What Distinguishes Real Power from Reactive Power in Electrical Systems?

In summary: AC circuit. Theta is measured in radians and is equal to the angle subtended at the point by the voltage and current waves. Theta is always measured at the point where the voltage and current waves are in phase. In summary, reactive power is a measure of the energy flow in an AC circuit, and is important because it can cause blackouts.
  • #1
sreedhar
2
0

Homework Statement



What is the exact difference between real an reactive power?


Homework Equations



As far as i know

real power =V*I*cos(teta)
reactive power = V*I*sin(teta)


The Attempt at a Solution


I have heard, in physics reactive power is not considered as its work is zero?
But how significant it in electrical field?
 
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  • #2
Reactive power is the part that just goes back in forth in the circuit. Sometimes it is positive and sometimes negative, but over the whole AC cycle it averages to zero. Real power averages to something positive over the whole AC cycle.
 
  • #3
Just a little tidbit of information... Although reactive power does indeed do no work, it is very important. The blackout of 2003 was caused in part by the lack of reactive power.
 
  • #4
A nice basic intro to work from, taken from my marine engineering notes:
"
In DC circuits, power is a result of the current and voltage multiplied together. This is acceptable because the current and voltage are in phase with each other. It is acceptable in AC circuits where the load is totally resistive. In reality the load onboard is more inductive (due to motor windings) and resistive (due to heating/lighting etc). In inductive circuits with AC, the constant changing on current and voltage causes a constantly changing magnetic field. This induces and emf into the windings which opposes the source creating it (Lenz'z Law) causing an inductive reactance. Reactance (whether due to inductance or capacitance) and resistance together combine to give impedance.
"

Remember that in AC circuits, a solenoid actually resists the current BUT does not use any power (and therefore do any work) in doing so. SO balancing this relationship of REACTANCE and RESISTANCE gives IMPEDANCE and that is used to form the power factor triangle (you gave the equations in your question). When this goes out of shape, you have blackouts and lots of wasted energy. Back in the good old days (I suppose World War 2 time'ish) industrial works and factories in England used to get a reduction in their electric costs if they could prove they had a good power factor, of say 0.8+.

Hope it helps.
 
  • #5
Reactive power involves an actual current flow, and hence heating, even though it produces no useful work. Because of this current, and the associated losses, it is is highly undesirable.

Power factor correction, alluded to by XaseR, is still very much practiced today. This is one of the reasons for the popularity of synchronous motors because with the proper excitation they can look like a capacitor on the line, thus offsetting inductive loads. Utility companies do not like customers with very bad power factors, and they will charge extra for such service.
 
  • #6
Some more description, which was almost said above: reactive power is the energy flow used in the creation and collapse of magnetic (inductors) and electric fields (capacitors) in the system. The energy could be desribed as sloshing back and forth as the fields build and fall, though this does not work. The sloshing still creates current flow, and thus greater requirements for on the electrical transmission system (conductor sizes, etc).

The 'theta' in the OP is defined as the phase angle between the oscillating current i(t) and voltage v(t)
 

Related to What Distinguishes Real Power from Reactive Power in Electrical Systems?

What is real power?

Real power is the actual power that is used to perform work or produce energy. It is measured in watts (W) and is the product of voltage and current.

What is reactive power?

Reactive power is the power that is required to establish and maintain an electric or magnetic field. It is measured in volt-amperes reactive (VAR) and does not perform any useful work.

What is the difference between real and reactive power?

The main difference between real and reactive power is that real power is the actual power used to perform work, while reactive power is the power required to maintain the electric or magnetic field. Real power is essential for performing tasks such as lighting a bulb, while reactive power is necessary for maintaining the stability of the electrical system.

Why is it important to balance real and reactive power?

Balancing real and reactive power is important for maintaining the stability of the electrical system and ensuring efficient use of energy. An imbalance between the two can lead to voltage fluctuations, increased energy losses, and reduced system efficiency.

How can real and reactive power be balanced?

Real and reactive power can be balanced by using devices such as capacitors and inductors, which can provide or absorb reactive power as needed. Additionally, proper system design and maintenance can also help in balancing real and reactive power.

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