Phase and Line current in 3 phase circuits

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Homework Help Overview

The discussion revolves around calculating phase and line currents in a three-phase circuit, specifically focusing on the relationship between power input, efficiency, and current calculations.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the use of different configurations (star vs. delta) for calculating currents. Questions arise regarding the appropriate power equations to use and the implications of efficiency on power input and output.

Discussion Status

Participants are actively questioning the assumptions made about power input and efficiency. Some guidance has been provided regarding the use of power equations, but clarity on the relationship between input and output power remains a point of contention.

Contextual Notes

There is a mention of specific values such as power input and efficiency percentages, which may influence the calculations but are not fully resolved in the discussion.

Cocoleia
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Homework Statement


upload_2017-10-30_13-2-55.png

I need to first find phase current in the load and line current from the supply

Homework Equations

The Attempt at a Solution


upload_2017-10-30_13-9-8.png

I thought it would be easier to work with a star because then the Ztl would be in series with it... I am not sure how to find the current but my best guess was using this power equation. For the second current, I am not sure how to proceed.
 

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You don't need to convert it in star. Keep it as it is and find the line current from the power equation.

Your attempt is unclear.
What is the active power input to the motor?
 
cnh1995 said:
You don't need to convert it in star. Keep it as it is and find the line current from the power equation.

Your attempt is unclear.
What is the active power input to the motor?
Can I use the same power equation that I had used ?

I guess the power input is 74600 W
 
Cocoleia said:
Can I use the same power equation that I had used
Yes.
Cocoleia said:
I guess the power input is 74600 W
What about efficiency?
 
cnh1995 said:
Yes.

What about efficiency?
If it is only 90% then only 67140 W. I use this as P.

WIll V be 240/sqrt(3)
 
Cocoleia said:
If it is only 90% then only 67140 W. I use this as P.
How can the input be less than the output? Use the efficiency correctly.
Cocoleia said:
WIll V be 240/sqrt(3)
No.
 

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