Need help from electrical engineers

S

scudmissile007

Disciple
Hi all, need some clarifications from electrical

engineers, in our industry we are upgrading a

three phase induction motor from 30hp(22kw)

to 50hp(37kw).my question is on what basis

the electrical Amps rating is given to motor.I

have seen some motors of 30hp whose amps

rating differ from 40 to 45 amps.So, what is the

correct method to measure amps?.Currently the

present 30hp motor draws current of

45amps,38amps&40amps in phase 1,2&3

phases respectively at full load.What would be

the current drawn from a 50hp(37kw) motor at

full load?.

TIA.:)
 
what's the PF of the motor ??
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scudmissile007 said:
my question is on what basis

the electrical Amps rating is given to motor.
Click to expand...

The Amp rating is directly proportion to its power, and its efficiency/power factor. The first factor is straight forward, but efficiency/P.F. obviously depend on the manufacturer's design, so can vary from motor to motor.

Current = W / (1.73 x V x P.F.)

Your existing 30hp/22kW 415V motor seems to have a 0.75 P.F.

Assuming a similar P.F. for the 50hp/37kW motor, it should be drawing ~69A.
 
According to the etm the pf is .927.

The line pf is .927, but don't know the pf of the motor.what is the standard Indian three phase voltage is it 400v or 415v or 440v.
 
Standard: 415 or 440... In our factory its keeps on fluctuating a lot between 400 to 460

Given : 50hp motor

Convert to KW : 1hp = 0.745 kw .... therefore, 50x0.745 = ~37.25kw

Formula : P/[squareroot(3)x v x cos(phi)] = I

Consider PF of this motor to be 0.85

Therefore: 37250/(1.732*415*0.85) = 60.96A

AFAIK, PF of that motor wouldnt be below 0.8
 
Crazy_Eddy said:
^ 'phi' in your formula is the lead/lag phase angle, not the P.F. So if you're considering a P.F. of 0.75, your phi should be ~41.41 degrees. Also you need to convert kW to W, i.e. multiply by 1000.
Click to expand...

Yup I know its not PF... But I have mentioned the general formula for calculation...
<
And then substituted PF in place of COS(phi)
 
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