings and two which connects to the armature windings. A supply source is connected to the first set of terminals to power the main field. When a torque is applied to the shaft of the generator current is produced in the armature because of induction so the armature terminals are the output terminals. The main field terminals are called the load terminals? In a self-excited generator both armature and main field windings are connected to the same terminals in either series or parallel or both depending if shunt, series or compounded. When a torque is applied to the shaft these terminals output current. So in a self-excited generator there are only one set of terminals? These are called the load terminals?

29th March 2012, 5:51 PM	#14
Silhorn Member Join Date: May 2008 Posts: 206	So for the larger machines that have 2 sets of terminals is that for both self and separately excited machines?

29th March 2012, 11:12 PM	#15
rainwulf Member Join Date: Jan 2002 Location: bris.qld.aus Posts: 2,679	well.. no. If they have a field terminal, they will need external excitation. __________________ derp