Power Factor Correction and power saving for home use? Dirty power & smart meters 7

[1Slick]

This IEEE article explains that PFC helps smart meters read correctly... otherwise they can overcharge you for power by up to 582%:

https://www.utwente.nl/en/news/2017...77t7UI_aem_k9r09uVSnRF4RH-OOvfz5Q#582-percent

This is in response to an old post on the benefits of PFC for home use:
Nobody ever tested smart meters with dirty/noisy power.

Assuming that this is still of interest to some in this forum?
...possibly some of the original posters are still around?

 

[jghrist]

The linked article is not an IEEE article. It is from The University in Enschede, Netherlands. It does not address power factor correction (PFC). It says that non-linear loads like LED lamps and dimmers can cause meter errors, some high, some low.

 

[che12345]

"..This IEEE article explains that PFC helps smart meters read correctly... otherwise they can overcharge you for power by up to 582%....This is in response to an old post on the benefits of PFC for home use.."

I have the following opinion.
1. These are two different subjects. I would only touch on the benefit of PFC for home use.
2. Generally, home usages are of low kW consumption. Most utilities do NOT impose any penalty on low pf. The electricity bill charge is based on the kWh consumed, irrespective of the pf. Pf of the load/customer is NOT metered. There are exceptions in some locations.
Che Kuan Yau (Singapore)

 

[waross]

It is a known issue that transients with a shorter period than the sample rate may cause metering errors.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[1Slick]

Did anyone read the full IEEE article or just the story about the article (the IEEE reference was included in the article)?

https://ieeexplore.ieee.org/document/7866234

The full article is available on ResearchGate:

https://www.researchgate.net/public...sed_by_conducted_electromagnetic_interference

Download link:

https://www.researchgate.net/profil...pY2F0aW9uIiwicG9zaXRpb24iOiJwYWdlSGVhZGVyIn19

Quote:
"Reducing the interference levels eliminated inaccurate reading in static meters."

If PFC reduces interference levels it would reduce/eliminate inaccurate reading in static meters.
It helps explain why users of PFC report savings in their power bills.
This response addresses the original post's question: Whether PFC is worthwhile for home use.


P.S. Waross summarises the problem nicely... and makes it seem very obvious.
"It is a known issue that transients with a shorter period than the sample rate may cause metering errors."
Metering errors rarely favour the user... but typically favour the power company (as per the IEEE article).

Born under a wondering star

 

[3DDave]

PFC is independent of noise. PFC is a shift of current vs voltage. Noise is noise.

The article doesn't mention power factor or power factor correction in the conclusion.

There are probably a large number of devices that can limit the transmission of noise to the power meters; if you want to, go ahead and buy a PFC system and install it or buy electrical components that have adequate noise filtering built in.

I would say the expense is not worthwhile. Eliminating faulty electronics is a better choice.

Better yet, demand a meter with a Hall effect current sensor and save money.

 

[waross]

Power factor is the ratio of real power to apparent power.
A shift of current vs voltage will cause the well known displacement power factor shift.
Distorted sign waves and switching transients may cause the apparent power to be higher than the real power.
This is distortion power factor.
Residential loads may cause "dirty"power to pass the meter.
Dirty power, such as may be caused by switching transients will cause displacement power factor.
Non-linear loads may cause distortion power factor.
But, this is not to be confused with metering errors cause by short period transients.
The report mentions over +500% over metering.
To be fair, what was the source of the "dirty" power?
500% over billing on a 7 watt LED dimmer is not worth spending much time or money on mitigation.
On the other hand, if the 500% over billing is the consumption of an electric steam boiler for an often used four person sauna, we have a problem.
Rather than think about mis-metered current spikes, if some inductive device is causing voltage spikes that are then multiplying the voltage for too long a period, we also have a problem.

A thought for comment:
If the duration of a transient that occurs at or near the start of a sample interval is 1/5 the sample rate, that may cause the effect of the transient to be multiplied by 5.
Comments friends?




--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

1. My observation on the field is " in generally, home usages are of low kW consumption. Most utilities do NOT impose any penalty on low pf. The electricity bill charge is based on the kWh consumed, irrespective of the pf. Pf of the load/customer is NOT metered ".
2. Even the kWh meter accuracy is affected by all modern electronic devices, it is NOT worth to install any pf correction (mainly capacitor) in your premises. Consider the initial cost, and it will NOT maintain its capacity/life for more than say 5 years.
3. Exception, unless the utility imposes heavy penalty on low pf, it may warrant consideration/study; not otherwise.
Che Kuan Yau (Singapore)

 

[waross]

The transients associated with distortion power factor are not metered.
However those transients may cause significant errors metering real power.
One solution may be to install capacitors.
The purpose of the capacitors is not to shift the current phase angle but rather to provide a low impedance path for very fast rise time transients before they reach the KWHr meter.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jghrist]

If PFC reduces interference levels it would reduce/eliminate inaccurate reading in static meters.
It helps explain why users of PFC report savings in their power bills.
This response addresses the original post's question: Whether PFC is worthwhile for home use.

OK. I read the referenced article and it still didn't address power factor correction. Why would you think that PFC would reduce interference levels? PFC could introduce resonant conditions that increase harmonic distortion.

 

[1Slick]

Quoting 3DDave
"There are probably a large number of devices that can limit the transmission of noise to the power meters; if you want to, go ahead and buy a PFC system and install it..."

Dave is right... any device that limits the transmission of noise should work.
It doesn't have to be a PFC.
PFC works because it uses a series of large capacitors... which would filter the power and remove the problematic noise.

PFC is often proposed as the solution to these high frequency spikes... and it was the subject of the orginal post which is being responded to.

Original post here:

https://www.eng-tips.com/viewthread.cfm?qid=110621

P.S. Dave is right that buying devices that don't generate this noise is also a solution:
You should always buy the quiet device as that addresses the noise at the source.
In practice it is often very hard to buy quiet devices (ever tried returing an electrically noisy device?)... as it turns out a lot of devices (particularly anything with a rotating motor) generate high frequency noise.
The simpler and probably cheaper solution is to filter out the noise.


Born under a wondering star

 

[waross]

A small capacitor is often enough to attenuate the very high frequency spikes.
Transients that are short enough to cause serious metering errors are easily shunted or absorbed by a relatively small capacitor.
PFC for displacement power factor correction are much more than enough.
And automatic PFC may not help anyway.
In the event that there is a large resistive load such as a toaster, oven, water heater etc., online, the residential PF may not be low enough to trigger the first step of an automatic PFC panel.
(Anecdote Alert)
A small machine shop was getting PF penalty charges.
Not much but the owner wanted it stopped.
He got two quotes for a PFC panel. $2000 and $4000.
He asked me if I thought that that was reasonable.
Let me see your back power bills.
His average PF was 89% and penalties started at 90%.
The KVARHrs needed per month to get above 90% average PF was so little that a run capacitor for a 1/2 HP motor connected across one phase eliminated the penalties.
Cost for the capacitor under $10 and an hour labour to hide it inside a breaker panel.
A PFC panel is intended to correct displacement PF and may not turn on for distortion PF.
(/alert)

Everyone who is not familiar with the difference between Displacement Power Factor and Distortion Power Factor should be following rather than posting.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

That's why I'm following rather than posting . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[1Slick]

Quoting Waross
"A small capacitor is often enough to attenuate the very high frequency spikes."

A long time ago (as a kid) an electrician told me to fit a capacitor to stop the crackle and pop on the TV and static on the radio.
It didn't seem to make much difference.

Years later after measuring the noise on the line we put a series of 20 micro farad capacitors in line:

http://stenulson.net/energy/Electro-Smog Filtering- Do It Yourself.pdf

It took about 13 capacitors scattered around the house to get rid of most of the noise.
These larger capacitors did make a difference.

Whether a small or a large capacitor is sufficient to make a smart meter read correctly probably depends on how sensitive these meters are to noise.
However PFC's seem to work... even if they are overkill.


Quoting 3D Dave
"...demand a meter with a Hall effect current sensor and save money."
Great suggestion. Why aren't these more accurate meters standard? Are they easy to obtain?

Born under a wondering star

 

[3DDave]

Per the article you posted, the Hall effect significantly underreported and were not accurate.

 

[waross]

Whether a small or a large capacitor is sufficient to make a smart meter read correctly probably depends on how sensitive these meters are to noise.

That is more a function of the meter algorithm than the hardware.

However PFC's seem to work... even if they are overkill.

It depends.
In some cases the calculated interest on the cost of the PFC may be greater than the saving in energy cost.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

A long time ago (as a kid) an electrician told me to fit a capacitor to stop the crackle and pop on the TV and static on the radio.
It didn't seem to make much difference.

The higher the frequency, the less capacitance is needed. (There is a formula for that.)
If you can hear the noise, it is under 20,000 Hz.
Transients that may affect metering are many times higher and the capacity needed is many times less.

Everyone who is not familiar with the difference between Displacement Power Factor and Distortion Power Factor should be following rather than posting.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[1Slick]

Responding to 3D Dave on the Hall effect:

Quote from the article:
"A deviation of +276 % was measured with one static energy meter,
+265% with a second and -46% with a third static energy meter.
After dismantling it was revealed that the meters with the positive
deviation used a Rogowski coil current sensor. The meter with a
Hall effect-based current sensor gave the -46% deviation. The
fourth meter, with a current transformer, resulted in -10% in one
experiment and +8% in another experiment..."

You're right... the current transformer seems to have given the lowest error when measuring useage (-10 ~ 8%).
However if you're a customer then you'd prefer the Hall effect meter... as the error is in your favour (-46%).



Born under a wondering star

 

[waross]

You're right... the current transformer seems to have given the lowest error when measuring useage (-10 ~ 8%).
However if you're a customer then you'd prefer the Hall effect meter... as the error is in your favour (-46%).

Interesting but meaningless without knowing the sample rate versus the transient period.
And were these certified revenue meters or Amazon DIY meters?



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[1Slick]

Quoting Waross:
"In some cases the calculated interest on the cost of the PFC may be greater than the saving in energy cost."

Many PFC users claim that the savings are ~1/3 of the power bill.
Given the potential metering error that claim sounds reasonable.
PFC (or some other method of filtering) should pay for itself quite quickly if you can save 10% or more... and more slowly if you save less.

The time honoured tradition to resolving such theoretical debates is to run an experiment? i.e. Fit one to see whether it affects your bill?
Any larger variation (>10%) should be easy to pick up.
If you need multiple data points, for a before and after comparison, try turning the PFC on and off on alternative months?

A known noisy location sounds like it's the ideal candidate.
Whereas a location that is known to have low noise would be a poor candidate.
The simple way to distinguish would be to run a high frequency meter over the location prior to fitting any attentuating devices.

Any location should be using a smart meter... not one of the older analog meters (which are immune to the phenomenon).
Households that experienced a large increase in power bills upon fitting a smart meter would also be logical candidates for this experiment.



Born under a wondering star