Phase and Line current in 3 phase circuits

In summary, the conversation revolves around finding the phase current in the load and line current from the supply using a power equation. The person suggests keeping the circuit in its original form rather than converting it to a star for easier calculations. They also mention finding the active power input to the motor and considering efficiency in the calculations. The conversation ends with a question about the input being less than the output and confirming the value of V.
  • #1
Cocoleia
295
4

Homework Statement


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

Homework Equations

The Attempt at a Solution


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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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  • #2
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?
 
  • #3
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
 
  • #4
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?
 
  • #5
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)
 
  • #6
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.
 

1. What is the difference between phase current and line current in 3 phase circuits?

In a 3 phase circuit, there are three phases of alternating current that are 120 degrees out of phase with each other. Phase current refers to the amount of current flowing through one of these phases, while line current refers to the total amount of current flowing through all three phases combined.

2. How are phase current and line current related in 3 phase circuits?

In a balanced 3 phase circuit, the line current is equal to the square root of 3 times the phase current. This means that the line current will always be greater than the phase current in a 3 phase circuit.

3. Why is it important to understand phase and line current in 3 phase circuits?

Understanding phase and line current is crucial for designing and troubleshooting 3 phase circuits. It helps determine the appropriate wire sizes, circuit breakers, and other components needed for safe and efficient operation. Additionally, understanding the relationship between phase and line current can help identify and troubleshoot issues in the circuit.

4. How do you calculate phase and line current in a 3 phase circuit?

To calculate phase current, divide the total power (in watts) by the voltage and then divide that number by the square root of 3. To calculate line current, multiply the phase current by the square root of 3. It is important to note that these calculations are only applicable in a balanced 3 phase circuit.

5. Can phase and line current be different in an unbalanced 3 phase circuit?

Yes, in an unbalanced 3 phase circuit, the phase and line currents can be different. This is because the current in each phase is not equal, so the total current in the circuit will not be equal to the square root of 3 times the current in one phase. It is important to take into account this imbalance when designing and troubleshooting unbalanced 3 phase circuits.

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