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LED inrush current and generator set

Julien Leblanc
Hello,


I'm currently working on a sport field application where i need to power some LED reflectors (30 kW total).

I will also use a generator set, in case the network fails.


The inrush current of the reflectors is 3 times higher than their rated current, but the duration is only 0.2ms.


Could anybody tell me if i should take into account the inrush current when I choose the generator set power (that is, to oversize the generator)?

Or i should ignore the inrush current and set the power of the generator a bit higher than the total power of the reflectors?

I'm not talking about the circuit breakers of generator's outputs. Let's say one can choose them so that they don't trip.

If those breakers don't trip, is it possible that anything else happen to the generator set, because of the inrush current?


I've been searching through the specifications of many generator sets, but i cannot find any data on this specific problem (short overload).






  • 0
    broadgage:

    The inrush current drawn by LED lamps is extremely brief and unlikely to have significant effects on a generator.

    I would however be inclined to oversize the generator on general principles, life and reliability will be enhanced by not running right at the limit.

    Load tends to grow.

    LED lights may have an odd waveform, also making oversizing prudent.


    They don't say anything about the waveform or harmonics... They only specify the power factor, which is 0.95.


    The theory says that a generator should ideally be loaded at 70...90% of its capacity.

    Oversizing considering that those 30 kW represent 70...80% of the generator capacity is enough, in your opinion?

    Considering that, in the future, only small changes in the load will be made...



     


  • 0
    If you really cannot avoid dropping all the load on at once, then the genset will need to be over-size by 2 or 3 to reflect that, though in many ways that is just wasteful. If you can drop down to a minimal emergency light level when the ATS kicks over and then bring the bigger load on just a little later it will be better.

    Have you got a tame genset supplier ?- the folk who make them are normally more than happy to advise this sort of thing, but as it depends on the build, the 'generic' information covering different internal designs is quite variable.
  • 0
    wallywombat:

    Of course if the genset is intended to automatically take over, all the light switches may already be physically in the on position; so you wouldn't get the advantage of a staggered power on. Which is another reason for something like time delay relays like Mike suggests.


    I was thinking of only one switch, which is connected to a PLC input. The operation of the ATS will result in a PLC reboot  and this will start the power on sequence. I'm not yet sure if my logic is ok.


  • 0
    mapj1:

    If you really cannot avoid dropping all the load on at once, then the genset will need to be over-size by 2 or 3 to reflect that, though in many ways that is just wasteful. If you can drop down to a minimal emergency light level when the ATS kicks over and then bring the bigger load on just a little later it will be better.

    Have you got a tame genset supplier ?- the folk who make them are normally more than happy to advise this sort of thing, but as it depends on the build, the 'generic' information covering different internal designs is quite variable.


    Yes, all genset suppliers i have contacted told me the same thing: choose a capacity which covers the added inrush currents of all LEDs.


  • 0
    AncientMariner:

    Since this is for a back-up supply for a sports field, I guess that the main need for lighting will be during a match etc.  Is it therefore worth hiring in a mobile generator, once the lights are in situ, to trial both a suitable staged switch on;  ie delays between banks being energised and the kVA rating of a suitable generator?


    That is what they want, a stationary genset.


  • 0
    I agree with the other responses here. For a step load of 30 kVA, you are probably going to need a generator rated at three times that to prevent the engine stalling, especially when cold. If you are going to apply a high step-load, it is better for the generator to be pre-heated to a reasonable temperature using an electric heater, so it is almost ready for load when it starts, to cut down on the “warm up time” you need to give it. The other issue you may have, is whether the AVC (auto voltage control) is going to be able to figure out the waveform of the led lighting. Some of the more cost effective ones won’t cope, and hunt round the target voltage, which is likely to be noticeable. 


    As Mike has suggested, you need to get a generator manufacturer on board fairly early, and ensure that if you do need to schedule the lighting to come on in a staged way over several seconds, you plan for it now. 


    Regards,


    Alan.
  • 0
    Regarding kVA or kW, the alternator may be rated in kVA but the diesel part will be kW so both will be important.

    The other consideration may be harmonics. As  there are electronics involved there may be significant 3rd harmonic which adds in the neutral so the neutral current could be twice the phase current. Again a reason to overrate your gen set.
  • 0
    If the customer insists on one step load, then the lamp inrush and concerns of KVA vs KW will pale beside the cost of installing a 70-90kVA machine with something that looks like a small bus or large van engine, when for 30kVA a enerator half the size and an engine about the size of one from the diesel version of the Ford Fiesta, with corresponding lower fuel consumption would do if you could sequence it.

    Even so  it takes time to crank over, start and get up to speed before any load can be connected and that will be total blackout, so battery EM lights will be needed anyway
  • Former Community Member
    0 Former Community Member
    Julien Leblanc:

    There will be an ATS installed, which will start the generator, then connect the load.

    Yes, one single switch.


    Thank you for the reply, is this an existing lighting installation to which you are adding the generator/ATS etc?


    And what is the budget for the generator, is it intended for safety purposes, such as lighting for a large crowd to be safe in the event of a mains failure or is it for revenue protection ie to prevent commercial events having to be abandoned due to lighting failure?


  • 0
    While I agree with the comment about the time taken to get the generator up and running, it might focus minds to ask what is the acceptable time for the place to be in total darkness. Most battery backed emergency lighting systems are short break transfer, i.e. sub one second of darkness.You might get a gen set up and running in less than 5 seconds for the first part of the load, 10 seconds for all the load. Is this acceptable? If not then additional battery backed lighting adds a whole new layer of complexity.

    Is it acceptable to be in complete darkness? How dark will it ever really be? Is the lighting is for safe evacuation or can folk simple stay where they are for 10 secs?

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