Current of delta 3 phase balanced power

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The discussion focuses on the calculation of L1's current in a delta 3-phase balanced power system using Kirchhoff's Current Law (KCL). Participants debate whether the equation should be IR-IB or IR+IB, considering the current directions and voltage polarities. It is noted that the choice of current polarities is arbitrary but must be consistently applied once defined. The conversation emphasizes that current and voltage polarities do not need to align, allowing for flexibility in definitions. Ultimately, clarity in the chosen conventions is crucial for accurate calculations.
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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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.
 
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?
 
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.
 
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.
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