Speed of a DC generator is proportional to the generated voltage?

Click For Summary

Discussion Overview

The discussion revolves around the relationship between the speed of a DC generator and the generated voltage, specifically addressing whether speed is proportional to the electromotive force (EMF) and output voltage. The conversation includes various types of DC generators, such as separately excited and shunt wound generators, and explores the implications of changing speed on EMF and voltage outputs.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants propose that the speed of a DC generator is directly proportional to the EMF, and by extension, the output voltage, assuming constant conditions.
  • One participant specifies that this relationship holds true for separately excited generators.
  • A participant presents a scenario involving a shunt wound generator, calculating the EMF and suggesting that halving the speed would result in halving the EMF and subsequently affecting the output voltage.
  • Another participant emphasizes that EMF is proportional to the magnetic flux produced by the generator's field winding, indicating that changes in terminal voltage also depend on field flux and resistance.

Areas of Agreement / Disagreement

Participants generally agree that speed is related to EMF, but there are differing views on how this relationship applies to different types of generators and the effects of changing speed on terminal voltage. The discussion remains unresolved regarding the specific implications for shunt wound generators.

Contextual Notes

Limitations include assumptions about constant conditions and the dependence on generator type, as well as the need for additional calculations involving field winding resistance to determine terminal voltage accurately.

ajskelly
Messages
4
Reaction score
0
Homework Statement
If the speed of a DC generator is reduced by half, will this reduce the Voltage and the EMF by half as speed is directly proportional to EMF? Resistance is staying constant,
Relevant Equations
E=V+IaRa
I'm confused as I'm aware speed is directly proportional to the EMF, but is it proportional to the voltage as well? If the speed of a DC generator is halved and everything else is remaining constant the EMF will have so will the output voltage half
 
Physics news on Phys.org
ajskelly said:
If the speed of a DC generator is halved and everything else is remaining constant the EMF will have so will the output voltage half
Yes, provided it is a separately excited generator.
 
How about a shunt wound generator, for example...

the output voltage is 200V
the Ia is 50A
the Ra is 0.03ohms

E=V+IaRa
E=200+(50X0.03)
E=201.5

The speed of the generator is now reduced by half. As the speed of the generator is directly proportional to the EMF, half the speed will mean half the EMF so...

E/2 = 201.5/2 = 100.75

Now if I wanted to find the current which would have changed, can I use

E=V+IaRa

so can I say,

100.75= 100+(IaX0.03)

100 being the 100V that was found by dividing the orignal voltage by 2 due to the speed being halved.

Hope this makes sense!

Thanks for your help
 
ajskelly said:
As the speed of the generator is directly proportional to the EMF
ajskelly said:
I'm aware speed is directly proportional to the EMF
I prefer 'emf is directly proportional to the speed'.

Also, emf is proportional to the magnetic flux produced by the generator's field winding.
This means emf is directly proportional to the product of field flux and rotor speed.
As the terminal voltage changes, the field flux also changes.
Hence, in case of shunt generator, you will need to do some math considering field winding resistance to find the terminal voltage.
 
Sorry I forgot to thank you cnh1995 for your assistance,
Cheers!
 

Similar threads

  • · Replies 13 ·
Replies
13
Views
3K
Replies
10
Views
5K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 8 ·
Replies
8
Views
8K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 15 ·
Replies
15
Views
2K