understanding your read out

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jballatore
Posts: 1
Joined: Fri May 03, 2013 1:55 pm

understanding your read out

Post by jballatore »

Please , I need the down and dirty of understanding the corelation of these categories,
to each other
total Kilowatt,
Net Kilowatt
total kilowatt 1,2,3,
current I understand, and also current amps, but how can you have a reading that exceeds the breaker?
Total watts
power factor
I am using the v.3 on a single phase 120 volt lighting system
Jameson
Posts: 860
Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA
Contact:

Re: understanding your read out

Post by Jameson »

Hello jballatore,

Total kWh: This is the amount of energy the meter has measured since being installed. It is Forward kWh (usually energy from the grid), plus Reverse kWh (energy sent to the grid, or generated energy).
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Net kWh: Net is Forward kWh - Reverse kWh (or another way to look at it is Forward kWh - (2 x Reverse kWh). This used in solar generation, if you have a Net kWh of "0" you have not overall sent power to the grid or received power from the grid. You could have used 1000 kWh and generated 1000 kWh in a months time, and your Net kWh would be "0". More on "Net Metering": http://en.wikipedia.org/wiki/Net_metering
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Total kWh 1,2,3 (described above). The Omnimeter Pulse v.4 keeps track of the Total kWh for each line individually.

Or you may be referring to Time-of-Use 1, Time-of-Use 2, Time-of-Use 3, Time-of-Use 4. The meter keeps track of how much energy was used in 4 time periods. Each period is like a bucket of power used for the given time period. If you are charged more for power in the middle of the day than at night, you can utilize the meter to keep track of this.
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Current is measured by the CT. Please let us know the Amp rating of your breaker and the amperage that the meter is reporting for that line.
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Total Watts is a real time value of Line1 Watts + Line2 Watts + Line3 Watts
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Power Factor : Power Factor is a measurement of the quality of the power. Some industrial utility customers are penalized if they negatively influence the Power Factor of the system.

A perfect Power Factor (1.00) is when the voltage sine wave and the amperage sine wave are in perfect alignment on top of each other. When the voltage and amperage sine waves are off of each other then you have less than perfect Power Factor. When voltage is leading amps it is considered leading (Inductive or L), when voltage is lagging amps it is considered lagging (Capacitive or C)
Energy in AC systems is actually measured as volts x amps x power factor = watts This is contrary to the commonly held perception that it is volts x amps = watts (this is only for DC systems, or AC systems with a perfect power factor of 1)

More information here: http://en.wikipedia.org/wiki/Power_factor
==
Thanks,
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371
johndjmix
Posts: 3
Joined: Fri Dec 20, 2013 2:30 am

Re: understanding your read out

Post by johndjmix »

jameson, one concept we do not understand is power factor....

You (and others) say that a power factor of 1 is perfect. Less than 1 is ... well, not perfect.

So if watts = amps x volts x power factor it would seem like a worse power factor (less than one) would give you a lower wattage, hence a lower utility bill price!

Please explain....

Thanks,

--John
vastnet.net
Jameson
Posts: 860
Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA
Contact:

Re: understanding your read out

Post by Jameson »

Yes, Power Factor can be a mind bending ball of wax.

Essentially if you have bad power factor you will be wasting energy (in the case of an electric motor it will wasted in the form of heat). But it really only negatively affects the utility as far as I know. You are essentially borrowing power from the utility that you are not paying back. This is why the utility will sometimes penalize you for creating bad power factor in the form of a fee (they recoup their loss). This is usually only for industrial customers.

In the case of a residential customer, I am not sure why a residential customer would be motivated to correct their power factor (except for being better for the environment). Residential customers usually do not get this bad power factor charge. I do think that a residential customer will NOT benefit from having bad power factor, but I am not sure of the downsides.

Im sure that I have holes in my understanding of power factor. I have found this post by CSA to be helpful from this page (the worse your power factor is the more reactive power you will be using): http://www.control.com/thread/1026238188
The first place you should look is http://www.wikipedia.org; search for 'reactive power'.

There are contributors to this site who will insist that reactive power doesn't "flow", or that there's no such thing as reactive "power". But for the purposes of this contribution (and per commonly acepted convention--see http://www.wikipedia.org) we will consider that reactive power does indeed exist and that it flows. And remember: the originator of this thread asked for an explanation in layman's terms, which for me, anyway, does not initially include vector diagrams and trigonometry and mathematical formulae. All of these things are necessary for a complete and proper understanding of the phenomenon, but not for a rudimentary understanding on which to base all of the formulae and vector diagrams, etc., which just serve as mathematical proofs of the principles.

In an AC power system, there are resistive loads and reactive loads. Reactive loads include inductive and capacitive loads--and the majority of loads on any grid are inductive (from induction motors used for everything from vibrators to elevators to refrigeration compressors to fans to all manner of pump motors (potable water, sewage, chemical, and so on)). Transformers are also an inductive load on the system.

So, since they're the predominant load, let's focus on inductive loads. In an induction motor, a magnetic field has to be induced on the rotor of the motor in order for it try to follow the apparently rotating magnetic field of the stator that is connected to the AC power source in order to produce torque. The act of inducing the magnetic field on the rotor of the induction motor causes a shift to occur between the AC current sine wave and the AC voltage sine wave of the AC power system. Some of the total amount of energy that's being consumed from the AC power system by the induction motor is used in the induction of the magnetic field on the rotor of the motor whiach allows the motor to produce torque. In other words, the total amount of energy being consumed by the motor does not end up as torque (real power).

The magnitude of the shift between the AC voltage- and current sine waves is measured or expressed in many ways: power factor, VArs, phase angle, etc.

The key thing to remember is that if nothing is done to try to contain or reduce the phase shift between the AC voltage- and current sine waves they can eventually shift so much that the ability of the AC system to supply real power will be reduced (such as when brownouts occur).

If we think of the induction of the magnetic field on the rotor of the induction motor as needing "power" and we call that reactive power, then we can think of reactive power as being consumed, in the same was as real power is consumed. We can measure the amount of power required to induce the magnetic field on the induction motor rotor in VArs. And, to counter the effect of the phase shift on the system of lots and lots of induction motors and transformers (which also induce magnetic fields on secondary windings) we can produce reactive power to reduce the phase shift and maintain the AC power system's ability to provide power.

We can produce reactive power to "compensate" for the inductive load on the system primarly by increasing excitation current to the rotors of synchronous generators over and above the amount required to maintain the generator terminal voltage equal to the voltage of the grid to which the generator is connected. This causes reactve power, called VArs to flow out of the generator terminals on to the AC power system, reducing the phase shift and supporting the AC power system's ability to transmit real power.

So, VArs are "required" or "consumed" to induce the magnetic field on the induction motor rotors commonly used everyhwere, and to increase or decrease voltage through transformers used to distribute AC power. The effect of VARs on the system is to shift the AC voltage- and current sine waves out of phase with each other. If they get too far out of phase, the ability of the AC power system to supply power is reduced. VARs can be produced by synchronous generators--but since that requires DC power, and that DC power usually comes from the AC power system, that power is not available for sale to consumers. Power factor correction capacitors can be used to help with controlling the phase angle between the AC voltage- and current sine waves, but they are usually expensive and have their own idiosyncracies.

Real power, watts, can be converted in to torque and work which is something we can understand and visualize. Reactive power, VArs, have no such tangible quantity that we can see or envision. A lot of people like to say that, "VArs are like foam on beer; it's just there but it doesn't do anything." Foam on a beer tells the drinker the beer is not flat. There's very little worse than a cold, flat beer especially on a hot day.

Okay, a hot, flat beer is worse. And if AC power systems aren't properly managed, the beer could be flat and hot.
If anyone out there can fill in some of the holes in my understanding, please chime in :)
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371
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