Ac circuit analysisabout power

Click For Summary

Discussion Overview

The discussion revolves around the analysis of an AC circuit involving an induction motor and synchronous motors, focusing on the calculation of power factors and reactive power. Participants explore the relationships between real and reactive power in the context of power factor adjustments.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a problem involving an induction motor with a specified power factor and seeks to determine the power factor of synchronous motors added to the system.
  • Another participant suggests using vector and algebraic methods to solve for unknowns, emphasizing the addition of real and reactive powers.
  • Confusion arises regarding the treatment of reactive power, particularly the distinction between lagging and leading power factors.
  • Participants discuss the need to express the total system's reactive power in terms of the synchronous motors' reactive power, noting that one is positive and the other is negative.
  • There is a question about how to find the reactive power of the synchronous motors without a given phase angle, with suggestions to use arccosine or Pythagorean theorem.
  • Participants express uncertainty about the equations being used and seek clarification on how to manipulate them to find the necessary values.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to solve the problem, and there are multiple competing views on how to handle the calculations involving reactive power and power factors.

Contextual Notes

Participants express confusion about the application of different equations and the implications of lagging versus leading power factors. There are unresolved questions regarding the necessary phase angles and the correct use of trigonometric functions in the calculations.

herbgriffin
Messages
17
Reaction score
0

Homework Statement


An induction motor load of 2000 kVA has power factor 0.80 lagging. Synchronous motors totaling 500 kVA are added an operated at a leading power factor. If the overall power factor is then 0.90 lagging, what is the power factor of the synchronous motors?


Homework Equations


i use power triangle to solve the values of powers in induction motor..


The Attempt at a Solution


i have solve the reactive power = 1200 kvar ; p=1600 kw..
i am confuse how to use the total power factor... in need to find the real power in the synchronous motors... in order to find the power factor of the synchronous motors...
 
Physics news on Phys.org
It's vectors and algebraic problem. Write down all all real and reactive powers and solve for unknowns.

We add real powers together and reactive power together.

Say, induction motor has pf of 'x'.

Your total system real power will be 1200+500*x
Your total system reactive power will be1600 + ...
Relation between total real and reactive power is given by pf of 0.9
 
hello sir i am the one who ask the question about ac circuit analysis power...i am confuse on what other equations i will make since there reactive power are different other one is lagging and other one is leading. i am really confused sir and i am afraid if the same procedure of problem will come out on our exam ... thank you sir and sorry for the disturbance

Yes the reactive powers are different: one is positive other is negative. Let's say reactive power of synchronous is Reactive_sync

Then the total system reactive power will be be 1600 - Reactive_sync

Now, we have x and y components of the total system.

y/x = tan (acos pf_total_system)...
 
rootX said:
Yes the reactive powers are different: one is positive other is negative. Let's say reactive power of synchronous is Reactive_sync

Then the total system reactive power will be be 1600 - Reactive_sync

Now, we have x and y components of the total system.

y/x = tan (acos pf_total_system)...

how can i find the reactive power of the synchronous motors when there is no given phase angle...will i use arccosine of x to find x?...
 
herbgriffin said:
how can i find the reactive power of the synchronous motors when there is no given phase angle...will i use arccosine of x to find x?...

Yes that's right. Or you can use Pythagoras theorem .
 
rootX said:
Yes that's right. Or you can use Pythagoras theorem .

is this equation correct (1600-arcos x...)/(P1+P2) = tan (arcos 0.90)
how will i find x when there is arcos...please help... i am really confuse...thank you for your time sir...
 
It wouldn't be as ugly if you use Pythagoras theorem.
 

Similar threads

  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 13 ·
Replies
13
Views
4K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 8 ·
Replies
8
Views
4K