Create a Phasor Diagram Easily: Step-by-Step Guide & Helpful Tips

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Discussion Overview

The discussion revolves around the creation of a phasor diagram, specifically in the context of a synchronous motor and its associated calculations. Participants are exploring the relationships between phase current, voltage drops, and power factors, while seeking guidance on how to represent these elements in a phasor diagram.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in creating a phasor diagram and provides initial calculations for phase current and stator reactive voltage drop.
  • Another participant challenges the existence of a "synchronous induction motor" and discusses the implications of power factor and current calculations from the network perspective.
  • A different participant clarifies that the current mentioned is the network current, while the motor winding current is 25.1 A.
  • One participant suggests that power factor and reactance should be calculated from the network point of view for an equivalent star motor, proposing a formula for total voltage drop.
  • A participant shares a vectorial diagram, indicating a potential representation of the phasor diagram.
  • A later reply corrects a previous statement regarding the voltage considered for the equivalent motor, emphasizing the need to use phase-to-phase voltage in the vectorial diagram.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the calculations and representations of current and voltage in the context of the motor. The discussion remains unresolved, with differing opinions on the correct approach to the phasor diagram.

Contextual Notes

There are limitations in the assumptions made regarding the type of motor and the definitions of current and voltage used in the calculations. Participants have not reached a consensus on these aspects.

Cassy85
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Hi, I'm struggling to find out how to create a phasor diagram. I have attached a photo of the question any help would be greatly appreciated.
Screenshot_20211003-194735.png

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
 
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First no such motor "synchronous induction motor" does exist .Since the power factor is leading it is about synchronous motor when the excitation current is more than rated.
The motor has an a.c. winding in stator part and a d.c. winding [poles] on the rotor. Since it is a separately E noted, the generated voltage is equal to supply voltage.
The generated voltage has to be in the load case.
If the power mentioned is "input power" the apparent power it is the ratio 25/0.8.
overexcited synchronous motor phasor diagram.jpg

The loaded current it is 25000/0.8/√3/415=43.475 A
 
Actually this is the current from the network. The current in the motor winding in triangle it is only 25.1A, indeed.
 

Attachments

  • Triangle currents.jpg
    Triangle currents.jpg
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In my opinion, the power factor and Xs are calculated from the network point of view so for an equivalent star motor. In this case the current IA= 43.475 A and is leading the phase-to-neutral voltage VAN with φ= 36.87 degrees. Then the voltage drop [total] is IA*[cosφ+jsinφ]*jXs and the reactive part is jIA*cosφ*Xs.
 
The vectorial diagram it could be like this one:
 

Attachments

  • synchronous motor vectorial diagram.jpg
    synchronous motor vectorial diagram.jpg
    48.4 KB · Views: 188
My mistake. The voltage considered for equivalent motor is not
“the leading the phase-to-neutral voltage” as I said but the phase-to-phase voltage. So, the vectorial diagram on the trigonometric circle it has to be like this:
 

Attachments

  • synchronous motor vectorial diagram.jpg
    synchronous motor vectorial diagram.jpg
    44.9 KB · Views: 199

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