Emergency Load Shedding
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Cold Fusion
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Pretty general question. Have you looked at the IEEE Orange Book?anbm said:Anyone knows any good resources to learn/read about emergency generator paralleling control and load shedding? Thank you.
IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications
cf
kingpb
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Cold Fusion said:
Ahh, another sole spouting IEEE references; careful Cold Fusion, your going to insight Charlieb's rath!
Cold Fusion
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Oh-oh. "Sole": Would that be as in shoe bottom, as in stepped on - if so, good pun:smile:kingpb said:Ahh, another sole spouting IEEE references; careful Cold Fusion, your going to insight Charlieb's rath!
Yeah, I am a standards kind of a guy. Never do original research if you don't have to - steal every good idea you can. Always give credit - It isn't plagarism if you give credit.
I'm an engineer, not a research scientist. Why wouldn't one want to use existing standards?
I'll just have to duck behind technical expertise, professional competence, and the civility one would give a perfect stranger. That should keep me from being "insight" of charlieb's rath. (Another good pun on your part
)cf
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noonan
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You mean like shed load when the gen capacity is at XX%, add when capacity is at YY%?
Cold Fusion
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The short answer is, "No, because you have no criteria". I recomend you do some research to refine your customers needs. Your question is so general, that I don't know any answers. Here are some examples of questions you may wish to ask:anbm said:
Are you:
multiple generators islanded?
generators and utility?
multiple utility services?
What are you trying to accomplish:
Keep the lights on?
Datacenter up?
Power to core process that could be life threatening?
Power to core process that would damage equipment?
Minimize environmental damage?
Does the utility have any loadshed requirements? Generally this is single item large power using machine, that the utility can dump with out screwing it up.
Do you want to loadshed on:
Frequency?
Spinning reserve?
Do you have any minimum life-safety loads that must be maintained?
Are critical loads on UPS? How long can they last?
My first response still stands - Try IEEE Orange book as start to getting a handle on exactly what you are trying to accomplish?
cf
Okay, more specific of example:
In hospital, we have several ATSs are fed from paralleling generators (5 generators) and utility xfmrs. When hospital looses normal utility power, generators will start, one by one at a time. Depending on emergency, all 5 generators can close on bus at some moment.
1. At begginning only one or two generators close on bus (or runs) to handle current emergency load. At sudden, emegrency load increase (several motor start for example) and generator capacities are not large enough to handle this load, we have to dump some ATSs off line to avoid overload current active generator.
2. When generator reach enough capacity, we have to reclose the ATSs that just off line. Of course we have to identify which ATSs need to be taken off in case generator overload.
3. When all 5 generators run and the emergency load decrease, the program will shuts down one or two generators to save energy, etc.
As my understanding, they call all this as load shedding, is this correct. My actual question is how we define (thread hold point) when and how to add and drop the ATSs as generator. Can this done automatically by generator PLC program by setting up some data, logic? I think this must depending on emergency load run. Are there any generator persons out there??? I am confused myself. (-:
anbm
In hospital, we have several ATSs are fed from paralleling generators (5 generators) and utility xfmrs. When hospital looses normal utility power, generators will start, one by one at a time. Depending on emergency, all 5 generators can close on bus at some moment.
1. At begginning only one or two generators close on bus (or runs) to handle current emergency load. At sudden, emegrency load increase (several motor start for example) and generator capacities are not large enough to handle this load, we have to dump some ATSs off line to avoid overload current active generator.
2. When generator reach enough capacity, we have to reclose the ATSs that just off line. Of course we have to identify which ATSs need to be taken off in case generator overload.
3. When all 5 generators run and the emergency load decrease, the program will shuts down one or two generators to save energy, etc.
As my understanding, they call all this as load shedding, is this correct. My actual question is how we define (thread hold point) when and how to add and drop the ATSs as generator. Can this done automatically by generator PLC program by setting up some data, logic? I think this must depending on emergency load run. Are there any generator persons out there??? I am confused myself. (-:
anbm
Cold Fusion
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Good start. You have defined some of criteria you need. This is the begining of your design document. I'd recomend you finish your design document before starting the design.anbm said:
All of your decisions are going to be:
Money versus Critical life-safety
Money vs needed loads
Money vs convenience
I can't help with this. You and your customer have to make these decisions
Okay, from the information we have so far, the scenerio is:
1. Utility failure
2. Running life-safety critical loads and other needed loads on generator power
3. Generators on-line meet minimum spinning reserve and very little more.
4. Start large motor loads with out dropping life-safety critical loads. Other needed loads may be temporarily shed.
Yes you can do this with a PLC. Starting large motor loads with minimal spinning reserve is non trivial. The starting motor is a huge inductive load, the power factor will drop, causing the voltage to sag. The sudden increase in power will cause the frequency to drop. Since you are running with low spinning reserve, the drivers (engines) are already near WOT. You have nowhere to go except to start dumping non-essential load, and you have maybe a second to do it. Sheding on frequency droop when the gensets are near WOT is tough to calibrate. If the loadshed frequency is to close, you get a lot of nuisance trips. Too far and the gens are too low to recover and trip. There are some pretty good protective relays that will watch the frequency, and rate of change. One of those can be programmed to initiate multi-stage load shed. You will have to accept the occasional nuisance trip. Your PLC will have to perform the watchdog functions for reset and re-load
Consider having your PLC look at each of the motors/loads that can cause you trouble. When a load gets a command to start, the PLC holds it out until the appropriate loads are shed or additional gens are put on-line.
Give this some thought. I have to go to work for a bit.
cf
You are trying to reinvent the wheel. Just specify a transfer switch with a load shedding feature. The transfer switch will monitor the generator frequency. When the generator gets overloaded, the frequency starts to droop. Then the transfer switch transfers back to normal.
You can't load shed the Life Safety or Critical branches. Only optional branches and maybe equipment branches. (I can't remember for sure about the equipment branch).
Steve
You can't load shed the Life Safety or Critical branches. Only optional branches and maybe equipment branches. (I can't remember for sure about the equipment branch).
Steve
Cold Fusion
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steve -steve66 said:
I'v seen UF trips on transfer switches. But I have never seen one that checks spinning reserve before initiating an AUTO transfer back to normal. Checking spinning reserve is only slightly less than medium complex.
Maybe Auto Transfer switches are available off-the-shelf that monitor spinning reserve, UF, UV, coordinate with other transfer switches that are ready to come back on line, calculate load and decide if there is sufficient spinning reserve to load-up - and if there isn't, then issue commands to start additional generator(s). I've seen a few systems that do that, all were custom built, programmed, non-trivial.
If there is box-stock stuff that does this, I'd be interested.
cf
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