Current of delta 3 phase balanced power

  • Thread starter david90
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  • #1
david90
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Hi,

Regarding the picture below, the author calculates L1's current with KCL equation IR-IB = L1. Why is the KCL equation not IR+IB = L1 if the voltage of phase B and Phase R at one point during their cycle can be both positive (Assume positive voltage means current go toward the node)? If Phase B and Phase R voltage are positive then their current move in the same direction and thus IR and IB should have the same signage?

https://www.electricaltechnology.org/2014/09/delta-connection-power-voltage-current.html
Screenshot 2023-08-29 231047.png
 

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  • #2
Isn't it just a matter of convention? Picture clearly shows current directions. You could mark IB as going up, that would change all equations, giving IB+IR for L1 (that's assuming I understand correctly what L1 is).

That would also make the system of equations a bit chaotic to my taste though.
 
  • #3
Borek said:
Isn't it just a matter of convention? Picture clearly shows current directions. You could mark IB as going up, that would change all equations, giving IB+IR for L1 (that's assuming I understand correctly what L1 is).

That would also make the system of equations a bit chaotic to my taste though.
How can phase shift of L1 be both IB+IR and IB-IR?
 
  • #4
david90 said:
Regarding the picture below, the author calculates L1's current with KCL equation IR-IB = L1. Why is the KCL equation not IR+IB = L1
The author has clearly chosen the current polarities with the indicated arrows. That's why.

It can be an arbitrary choice, you may choose a different definition. But once the choice is made it must be followed.

There is no requirement that the defined current polarities match the voltage polarities. They can be defined separately, arbitrarily.
 
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  • #5
I agree with DaveE. In order to keep a more clear rule we take R as more than S and S more than T and the direction of current from S to R,from T to S and from R to T.
1693548033334.png
 

Related to Current of delta 3 phase balanced power

What is the current in a delta 3-phase balanced power system?

In a delta 3-phase balanced power system, the line current is √3 times the phase current. This relationship arises because, in a delta configuration, each line current is the vector sum of two phase currents.

How do you calculate the line current in a delta 3-phase balanced power system?

To calculate the line current (I_line) in a delta 3-phase balanced power system, you use the formula: I_line = √3 * I_phase, where I_phase is the phase current. This formula results from the vector addition of the phase currents in the delta configuration.

What is the difference between line current and phase current in a delta 3-phase balanced power system?

In a delta 3-phase balanced power system, the phase current flows through each of the windings of the transformer or the load, while the line current flows in the external circuit connected to the power source. The line current is √3 times the phase current due to the vector addition of the currents in the delta configuration.

Why is the line current higher than the phase current in a delta 3-phase balanced power system?

The line current is higher than the phase current in a delta 3-phase balanced power system because each line current is the vector sum of two phase currents. This results in the line current being √3 times the phase current, reflecting the geometric relationship between the currents in the delta configuration.

How does the power factor affect the current in a delta 3-phase balanced power system?

The power factor affects the current in a delta 3-phase balanced power system by influencing the real power delivered to the load. A lower power factor means more reactive power and higher current for the same amount of real power. The line current calculation still follows the relationship I_line = √3 * I_phase, but the phase current itself will be higher if the power factor is lower.

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