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# What is reactive power?

Updated: 8/30/2023 Wiki User

8y ago

Reactive power is an odd topic in AC (Alternating Current) power systems, and it's usually explained with vector mathematics or phase-shift sinewave graphs. However, a non-math verbal explanation is possible.

Note that Reactive power only becomes important when an "electrical load" or a home appliance contains coils or capacitors. If the electrical load behaves purely as a resistor, (such as a heater or incandescent bulb for example,) then the device consumes "real power" only. Reactive power and "power factor" can be ignored, and it can be analysed using an AC version of Ohm's law.

Reactive power is simply this: when a coil or capacitor is connected to an AC power supply, the coil or capacitor stores electrical energy during one-fourth of an AC cycle. But then during the next quarter-cycle, the coil or capacitor dumps all the stored energy back into the distant AC power supply. Ideal coils and capacitors consume no electrical energy, yet they create a significant electric current. This is very different from a resistor which genuinely consumes electrical energy, and where the electrical energy flows continously in one direction; moving from source to load.

In other words, if your electrical appliance contains inductance or capacitance, then electrical energy will periodically return to the power plant, and it will flow back and forth across the power lines. This leads to an extra current in the power lines, a current which heats the power lines, but which isn't used to provide energy to the appliance. The coil or capacitor causes electrical energy to begin "sloshing" back and forth between the appliance and the distant AC generator. Electric companies must install heavier wires to tolerate the excess current, and they will charge extra for this "unused" energy.

This undesired "energy sloshing" effect can be eliminated. If an electrical load contains both a coil and capacitor, and if their resonant frequency is adjusted to exactly 60Hz, then the coil and capacitor like magic will begin to behave like a pure resistor. The "energy sloshing" still occurs, but now it's all happening between the coil and capacitor, and not in the AC power lines. So, if your appliance contains a large coil induction motor, you can make the motor behave as a pure resistor, and reduce the current in the power lines by connecting the right value of capacitance across the motor coil.

Why is reactive power so confusing? Well, the math is daunting if not entirely obscure. And the concept of "imaginary power" puts many people off. But this is not the only problem. Unfortunately most of us are taught in grade school that an electric current is a flow of energy, and that energy flows back and forth in AC power lines. This is completely wrong. In fact the energy flows constantly forward, going from source to load. It's only the charges of the metal wires which flow back and forth.

Imagine that we connect a battery to a light bulb. Electric charges already present inside the wires will begin to flow in the circle, and then electrical energy moves almost instantly to the light bulb. The charge flow is circular like a belt, but the energy flow is one-way. Now imagine that we suddenly reverse the connections to the battery. The voltage and current will reverse... but the energy still flows in the same direction as before. It still goes from battery to bulb. If we keep reversing the battery connections over and over, we'd have an AC system. So, in an AC system, only the voltage and current are "alternating," while the electrical energy flows one-way, going from source to load. Where AC resistive loads are concerned, electrical energy does not "alternate." To understand energy flow in AC systems, it's critically important that we understand the difference between charge flow (current, amperes) and energy flow (power, watts.)

What is imaginary power? Simple: it's the unused power which flows backwards and forwards in the power lines, going back and forth between the load's coil or capacitor and the distant AC generator. If your appliance was a pure capacitor or inductor, then it would consume no electrical energy at all, but instead all the flowing energy would take the form of "sloshing energy," and we'd call it "imaginary power." Of course it's not actually imaginary. Instead it's reflected by the load.

What is real power? Even more simple: it's the energy flow which goes continuously from the AC generator and into the appliance, without any of it returning back to the distant generator.

Finally, what is "apparent" power? It's just the combination of the above two ideas: it is the continous-forward-moving or "real" energy flow, combined with the sloshing or "imaginary" energy flow. Wiki User

8y ago   Wiki User

11y ago

It is product of Current,Voltage and Sin angle between current and voltage.

Reactive Power = Current(I)*Voltage(V)*Sin(angle B/W Voltage and Current)

It is also know as the power used in transformation of energy in one form to another form.

AnswerReactive power is the rate at which energy is alternately stored in a magnetic or electric field and returned to the supply of an AC circuit, and is expressed in reactive volt amperes. Reactive power is associated with inductive or capacitive loads.

The vector sum of reactive power and true power (watts) is called the apparent power (volt amperes) of the circuit.   Earn +20 pts
Q: What is reactive power?
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Still have questions?  Related questions

### Why reactive power is named as reactive?

Actually reactive power is a power which flows in between load to source which is a reactive action of the power given from source to load.the given power to load will not be utilised fully.some power will be oscillating from load to source.this is called reactive power.

### Why wattmeter measure the reactive power?

A watt meter will measure active power, not reactive power.

### What happens to reactive power in a circuit that has both inductance and capacitance?

Inductors are considered to be a load for reactive power, meaning that they will draw reactive power from the system. Capacitors are considered to be sourced of reactive power, they feed reactive power into the system. If you have a circuit that is at unity (balanced with inductors and capacitors) no reactive power will be drawn from the source. You will have unity power factor. If your circuit is more inductive than capacitive it will be drawing reactive power from the source. The opposite is also true for capacitors.

### Which line requires compensation?

Basically an AC transmission line require compensation in terms of reactive power. To push the active power across a transmission line certain amount of reactive power is necessary. In AC transmission line reactive power is generated and consumed. Generator is responsible for the production of reactive and active power both. Than this reactive power is consumed by the load and transmission line. Additional reactive power s supplied by the capacitor. This extra power supplied by the capacitor is termed as reactive power compensation. Requirement of this reactive power is there because reactive power is necessary to maintain the voltage stability.

### How can you reduce reactive power?

If, for example, the reactive power of a load is due to its inductance, then installing a capacitor in parallel with the load will reduce the overall reactive power.

### Which excitation synchronous motor drawn reactive power?

Hi, Under excitation - inductive reactive power Over excitation - Capacitive reactive power.

### Is that the reactive power is a combination of both reactive power and imaginary power?

No. It is apparent power (expressed in volt amperes) that is the combination (vector sum) of true power (expressed in watts) and reactive power (expressed in reactive volt amperes). 'Imaginary power' is simply another name for 'reactive power' -where 'imaginary' is simply mathematicians-speak for 'quadrature' or 'right angles'.

### Is reactive power a vector or scalar?

I am not sure what exactly you mean by "reactive power" (I guess you mean electrical reactive power), but power is the ratio of energy for a period of time. So that makes power (and reactive power as well) a scalar, since you can describe it with only one number. The fact that electrical reactive power is drawn on a XY plane, should not confuse you.

### Is reactive power greater than true power?

Use a wattmeter, as it only reads 'real power' of your load. Use an ammeter and a voltmeter, and the product of the two readings will give you 'apparent power' of your load. Since apparent power is the vector sum of real power and reactive power, use the following equation to find the reactive power of your load: (reactive power)2 = (apparent power)2 - (real power)2

### What is the power factor of AC generator when the reactive power is equal to zero?

Per factor is 1 when reactive power is zero.

### What is the role of reactive power in a power system?

To supply the reactive power demand of load and to regulate of output volage at the grid

### What happens if reactive power enters the system?

Reactive power entering the system will increase the system voltage.