What is the Difference Between Active and Reactive Power in A.C. Circuits?

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Homework Help Overview

The discussion revolves around understanding the concepts of active power, reactive power, and apparent power in the context of an A.C. circuit involving a capacitor, a heater, and an impedance. The original poster seeks clarification on the definitions and calculations related to these power types.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the meanings of VAR and VA, with some seeking to understand how to calculate the different types of power. Questions arise regarding the implications of the impedance rating and the relationship between real and apparent power.

Discussion Status

The discussion has progressed with some participants clarifying definitions and relationships between different power types. There is an ongoing exploration of the implications of the heater's specifications and the power triangle, with no explicit consensus reached yet.

Contextual Notes

Participants note potential confusion regarding the heater's rating and the apparent power associated with the impedance, questioning how these relate to the definitions of active and reactive power.

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Homework Statement



A capacitor of rating 50 VAR, a heater of rating 1000 W and impedance rating 500 VA at a power factor of 0.8 lagging are connected in parallel to a 230V, 50 Hz power-supply system.Find

a) The system-active power
b) The system-reactive power
c) The system-apparent power
d) The system-power factor.


The Attempt at a Solution



I don't understand what VAR and VA stand for. What are active and reactive powers?
 
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VA is volt amperes, a power unit. VA is used to designate apparent power. VAR is reactive power. Real power is given in watts.

Look up "power triangle".
 
ok I understood their meanings.
How do I find out each of them?
 
Abdul Quadeer said:
ok I understood their meanings.
How do I find out each of them?

Good question. I'm not sure what the designation "impedance rating 500 VA" means. Does your text give any enlightenment? If it were an apparent power for a given power factor I could understand it, but it's associated with a "1000W" heater. The real power should not be greater than the apparent power (which forms the hypotenuse for the power triangle).
 
I just know the answers
1400W, 250VAR, 1422VA, 0.98
 
Okay, it's not a "heater of rating 1000W and impedance rating 500VA". It's a heater of rating 1000W, and a separate impedance with an apparent power of 500VA when the power factor is 0.8; They are describing two separate components. That should clear things up nicely, right? :smile:
 
Yeah cleared up a little.
I want to ask one thing - the power which we calculate using P = VIcos(phi), where V and I are r.m.s. voltages, is it the apparent power?
 
Abdul Quadeer said:
Yeah cleared up a little.
I want to ask one thing - the power which we calculate using P = VIcos(phi), where V and I are r.m.s. voltages, is it the apparent power?

The apparent power (in VA) is on the hypotenuse of the power triangle. Real power (in watts) is the horizontal leg, and reactive power (in VAR) the vertical leg.

VA2 = W2 + VAR2
 
You did not get my question.
The average power in a complete cycle is Vr.m.s.Ir.m.s.cosΦ
Is it equal to the apparent power?

EDIT: Got it. That is true power.

Thanks for your help!
 
Last edited:
  • #10
Ah. I get you now. The average (or mean) power is the real component of the power triangle, not the apparent power.
 

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