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Thread: Difference between: Power factor correction, Voltage regulation and Voltage stabisizi

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    Email problem BigRed's Avatar
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    Difference between: Power factor correction, Voltage regulation and Voltage stabisizi

    Hi all

    Can anyone possibly explain what the differences between the following are:

    Voltage stabilizers
    Voltage regulation
    Power factor correction units?

    We run a large fabrication shop with five large welders and other power consuming devices.
    From what I understand above, the power factor correction units, using capacitors even out the sin wave between reactive and active current flow.
    Voltage regulators give one a even (constant current) similar to stabilizers.

    But, in a factory (or shop, or even common household) one will be better or more suited than the other.

    Anyone able to explain in layman's terms what the difference is?

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    Diamond Member AndyD's Avatar
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    Voltage stabilizers and voltage regulators are essentially the same thing. Stabilizers are linear regulators.

    Power factor correction units are installed to compensate for electrical loads with a poor power factor. If the load is inductive (such as large transformers in welding machines) then PFC will take the form of added capacitance.

    The more reactive power in a circuit the worse the power factor is. Reactive power is power that is stored and released by the inductance and capacitance in a load. Reactive power is measured in kVAr. Even with poor power factor you are still using the same amount of energy so if you are billed for your electricity in kWh (real power) then your power factor makes no difference to your bill. Poor power factor just means that higher losses will be incurred by Eskom during the supply of electricity to you premises.

    The power Triangle shows the relationship between Real Power, Reactive Power, Apparent Power and Power Factor. As can be seen Apparent Power is the vector sum of Real Power and Reactive Power. The Apparent Power value of a supply will always be equal to (if Cos φ = 1) or greater than (if Cos φ = <1) the Real Power value.

    http://www.theforumsa.co.za/forums/a...1&d=1265619338

    Quote Originally Posted by BigRed View Post
    Voltage regulators give one a even (constant current) similar to stabilizers.
    Voltage regulators regulate voltage, not the current. The more work a machine is doing, the more current it will draw.

    Edit, you can reproduce and distribute any of my graphics under the beerware license.
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    Last edited by AndyD; 08-Feb-10 at 11:09 AM.

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    Email problem BigRed's Avatar
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    So, do I read this correct that a voltage regulator / stabilizer wont decrease the reactive power but the power correction unit will?

    Thanks for your answer btw

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    Email problem BigRed's Avatar
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    Andy

    Why would a Wollies or PnP be interested in reducing electricity bills with a voltage stabilizer and our fabrication shop in a power correction factor unit?

    A retail shop has plenty of fridges running who's fridges should have a constantly changing draw as our welding machines having constant on / off power requirements.


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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by BigRed View Post
    So, do I read this correct that a voltage regulator / stabilizer wont decrease the reactive power but the power correction unit will?

    Thanks for your answer btw
    A voltage stabilizer ensures a constant voltage output regardless of voltage fluctuations on the input. It protects against under and over voltage to the load or machinery being run. It might also iron out spikes from lightning etc. Power factor correction and voltage regulation are two separate things but it is possible that a multitasking unit could address both issues in one box so to speak.

    Quote Originally Posted by BigRed View Post
    Andy

    Why would a Wollies or PnP be interested in reducing electricity bills with a voltage stabilizer and our fabrication shop in a power correction factor unit?

    A retail shop has plenty of fridges running who's fridges should have a constantly changing draw as our welding machines having constant on / off power requirements.

    I might be missing something here but I don't see how a voltage stabilizer would really make a noticeable difference to your electricity bills. There might be a small saving because machinery is at its most efficient when it's running at the correct voltage, there might be increased machinery reliability spin offs as well but I think you'd be hard pushed to classify this as a significant saving or use it as incentive to sell voltage regulation or stabilization as an energy saving technique.

    From a power factor correction point of view it's very difficult to PFC a constantly changing load such as dozens of refrigeration / Aircon units. To PFC them efficiently, each unit would need an associated PFC capacitance to be added at each of the load points themselves. If you just take an average power factor of the load as a whole and a single PFC unit at the main DB then you will be over-correcting at night when most of the refrigerators are switched off and under correcting when they're all running during the day. Over correcting is as bad as not correcting at all, it just makes poor power factor in a different quadrant.

    There are single point PFC systems with intelligence built in. They constantly monitor the power factor of the load and constantly alter the amount of PFC applied to compensate accordingly. These systems are very costly.

    Introducing effective PFC isn't a cheap exercise and like I said above if you're billed in kWh it won't save you anything on your bill. If you are billed in kVA/h then there would be a saving to be had but I would certainly conduct a comprehensive power audit of your factory to establish exactly what the saving will be and establish an estimated payback time, from there you can decide if it's worth the capital outlay.

    If you can provide more info on the Woolies or P&P systems then I'm sure you will get more accurate info here about where the savings are coming from.

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    Email problem BigRed's Avatar
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    Thanks Andy

    I'm the mechanical guy, I leave the sparky things to the sparkies

    Reason behind the question is that my brother in law has become the agent for a voltage stabilizer and in the process of selling one to Woolies, doing an electrical survey this week.

    At the same time, for a new factory we are building, the power correction factor devices were talked about at the electrical council, as to weather we are putting them in or not!

    Hence a little reading up on the different systems.

    We are receiving a quote this week looking at our existing consumption and looking if a PFC will make a remarkable difference or not.

    Cheers

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by BigRed View Post
    Reason behind the question is that my brother in law has become the agent for a voltage stabilizer and in the process of selling one to Woolies, doing an electrical survey this week.
    Can you give the details of the equipment he's the agent for? I would be interested to read up on the spec sheets and find out about the benefits it provides.
    Quote Originally Posted by BigRed View Post
    At the same time, for a new factory we are building, the power correction factor devices were talked about at the electrical council, as to weather we are putting them in or not!

    Hence a little reading up on the different systems.
    I would do more than just reading up on different systems if I were you. You should discuss this type of investment/installation with an independent consultant before taking any decisions. I wouldn't let yourself get railroaded into a PFC installation of this nature by the supply authority of the agents of the equipment.

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    Site Caretaker Dave A's Avatar
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    I'd expect the voltage regulator's main benefit is protecting electrical equipment from (particularly) brown-out type damage. My electricians are forever remarking on how much variance they're finding in the mains supply voltage on the properties we test.

    We've also had quite a few requests for low-voltage cutout switches to protect some classes of electrical plant - particularly electric motors.

    Would voltage stabilisation not perhaps be targeting voltage spikes?
    The trouble with opportunity is it normally comes dressed up as work.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Dave A View Post
    I'd expect the voltage regulator's main benefit is protecting electrical equipment from (particularly) brown-out type damage. My electricians are forever remarking on how much variance they're finding in the mains supply voltage on the properties we test.
    The supply voltages in SA can be a little hairy depending on the area you're in. Stabilizers or regulators would prevent low voltage damage.

    Quote Originally Posted by Dave A View Post
    We've also had quite a few requests for low-voltage cutout switches to protect some classes of electrical plant - particularly electric motors.
    With motors you're between a rock and a hardplace.
    You want a motor with a constant load to be sized so it's running at about 90% of it's full load capabilities, this is where the motor is at its best efficiency.
    Problem is when the voltage drops the run current increases so the motor can end up drawing more than its rated maximum current and it overheats.
    If the overheating is marginal then the chances are that bearing lubricants will break down over time and the bearings fail prematurely. If the overheating is more acute then winding insulation will fail resulting in electrical tracking across the windings or the windings down to earth.

    Voltage differences in the three phases supplying a motor can be equally catastrophic.

    High supply voltage is equally bad for motors, it also causes high running currents. This is due to flux oversaturation in the motor also having a detrimental effect on efficiency.
    It's not just the run current that rises, the power factor gets worse so this increases the supply losses for the utility company which adds to the reactive load.

    Many motors are of European origin and rated 380-440volt so a good supply voltage in SA (380-400v) is already at the lower end of the motors design voltage. Add all these problems together and you have an epidemic of premature motor failure.
    Bottom line is that motor voltage is critical to the the motors lifespan.
    Lighting also takes a hammering with voltage variations, marginal overvoltages can reduce the life of filament globes (bulbs) by 50%, this includes halogen downlights.


    Quote Originally Posted by Dave A View Post
    Would voltage stabilisation not perhaps be targeting voltage spikes?
    Surge protection targets voltage spikes (lightning protection). This is a different animal to a voltage stabiliser but both systems could be combined in a device aimed at improving power quality.

  10. Thanks given for this post:

    Dave A (09-Feb-10)

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