Load Shedding

[ksheldon]

I plan to use an inverter-generator to provide backup power to a residence. I am looking for a system to shed loads when the total demand exceeds the maximum continuous output of the inverter generator. I have seen systems that trip when the frequency of the supply drops below a threshold. That works when the generator starts to slow under heavy load. In the case of an inverter, I think the frequency would remain constant, though the voltage would drop when the load exceeds the capacity of the generator. I am looking for a load management solution that triggers when the total system current exceeds a threshold, or when the voltage drops below a threshold. Any suggestions?

 

[ptonsparky]

I plan to use an inverter-generator to provide backup power to a residence. I am looking for a system to shed loads when the total demand exceeds the maximum continuous output of the inverter generator. I have seen systems that trip when the frequency of the supply drops below a threshold. That works when the generator starts to slow under heavy load. In the case of an inverter, I think the frequency would remain constant, though the voltage would drop when the load exceeds the capacity of the generator. I am looking for a load management solution that triggers when the total system current exceeds a threshold, or when the voltage drops below a threshold. Any suggestions?

I could make you one, but I am retired. Motor controls.

 

[JoeStillman]

I did something similar with a Time-Mark relay like this...

http://time-mark.com/Documents/Datasheets/Time-Mark-2734-Over-Current-Sensitive-Relay.pdf

 

[ksheldon]

I did something similar with a Time-Mark relay like this...

http://time-mark.com/Documents/Datasheets/Time-Mark-2734-Over-Current-Sensitive-Relay.pdf

That may do the trick.
Thank you for the idea.

 

[NewtonLaw]

I believe they make some transfer switches that have the capability of selecting some load that will be dropped from service if it will overload the generator. Is anyone aware of these ATS units?

 

[Hv&Lv]

I believe they make some transfer switches that have the capability of selecting some load that will be dropped from service if it will overload the generator. Is anyone aware of these ATS units?

A generac panel does that by priority.

 

[ksheldon]

A generac panel does that by priority.

What mechanism does a generac panel use to determine certain lower priority loads would exceed the capacity of the generator?

 

[ptonsparky]

What mechanism does a generac panel use to determine certain lower priority loads would exceed the capacity of the generator?

Your choice. You connect the load to an interposing control relay.

 

[NewtonLaw]

What mechanism does a generac panel use to determine certain lower priority loads would exceed the capacity of the generator?

The ATS I installed was made by Briggs & Stratton but is very similar to the Generac model. You select specific loads that you want to drop from service during operation of the emergency generator as it approaches full load to ensure you do not overload the generator. I believe some units allow anticipation of a motor start but that is a pretty extensive control system.

 

[ksheldon]

How is the potential overcurrent condition detected? If it is based on current at the generator inlet, that will work with an inverter. If it is based on frequency, then it will not. Inverters do not slow when overloaded.

 

[ptonsparky]

How is the potential overcurrent condition detected? If it is based on current at the generator inlet, that will work with an inverter. If it is based on frequency, then it will not. Inverters do not slow when overloaded.

I can stall one of my small ones. 2000 watt IIRC.

 

[JoeStillman]

For most loads, generators will stall before experiencing overcurrent. You need to have a power factor below 80% to overdrive the alternator without overdriving the engine.