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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
    Hi

    If you need to supply only LED lights for this application, well there are already dedicated Lighting Towers on the market already with different ratings up to 2000W.These are already well designed and rated as per specific application.

    b62c9c7229266ca5434b8ae214b80049-original-image.png

    This will be suitable only if you do consider to provide current for LED lights only .Then for connection via PLC , then you must check if there is the option of bus connection on the main board for this type which I doubt.

    If you need light and plus other current on other phases,then instead of a single phase gensets maybe you need to consider a 3 phase gensets and maybe >=50KVA but please reconsider the load calculation. Typically on a 50 KVA 3 phase,there is already the bus connection for plc connection and connectivity,However recommended to check on the specs.

    Note that the higher the KVA the higher the cost.The gensets have 0.8 PF and rated on KVA only. For the ATS,these are available on gensets or separeatley modules depending on options and models or availability.

    Hope these may have been of help.

    Thank you.

  • 0
    mapj1:

    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


    The max. time of total blackout is 5 s. I think there is no genset  which can become operational so fast?


  • 0
    weirdbeard:
    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?




    It's a new installation.

    The generator is necessary for safety purposes and also for the continuation of the events, in the case of a mains power failure.


  • 0
    Harry Macdonald:

    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?



    After a mains failure, the lights (at least a part of them) should become available in 5 s. I think it is not realistic with a genset.

    As i read in some specifications, the ATS doesn't start the generator immediately, but after t1= 5 s of delay, necessary to ensure that there is a true power failure. 

    After the start, another t2=5 s are necessary to warm up the engine... That makes a total of 10s.

    Unless t1 can be set to zero, but in this case the genset would start even in the case of a very short power failure and I'm not sure if it's ok.

    Given that the sport events are rather rare, the starting of the genset due to false alarms would be acceptable?

    Or even keeping the genset running, is it customary to do so?



  • 0
    Sheilen Singh (Kevin) Hookoom:

    Hi

    If you need to supply only LED lights for this application, well there are already dedicated Lighting Towers on the market already with different ratings up to 2000W.These are already well designed and rated as per specific application.

    b62c9c7229266ca5434b8ae214b80049-original-image.png

    This will be suitable only if you do consider to provide current for LED lights only .Then for connection via PLC , then you must check if there is the option of bus connection on the main board for this type which I doubt.

    If you need light and plus other current on other phases,then instead of a single phase gensets maybe you need to consider a 3 phase gensets and maybe >=50KVA but please reconsider the load calculation. Typically on a 50 KVA 3 phase,there is already the bus connection for plc connection and connectivity,However recommended to check on the specs.

    Note that the higher the KVA the higher the cost.The gensets have 0.8 PF and rated on KVA only. For the ATS,these are available on gensets or separeatley modules depending on options and models or availability.

    Hope these may have been of help.

    Thank you.

     


    Thank you for the reply.

    I didn't think of communicating with the PLC through a bus connection... It seems interesting.

    I only thought of coordinating the start of the group of loads with the PLC.

     


  • 0
    There are installations where a diesel generator assumes full load in 3 seconds from cold start but they are rather specialist and I don't know to what extent the generator was oversized to allow this.

    I don't think it unreasonable to start the generator immediately but to let it run for 5 secs before initialing the change over to see if it is a real power cut. Then you hit the step load issue and need to keep the load steps below 1/4 of capacity per step so 5 steps changes in the next 5 seconds should be reasonable.

    However this all needs careful control and you also need to think about how the transfer back to mains power is arranged. Automatic or manual? What happens if the power if restored while the loads are being switched on the the generator?
  • 0
    It is perfectly reasonable to start a genset and get it connected to full load in a little under 5 seconds, but it is not often achieved. Firstly that will be a machine with an oversize turbo charged diesel and not such a heavy flywheel, so it will not be so good on step loads, and if you want it to start and rev hard, it will start with a great cloud of black soot, compared to a slow spin-up design.


    Normally for events we'd program in some hang over to the genset, so that if it decides to come on it then keeps running  for at least a few minutes, even if it is not needed because the power comes back on almost straight away.


    For seamless power transfer there are battery inverter based UPS systems, that basically join the inverter waveform on to the incoming mains to the nearest whole cycle,  but these are large, expensive and probably overkill and harder to maintain than a selection of maintained emergency lights. With an inverter UPS expected to  hold up for say 30- 60 seconds (from a design with batteries sized for a run time of maybe 5  to 10 minutes at full load ) you can afford to have a 10 second start time, or longer, allowing for a few crank and coughs from the gensset and set a long pre-trigger delay to avoid the false start problem on every flicker of the mains.  I think the times you are looking at are from that sort of design.

  • 0
    How often/long would the standby facility be required? If it's for something like a football club and only needed when there's a proper match on - perhaps a few hours once a week or once per fortnight - might there be any mileage in starting the generator and have it just ticking over during the match, so as to be almost instantly available, but shutdown for the other 98% of the time?

       - Andy.
  • 0
    Harry Macdonald:

    There are installations where a diesel generator assumes full load in 3 seconds from cold start but they are rather specialist and I don't know to what extent the generator was oversized to allow this.

    I don't think it unreasonable to start the generator immediately but to let it run for 5 secs before initialing the change over to see if it is a real power cut. Then you hit the step load issue and need to keep the load steps below 1/4 of capacity per step so 5 steps changes in the next 5 seconds should be reasonable.

    However this all needs careful control and you also need to think about how the transfer back to mains power is arranged. Automatic or manual? What happens if the power if restored while the loads are being switched on the the generator?


    Sorry for the delayed answer.

    Thank you for reminding me about these details.

    I think that the simplest way is that the transfer back to mains to be made manually. I think some ATS have implemented this function - i found this text on a specification: "if the mains supply becomes available again before the generator circuit breaker has closed then the mains circuit breaker remains closed (or recloses if it has opened) and the generator will not go on load.".

    Are all these details manageable by a PLC?


  • 0
    mapj1:

    It is perfectly reasonable to start a genset and get it connected to full load in a little under 5 seconds, but it is not often achieved. Firstly that will be a machine with an oversize turbo charged diesel and not such a heavy flywheel, so it will not be so good on step loads, and if you want it to start and rev hard, it will start with a great cloud of black soot, compared to a slow spin-up design.


    Normally for events we'd program in some hang over to the genset, so that if it decides to come on it then keeps running  for at least a few minutes, even if it is not needed because the power comes back on almost straight away.


    For seamless power transfer there are battery inverter based UPS systems, that basically join the inverter waveform on to the incoming mains to the nearest whole cycle,  but these are large, expensive and probably overkill and harder to maintain than a selection of maintained emergency lights. With an inverter UPS expected to  hold up for say 30- 60 seconds (from a design with batteries sized for a run time of maybe 5  to 10 minutes at full load ) you can afford to have a 10 second start time, or longer, allowing for a few crank and coughs from the gensset and set a long pre-trigger delay to avoid the false start problem on every flicker of the mains.  I think the times you are looking at are from that sort of design.

     


    It seems that a system with a UPS is the perfect solution, but it is very expensive.

    I will try to solve the problem without a UPS, only with a genset.

     


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