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Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit
2

Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

(OP)
Hello to all. Should the following formula be used to calculate the voltage drop of the motor in the delta condition in a star-delta system considering that there are 2 cables between the panel and the motor and the current of this cable is 1/1.73 of the motor current?

voltage drop=Irated/sqrt(3)*(2*R*cos(phi)+√(1-cos(phi)^2)*2*X)

RE: Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

Yes, if you have a star-delta starter and six leads going to the motor, the VD in those leads is based on the current in any one of them, so 58% of the motor FLC.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

(OP)
Should the length of the cable be considered twice?

RE: Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

Mr. zaboli (Electrical)(OP)10 Jul 23 09:54
".... Should the following formula be used to calculate the voltage drop of the motor in the delta condition in a star-delta system considering that there are 2 cables between the panel and the motor and the current of this cable is 1/1.73 of the motor current?.....Should the length of the cable be considered twice?"
I look at it this way for your consideration.
1. For simplicity, take the motor (run/delta) or rated current be I A.
2. A SD starter, when in run/delta condition:
a) the source current is I A.
b) the current flow through the main contactor = the delta contactor= the current flow through each of the six conductors.
c) the current is [ 0.732 x I] A.
3. The VD is calculated based on the current above 2. c).
4. For simplicity, the pf may be taken as 1.0, instead of the rated; as it varies within a small range, depending on the load.
Che Kuan Yau (Singapore)

RE: Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

Item c. is incorrect. It’s not 0.732 x 1. It is 1 / 1.732 which is .577 (58%).


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Formula for calculating motor voltage drop in delta condition in a star-delta motor circuit

@ Mr. jraef (Electrical)11 Jul 23 17:31
"...Item c. is incorrect. It’s not 0.732 x 1. It is 1 / 1.732 which is .577 (58%)".
Thank you Sir. My sincere apology for the typographical error.
Yes, it should be [0.577 x I ] A.
Che Kuan Yau (Singapore)

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