Hi, I've just got into my electrical engineering course and I need some

Hi,

I've just got into my electrical engineering course and I need some help with a question of mine here.

During a site visit, we were shown a main LT panel which has switchgears, ammeters and different kinds of relays and the distribution network from that panel. In the main LT panel I've noted down the current readings as Ir - 163A, Iy - 150A and Ib - 147A. The Line to Line voltage is 415 V at 50 Hz and Line to Neutral voltage is 230V at 50 Hz.

From the above details, how would I calculate the kVA rating of transformer? The primary side voltage of the transformer is 11 kV and the secondary side voltage is 415V and the frequency is 50 Hz.

Question Posted / confused.elec

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Hi, I've just got into my electrical engineering course and I need some help with a question..

Answer / 7anoter4

Something is not correct. If VL_L=415 V then VL_N=240 V
[not 230 V] and then

both calculation results will be the same [no error].

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Hi, I've just got into my electrical engineering course and I need some help with a question..

Answer / 7anoter4

The transformer actual load [apparent power] S=0.23*
(163+150+147)=105.8 kVA.

You may calculate approximately taken the average current
(163+150+147)/3=153.33 A and the formula sqr(3)
*0.415*153.33=110.2 kVA [4% error].

But this is not the rated power. The rated power and the
rated current have to be written on manufacturer rating
plates.

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