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  1. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    Hi all,

    Got a bit of a problem with a new generator when starting a 60hp motor.

    It's a 250kva generator with a 125A mounted plug, the plug is protected by a C125 A Merlin gerin c120h MCB with combined 300mA RCD, the motor starts fine but when it changes over to delta it trips the 125A mcb (I temporarily removed the rcd to prove it wasn't that as the are coupled together)

    The motor is a 45KW 60hp motor, it is driving a hydraulic pump (tripping with no real load on the motor). After a few goes it will eventually hold, I'm guessing the oil heats up a bit and isn't as thick.

    I have done an insulation test between the windings and to earth and all is good, all phases are balanced aswell, the motor is only 2 years old, full load current is 82A if I remember correctly, timer set at 5sec with an 80ms delay between star and delta

    So I am putting this purely down to inrush current, will putting a D125 on it resolve this problem of tripping, I have tested using a clamp meter and under some circumstances the current peaks at 150amps for a split second.

    None of this was an issue with he old generator however the plug was protected by a 150A MCCB no rcd.
     
    Last edited: Jul 22, 2017
  2. timbobelfast
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    timbobelfast Electrician's Arms

    Location:
    Belfast
    No sure if I would be selecting an RCD for this application TBH. Is this a client requirement ?
     
  3. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    is yourZs low enough for a type D? i'd be inclined to check it first and maybe try a type C first.
     
  4. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    I doubt it is an IR problem if in runs in star. It is possible the oil density is retarding the motor as it should reach 75 - 80% of its full speed before the transition to delta where for a fraction of time you get a current spike so the slower the star run speed the higher the spike. Can you increase the time at the starter before the delta transition occurs.
     
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  5. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    An rcd is required as flexible cables h07rnf are being used, it is an amusement ride.

    It is a short 35mm 5 core always supplying the same ride, I have tried a type c and this is what it is tripping.

    Timer set at 5Seconds at the moment, I can try increasing this but motor sounds like it is up to speed.

    Do you think it should be holding on an a 125A type C?
     
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  6. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    I suspect the mcb is the problem if you never had such an occurrence with the mccb. You could increase the time to say 10 sec and see what happens. This method of starting may reduce start up currents but there will always be a current spike on the transition to delta and mcbs are not ideal devices for motor protection.
     
  7. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    The C120 range comes with B, C & D tripping curves, don't assume that because it says C120 it's a C type, it could be anything.
     
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  8. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    How else would you provide fault protection? A 250kVA generator will not be capable of providing the fault current necessary to operate the mcb in time
     
  9. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Zs is irrelevant, a 250kVA generator will not be able to deliver enough fault current, the engine will stall first.
     
  10. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Why does the type of cable require a 300mA RCD?
    It is there to provide fault protection
     
  11. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    I know C120H is the range, well aware of that, it is a C125 MCB, you don't get 120Amp MCB.

    If it was an armoured to the machine you wouldn't require an RCD.

    I understand that it is a requirement under regulation 740.410.3


    I agree the MCb is the problem, but harder to intigrate RCD protection with an mCCB

    I have been down turned up the star delta change over time, helped a bit, but he said it also tripped once mid ride, far from ideal. So reluctant to keep the C125, measured it with my clamp meter with max function and it peaked at 175A, also measured earth leakage, it was around 30mA until the motor was started, meter maxed out then dropped to 120mA while motor was running, but I'm unsure if he meter would accurately read when the motor starts as there's such a high inrush. The next question is the RCD time delayed, I don't know it doesn't say type S. See picture this is what they have at the moment, as you can see not easy to fit anything other than this set up. This box supplies a 63A, 2x 16A and 32A. There is an main RCD on the generator but have this turned off as a fault in one ride cannot shut the whole lot down when they are open.

    I'm not sure what to suggest.

    IMG_0708.JPG
     
  12. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    A very much doubt the rcd is the problem.
     
  13. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    I'm going to ask them to try the C125 now that I have increased the time and see how they get on, if not they'll have to try the type but not cheap, just wanted to here everyone else's thoughts.
     
  14. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    So the trip during mid ride occurred when the motor was up to speed not during the transition to delta.
     
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  15. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Yes you would require an RCD whatever type of cable it is, it is needed for fault protection due to the generator being incapable of delivering enough current under fault conditions to operate the mcb within the required time.
     
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  16. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    It's not too hard to integrate earth leakage protection into an MCCB, just fit a shunt trip operated by an earth leakage relay.

    How does the generator behave when the mcb trips? Does it throw up any faults, lose speed, send up a cloud of black smoke etc?

    Switching out the main RCD on the generator may not be a very sensible idea, and may not be compliant with the requirements of bs7909. You should adjust the tripping current and time delay in order to achieve discrimination.
     
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  17. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    You would also need to Integrate CT coil and earth leaks the relay as well as the MCcb, and there is no extra space.

    The generator does noticeably change speed when the motor changes over but no smoke

    The generator came from an sound and lighting company so I would imagine it implies with bs7909

    Apparently it did once but I am notsurprised as I have measured peaks of 175A for a few seconds.

    The particular ride is a Miami,they are notoriously had to drive as the motor is subject to high load then very little very frequently.
     
  18. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Still don't seem to know what protection curve the MCB is....
     
  19. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    When did you measure these peaks during change over or when it was up and running.
     
  20. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    The generator cannot comply with bs7909 on its own! Bs7909 is the standard which covers your whole installation from generator through to the ride.

    If the generator is noticeably slowing down then the output voltage and frequency will also dropping, this will have a knock on effect on everything it is powering.
    Are you running this whilst other loads are on the generator, or is it the only load?
     
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  21. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    See pitcture

    When up and running, it wasn't this high when changing over,


    I admit i am not familiar with the standard but all the leads over 32A are covered by 300ma RCD and correct overcutrent protective devises and anything under this 30mA double pole rcbo, I'm sure there is more to it, it's not somign I am involved with every day, just been asked to look at this for them.

    The voltage and frequency do not change, there are meters on the machine so you can watch them while transferring.

    There are other loads about another 75 amps/ phase on at the same time.

    IMG_0824.JPG
     
  22. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Those measurements are more than double its expected flc and it sounds like the other loads are also contributing. Sounds like this new generator maybe inadequate for the expected loading.
     
  23. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    It all used to run off a 200kva with no issues, this was captured by my clamp meter with the max function it may have only existed for a second, the whole ride with motor running but no load (lights ect) was only drawing about 50amps/phase.

    It has been designed to run off a 125A socket from day one, the machine itself has a 160Amp Mccb albeit someone has fiddled with it and turned it up to its max, the adjustment screw is chewed to bits.
     
  24. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    You said the generator slowed down, but you are also saying that the voltage and frequency do not change. This is not possible, The frequency is governed by the generator speed, if one drops then the other must.
    Also when you apply or remove a load on a generator it has to react to compensate, the speed and frequency will change. How big a change this is will depend on the magnitude of the change in load.
     
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  25. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    I was wrong to say it slowed down, you could tell it Was working harder but it was coping fine, it drives the machine easily
     
  26. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Is it possible to ditch the ancillary loads and just run the motor.
     
  27. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    Do you mean the lighting on that ride or the other loads on the generator, the other main loads are run from other plugs with their own protection all of which are fine, it's just when the motor changes to delta and the very odd time while the ride is operating, I am confident the generation is well capable of driving it, as well as other rides at the same time.
     
  28. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Yes ignore my last post I misthought the ancillary loads were affecting the motor load. I think the mcb tripping on the delta transition is down to the fact it is an mcb. Tripping when it is running could be down to a number of factors such as poor maintenance placing additional loading on the motor through poor lubrication, worn bearings etc.. Is the passenger capacity being exceeded.
     
  29. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    So you don't think changing to a D curve would make a difference?

    You cannot really exceed the ride capacity as there are a fixed number of seats. There is also counter weights to off set the "boat" so I can't see where the load is really.
     
  30. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    It may do but it also sounds like is is prone to an overcurrent issue and changing the type may not resolve it.
     
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  31. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    Trouble is it's £250 to find out.
     
  32. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Think you need to explain to the owner this and that there is no guarantees it will resolve it. Why did they replace the old generator.
     
  33. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    I will do, this is a vast improvement in terms of protection on the usual set up, the sockets are usually straight onto the bus bars of the generators and the older ones don't have RCDs built in! So this is all quite hard to explain and hard to get them to understand why you need all this.

    They will also want suggestions how to overcome this but there's space to fit a Mccb.

    How would you normally supply this size of motor?
     
  34. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    BS88 fuses or a suitable mccb.
     
  35. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    The motor is actually supplied buy 2x 100 A and an 80amp bs88 fuses (not ideal) before the star/delta contractors and these are holding up, by the looks of it the 80amp is an original.
     
  36. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    The mcb I feel is the Achilles heel as they are not suitable for large size motor protection.
     
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  37. Cadgey123
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    Cadgey123 Regular EF Member

    Location:
    London
    Link the MCB out the equation to see what happens?...

    You said you had added protection in regards to the other fuses.
     
  38. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    They have fitted a 4 pole isolator at the moment so that can operate, but ther is no protection for the cable and socket other than the MCcb in the generator with is about 400Amps
     
  39. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Link out the mcb is just removing the problem not solving it plus you remove circuit protection for the socket.
     
  40. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    what is the overload trip on the starter doing during all of this? Assuming it is set correctly then that should be providing the overload protection so the mcb or whatever will only be needed for fault protection.
     
  41. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    The relay would be more tolerant to current peaks whereas the mcb is not and that is the problem. The same goes for the BS88 fuses.
     
  42. Nigel Martin
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    Nigel Martin Nitramlegin

    Location:
    saddleworth
  43. Nigel Martin
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    Nigel Martin Nitramlegin

    Location:
    saddleworth
  44. Rocboni
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    Rocboni Trainee Access

    Location:
    Scotland
    I turned the changeover time up to 10 seconds and it's been fine ever since however I have ordered a D type so will fit that for piece of mind.
     
  45. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    That is what I suggested way back in #6, glad it seems to have resolved it.
     
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