DC Shunt Generator: Armature Current, Terminal Voltage & Efficiency

In summary: No, you would also need to add in the mechanical loss (115W). You can find the total resistance by multiplying the individual resistances together.No, you would also need to add in the mechanical loss (115W). You can find the total resistance by multiplying the individual resistances together.
  • #1
TimWillz
5
0

Homework Statement


A shunt generator has an armature resistance of 0.8Ω, a field winding resistance of 120Ω and a mechanical loss of 115W. The load resistance of 8.5Ω is connected to the output terminals of the generator. An external mover rotates the shaft of the generator at a speed of 1670rpm. If a back e.m.f. constant of the generator is 0.86Vs/rad calculate:

a) armature current
b) terminal voltage
c) efficiency

I really can't get going on this question, can anyone help me out?


Homework Equations





The Attempt at a Solution

 
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  • #2
Is there any way to find a voltage from the back e.m.f.?
 
  • #3
TimWillz said:
Is there any way to find a voltage from the back e.m.f.?

Yes there is. Can you draw the equivalent circuit? You have the internal EMF with the armature resistance in series, and then both the field resistance and load resistance in parallel to complete the circuit. The terminal voltage is the one across the parallel resistors.
 
  • #4
uart said:
Yes there is. Can you draw the equivalent circuit? You have the internal EMF with the armature resistance in series, and then both the field resistance and load resistance in parallel to complete the circuit. The terminal voltage is the one across the parallel resistors.

Hi, thanks for the reply. I have tried to draw the equivalent circuit and calculate the values but to no success, is there any way you could show me how you would do it?

Thanks
 
  • #5
Ive got this as the circuit, I'm not sure if its correct though.
 

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  • #6
TimWillz said:
Ive got this as the circuit, I'm not sure if its correct though.

Yes that looks right. Use the rotational EMF constant to find Ea and also combine the field resistance and the load resistance into a single equivalent resistance. Now you can use the voltage divider formula to find the terminal voltage.
 
  • #7
uart said:
Yes that looks right. Use the rotational EMF constant to find Ea and also combine the field resistance and the load resistance into a single equivalent resistance. Now you can use the voltage divider formula to find the terminal voltage.

Thanks! I've got Ea = 0.86*174.9 = 150.4v

Is it just (RA*RF*RL)/(RA+RF+RL) to find the total resistance?
 

1. What is a DC shunt generator?

A DC shunt generator is a type of electrical generator that produces direct current (DC) output by utilizing a shunt field winding. It consists of an armature, which is the rotating part that generates the electrical power, and a shunt field winding, which controls the output voltage.

2. How does the armature current affect the output of a DC shunt generator?

The armature current is the current that flows through the armature of the DC shunt generator. The magnitude of this current is directly proportional to the output power of the generator. This means that as the armature current increases, the output power of the generator also increases.

3. What is the relationship between terminal voltage and armature current in a DC shunt generator?

The terminal voltage of a DC shunt generator is directly proportional to the armature current. This means that as the armature current increases, the terminal voltage also increases. This relationship is known as Ohm's law, which states that voltage is equal to the product of current and resistance.

4. How is efficiency calculated for a DC shunt generator?

The efficiency of a DC shunt generator is calculated by dividing the output power by the input power. The output power is the electrical power generated by the generator, while the input power is the mechanical power supplied to the generator. The efficiency is expressed as a percentage and can be improved by reducing losses in the generator.

5. What are some factors that can affect the efficiency of a DC shunt generator?

The efficiency of a DC shunt generator can be affected by various factors such as the quality of the materials used, the design of the generator, the speed at which it operates, and the load it is connected to. Other factors that can impact efficiency include temperature, friction, and electrical losses such as resistance in the windings.

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