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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
    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.
  • 0
    AJJewsbury:
    Also is there a single on/off switch that controls all 30 kW of lighting at once?

    Indeed - simple sequential start arrangements (anything from a lot of carefully co-ordinated on-delay timers to just a bank of separate lightswitches) can side-step a lot of inrush problems.

       - Andy.


    This will be the final solution.

    I was just trying to understand if the generator could be damaged from high currents of short duration.


  • 0
    Simon Barker:

    Is that 30kW or 30kVA?  LED lamps can have quite poor power factors, and generators are normally rated by kVA, not kW.


     



    30 kW, with 0.95 power factor


  • 0
    There will be an ATS installed, which will start the generator, then connect the load.

    Yes, one single switch.
  • 0
    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?
  • 0
    Regardless of inrush, no normal genset will appreciate steps in the load of more than about 30-50 % of the nominal rating - this depends a bit on the design, but it is certainly possible to stall a typical genset by letting it stabilise at, or near no load, with the fuel rate into the engine very low,  and then slamming on the full load.

    Gensets built to supply very impulsive nodes tend to be induction units, (so no brushes) and also to have deliberately heavy flywheels on the propshaft. This in turn makes initial turn on and getting up to the right speed take longer however - there is no 'free lunch'.

    Bringing the load on in stages, so the engine controls have time to open the throttle and get the speed up between steps, is the only way to get from nothing to full load without problems.

    If you can divide your load into 3 or 4 banks and space them by a second (time delay relays and contactors) it will go a long way to easing the problem.
  • 0
    Also is there a single on/off switch that controls all 30 kW of lighting at once?

    Indeed - simple sequential start arrangements (anything from a lot of carefully co-ordinated on-delay timers to just a bank of separate lightswitches) can side-step a lot of inrush problems.

       - Andy.
  • 0
    Is that 30kW or 30kVA?  LED lamps can have quite poor power factors, and generators are normally rated by kVA, not kW.
  • Former Community Member
    0 Former Community Member
    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).






     


    Hi JLB, how is the generator proposed operated in the event of a mains power failure? Also is there a single on/off switch that controls all 30 kW of lighting at once?


     


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