Can someone explain what KVA is......

[ian.settle1]

Is kva not simply kilowatts?

If a pure resistive circuit then yes otherwise no

 

[Des 56]

If you and the missus were at it
When you thrust,the missus does the same at the same time,result,bliss (good power factor)

If you and the girl next door were at it
When you thrust, she is little bit faster than yours,result,out of sinc ( possible dis conection even ) (poor power factor)

Power factor is trying to achieve unity ( 1 to 1 ) It may be only 0.8 or so or worse even)

volt x amps (x power factor) = true power

So the better the power factor the more the unchanging volt amps value matches the true power

 

[TF and the wire]

If you and the missus were at it
When you thrust,the missus does the same at the same time,result,bliss (good power factor)

If you and the girl next door were at it
When you thrust, she is little bit faster than yours,result,out of sinc ( possible dis conection even ) (poor power factor)

Power factor is trying to achieve unity ( 1 to 1 ) It may be only 0.8 or so or worse even)

volt x amps (x power factor) = true power

So the better the power factor the more the unchanging volt amps value matches the true power

I don't remember that at college, I also didn't realise that women were supposed to move.

 

[hoover]

Sounds like someone might have got one of those forms to fill in for a new or increased electricity supply, as these ask for amongst other things, how many kVA do you require. I always put 21kVA as this ensures that a 100amp fuse is fitted. Anything above about 25 kVA puts you onto 3 phase.

I'm a bit too long in the tooth for serious maths, and i've forgot most of the formulaes i sort of learnt 30 odd years ago. I'll stick with V over IR etc etc.

Cheers........Howard

Correct mate, i do have one of these forms to fill in. So i have a load of 83kw so i devide or multiply this by 0.8 to get my kva? Its a 3 phase supply i need so do i devide the 83kw by 230 or 415 to get my ampage? Cheers in advance.

 

[john.irvine]

Correct mate, i do have one of these forms to fill in. So i have a load of 83kw so i devide or multiply this by 0.8 to get my kva? Its a 3 phase supply i need so do i devide the 83kw by 230 or 415 to get my ampage? Cheers in advance.

(83kW x 1000) / (230 x 1.73 x 0.8) = Amps

 

[hoover]

Correct mate, i do have one of these forms to fill in. So i have a load of 83kw so i devide or multiply this by 0.8 to get my kva? Its a 3 phase supply i need so do i devide the 83kw by 230 or 415 to get my ampage? Cheers in advance.

(83kW x 1000) / (230 x 1.73 x 0.8) = Amps

Where does the 1.73 come from mate?

 

[john.irvine]

Where does the 1.73 come from mate?

Its the square root of three, it converts single phase to three.

83kW x 1000) / (230 x 0.8) = Amps single Phase
83kW x 1000) / (230 x 1.73 x 0.8) = Amps Three Phase

 

[IP4X]

Where does the 1.73 come from mate?

If you are really interested try this: Seriously...
Its also a good way to see the star/delta relationship

1. Draw a triangle with equal sides. (all angles 60 degs) call each point A,B,C
2. inside the triangle draw a line from each point to the centre of the opp side.
3. Where the three lines intersect you have now created a star point...used as a neutral, call it N
4. You have also created 6 right angle triangles with angles 60, 90 and 30 Degs.

So use basic trig to find the relationship between the relevant sides of the star/delta triangles...

So Cos(30) = (half of CA)/ BN ............Cos(x) = adjacent/hyp
0.866 = (0.5 x CA)/ BN
BN = (0.866/0.5)CA

or BN = 1.732 CA

Hope that helps.
Also remember that a power factor of 0.8 may be common and that is probably why they use it in the classroom examples but this figure will differ in every installation!
Cheers