Exlaining Reactive Power

[benbo]

Anybody got any creative analogies for explaining reactive power to lay people? Occassionally I am called on to do this, explain VARS, bucking and boosting, etc. Starting with the fact that I don't understand it all that well myself, I generally analogize it to a man made aqueduct that you want to use to float boats with goods downstream. THe aqueduct must have a certain level of water - not too much, not to little, in order for the boats to float. Filling the aqueduct and keeping it full is analogous to the VARS. You can't really use any of it, but it is necessary to have it full to move the actual boats (which represent the power) downstream.

Similarly, an electric system is modeled as a bunch of inductors, capacitors, and resistors. THere is a certain amount of "energy" necessary to establish the fields and such necessary for the transmission of power. You can't use this energy, but it is essential nonetheless. This represents the VARS.

Suffice to say, after this explanation most people are just as confused as before. Any ideas? I don't want to use numbers or mention a power traingle or anything like that. Or am I the only person who has run into this dilemna?

 

[Dark Knight]

I kind like it.

I was trying to explain the VAR concept the other day to our dispatchers. They questioned me why they needed the cap banks to improve the voltage some times.

My explanation was that because most of the load on a power systems is inductive( because of the motors) we needed the cap banks to off-set the effect. To make the motors run they need a magnetic field to be created. The power needed to create that magnetic field is the reactive power or VAR.

 

[benbo]

I kind like it.
I was trying to explain the VAR concept the other day to our dispatchers. They questioned me why they needed the cap banks to improve the voltage some times.

My explanation was that because most of the load on a power systems is inductive( because of the motors) we needed the cap banks to upset the effect. To make the motors run they need a magnetic field to be created. The power needed to create that magnetic field is the reactive power or VAR.

Yeah - that's probably a good enough explanation. I may be dumbing it down a bit too much, and just confusing things.

 

[mudpuppy]

That's a neat analogy benbo, I like it. I've never had any luck trying to explain reactive power to non-EEs; you're definitely not the only person who's run into this issue.

 

[Art]

F E M

Freakin'

Electrical

Magic

 

[Ilan]

This is how my professor explained to me.

Let us imagine the power system as a pipeline supplying water.

Pipeline - Power system

Water - Real power

Pressure - Voltage/Reactive power

You need to maintain the pressure(voltage) in a pipeline to deliver water(real power). Reactive power helps you maintain the pressure (voltage). Inductive elements are like pipelines with bigger diameters - reduce the pressure (voltage) and decrease the speed of water (flow of real power) and capacitors are like pipelines with smaller diameters - increase the pressure (raise the voltage) and helps the delivery of water (Real power). Inductive and capacitive elements do not affect the total amount of water (Real power) flowing through them just affect the pressure (voltage).

:2cents:

Ilan.

 

[Steve Wallace]

I know that this does not really apply, but I like telling it.

Power Factor - Beer

Me and you go to a bar and order a pair of pints. We each have a different bar tender.

My bar tender is new and has not spent much time drafting beer. He simply pulls the handle and allows the beer to fill the glass. This as we all know produces a considerable amount of head.

Your bar tender is a veteren. He opens the tap slowly and tilts the glass producing the perfect amount of head.

Now, we are back at the table compairing the two glasses. Side by side they are the same size glasses and we paid the same for them, but the amount of drinkable beer in your glass is much greater. Who received the greater value for is dollar spent on a pint.

I used something similar to this to explain how power factor works and he understood it and signed off on the $1.5 Million project.

GOOD TIMES!

 

[Dark Knight]

I know that this does not really apply, but I like telling it.
Power Factor - Beer

Me and you go to a bar and order a pair of pints. We each have a different bar tender.

My bar tender is new and has not spent much time drafting beer. He simply pulls the handle and allows the beer to fill the glass. This as we all know produces a considerable amount of head.

Your bar tender is a veteren. He opens the tap slowly and tilts the glass producing the perfect amount of head.

Now, we are back at the table compairing the two glasses. Side by side they are the same size glasses and we paid the same for them, but the amount of drinkable beer in your glass is much greater. Who received the greater value for is dollar spent on a pint.

I used something similar to this to explain how power factor works and he understood it and signed off on the $1.5 Million project.

GOOD TIMES!

I am not sure about the explanation but this one is going to be a fan favorite.

 

[niffur]

I am not sure about the explanation but this one is going to be a fan favorite.

Well it doesn't necessarily explain the concept of reactive power, but it sure explains the impact of having a high power factor!

 

[phizer]

I like the beer analogy, too.

I think of reactive power as something that uses up transmission capacity, just like foam uses up the capacity in the frosty mug.

It takes current flow to transmit reactive (imaginary) power, and it takes current flow to transmit active (real) power. Current flow always causes resistive heating losses in conductors, because nothing is ideal. So the more reactive current you've got passing through your transmission system - which really doesn't help you deliver power to your load - the more losses you will have, without accomplishing anything useful.

Every piece of current carrying equipment is limited by the amount of heating it can handle before it either fails, causes some external damage, or breaches some safety margin. So, the reason why you (and whoever is supplying your power) like to have a high power factor is so that you can buy the equipment with the least capacity (i.e. spend the least amount of money on those expensive copper conductors and transmission lines, and transformers, etc.) and still accomplish all the work you need to do.

Not only do you benefit from not needing the bigger equipment, but you also don't have to pay for all the lost energy from shuttling reactive current through your system.

 

[Undertaker]

Nothing to say or add. I'm here for the beers. :beerchug:

 

[Texass]

i might be able to explain it a tad bit more, as i deal with it everyday in quantum..... first, imaginery power is REAL power. the only thing imaginery about it is that based on newtons law that you can create a reference point for any mass, i.e. x-y axis, that using those reference points would cause you to need to take the square root of a negative number, but that number is only negative because of the arbitrary reference point. It is a real number and has real properties. basically in the universe there are only 4 forces. one of which is the strong force, i.e. the force that you can feel and one is the weak, the force responsible for complimentry forces not seen. imagine this if you will, a train would have an associated, noticable force with it (it has mass & acceleration). This would be the strong force. However for this train to opperate correctly and build up that acceleration, weak forces must be active holding the train parts, bolts, equip., etc. together because the force that the train has due to f=ma is not enough to keep the "system" in tact.

now, when we talk about it in EE, its slightly different, but same concept. The "weak" forces are the voltages and currents needed for the "system" to opperate, but they would not be in the input or output, so they are not noticed, for lack of a better word. Thats because these voltages and charges come from with in the system, i.e. caps and inductors. The capacitors and inductors draw this power, but they will oppose it with their own forces thus canceling it out. The reason why you don't pay for it at home is because the loads might demand it, but they will return it, so a net of zero.

when you do not have enough inductance to cancel out your capacitance, there is a phase shift. ideal reactive power is on a 1/4 wave, so for every full sine wave, there is 1/2 "positive" active power and 1/2 "negative" active power (~), the reactive power would have 1/2 'positive' and 1/2 'negative' cycle every 1/2 of the active wave. therefore, one full active wave (2 parts) would have 4 parts reactive. this is what is meant by reactive power is supplied and returned. now, large motors with large coils that have lots of inductance, but not enough capacitance to cancel it out, so power companies could provide this power to you, but the transmission and equipment would have to be sized to carry the additional load. instead, you can install a capacitor system on the load side to cancel out the inductance so that for every reactive power that is consumed, it is equally returned in one complete half cycle of active power.

hope that makes sense, basically its the "work" or "force" needed to have a noticable outcome.

the motor wouldn't be able to convert electric energy to mechanical energy without having to do some work. this work is done internally in the motor and helps the system create an input and output. it is the component that allows magnetic and electric fields to "work" together (use force to keep from seperating) and create an electromagnetic field.

it has many appilications and is one of the 4 basic fudemental forces in the universe.