6,6 KV Alternator KVA calculation

[Greek35]

I am working on a HV Y alternator in a marine installation. The Alternator is rated 5375 kva 470 A 0.8 pf @50C
When I am using the formula for line to line voltage for A Ia=1000xSkva/(1.73xV) and substitute the values I get the name plate value for amps (475).
When I use the line to neutral formula for kva { S=3xIaxV/1000} get a slightly different value(5379) but with in calculation I believe.
However if I apply the line to line formula {S=1.73xIaxV/1000) I get a value of 5366. I am missing something and would like some advise in order to calculate KW accurately after that and proceed with other calculations. To be noted that the neutral ground point resistor is not on the generator itself but on the HV buss.
Any suggestions are much appreciated.
Thanks.

 

[Smart $]

Rounding error.

It's the result of using 1.73 as a rounded approximation of the square root of 3. Replace 1.73 with square root of 3 in your calculation and most of that error should disappear.

 

[Besoeker]

Rounding error.

It's the result of using 1.73 as a rounded approximation of the square root of 3. Replace 1.73 with square root of 3 in your calculation and most of that error should disappear.

I did and, as expected, it does.

 

[Smart $]

FWIW, any remaining error would be from using voltage values which are not exactly a square-root-of-3 factor. For example, 480 ÷ sqrt(3) is not exactly 277, nor is 120V × sqrt(3) exactly 208.

 

[Besoeker]

FWIW, any remaining error would be from using voltage values which are not exactly a square-root-of-3 factor. For example, 480 ÷ sqrt(3) is not exactly 277, nor is 120V × sqrt(3) exactly 208.

But probably not relevant in this case if, as you suggest, you use sqrt(3) to get line to neutral voltage from the 6.6kV.

 

[Smart $]

But probably not relevant in this case if, as you suggest, you use sqrt(3) to get line to neutral voltage from the 6.6kV.

Without rounding, correct. Often times when calculating in Excel, for example, I'll use =480/sqrt(3) instead of entering just 277. The displayed value can be shown rounded to 277, but for internal calculations Excel uses the unrounded value (though there is a setting to calculate as displayed in Advanced Options; disabled by default).

 

[Besoeker]

Without rounding, correct. Often times when calculating in Excel, for example, I'll use =480/sqrt(3) instead of entering just 277. The displayed value can be shown rounded to 277, but for internal calculations Excel uses the unrounded value.

I'm aware of that which is why I stated it as sqrt(3) in my response.

 

[Greek35]

My thanks to all for your time and effort you took to reply.
Thanks again.