Camara Chp. 40, Problem 4

[frecoder78]

I don't understand why when calculating the line current IL, the Line Voltage needs to by divided by sqrt 3? Any suggestions?

prob4__chp40.doc

 

[Dark Knight]

I am very rusty right now Freecoder but it is not the line current sqrt of three of the phase current?

I should be able to confirm my notes tomorrow. I am sure somebody will help you before that.

 

[Flyer_PE]

The voltage isn't being divided by sqrt(3). Camara is combining a couple of steps into one equation.

Here is how this breaks down:

Motor HP = 200

Efficiency = 0.85

Power Factor = 0.91

Apparent Power (S) = (HPx746)/(pfxeff) = (200x746)/(.91x.85) = 193kVA

S = sqrt(3)xVLinexILine

Solving for I: ILine = S/(sqrt3xVLine) = 193kVA/(sqrt3x.44kV) = 253 Amps

 

[frecoder78]

The voltage isn't being divided by sqrt(3). Camara is combining a couple of steps into one equation.
Here is how this breaks down:

Motor HP = 200

Efficiency = 0.85

Power Factor = 0.91

Apparent Power (S) = (HPx746)/(pfxeff) = (200x746)/(.91x.85) = 193kVA

S = sqrt(3)xVLinexILine

Solving for I: ILine = S/(sqrt3xVLine) = 193kVA/(sqrt3x.44kV) = 253 Amps

AHH! I can't believe I didn't see that before! :smileyballs: Thanks guys for your help! Now I can sleep restfully!