Generator Minimum Speed

[gray.one]

I have seen a diesel genset with a note that it will shutdown to protect itself if it runs at less than 58HZ for 3 seconds. Why is there a minimum speed?

I'm working on a stability study for an industrial plant.

The only thing I can think of is directly connected fans not cooling the engine enough.

Thanks


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[Ingenieur]

I would assume overload is dragging it down

 

[Fnewman]

Is it running isolated, or synchronized to the utility and/or other generation equipment? Either way, low frequency is the result of more load than the engine can support or a problem with the speed regulator. Both are situations requiring correction.

 

[GoldDigger]

Is it running isolated, or synchronized to the utility and/or other generation equipment? Either way, low frequency is the result of more load than the engine can support or a problem with the speed regulator. Both are situations requiring correction.

The problem is not the low speed itself but rather the reason the speed is low.

mobile

 

[Ingenieur]

He's not saying it is running low
he is saying it has an abnormal shutdown alarm IF it runs <58 Hz for 3 sec
and wants to know why you would want to shut it down under this condition
either a governor fault or over loaded
imo overloaded, if it is drug down for 3 sec shutdown
probably adjustable if a high inertia motor load is powered

genset control pkg https://pdf.wholesalesolar.com/inverter pdf folder/AtikinsonGSCM.pdf
has adjustable under/over freq shutdown with fixed td

 

[Ingenieur]

[h=5]Low Frequency (FC_5)[/h][h=5]This fault is indicated by fault code FC_5 and five blinks on the LED indicator. This feature protects devices connected to the transfer switch by shutting the generator down if the engine runs slower than 55 Hz for three seconds.
This condition is caused by a failed engine component or by excessive loads on the generator. To remedy the problem, contact your installer or an authorized service dealer. Return to Fault Chart

https://www.briggsandstratton.com/lam/es/support/faqs/home-standby-generator-fault-codes



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[gray.one]

Generator Minimum Speed

The protection I described is part of the genset onboard controls. We are setting the system load shedding.

Definitely a reason for a slowdown could be overload. As Ingenieur pointed out, it could be a failure of a genset component.

I'm familiar with the electrical side but not the mechanical.

It's interesting that the B&S thing says that the feature protects load devices.

55 Hz sounds like they are protecting transformers which can handle 10% over voltage at 60HZ. The transformer design margin is actually 10% margin for voltage/frequency.

Thanks. I wonder why mine is 58HZ.


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[Jraef]

Lots of electronics have a minimum frequency as well, because switching pulse timing is determined off of the line frequency. SCR firing controls in things like soft starters and heating controllers are especially sensitive to this. If you read the specs, they will say +-2Hz, with a switch to select 50 or 60 Hz as the base frequency. Phase angle firing techniques require knowing where the sine wave crosses zero, which requiring measuring two phases at the point where the sine waves are the same potential, then timing from there to predict the zero cross. Messing with the frequency throws that time measurement off and gets everything out of whack, leading to misfires and either shutdown or failure. 25+ years ago when soft starters took off, it was a huge problem with genders that had old mechanical AVRs (Automatic Voltage Regulators). Genet Meg's eventually fixed the issue, by tightening up the frequency specs.