How do Capacitors and Inductors Add/Remove VARS in AC?

In summary: However, real power ( watts ) will not unless it is isolated to a specific area of the circuit. The reason reactive power ( VAR) is isolated to a specific area of the circuit is that it contains energy that may not be safe to release ( sparks, heat, etc ).
  • #1
scrubrug
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To my understanding, capacitors cause the current to lead the voltage which adds VARS to the circuit and inductors cause the current to lag behind the voltage which removes VARS (in AC circuits). Also, it is my understanding that VARS increase voltage. I work for one of the largest utilities in the nation as a system operator and literally no one I ask can give me a halfway decent answer on this.

My questions are the following,
How does the current leading the voltage (adding VARS) raise voltage?
How does the current lagging the voltage (removing VARS) lower voltage?
Why is Reactive Power (VARS) isolated to a specific area of a circuit and is unable to travel freely through the circuit like Real Power (Watts)?
What is physically happening in the capacitor that causes current to lead voltage and add VARS?
What is physically happening in the inductor that causes current to lag voltage and add VARS?

If I'm wrong about any of my assumptions or understanding please call me out on it. Also, if you only know the answer to some of my questions or have any info, please share what you know. I'm very interested in getting any information on any of these topics.
 
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  • #2
Hello rugscrub, :welcome:

Can you tell us what you mean with VARS ? I'm pretty sure that I am not the only one who has no idea what you mean with that ...
 
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Likes Harrison G
  • #3
BvU said:
Hello rugscrub, :welcome:

Can you tell us what you mean with VARS ? I'm pretty sure that I am not the only one who has no idea what you mean with that ...
Sure, VAR is Volt Ampere Reactance, which is a measurement of reactive power.
 
  • #4
Haha, I googled VARS and ended up with a skiing resort. Should have googled electrical vars and that would have given your link.

OK, here goes: For a halfway decent answer you need something that you can understand, but then you'll need to indicate a bit better what that could be. A school book on AC circuits ? Perhaps hyperphysics can help a bit ? There is plenty of material on the net, so it's more a matter of helping you to find that than to explain things to you that are being explained much better elesewhere.
 
  • #5
A "VAr" is the unit for reactive power, which means that the direction of the power is switched for every half period ( example: 120 times per second by 60 Hz ac ).
So reactive power will not be accumulated over time to e.g. energy that may heat up a kettle of water.

You can charge a battery and then discharge it again: After that the battery will have no energy left.

A capacitor acts like a battery: Connecting it to ac-voltage, it will be charged and discharged in turns.

http://www.regentsprep.org/regents/math/algtrig/att7/phases17.gif

In the above figure, the red curve is voltage and the blue curve is current. Whenever the voltage is constant ( red curve at top/bottom ) the current will be zero because the capacitor is not charged/discharged. Now, because the current is ahead of the voltage, we say that the capacitor produces reactive power ( just a convention ).

Connecting an inductor to ac-voltage, the voltage will be ahead of the current, and we say that an inductor consumes reactive power.

Reactive currents in e.g. power lines create active power losses ( P = I2 * R ). So we want to get rid of reactive power/current, mainly created by transformers and electric motors, containing coils/inductors that consumes reactive power. So if we connect a capacitor in parallel to a transformer/motor, the capacitor will locally produce reactive power consumed by the transformer/motor.

Hence no reactive power/current will flow in the power lines, creating active power losses. That's clever.

Adding/removing VAr's does not automatically increase/decrease voltage. You may say that minimizing reactive power/current will increase voltage ( decrease voltage drop in power lines ).

Reactive may travel freely in a circuit.
 
Last edited:

1. How do capacitors and inductors add or remove VARS in AC circuits?

Capacitors and inductors are passive components in AC circuits that store and release energy in the form of reactive power, also known as VARS (volt-ampere reactive). Capacitors store this reactive power in the form of electric fields, while inductors store it in the form of magnetic fields. In AC circuits, capacitors and inductors add VARS by absorbing reactive power from the circuit and releasing it back into the circuit in a cycle. This helps to balance out the flow of active power (measured in watts) and maintain a constant voltage.

2. How does a capacitor add VARS to an AC circuit?

A capacitor adds VARS to an AC circuit by storing reactive power in an electric field. When an AC voltage is applied to a capacitor, it charges the capacitor and stores energy in the form of an electric field between its two plates. As the voltage changes, the capacitor discharges this energy back into the circuit, which adds VARS. The larger the capacitance, the more reactive power a capacitor can store and add to the circuit.

3. How does an inductor remove VARS from an AC circuit?

An inductor removes VARS from an AC circuit by storing reactive power in a magnetic field. When an AC current flows through an inductor, it creates a magnetic field around the inductor. As the current changes direction, the magnetic field collapses and releases the stored energy back into the circuit. This helps to balance out any excess reactive power in the circuit and remove VARS. The larger the inductance, the more reactive power an inductor can store and remove from the circuit.

4. Can capacitors and inductors be used to control VARS in AC power systems?

Yes, capacitors and inductors can be used to control VARS in AC power systems. In fact, they are commonly used in power factor correction systems to improve the power factor and reduce the amount of reactive power in an AC circuit. By adding or removing VARS, capacitors and inductors help to balance out the reactive power and maintain a more efficient flow of active power in the circuit.

5. What is the difference between capacitive and inductive reactance in AC circuits?

Capacitive reactance is the opposition to the flow of AC current caused by a capacitor, while inductive reactance is the opposition to the flow of AC current caused by an inductor. They have opposite effects on the flow of reactive power in an AC circuit – capacitive reactance adds VARS, while inductive reactance removes VARS. The value of capacitive reactance decreases as the frequency of the AC signal increases, while inductive reactance increases with frequency. This is why capacitors and inductors have different effects on AC circuits depending on the frequency of the signal.

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