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Thread: VD and generator

  1. #1
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    VD and generator

    Does anyone think a large voltage drop caused by equipment being started from inside a plant fool a generator to be started to backup the utility service ? The electrical service has been suspect as being undersized and there has been times the generator kicked on without there being a diffenite answer as to a loss of utility power.
    Thank you for your time in advance.

  2. #2
    T.M.Haja Sahib Guest
    Quote Originally Posted by jimbo123 View Post
    Does anyone think a large voltage drop caused by equipment being started from inside a plant fool a generator to be started to backup the utility service ? The electrical service has been suspect as being undersized and there has been times the generator kicked on without there being a diffenite answer as to a loss of utility power.
    Thank you for your time in advance.
    If mains voltage drops below the limit due to any large voltage drop caused by equipment being started from inside a plant,the mains contactor will be deactivated and mains supply would be cut off to the plant and the diesel generator would be started only after a wait period.But if mains phase voltages and frequency are restored to the programmed limit within the wait period,mains supply would be reconnected and the diesel gen set would not be started.

  3. #3
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    VD could be a problem but you should have some parameters at the gen or transfer switch to prevent this.

    Are you sure the Gen isn't going through a programed test run?
    Tom
    TBLO

  4. #4
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    Two things come to mind.

    1. The generator sense leads should be at the service disconnect, not downstream where there would be larger voltage drops. Could be an undersized service feeder or poor connections if the voltage is sagging.

    2. The generator should be able to be programmed in some way to adjust the Set Point at what voltage it will come on line.

  5. #5
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    Can you put a recording volt/ammeter on the service or some of the feeders for a while? That'll answer the undersized service question. Also, check the low-voltage transfer threshold and delay in the ATS; some of those are ultra-sensitive and ultra quick.

  6. #6
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    I like to say thanks to you guys for the troubleshooting tips to check this on going problem. There is a couple of things to look at before we call in for help from a specialist.
    We do need some more infomation available to us like the recording meter to see what is going on.
    thanks again.

  7. #7
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    I agree with every one else, the utility voltage is dropping below the set point. Or the set point is real close to the actual utility voltage. The set point is usually a drop in percentage of the incoming voltage. Depending on brand and model of ATS that percentage may be adjusted in the ATS.
    As a side note a lot of the Generac air cooled models are pre set with 65% Utility drop which has caused damage to equipment running on low utility power.
    Organized people are people that are just too lazy to look for their stuff

  8. #8
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    I see this often with small plants that have added considerable load, or especially chicken houses and hog houses that a lineman hung a 15 or 25 kVa pot for a temporary and the final service was connected without changing the XF to the right size. Many of the generators I see have a minimum setting around 116 volts. When our regulation gets below this point, the generator takes over. After running for a predetermined time, the generator will transfer load back to the utility, where the voltage will dip below 116 volts again, repeating as loads change.

    Check to see what your minimum setting is, as the others have suggested. If you suspect something is too small, call and complain to the POCO. It would be best if you could back up your complaint with the low voltage measurements.

  9. #9
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    Hog farms. Hmmmm. Had a customer some miles away that was having problems at peak load on Utility power. Their load was imbalanced enough that the voltage went way down on one leg. Gen would start and everything was good. They balanced the load and no problems since.
    Tom
    TBLO

  10. #10
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    There also may be a time delay setting on the generator sensing circuit (usually in the ATS actually) that is set too short to allow for minor voltage drops from normal motor starting.
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