Understanding the Working Principle of Energy Saving Devices

In summary: Domestic installations don't pay for reactive power, only real power is metered.Industrial users however often pay a tariff that depends upon their power factor, in essence they may be charged a penalty rate if their PF is too low.Basically when you have an inductive load it causes the net current to be out of phase with the supply voltage. This net current can be thought of as two component, an in phase component corresponding to (when mult by V) the Wattage being consumed and a purely inductive component (90 degree lagging) corresponding to the reactive power being consumed. A power factor correction circuit merely "generates" this reactive power component locally so that the power company doesn't need to distribute this
  • #1
b.shahvir
284
25
Hi Guys, :smile:

I have heard of many energy saving devices available commercially, which when connected in parallel with the household mains, cause reduction in electricity bills. In smaller sizes they can be connected in parallel with any household power recepticle and cause reduction in energy consumption in any electrical appliance connected to that power recepticle.

Can someone please provide me with any information on the working principle of such a device, since I fail to understand how can any device connected in parallel with an electrical system, load or appliance cause a reduction in energy consumption in that load or system ? I would be very grateful.

Thanks & Regards,
Shahvir
 
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  • #2
The only ones that work do so by stealing from your power company
And can't be discussed here
 
  • #3
He might just be talking about simple power factor correction. Actually this does save power, though it usually won't be reflected on your bill, it saves the power company by reducing their distribution losses.

Domestic installations here in Australia don't pay for reactive power, only real power is metered (though I think the larger domestic appliances probably have to meet some power factor specifications to be sold).

Industrial users however often pay a tariff that depends upon their power factor, in essence they may be charged a penalty rate if their PF is too low.
 
  • #4
uart said:
He might just be talking about simple power factor correction.
Yes I know - I received a warning for mentioning them to someone. Apparently like mod-chips or DVD region hacks we aren't allowed to discuss them here. I imagine the forum is hosted in the land of too many lawyers!

Domestic installations here in Australia don't pay for reactive power, only real power is metered
Isn't that the point of them - they change the power factor so you receive more power than you are paying for?
 
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  • #5
mgb_phys said:
Yes I know - I received a warning for mentioning them to someone. Apparently like mod-chips or DVD region hacks we aren't allowed to discuss them here. I imagine the forum is hosted in the land of too many lawyers!


Isn't that the point of them - they change the power factor so you receive more power than you are paying for?

I thought they just reduced the amount of imaginary power you used, and didn't touch your real power? It's just that they're completely useless for the vast majority of people, and thus all too often marketed to those that don't know any better.
 
  • #6
Yes, just been reading up on power factor. It looks like the reason against power factor converters is that they waste electricity that you aren't paying for!
Even then only if you have significant reactive loads.
 
  • #7
mgb_phys said:
Isn't that the point of them - they change the power factor so you receive more power than you are paying for?

No, quite the contrary. You are normally metered for the power you consume, not the amount of current it takes to consume that power. So when power factor correction is applied it reduces the amount of current that the power company needs to distribute to you in order to supply a given power level (wattage). The bottom line is that it saves the power company money by reducing the losses in their distribution system but saves you nothing (as a domestic consumer). Consequently there's not much incentive for a domestic consumer to do anything about power-factor correction (though not so for industrial users as I mentioned above)

The above is how it is for domestic installations here in Australia anyway. If (elsewhere in the world) you have a system where the power companies can meter only VA (instead of Watts) and charge based only on that figure then yes adding power factor correction would cut your power bill. I'd hardly call that stealing from the power company though.
 
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  • #8
mgb_phys said:
Yes, just been reading up on power factor. It looks like the reason against power factor converters is that they waste electricity that you aren't paying for!
Even then only if you have significant reactive loads.

No, I wouldn't really put it like that. Power factor correctors (the simplest form of which is just a parallel capacitor) can rightly be thought of as being a local generator of reactive power (an inductive load being a consumer of reactive power).

Basically when you have an inductive load it causes the net current to be out of phase with the supply voltage. This net current can be thought of as two component, an in phase component corresponding to (when mult by V) the Wattage being consumed and a purely inductive component (90 degree lagging) corresponding to the reactive power being consumed. A power factor correction circuit merely "generates" this reactive power component locally so that the power company doesn't need to distribute this "wasted" current. You're doing them a favour!

As I say, here in Australia we are only billed for the Wattage consumed in domestic installations, so the poor old energy company has to supply that reactive component of the current free of charge to us (up to a limit though, by law the PF of a domestic load can't be lower than 0.8). Obviously this situation could be different in different countries, perhaps someone familiar with how energy is typically metered and billed in the US or Britain could fill us in on the details of their system.
 
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  • #9
All domestic customers get billed on assumed real power - the electric meter is just a current meter.

Sorry I wrote my answer the wrong way round - WITHOUT a power factor converter you are wasting the power company's electricity - that you aren't paying for.
 
  • #10
Thanx guys for such an overwhelming response! one thing is for sure, these energy saving devices might be a marketing farce..as far as the individual consumer is concerned.

Also, i just wanted to verify one thing though, does the Energy meter only record real power (Watts), or does it record apparent power (VA)?

Kind Regards,
Shahvir
 
  • #11
I'm 99% sure that power meters measure actual power which is reported as actual energy consumed. As in;

Imaginary Power x Power Factor = Real Power

Just about all residential power saving devices are going to be BS as the real ones are usually only manufactured for large amounts of power consumption (industrial) since they are only cost effective at large scales. The only exception to that rule is if you have a home with solar plant or a wind farm near by which operates in parallel with your local grid. Some of the more advanced models have power factor correction (~0.95) along with ride through capability.
 
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  • #12
b.shahvir said:
Also, i just wanted to verify one thing though, does the Energy meter only record real power (Watts), or does it record apparent power (VA)?
Real power - it only measures current.
 
  • #13
mgb_phys said:
Real power - it only measures current.

Thanx, but why is the reactive power (or current) not measured/recorded by the Energy meter even though it passes thru the meter too ?? :confused:

Kind Regards,
Shahvir
 
  • #14
mgb_phys said:
Real power - it only measures current.

Maybe I'm just missing something or having another dumb moment, but how do you measure real power with only current? Don't you need to measure the peak voltage, current, and phase difference to determine real power?
 
  • #15
Remember real power is really the real power supplied it's only the real part of the power supplied !
Real power is just measured current * assumed peak voltage (110V/230v) and assumed purely resistive load.
 
  • #16
I built an active power factor correction circuit many years ago. They only work on induction motors like in the refrigerator. What the circuit does is monitor the power factor of the load, and reduce the motor voltage until the power factor rises to a preset value. In my case, the refrigerator motor voltage dropped to about 90 volts after a few seconds.
Separately, I measured the watts and volt-amps of an unloaded 1/4 HP induction motor running at 120 V. Result; 110 watts, 425 volt-amps.
 
  • #17
mgb_phys said:
Remember real power is really the real power supplied it's only the real part of the power supplied !
Real power is just measured current * assumed peak voltage (110V/230v) and assumed purely resistive load.

um, no. for RLC loads, you must consider the phase between the voltage and current. to get the real power supplied, you multiply the real part of the current by the voltage. but to just look at measured current is to look at the sum of both real and imaginary current, which is always greater than the real current.

for situations with a bunch of non-linear loads, it's not even that easy. you'd need a device that looks across the entire cycle to compute the power.
 
  • #18
mgb_phys said:
All domestic customers get billed on assumed real power - the electric meter is just a current meter.
Residential customers get billed for real power, commercial customers get a surcharge added if their power factor is bad (generally below 85%, I think). So such a device would benefit a commercial customer (and capacitor banks are very common in commercial/industrial buildings) and would do nothing for a residential building.
 
  • #19
Topher925 said:
Maybe I'm just missing something or having another dumb moment, but how do you measure real power with only current? Don't you need to measure the peak voltage, current, and phase difference to determine real power?
mgb_phys said:
Remember real power is really the real power supplied it's only the real part of the power supplied !
Real power is just measured current * assumed peak voltage (110V/230v) and assumed purely resistive load.
Power meters are basically a totalizer function that multiplies the amperage by the voltage without measuring the phase shift. Since the amperage and voltage are not in phase if the power factor is bad, multiplying them together yields only the real power. This isn't as complicated as it sounds, though:

Put another way, a typical residential power meter is just an electric motor wired in series with your house.
The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts.

The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil. [1]This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc - this acts as a brake which causes the disc to stop spinning when power stops being drawn rather than allowing it to spin faster and faster. This causes the disc to rotate at a speed proportional to the power being used.
http://en.wikipedia.org/wiki/Electricity_meter
 
  • #20
Bob S said:
I built an active power factor correction circuit many years ago. They only work on induction motors like in the refrigerator. What the circuit does is monitor the power factor of the load, and reduce the motor voltage until the power factor rises to a preset value. In my case, the refrigerator motor voltage dropped to about 90 volts after a few seconds.
Separately, I measured the watts and volt-amps of an unloaded 1/4 HP induction motor running at 120 V. Result; 110 watts, 425 volt-amps.

Dear Bob, :smile:

But did your circuit save electricity or reduced your electricity bills upto some extent? please reply, i need to know.

Thanks & Regards,
Shahvir
 
  • #21
b.shahvir said:
Dear Bob, :smile:

But did your circuit save electricity or reduced your electricity bills upto some extent? please reply, i need to know.

Thanks & Regards,
Shahvir

I never attempted to check whether power factor corrector (PFC) circuit reduced my electricity power bill. I do know that induction motors under light load run cooler at reduced sinewave input voltage, which implies that the input current is also less.
 
  • #22
Bob S said:
I I do know that induction motors under light load run cooler at reduced sinewave input voltage, which implies that the input current is also less.

Dear Bob, :smile:

Thanx for replying. In your opinion, what would be the effect of reduced input voltage at full load or near full load (say 50%-75% loading)? This part is quite important for me to understand hence i will be grateful if you give a suitable response.

Kind Regards,
Shahvir
 
  • #23
Hi Shahvir-

These power factor corrector (PFC) units are nice toys, and I learned a lot by building one. The commercially available ones for homeowners on the market cost a lot and I suspect you will never get your investment back in power savings. The only unit in a home that may warrant a PFC unit is the refrigerator. I worked at a lab many years ago that had megawatts of induction motors on line. It also had some large salient pole synchronous motors that they would sometimes use as synchronous capacitor to correct the power factor.
 
  • #24
Bob S said:
Hi Shahvir-

These power factor corrector (PFC) units are nice toys, and I learned a lot by building one. The commercially available ones for homeowners on the market cost a lot and I suspect you will never get your investment back in power savings. The only unit in a home that may warrant a PFC unit is the refrigerator. I worked at a lab many years ago that had megawatts of induction motors on line. It also had some large salient pole synchronous motors that they would sometimes use as synchronous capacitor to correct the power factor.

Dear Bob, :smile:

But do these 'toy PFCs' :biggrin: bring about a reduction in power consumption (apart from PF correction) by reducing the input voltage as u had mentioned earlier?

Thanks & Regards,
Shahvir
 

What is the working principle of energy saving devices?

The working principle of energy saving devices varies depending on the specific device, but they all aim to reduce energy consumption and save money in the long run. Some devices use sensors to detect when a room is occupied and automatically adjust the temperature or lighting, while others use timers or programmable settings to control energy usage. Overall, the goal is to use less energy without compromising comfort or functionality.

How effective are energy saving devices?

The effectiveness of energy saving devices also depends on the specific device and its usage. Some devices, such as LED light bulbs, can reduce energy consumption by up to 80%, while others may only have a small impact. It is important to research and choose energy saving devices that are suitable for your specific needs and habits.

Do energy saving devices require any special maintenance?

In general, energy saving devices do not require any special maintenance. However, it is important to regularly check and replace batteries in devices that use them, as well as clean or replace air filters in energy-saving HVAC systems. It is also important to read and follow the manufacturer's instructions for proper usage and maintenance of each device.

What are the benefits of using energy saving devices?

Using energy saving devices can have several benefits, including reducing energy costs, decreasing carbon footprint, and contributing to a more sustainable environment. Energy saving devices can also improve the overall efficiency and lifespan of appliances and systems, saving money on repairs and replacements in the long run.

Are there any disadvantages to using energy saving devices?

One potential disadvantage of using energy saving devices is the initial cost. Some devices may be more expensive upfront, but the long-term savings on energy bills can outweigh this initial investment. Additionally, some devices may require a change in habits or behaviors, such as manually adjusting thermostat settings or turning off lights when leaving a room. However, these minor inconveniences can lead to significant energy savings in the long run.

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