Generac and frequency control

There are a few other posts about this but I'm going to chime in
also.
We just installed a Generac 16KW generator at our office to supply our
server room, network backbone, phone system, and supporting air
conditioning. First test after installation showed that every APC UPS
would NOT accept the power from the generator... this is pretty much
all of the gear that we are trying to protect. Frequency checks on
the generator indicate that it's low... around 57 to 58 Hz (no means
to adjust it). Called Generac and was told this is a known issue and
that this generator won't maintain 60 Hz until it's loaded to the
upper end of it's capacity (we're currently running about 55% load).
I'm pretty surprised that Generac is selling a product like this and
apparently it's only an issue in their V-twin engine models. I've
worked in the electrical generation/distribution field and I've never
heard of anything like this before. Even my cheap house and camper
generators maintain frequency throughout their load range.
One additional note on the UPS units. We noticed that the Tripp Lites
do accept the power because their frequency tolerance is twice that of
the APC line. Also, the larger rack mount APCs do have a sensitivity
adjustment which, when adjusted fully, will accept the low freq
power. End result is that we're looking at replacing all our smaller
UPS units or working in additional load to the generator.
Reply to
Nate
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Just a comment about the UPSes. If you're going to undertake replacement, see if you can move the UPS boxes _outside_ the air conditioned server room area.
Reason: They typically add another 10 percent (very rough figure...) in electrical demand due to their inefficiencies. So a 2 kw load becomes a 2.2 one, adding to the heat in the room, and thus the needed air conditioning.
(They'll pull X amount weather loaded or not, and then a small percentage of the throughput that'll vary with the load).
Reply to
danny burstein
That's one of the risks you take when trying to cheap out and use a consumer line home backup generator in a commercial setting. Purchase the correct commercial rated generator from Generac (or Kohler, or Onan, or Cat or Detroit, etc.) which will have a "real" governor and you won't have any problems. Bottom line - select the correct product for the application.
Pete C.
Reply to
Pete C.
Additionally, you should also be using commercial grade UPSes which have adjustable set points. The frequency set points should be set for the 45-65 Hz range which pretty much anything you have there should be rated to accept.
Pete C.
Reply to
Pete C.
Well, that's just a "feature" than cuts back power when there isn't much load. Most generators that size have that "feature." The idea is to save fuel while keeping the generator ready to take on full load.
Basically, you buy a generator without this "feature."
There are cheap generators and expensive generators. A 16 KW would be at the high end of "home" generators because it's big enough to handle most heat pumps (with the strip heaters disconnected), the water heater, the stove, etc. without excessive "power management."
Well, for some applications, this "power down" feature is useful.
It's not whether it's "commercial" but whether it can handle the job.
Reply to
<nni/gilmer
Maybe you should have HIRED, a competant Electrical Engineer to design you System in the "First Place". Looks like you got what you paid for. Cheap Junk.......
Reply to
You
The "Generac 16KW" should be enough to narrow it down to the Generac residential automatic backup generators as seen at Depot / Lowe's and similar. The Generac commercial grade line starts at 18KW and goes rapidly up from there.
Agree it doesn't make sense and is contrary to any basic mechanical governor generator I've dealt with.
The governor could be adjusted, but that's not where the problem lies as 57 Hz is perfectly acceptable to any piece of server, network, phone or A/C equipment built in the last couple decades.
Right, the commercial / industrial generators have the "Isochronous Electronic Governors".
Close, the problem is in both the UPS and generator selection. They're trying to support a commercial operation with consumer components, both a consumer residential generator and mostly consumer UPSes as well.
Given the wide input voltage and frequency tolerance of most every server, network and phone product of any recent vintage, the first step is to get the UPS set points adjusted to more reasonable limits, replacing the little consumer UPSes with no adjustability. Next on the list after getting the UPS issue under control is to test and see just how far out of spec things go when the A/C compressor(s) switch on and off.
The OP indicated they're loading the generator to about 55% load, but without a breakdown of how much of that is the constant load from the electronics vs. the variable load from the A/C and if they just used the listed running load of the A/C or if they accounted for the starting load, we don't know how undersized the generator is.
Reply to
Pete C.
Probably, but then I'm not going to go looking and guessing just to give free advice.
Umm, seems to me Google started out with "consumer" equipment. The equipment's tagging ("consumer" or otherwise) has nothing to do with the problem. Since I presume that this guy doesn't want to change out all his UPSs or change the generator and is looking for a low cost solution, I point at the problematic UPSs.
The lowest cost solution is simply to adjust the governor such that the frequency spread of the generator falls within the acceptance range of the UPSs. As you note, not much else other than line-operated clocks give much of a damn about frequency.
At the same time I would be trimming the generator frequency I'd be looking at the offending UPS to figure out how to broaden its acceptance range. There may be an internal pot or DIP switches or something else that sets the range. I'd spend a little time figuring that out before I'd start spending money to change out equipment. If I were incapable of figuring that out then I'd spend a little money on a technician who could before I spent a LOT of money on equipment changeouts.
BTW, it doesn't take electronics to make a full PID governor. Woodward, among others, has made a full PID self-contained hydraulic/mechanical governor for decades. Rare to find one on a generator below about 100KVA.
John -- John De Armond See my website for my current email address
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Reply to
Neon John
The governor is electronic and, as stated in the original post, Generac admits it's a known issue with this governor and the V-twin engine. I spent half my career in power generation, have operated large scale turbine generators, motor generators, and have been to Fort Collins CO for Woodward governor training. You really should stop talking down to people who you know nothing about (your previous posts).
Several points here. Not sure why you keep assuming all the APCs are consumer grade but you don't seem to pay attention much. As stated in the OP, several of these are rack mount units (several thousand dollars each). FYI, even the smaller ones are several hundred dollar units that are on small loads such as firewalls, switches, routers, etc. None of the APCs tolerated this frequency. The APC rep knew immediately what the issue was and, by default, pretty much all APCs are set for a 5% (3Hz) tolerance. Again, as stated in the OP, you can adjust these beyond that. Also, how in the world is the generator undersized? If you'd read the OP, it's well oversized. It's running 55% load and we may have to ADD load per Generac to get the frequency where it needs to be.
Danny thanks for your respectful and attempted helpful input. The rest of you guys, the problem IS the generator (the manufacturer admits it for crying out loud) and it was installed by a licensed electrician who has installed many small gen sets.
I'm not going to respond further to some of the ridiculous crap that I know will follow but please feel free to continue putting forth incorrect conclusions based on assumptions that are coming from who knows where.
FYI, there's not a single question in the OP... it was just a warning to anyone who was thinking about purchasing one of these.
Pete, get a life. You spend way too much time on Usenet.
Later.
Reply to
Nate
Switch that Generac out for a better make. It will be a problem from here on. If my generator wouldn't maintain 60Hz, I would make the vendor eat the cost. What is more basic than accurate power?
Reply to
Long Ranger
a bit more
generators if
Nate - Thanks for the warning.
My first thought when I saw the original post was "?I wonder if that's an electronic governor unit?"
I'm a bit surprised that you feel that the 57-58hz to be a generator problem.
I thought perhaps the generator drops below 57hz momentarily when something like an AC unit kicks in. But your description sounds like the all the APC units fail to accept the Generator feed even under steady 55% load.
At the Generac site, This 16kw model
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a spec sheet
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the CONTROLS tab shows 60hz +- 5%.
If you really are getting 57-58hz, why don't you feel it is an APC problem? I suppose alternatively, APC might say it was a problem in choosing a generator with too wide a tolerance or too low initial set point.
If it were only one or two UPSs, I'd think it was a tolerance stack issue - but for all of them to not accept 57-58hz when the APCs say that they have a 5% tolerance, seems like they (APC) should accept some of the responsibility.
Is there any hope of Generac offering a mechanical governor option? Or retrofitting one? Or alternatively, obtaining an electronic module with a 62 hz set point?
I wonder if anyone makes a separate adjustable electronic governor controller.
Phil
Reply to
philkryder
It sounds like he has more than adequate capacity to deal with the 10% overload. And moving the AC load from the UPSs may just make it more difficult to deal with.
Reply to
philkryder
Interestingly, here is a spec sheet for an Onan commercial unit that shows a similar 5.0% variation in frequency.
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while this Kohler
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0.5%.
Reply to
philkryder
Well then, Nate, ole buddy, if you're the expert then why are you here asking for help? (True, you didn't explicitly say "help me" but one would presume you weren't just saying "look at me, what a dumbass mistake I made" with your post.) I wasn't talking down to you then but I sure am now. Frankly, you struck me as someone in WAY over his head but I decided to try to help nonetheless. After all, I've made a LOT of money following behind guys like you. Why not give some back?
BTW, I would be impressed with your apparent training and experience - if any had stuck.
If I may point out a few things. You did NOT mention in your original post that this generator has an electronic governor. In fact, you made no mention of a governor at all. As far as "Generac admitting..." I take that with a grain of salt until more information is given. Who at Generac? The dealer's parts changer? Some contract tech support dude at some call center who was sweeping floors last week?
Which brings up the next point. You STILL haven't bothered to tell us which generator you're dealing with. Presuming that it is this one:
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and downloading the 16KW manual, I see that the manual specifies the frequency range of this generator over its entire load range. Had you read this manual and read the APC manuals, that the two were incompatible out of the boxes would have been obvious.
I should point out that if your reported numbers are correct - "around 57 to 58 Hz" - then your unit is operating out of spec (reading the manual really does help).
You mentioned that your "RV generator" holds tighter frequency than this one. That indicated to me that you didn't have a clue, as the RV line of Generacs behave just like the corresponding non-inverter generators from Onan. NONE hold tight frequency control. I have a LOT of experience in that area. I also have a Generac QuietPack RV generator mounted on a cart sitting in my basement that I use for standby power. I've completely characterized that unit and tuned the governor as tightly as I can and it STILL sags with load, as one would expect for proportional-only control. With your training and experience (sic) you should know better.
Now that you're a self-proclaimed expert, I have to join others and ask what kind of expert bozo are you to specify a consumer-grade generator before confirming the compatibility of the generator and your loads. As I mentioned above, sufficient information to determine the incompatibility of the generator and APS boxes is in the literature. Confirming compatibility before buying hardware is pretty basic system engineering. Oh wait, I forgot. You're a tech. I have to agree with the others - your company should have hired a competent engineer to design this system.
I have no problem with the consumer-grade generator per se. A properly selected one would probably do the job. I have to say "probably" because at this point I have little idea what loads actually exist, given your amateurish and incomplete presentation. That selection process involved work that was obviously over your head and now your company is going to pay the price. I wonder how long it'll take your boss to figure out that you're flailing around trying to cover your ass?
Since you're the expert AND a smart-ass, I'm going to sit on my thumbs and let you wallow in the mess you made. After reading the manual (did you bother to do that?) the solution is fairly obvious but I'm going to keep that to myself - at least until someone is paying my fee.
John -- John De Armond See my website for my current email address
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Reply to
Neon John
This is not some sort of "econo throttle" feature, that is only found on small portable generators, not fixed standby ones, and the generators that do have it throttle down well below the few percent that 57Hz vs. 60Hz equates to.
As noted elsewhere, the commercial standby generators are quite a bit different from the residential standby generators, the change from a basic mechanical governor to an much more sophisticated one being a notable difference.
Pete C.
Reply to
Pete C.
I didn't say that the small variation in frequency was the cause of the problem. There will be a much larger variation in frequency seen when the OP's A/C kicks on which will be an additional problem. The residential standby generator he is using (as noted the Generac commercial start at 18k) won't hold frequency anywhere near as well as the commercial line which have superior governors.
Pete C.
Reply to
Pete C.
a bit more
The Generac residential standby generators don't even have a specification given for frequency regulation, so your 57Hz certainly falls within what can reasonably be expected of the unit.
If you spent half your career in power generation as you say, then you should know that you can't expect a rock solid 60Hz from a small consumer grade generator.
generators if
Every small APC unit I have ever seen is indeed consumer grade. Even some of their rack mount units are still consumer grade in a spiffy chassis (think Hummer2). APC does make commercial grade units, but from the information you have provided it's fairly apparent that the installation in question has grown in drips and drabs, with a bunch of little consumer grade UPSes instead of a couple large commercial grade units.
Price does not equal quality. As I noted, some of APCs rack mount units are still consumer grade in a spiffy case.
The very fact that you have all these separate small UPSes shows the necessity of a full facility review and upgrade.
Have you noticed that the 57Hz you indicate the generator supplying falls within this 5% / 3Hz tolerance?
Again, you haven't told us if that 55% load accounts for the starting draw from the A/C, and what proportion of that 55% load represents static load vs. dynamic. As for "getting the frequency where it needs to be", the 5% low you're getting is within reasonable expectations for such a generator and also appears to meet the published specifications for those generators since they don't appear to even have a claimed frequency regulation tolerance. They do specify +/- 2% voltage regulation implying that the lack of a frequency regulation rating isn't an oversight.
The problem is your expectation of the generator, not the generator. The manufacturer indicated the 5% low frequency is known on that unit, but given the lack of a stated frequency regulation tolerance, it is not a problem or a defect.
I guess you never looked at the manufacturers specifications for the generator or you would know where the claims are from.
People purchasing that generator for it's intended purpose - "Residential Standby" - are unlikely to have any issues. You are simply expecting your Chevy to perform like a Ferrari.
Yes, I do. It's one of the few things I can do while waiting impatiently for the corporate bureaucracy at work to grind through it's absurd overhead so that I can actually get some work done. It's no wonder this country is on the fast track down the tidy bowl swirl...
BTW, the UPSes and generators in our facilities are redundant, 480V 3ph and total in the MW range so I have some familiarity with the subject.
Pete C.
Reply to
Pete C.
I was wondering why no one else was saying this..... If it's new, and doesn't work properly, why haven't you gotten your money back and moved on?
Reply to
Jim
at a bit more
results in
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Tellico Plains, Occupied TN
John - If the Generac says 60 +-5% how is 57hz out of spec?
Reply to
philkryder
With the fully digital electronic governor, there is no reason that this particular line of residential generators couldn't hold the long term frequency tolerance to within a fraction of a cycle and transient tolerance to a cycle or two. Generac could have implemented a full PID governor, even included feedforward functionality if they desired. Whether they did remains to be seen.
I can say that the electronic governor on my Generac Impact RV inverter generator works fairly well. It doesn't need tight RPM control since it's variable speed. What impresses me is the good transient response. There is zero frequency shift and almost no voltage sag even when my RV's AC kicks on - representing a significant portion of the full load rating of the genny.
John -- John De Armond See my website for my current email address
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Reply to
Neon John

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