Voltage fluctuation

  1. why voltage fluctuation is there?
    since all the houses are in parallel,so all of them recieve same voltage..then why voltage fluctuation is there? and why not current fluctuation?
    why voltage stabilizers are used ?
  2. jcsd
  3. psparky

    psparky 871
    Gold Member

    More details in your question would help.

    For example, what makes you ask the question in the first place?

    Where are the voltage fluctuations? How were they measured? Why were they measured?

    What country are you pertaining to?
  4. ohkay. i have seen a avoltage stabilizer attached to my computer. i was told it is to remove any voltage fluctuation occuring in supply.
    but, my query is...why voltage fluctuation will occur and not current fluctuation?
  5. yeah, in this it is written:" if you add an extra element, the other elements will still have the same amount of voltage as before. If you remove an element, the other elements will also still have the same amount of voltage as before"
    so why there is voltage fluctuation??
    there should be current fluctuation, because it does not remain same in a parallel circuit.
  6. [​IMG]

    You have a voltage fluctuation because the voltage source (generator/transformer) and wiring (mainly resistive losses in transmission lines) are overloaded from the current draw so the overall voltage level drops as the current increase above some level.

    Last edited: May 2, 2014
  7. thanks for your reply.
    i have gone through the above link. in that they are telling the reason of voltage drops in transmission and distribuition lines. i think you haven't understood my question.
    so, in every transmission and distribution lines there would be certain drops, reason may be the lenght,size etc. these drops would be same for all the homes which are being powered by that distribution line.
    then why we use voltage stabilizer in our homes? is volatge fluctuating due to high current drawn by load?
  8. [​IMG]

    As you can see on that link the voltage drop at a home depends on it's position in the distribution line. Each segment with a house drawing a load current is a voltage divider (a length of line to it with resistance R1 and a load current with resistance R2) that depends on the load currents before in a 'voltage divider' and after it's location RL. Changes in loads before and after can effect the voltage at one location even if it's load is constant. If many homes at 400m+ on the line want to increase the voltage back to 220 using voltage stabilizers, this will draw more current from the line voltage (about 140 at the end) causing the R2 load resistance to decrease and lower the utility voltage even more along the line. The primary key to reducing voltage fluctuations in a situation like this is lowering the losses in transmission but that means spending large sums of money on basic infrastructure.
    Last edited: May 2, 2014
  9. Baluncore

    Baluncore 2,703
    Science Advisor

    The AC power distribution system supplies a predictable voltage through a low resistance cable. The limit to the current that can be drawn is determined by the resistance of the network. If the supply voltage falls more than 5% below that specified, then more current is being drawn than the cable was designed to carry. The current drawn must be reduced, or the cable resistance reduced by using a thicker more expensive cable.

    Since the power distribution is more like a tree structure than a grid, and the current drawn varies with time and location, all houses do not have the same voltage drop. There are times and places where the network is significantly overloaded due to lack of engineering, unplanned growth or energy theft.

    You should not need an external voltage stabiliser with a computer. Any variation in supply should be compensated for by the internal switching power supply and voltage regulator.
  10. No kidding. This is a typical power pole in some countries.
  11. davenn

    davenn 3,664
    Science Advisor
    Gold Member
    2014 Award

    exactly, and the OP still hasn't told us what country he is from ??

    Baluncore, not all countries have stable power supplies like the USA Australia and UK to name a few

    You wanna try living in countries like the Philippines where my wife comes from.... steady non-fluctuating mains power is but a dream. There are huge variations in supply voltage, constant brownouts and regular blackouts.
    There it isn't just a good idea to have a UPS on your computer and other sensitive equip, its an essential part of life.

    a pic from one of my Phil's visits


    Attached Files:

  12. Baluncore

    Baluncore 2,703
    Science Advisor

    Lovely pictures.

    Many switching supplies are now rated from 90V to 250V. The point I was trying to make was that a switching power supply will handle input voltages over a very wide range, maybe even wider than a voltage stabiliser. So I can understand a computer needing a UPS to survive blackouts, but it should not need a voltage stabiliser for brownouts.
  13. jim hardy

    jim hardy 4,768
    Science Advisor
    Gold Member
    2014 Award

    are you sure current does not fluctuatealso ?

    Perhaps this is simple terminology.

    What we tend to measure first is voltage because it's the driving force for current. Ohm's law .. If voltage changes, current usually does too.

    Parallel connection implies zero resistance in the wires that interconnect the circuit elements, as in top sketch of that link spook posted .
    real wire has resistance .
    Different houses are supplied different transformers which have resistance and inductance.
    Each house has a fuse or circuit breaker panel which has resistance.

    So to say that all houses are in parallel is only an approximation but it's so close to the truth we usually use it as if it were true.

    Your stabilizer protects your computer from fluctuations in voltage that'd probably affect your neighbors as well as you. They might arise from changing local loads or from system troubles like lightning or line switching..
    1 person likes this.
  14. The sad thing is the US grid unless we do something quickly will become as unstable in places as the countries with those power poles. It won't happen everywhere as some places have huge local excess generation and transmission capacity like the PNW but I think California is in for a rough period if hydro is reduced locally.

    Last edited: May 3, 2014
  15. Baluncore

    Baluncore 2,703
    Science Advisor

    nsaspook; interesting link. We are all having interesting times as we rebalance our generation management philosophy to better handle under and over generation situations.

    Peak loads here are air-conditioning on hot summer days. These are best supported by distributed PV. But PV on cool clear days tends to take over the grid and so result in “Solar Islanding”. http://en.wikipedia.org/wiki/Islanding

    It is still more economic to pay big users not to use power than it is to build more peak generation capacity. We may have to come to terms with the complexities of efficient negative pricing as a way of maintaining supply stability.
  16. Wind (primarily) and solar without storage is causing major problems here already. The mandate to use renewable energy (mainly wind here) is forcing hydro to be used as peak supply (causing wear on systems designed to be mainly steady state) instead of pure base-load generation. What's badly needed is on-demand storage near the usage locations and high capacity transmission to direct power to were it's needed the most because now we a wasting a huge amount of energy.

    Last edited: May 3, 2014
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