mains supply or generator supply?

Discussion in 'The Projects Forum' started by mailus, Sep 4, 2013.

  1. mailus

    Thread Starter New Member

    Jun 16, 2012
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    I am in need to design a circuit that must detect the supply type(mains or generator) by using a wall socket.
    yes the supply is to be detected by using two wires (phase and neutral).if supply is generator means i want to glow a LED.
    any ideas to design this circuit.

    (by using a controller or analog electronics or digital electronics)
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Its called a relay.
    Switch the LED with a contact.
    Max.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    My guess is that a generator doesn't hold the line frequency as well as the power company. Perhaps a way of monitoring the period length with a zero-crossing detector, and detecting the error from the the expected line voltage period.

    Ken
     
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  4. richard.cs

    Member

    Mar 3, 2012
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    If it's a small generator you could look for frequency instability. They tend to drift more rapidly in frequency and have a greater level of variability than the mains. They probably also have frequency components relating to the pulsing of the engine.

    The other thing you could consider is something that does a loop impedance measurements at regular intervals. Once a minute say you use an SCR to throw a 10 Ω resistor across the mains for half a cycle and measure the drop in mains voltage (and hence loop resistance). If you get a loop of under an ohm you're probably on the grid and if it's a few ohms you'll be on generator.

    What country are you in? If it's somewhere with a less developed power grid it may be hard to tell the two apart.
     
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  5. mailus

    Thread Starter New Member

    Jun 16, 2012
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    i am from India. here we follow AC supply 230V-50Hz.
    the generator is supply the load for an apartment so it is bigger one.
     
  6. richard.cs

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    Mar 3, 2012
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    That makes it more difficult as there will be less difference between the two supplies. You could probably still use the methods above but the difference won't be as obvious.

    Can you make changes to the generator? For example set the generator to run at 52 Hz for an easily measurable difference. Or maybe inject an audio frequency pilot tone into the mains wiring.

    Why do you need to know? And is it essential that it can be detected only from phane and neutral?
     
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  7. mailus

    Thread Starter New Member

    Jun 16, 2012
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    There is no way to modify the parameters or the extra circuit in the generator part. because it is private owned.

    yes,because it is needed for an apartment. no way to change the wiring or any changes in the electrical network.
     
  8. richard.cs

    Member

    Mar 3, 2012
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    My point was that if the generator supply is so similar to the mains supply that you can't tell them apart why does it matter which supply you're using?

    In any case I'd expect you to be able to detect the frequency variation from the generator. Depending on the generator size and mains supply you may not be able to measure the change in source impedance. Measuring the frequency is best done with a crystal-clocked microcontroller.
     
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  9. mailus

    Thread Starter New Member

    Jun 16, 2012
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    is it possible to use the PF(power factor) or harmonics in supply.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    A voltage by itself has no power factor. That's a phase measurement between voltage and current.

    Measuring harmonics might work if you have a good spectrum analyzer.

    Why do you need to know when the power is being supplied by the generator?
     
  11. mailus

    Thread Starter New Member

    Jun 16, 2012
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    to reduce loads.this is needed for an apartment so they can switch off their extra loads on generator supply(motors,fridge,etc.,).
     
  12. richard.cs

    Member

    Mar 3, 2012
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    Another possible suggestion: Most diesel generators in the 50-1000 kW range are 4-pole machines turning at 1500 rpm direct coupled to the engine so each full mains cycle is only half a turn. There may be some measurable asymmetry between adjacent cycles, particularly if the engine is 6 cylinder rather than 4 or 8. It would be a small effect but might be visible by averaging over many cycles.

    One more thought - is the generator visible from the apartments? That would open up a whole load more ways to see if it's running (bounce a laser and look for vibration, look for infra-red from the exhaust, etc) and a single sensor in one apartment could communicate to all the others by coupling something into the mains wiring.
     
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  13. wayneh

    Expert

    Sep 9, 2010
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    I think that's the key; communication over power lines is a well known technology already available in commercial products. You only need to determine the source of the power in one spot, and then communicate that over the power lines to all the other units.

    The logical spot to make the determination is at the generator, since it already "knows" what state it is in.
     
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  14. crutschow

    Expert

    Mar 14, 2008
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    Perhaps some form of WiFi transmitter on the generator that would transmit a signal when the generator is on.
     
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  15. mailus

    Thread Starter New Member

    Jun 16, 2012
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    please give me some information about this method.........
     
  16. wayneh

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    Sep 9, 2010
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    You might look here or here for ideas.
     
    Last edited: Sep 4, 2013
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