What is reactive energy?

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  #1  
Old 03-04-16, 05:08 AM
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What is reactive energy?

Our electric bill just came and as always included measurement from the two wheels on the meter. The main one and the second which measures something called reactive energy.

The consumption was off the chart compared to the previous two month period and most of that was in the second reading which has always been lower.

Checking the utility website when the ratio of the two readings exceeds a certain amount you're billed for reactive energy at approximately 2x the rate per kwh as normal electricity.

So could someone explain to me what it is? Why its so expensive and how to reduce it relative to total use?
 
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  #2  
Old 03-04-16, 05:23 AM
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Good morning Esand,
I'm not a top pro on electrical power and will be waiting to see how they sort this out. From what I know, power is a measure of voltage times amperage and with a non-reactive load those two are in phase. With a reactive load the phase has shifted so multiplying the twp together no longer provides a true measure of the power being consumed. If you are running a lot of motors where the current and voltage are not perfectly in phase then they want to increase the reading to be paid for the actual power. As for what equipment is responsible for the shift your meter is recording, tell us what is being powered.

Also, where are you, I see non-us but the pros may want to know if that is Canada or Australia.

Bud
 
  #3  
Old 03-04-16, 06:37 AM
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Alternating current does not jump to 120 volts and 1/120 second later jump to minus 120 volts and 1/120 second later jump back to (plus) 120 volts and so on. Rather it gradually rises (and overshoots 120 which is another and OT program) and gradually goes down to overshoot minus 120 etc.

Non-motorized e.g. infrared heaters and incandescet lights are pure resistive (non-reactive) loads. For every microsecond, the amperes drawn equals the volts at that moment divided by the resistance of the load.

Reactive loads include motors and some electronics. For a motor, for every microsecond, the amperes drawn in the straightforward sense does not necessarily equal the volts divided by the resistance, thus violating Ohm's Law. Specifically for a motor, the amperes draw does rise as the voltage rises, microsecond by microsecond but the amperes rise lags behind the voltage rise. The amperes drop also lags behind the voltage drop from plus 120 to minus 120 etc.

Using more complex mathematics (the buzz word is "complex numbers") this behavior is still computed to obey Ohm's Law, amperes equals voltage divided by a special definition of resistance called impedance. When I learned about complex numbers, it was in high school in a course called Algebra 2. At least half the student body back then including all students interested in natural sciences took that course.

(unofficial Common Core complex number exercise) Take a piece of paper and draw a line from near the center a little ways to the right. (Think "east" on a map.) This stands for a pure resistive load. Then, for a somewhat reactive load, draw a line from the same center point "upwards" and a little to the right (think "north-northeast") out as far to the right as the first line. The second line is longer and the length of the line represents the power consumed in terms of what the generating station has to do work to produce. Now hold the paper up at eye level and tilt it to be nearly horisontal but with the lines still in view. You will see that the "NNE" line seems to get shorter to almost the same length as the "east" line. An ordinary electric meter measures the power as approximately the same for both loads.

The overall load in a typical home has a very small reactive component so most of the time the power company does not care about the difference. But factories and other industrial power customers have a large reactive load.

Electric meters might use an analog (or digital) mechanism to relate this current lag to power usage and it is expressed as a "regular" energy usage plus a "reactive" energy usage.

Connecting capacitors hot to hot (or hot to neutral) reduces (actually cancels out) reactive load caused by motors. However when the motors are turned off, if the capacitors are left in place the capacitors will introduce a significant reactive load of their own.
 

Last edited by AllanJ; 03-04-16 at 07:10 AM.
  #4  
Old 03-04-16, 09:57 AM
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The reason power companies include a reactive surcharge is that it does actually cost them more to provide that power. They either end up driving the transformers with more current (which costs them money) or installing reactive compensation devices such as series compensators on lines or capacitor banks at substations or they have to run more expensive power plants that are closer to the load. Excessive reactive power consumption also makes the grid more unstable during peak usage times so they need to encourage customers to use less and they do so by passing that cost on through the billing.

Roughly speaking the ratio of real power to reactive power represents a measurement called the power factor. Loads which have a PF of 1 do not use reactive power. Loads with a PF closer to 0 use more reactive power. An industrial motor might have a PF of 0.5, a washing machine 0.6, a fluorescent light ballast 0.8, a computer power supply 0.8, a high efficiency computer power supply 0.9, and a standard light bulb 1.0.

In the US, residential customers are not billed directly for reactive consumption because most households have a typical amount of usage and it is averaged into the standard billing rates. Commerical and industrial customers are billed for reactive use, usually a monthly average and a peak.

You can reduce reactive power use by using appliances and motors with both passive and active power factor correction. For example this is one of the consideration that goes into appliances with the Federal "energy star" logo in the US. They usually cost more upfront but use less energy over time. Passive correction is a fixed capacitor that is wired in parallel with a large motor to cancel out some of the bad power factor. Active correction is a bank of capacitors and a smart switching unit that progressively switches in and out capacitors to try to keep your overall power factor close to 1 as various loads turn on and off in the building.
 
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Old 03-04-16, 10:07 AM
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The utility company charges extra for this on RESIDENTIAL bills? I've only heard of it for industrial consumers--where large reactive loads are common.
 
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Old 03-04-16, 10:19 AM
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Not in this country. The OP is located in South America.
 
  #7  
Old 03-04-16, 12:46 PM
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Ok maybe they didn't charge me for reactive energy? I miss read the pricing on the bull, I think. But there are two numbers on the meter. Usually reading 1 in black is around 1100kwh per 2 month period and the 2 in Red is a couple hundred. For an average bill of about 1800kwh Last two month period the bill came in 5977kwh. With 2509kwh being reading "1" and 3468 being reading "2".

So this two month period corresponds with one of the hottest Summers on record and obviously a decent part of that is the A/C but can it really be that much? And what is with the two numbers? If it's not counting reactive energy what is it counting?



Allan, Bud, Ipbooks: even if it turns out that they're not charging me for reactive energy, I appreciate the lesson. Fascinating the amount of work that goes into the infrastructure that lets us flick a switch and have light, climate control, the internet.
 
  #8  
Old 03-04-16, 02:24 PM
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It's more likely your meter is registering, showing you, peak and off peak usage.
 
  #9  
Old 03-04-16, 03:27 PM
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There is no peak charge here and none of the neighbors meteres have different numbers either. Just 1 number. As you can see on the meter it was made in 1988 so maybe there used to be peak charges? Seems unlikely...


edit I think you're right.

as for reactive energy, I called the utility, anything under a PF of .85 gets a higher rate. I doubt I'd get under that since.
 
  #10  
Old 03-05-16, 10:54 AM
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Just curious what the writing on the meter is saying.
tetrafilar=4 wire; i also see 40Amps max? And is this a 3 phase system?
What are the words above the red digits?
 
  #11  
Old 03-05-16, 11:24 AM
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If the person on the phone or your electric bill mentions "power factor" or "reactive" then I'm quite sure that reactive energy is the subject of that second dial.
 
  #12  
Old 03-05-16, 11:44 AM
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Too much reactive power caused the Northeast Blackout of 1965. People have been arguing about the cause for years, but the cause was right in the FPC report. But nobody noticed it. I found it and reported it.

I have worked with reactive power metering in businesses. It is common for a large power consumer to be charged for reactive power. Large electrical motors are the chief causes of reactive power.

Reactive power is not produced by the power generators. It is produced inside an electric motor and sent back out onto the power lines as a phase shift between voltage and current.

Reactive power does not cost the power company anything in power generation. But it does cost the power company more in the necessity of larger wires to carry the higher total complex current, the installation of capacitor banks to compensate for the reactive power, and occasional power failures when reactive power causes generators to drop out of synchronization with each other.

There are different measurements for these kinds of power:

Ohms (resistive) = no phase shift resistance
Farads (capacitive) = 90 degree current lead
Henrys (inductive) = 90 degree current lag
Ohms (reactive) = reactance at 90 degrees
Ohms (impedance) = resistance and reactance combined.

W = Watts = In phase voltage and current (resistive) power
VAR = Volt-Amps Reactive = quadrature (90 degrees - reactive) voltage and current power
VA = Volt-Amps = complex (odd-angle impedance) voltage and current power

Put a K in front for kilo, or an M for mega: KW, KVAR, KVA, MW, MVAR, MVA

Usually there are two complete metering devices, one for KW and one for KVAR. They are identical meters, except that one has a phase shift built into the voltage coil circuit. Often they are built into the same unit.
 
  #13  
Old 03-05-16, 12:02 PM
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There is an easy way to tell which is happening:

Observe the meter. If the black numbers are changing during normal hours and the red numbers are changing during peak hours, it is a peak hour meter.

If both number are seen to change at any time, it is a resistive/reactive meter.

Or call the power company and ask them what the red numbers are.
 
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Old 03-05-16, 07:40 PM
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The meter says industrial at the top. I'll bet the two indicators I circled change from top to bottom.

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  #15  
Old 03-07-16, 07:32 AM
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Just curious what the writing on the meter is saying.
tetrafilar=4 wire; i also see 40Amps max? And is this a 3 phase system?
What are the words above the red digits?
I'm not exactly sure what everything it says in the line with amps
Here's a clearer picture



So Medidor Trifasico Tetrafilar = Three Phase 4 wire meter.
3*380/220v 50 Hz. = Obvious

The next line is 5A Imax. 40A. Does that mean max amps are 40? or 5? Or something else? I is current right?

What it says above the red numbers. Its Industria Argentina which just means "Made in Argentina".

According to the utility I was not charged for reactive energy although I would be if the power factor of my consumption dropped below .85

As I mentioned before my normal power bill every 2 months is ~1800kwh. But from december to feb it was it was almost 6000kwh. Unless my neighbors are stealing my electricity I'm attributing that entirely to the AC and maybe fridges working harder in a summer of record heat.

The interesting thing is that in a normal period the red number is usually about 300kwh of the 1800kwh total. Where as in this bill it represented it represented almost 4000kwh of the 6000kwh total.

Logic would say that I could attribute that again to the AC. Which would seem to run counter to the peak hour argument. A/C compressors are motors, blower fans are motors and based on what I've learned here those are the loads with lower power factors. The A/C compressor is also a 3p motor, is there any reason that a meter would (or could) measure those loads with a different counter?

Its a mystery.
 
  #16  
Old 03-07-16, 08:18 AM
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Reactive power is measured in kvar (kilo volt amp reactive), not kw (kilo watt). Kwh is the only unit marking on that meter leading me to believe is it a standard residential meter that does not measure reactive in any way.

Sounds like your air conditioning unit just got one heck of a workout this month. An abnormally warm season could be the culrpit, but it could also point to the unit needing a tune-up. Perhaps a service call for an HVAC tech to check out the freon level might be worthwhile. Make sure all of the air filters are clean and the coil isn't freezing up. If the coil ices up, the unit will run continuously but the cooling efficiency drops significantly. The coil can freeze if the freon level, pressure or flow is wrong, if the fan blower speed is too low or if air flow through the system is restricted by a soiled filter or ducts being obstructed (e.g. registers closed, sofa pushed up against the return grate)
 
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