Calculation of cable size

Hello,

With reference to your cable sizing calculation, you have written I/P in kVA By 1.2 times. Kindly clarify this statement.

Regards
Jhotha
 
S

s.balasubramanian

Dear

The method you have given is not correct, although your answer and answer you get by vector addition will not differ as pf you consider in each equpt is not very different from your general assumption. if you take pf as say 0.9 and then compare your figure with vector addition it will be different to a good value

what you have to do is
1.find kW and Kvar wrt the actual loading of motor
2. add all kws and kVars
3.find kVa by hypotenuse formula for trafo capacity
 
Hi,

Just want to confirm, for the sizing of the transformer, is it to consider the total connected load or max. demand? I think for saving of the money, better go for the max. demand.
Any advise from experts? TQ
 
Wady... in general, transformer size is never based on "connected" load! Neither will "maximum demand" result in an economical solution, because load profile is extremely important!

Also, because there is no "one size fits all" approach, I suggest you contact several transformer manufacturers. Many are happy to provide you with a "Product Specifier", or the like, to aid you!

If you have a specific application in mind, and you are unable to find a suitable answer on the web, I'd be glad to help!

Regards, Phil Corso
 
Hi there

I did a calculation there recently and my derating factors came to about .4 - is this between over cautious. As you can imagine the size of the cable ballooned. Does that sound right- i'm not 100% thanks

>Anonymous, following is a list of many
>factors that must be considered:
>
>o Allowable voltage-drop for normal operating load.
>o Allowable voltage-drop for future operating load as determined by motor's Service Factor

----- snip -----
 
John... it appears your question is directed to my 10-Jul-07 (19:55) reply to Anonymous! It is possible to end up with a derating factor equal to 0.4. However, in order to answer you quantitatively please provide some detail!

Regards, Phil Corso
 
P

prince mukhia

Hello Sir

can you explain calculating KW in three phase supply like we have current R=55 Y=78 B=90 and W=root3*VI*power factor so which value of current we have to put either highest or average
 
Prince... presuming you are interested in determining the overall power, please supply the following values:

o R-Y Volts.

o Y-B Volts.

o B-R Volts.

o R-Neutral Volts.

o Y-Neutral Volts.

o B-neutral Volts.

o PF associated with Line Volts R-Y and R Amps.

o PF associated with Line Volts Y-B and Y Amps.

o PF associated with Line Volts B-R and B Amps.

o Phase sequence or rotation, R-Y-B or B-Y-R.

Regards, Phil Corso (cepsicon[at]AOL[dot]com)
 
P

prince mukhia

Dear Sir
can you please help me to calculate Kilowatt with following data:<pre>
R 161A
S 145A
T 117A
Power(KW) ?
Phase to phase voltage =380v
Cosine of phi =0.8</pre>
please calculate overall kilowatt
thanking you
regard,Prince
 
P

prince mukhia

Dear Sir
> can you please help me to calculate

---- snip ----

actually i need to know only how i will put the value of current while calculating watt because i hav three valur RYB so either i hav to take average of RYB or take or by applying VIcos phi with each phase current

thanking you
regard, Prince
 
Prince... in answer to your 12-Sep-11 (00:16) an approximate (I emphasize 'approximate') formula, based upon the data you provided is:
<pre> o kW = [Sqrt(3) x Vavg x Irms x Cos(phi)]/ 1,000, where,

o Vavg = [( Vry + Vyb + Vbr)/3.0].

o Irms = [Sqrt (Ir^2 + Is^2 + It^2)/3] </pre>
I will provide the 'more/ accurate method later. Regards, Phil Corso
 
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