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

In summary, the relationship between speed and EMF in a DC generator is directly proportional, meaning that halving the speed will result in halving the EMF. However, this relationship may vary depending on the type of generator, such as a separately excited or shunt wound generator, and considerations like field winding resistance may need to be taken into account when determining the terminal voltage.
  • #1
ajskelly
4
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
 
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  • #2
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.
 
  • #3
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
 
  • #4
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.
 
  • #5
Sorry I forgot to thank you cnh1995 for your assistance,
Cheers!
 

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

1. How does the speed of a DC generator affect the generated voltage?

The speed of a DC generator is directly proportional to the generated voltage. This means that as the speed of the generator increases, the generated voltage also increases. Conversely, if the speed decreases, the generated voltage will also decrease.

2. Why is the speed of a DC generator important?

The speed of a DC generator is important because it directly affects the generated voltage. In order to produce a certain voltage, the generator must be operated at a specific speed. If the speed is too low, the voltage output will be too low and if the speed is too high, the voltage output will be too high.

3. How is the speed of a DC generator controlled?

The speed of a DC generator can be controlled through various methods such as adjusting the load on the generator, changing the field current, or using a speed control device. These methods allow for precise control of the generator's speed and therefore, the generated voltage.

4. What happens if the speed of a DC generator is too high?

If the speed of a DC generator is too high, it can lead to an increase in the generated voltage beyond the desired level. This can cause damage to the generator and any connected equipment. It is important to properly control the speed of the generator to prevent these issues.

5. Is the speed of a DC generator always directly proportional to the generated voltage?

In most cases, the speed of a DC generator is directly proportional to the generated voltage. However, there are some factors that can affect this relationship, such as the design and condition of the generator, as well as the load on the generator. It is important to consider these factors when operating a DC generator to ensure proper voltage output.

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