synchronize genset with utility - load flow 2

[deltawhy]

Hello,
I have a question regarding synchronizing a small generator with the utility. I have a 15kW genset that a client wants to sync to the utility feeding his building. The synchronization can be done using a contactor and a synchronizing controller (like easygen or woodward EGCP-2). My question is more based on theory of operation. Will the generator be able to feed the building loads (about 8kW), or will the utility be providing for all the required loads? I did a very quick load flow analysis on etap and it showed my generator feeding 0kW, 0kvar, while the utility covered the entire load. Is there any way to ensure my genset will be providing at least 50% of the building load, while the utility covers the other 50%?

Thanks.

 

[mgtrp]

Try setting the generator in ETAP to "voltage control" mode, and then enter the amount of load that you want it to supply. Then run your load flow again to see your voltages etc.

 

[deltawhy]

Thanks for the response, I made those changes into Etap. My question really boils down to: in practice, will the genset be able to share the building load with the utility at an 80%/20% split? If so, what characteristics of the generator would I go about controlling to get this done?

Thank you.

 

[cranky108]

Again it depends on the governer settings in the generator. If the governer is set to control frequency, it will output zero load, but if it is set to regulate voltage, and set a defined load, it should hold that load.
The issue is if you want a defined split in the load, or will a fixed generator output surfice. A defined split will require more equipment than a fixed generator output.

 

[deltawhy]

Thanks for the responses guys.

 

[catserveng]

I don't usually do that small of a unit in parallel to grid, but I would say the first question to ask is what are the utility interconnect requirements? They will define the required protections needed, the amount of minimum import or allowable export for real power the unit can provide, any anti-islanding protections needed, and what would be required to meet worker safety requiements for utility workers.

In parallel to grid the easyGen or the EGCP can either operate in Baseload or Remote Load control modes. If the site loads are stable or always above the capacity of the installed genset when you want the unit on line, Baseload will work fine for most situations. If you want to perform some type of load following, to minimize import and prevent any export, the controls get a bit more complex. VAR control can be done with either Woodward unit, provided the voltage regulator on your little generator will interface properly with them. You could run the voltage in droop, as long as the AVR will manage it properly, most small sets don't in my experience.

Hope that helps, Mike L.

 

[waross]

I doubt that the utility will allow this. Well, they may, but if they do, the minimum requirements for protection and control will probably be so expensive that it is not worth considering.
An alternative may be to look at a large UPS, 100 amps more or less, and put all or part of the building load on the UPS. Then use the genset to charge the batteries.
Just for fun, lower the system voltage a little in ETAP. Say about 10% to simulate heavy grid loading. Look at what happens to your reactive current and gen-set power factor. You may have to consider a more sophisticated (and more expensive) AVR to follow the grid voltage and lessen swings in power factor and reactive currents due to grid voltage variations.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Etap simulations and real life will likely be much different. Especially if you have not modelled the genset exactly how it really functions.

In the bigger picture, you set the genset to output a certain power and it goes out into the power wires. The power leaving the genset doesn't know the difference between the customers building or another load 100's of miles away. The fact that you're confused about what will really happen because Etap isn't modelling it correctly points out that you might not be the correct person for this job. You should likely seek help, and this forum doesn't count.

To get back to the complete basics, control the throttle to vary the kW output and control the field voltage to control the kVAR output. So, as Waross already mentioned, you need a control system (AVR) that can accomplish both of these. I highly doubt that 15kW genset built for stand-alone duty has the necessary controls as is.

Also, are you leaving out some detail such as not being able to or not wanting to supply power back into the grid? I would expect you could set-up equipment to measure the building power and then use those readings as an input to a decent genset controller which would ensure the genset output tracks the building power demand.

 

[deltawhy]

Thanks for the information everyone. But yes, I'm fully aware that the depth of the parameters required for correct simulation cannot be covered at this time. No big deal. Just needed confirmation that load sharing at this scale is possible (however expensive it may be). I've done synchronizations on larger gensets before and just with parallel gensets, not the utility (infinite bus). There will be no export of power to the grid, but an import to cover the net load not produced by the genset. As for protection and control, here is what I have planned to keep costs down to an absolute minimum:
- Synchronization will be done by using an EGCP-2 controller, in conjunction with a simple contactor (yes interface may be interesting).
- All required relays (ANSI #'s 50/51, 50G/51G, 25, 27, 47, 59, 81, 32, 46) will be internal to the EGCP-2, and will send a signal to a shunt trip on a smaller MCCB to trip on any condition outside of normal operating parameters. Inputs will be CT's and PT's on the genset output bus and utility bus.
- Votlage +/- bias, analog signal, interface with whatever AVR
- Prime mover control, analog signal, interface with whatever governor is supplied

Of course the whole setup will have to be magically approved by the local authority and by the utility, but thats another battle.

Thanks everyone.

 

[catserveng]

On smaller projects lately have found the easyGen to provide better features/interface with a wider range of prime movers and generators. Also like their excitation protection system over what is available in the EGCP-2. It can also do the load following since it has voltage and current for mains and gen, although only a single CT input for mains, but in all applications I have done have worked fine. Did some digester fueled small cogens, 50 kW in parallel with the easyGen's, so far no complaints from the dairy operatora.

Good luck! Mike L.