How Do You Calculate Per Unit Values for a 20MVA Motor at 13.8kV?

In summary: Express these quantities in per unit form using the apparent power of the motor as the VA base, and the motor rated voltage as the base voltage.In summary, the rated load current for a 20MVA induction motor connected at 13.8kV is 1.0 p.u.
  • #1
DireStraits1
2
0
1) I'm not sure how to solve this question



A 20MVA induction motor connected at 13.8kV draws a load current of 1.0 p.u, 0.85 power factor lag. Calculate the rated load current in Amps and the real power and reactive power drawn by the motor. Express these quantities in per unit form using the apparent power of the motor as the VA base, and the motor rated voltage as base voltage.
 
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  • #2
I know I'm not supposed to post homework questions but my profesor told me like literally three different variations of apparent power formulas and at this point really I don't even know what formulas to use
 
  • #3
There is a homework section where this should have been posted
along with a set of guidelines on how to set out your query

i suggest you repost in there using the format that is given and
that may engender some help for you :)

BTW welcome to PF :)

Dave
 
  • #4
Doubtless a mod will eventually move this to homework.

Meanwhile the first question is do you understand the per unit method and terminology?

In particular what do you think 1.0 pu means?
 
  • #5
DireStraits1 said:
1) I'm not sure how to solve this question



A 20MVA induction motor connected at 13.8kV draws a load current of 1.0 p.u, 0.85 power factor lag. Calculate the rated load current in Amps and the real power and reactive power drawn by the motor. Express these quantities in per unit form using the apparent power of the motor as the VA base, and the motor rated voltage as base voltage.

A good starting point would be to select base values for the power and voltage.

Once you have the rated values of power and voltage in per unit form finding the rated load current shouldn't be to difficult.
 
  • #6
DireStraits1 said:
1) I'm not sure how to solve this question
Can you solve it when worded like this:

A 20MVA induction motor connected at 13.8kV draws full rated load current at 0.85 power factor lag. Calculate the rated load current in Amps and the real power and reactive power drawn by the motor.
 

FAQ: How Do You Calculate Per Unit Values for a 20MVA Motor at 13.8kV?

1. What are per unit calculations?

Per unit calculations are a method used in electrical power systems to standardize different quantities, such as voltage, current, and power, by expressing them in per unit values. This allows for easier comparison and analysis of different components within a power system.

2. How are per unit values calculated?

Per unit values are calculated by dividing the actual value of a quantity by its base value. The base value is typically the rated value of the component or system being analyzed. For example, if a transformer has a rated voltage of 100 kV and the actual voltage is 80 kV, the per unit value would be 0.8 (80/100 = 0.8).

3. Why are per unit calculations used?

Per unit calculations are used to simplify and standardize the analysis of electrical power systems. This is because the actual values of different components can vary greatly, but their per unit values will be similar and easier to compare. Per unit calculations also help to reduce the complexity of equations when analyzing power systems.

4. What are some common applications of per unit calculations?

Per unit calculations are commonly used in power system analysis, such as in load flow studies, fault analysis, and voltage regulation. They are also used in protective relaying, where the per unit values of different components are compared to determine if a fault has occurred.

5. Are there any limitations to per unit calculations?

While per unit calculations are useful in simplifying and standardizing power system analysis, they do have some limitations. Per unit values do not take into account the physical size or location of components, and they assume all components are operating at the same frequency. Additionally, per unit calculations may not accurately reflect the behavior of non-linear components, such as transformers and motors.

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