Help with phasor diagram

Thread Starter

Cassy85

Joined Oct 3, 2021
2
Hi all, I'm new to the forum. I'm looking for help with the following questions I have uploaded.

cassy85_Screenshot_20211003-194735_cropped.png

Any help would be greatly appreciated.

Thanks in advance.

Moderators note : cropped image and showed full size.
 
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Thread Starter

Cassy85

Joined Oct 3, 2021
2
This is what I have attempted so far.
It's question 2b I am really struggling with.
I'm not looking for the answers just looking for some direction.

  1. Calculate phase current

Phase current = 250003 x 415 x 0.8


Phase current = 25.1 Amps


cos-10.8=36.87


I = 25.1 ∠36.87° Amps


  1. Calculate the stator reactive voltage drop IXs

Voltage drop = IaXs



25.1 x 4 ∠36.87° + 90°


Voltage drop (IXs) = 100.4 ∠126.87° volts
 

dcbingaman

Joined Jun 30, 2021
602
Phase current = 250003 x 415 x 0.8

Watts multiplied by Volts does not give you Amps.
There appears to be something wrong here just from dimensional analysis. Power being voltage times current. I would think the correct formula would be 25e3 (W)/415 (V) = 60Amps * (0.8) = 48 Amps.

Watts over volts gives amps and power factor is a unitless quantity. But I am not 100% sure. I have not dealt much with problems involving 3 phase delta connected synchronous motors.
 

BobaMosfet

Joined Jul 1, 2009
1,996
Phase current = 250003 x 415 x 0.8

Watts multiplied by Volts does not give you Amps.
There appears to be something wrong here just from dimensional analysis. Power being voltage times current. I would think the correct formula would be 25e3 (W)/415 (V) = 60Amps * (0.8) = 48 Amps.

Watts over volts gives amps and power factor is a unitless quantity. But I am not 100% sure. I have not dealt much with problems involving 3 phase delta connected synchronous motors.
@dcbingaman is correct. The basic formulas are Ohm's Law and Watt's Law I = E/R
 

Papabravo

Joined Feb 24, 2006
18,783
... power factor is a unitless quantity....
This is absolutely correct. Angles are dimensionless (unitless) since they are the ratio of two distances. Any transcendental function of a dimensionless quantity is also a dimensionless quantity. Power factor is the cosine of the phase angle between the voltage and current of an AC waveform.
 
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