Unexpected frequency residential standby generator 1

[Rectified]

The installation is a new 22kW Generac natural gas-powered standby generator in the U.S. At initial startup, with no load connected, the frequency readout is both abnormal and unstable, rising to about 419 Hz. I get the same reading at the automatic transfer switch and the generator (with the output conductors disconnected). By its sound, the engine speed is stable and seems normal, and the voltage is normal and stable. Also note that the engine runs continuously with this condition -- no over-frequency shutdown. Could there be distortion, such as might be encountered on a variable speed motor drive, causing a false reading on my DMM?

The meter is a Klein CL700 digital multimeter, with only one auto-ranging frequency setting. I used it to test the utility and a portable generator (inverter type). Both came in stable at almost dead-on 60.00 Hz. I have not connected a load to the generator, because manufacturer instructions forbid doing so if the measured frequency is not normal. The labels claim the unit was tested at the factory. The factory tech support had never heard of such a problem.

 

[davidbeach]

That unit, at 60Hz, either runs at 1800 or 3600 rpm. 419Hz would be either 12570 or 25140 rpm. I kinda doubt that. Check your numbers and your measurements. Pretty sure you didn't get 419Hz.

 

[waross]

Get another meter.
Your frequency meter is picking up harmonics, probably more than one.
That is a common issue when attempting to measure the frequency of a small generator with a frequency meter more suited to RF frequencies.
I have seen the same issues measuring the frequency of a properly running generator with a DMM.
That is, an unstable and very high reading.
Typical no-load frequency of a standby generator is 61.8 Hz, dropping to 60 Hz at full load.
If you can find a very old electric clock driven by a small synchronous motor that makes an excellent frequency meter.
With no load on the generator the clock should indicate about 62 seconds (61.8 seconds) every minute measured by an accurate time piece.


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

 

[thermionic1]

Klein CL700, like you got it in the electrical section at Home Depot? I second the notion to use a different meter. See if you can get your hands on something like a Fluke 87, 117, 289 something a little better. What is the voltage at the point you are measuring this 419Hz? The only thing in that range could be some kind of Aerospace AC Power Generator, which operates at 400Hz. 22kW is not an insignificant amount of power. DO you have something like a large electric heater that you could connect to place some load on the generator while making a measurement?

 

[Rectified]

Thank you for these responses, which confirmed my suspicions about the DMM. (Yes, I did get it from the electrical section at Home Depot! Had to replace my old one when my truck got stolen awhile back.) I will try a different tack, and if I will be working with a lot more of these generators, think I'll pop for an 87. Love the clock idea. BTW, absolutely nobody else I contacted could answer the question -- certainly not the factory techs themselves. UPDATE: Adding loads didn't really do trick. I plugged in the equivalent of 4 portable space heaters, about 5500W total. The frequency reading changed as I added loads, but in both directions, and it never settled down near 60 Hz. Looking for a clock.

 

[waross]

Forget the meter.
The only time I have seen a factory set with the wrong frequency was when the owner of a new set asked his mechanic to check it out.
Of course the mechanic knew more than the factory and set the frequency wrong.
I have had multi meters give the same off the wall readings connected to the grid.
And don't forget;
The frequency will only be 60 Hz at full load.
No load frequency will be 61.8 Hz.

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

 

[Rectified]

Thank you for your help, which led to the completion of the job. In the end, I used a resonant reed type of meter that a friend had stashed in his curio pile, and it was perfect. As suspected, there was no problem with the generator frequency at all, only difficulty reading it with my DMM. It was suggested that the frequency test was uncalled for with a brand new generator, and I agree. Never been called for before. Seems like Generac's lawyers got squeamish, and are now insisting we verify the frequency. Perhaps this would give them an out if there is a problem and I DON'T run the test. Whatever. I now have a 60 Hz analog meter at my disposal that will serve the purpose that my DMM could not handle.

 

[catserveng]

So the larger Guardian series home generators, and most of the large "business" class of standby's have electronic governors and AVR's, here is a data sheet,

https://www.generac.com/generaccorp...6kw-7036/guardian-series-spec-sheet-16-22.pdf

I have not done any work on the residential models, however earlier this year I got a number of calls for midsize Generac standby's with instability and voltage variations. Supposedly these units with the "True Power" technology are supposed to provide 1% voltage regulation and no more than 5% THD, we found problems with a number of units that Generac came out and "fixed". No explanation, but likely since they are using some new controllers I suspect they had either hardware or firmware/programming issues.

Possibly the call to "check frequency" is to make sure these problems are not occuring across the board. If your inexpensive meter is getting flaky Hz readings, it may that the voltage sine wave is not clean, and possibly not producing less than 5% THD.

I have the luxury of having a scope and a three phase power analyzer on my truck all the time, you may want to take a closer look, unless you feel it is supporting the installed loads just fine and leave it at that.

Hope that helps, MikeL

 

[waross]

Hi Mike. Is 3% droop still standard on standby sets?
That Generac blurb doesn't say much.
Electronic Governor covers almost anything except a centrifugal mechanical governor.
No mention of UFRO either.
Holding 1% voltage regulation when the frequency is dropping is not a good thing.

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

 

[catserveng]

Bill,

I rarely see droop on a governor on just about any size unit I see anymore, and I see a lot of different units in the course of the year. Not so much below 500kW. Some systems, such as a military vessel or critical manned facility, may have the ability to go into droop mode during manual operation, but frankly the ability of the current real and reactive power sharing controls are very robust and reliable, and doesn't require much in the way of operator training. Once in a while I'll get around a "small" utility set that is still in droop, but those sites have full time operation staffs. I don't much work on units above 20MW.

If it is still using a mechanical governor then of course it will have some droop depending on the flyweights and speeder spring, but the cost of small electronic governors has gotten so low, plus that fact that most users don't understand or want speed droop, that it is getting rare to see mechanical or pneumatic governors in most of the units I get around.

On the Generac AVR's for smaller units I'm not sure if V/Hz (UFRO) is still an option, likely it is a fixed parameter but haven't actually tested any of the small guys. On their larger units you can adjust the V/Hz slope and knee frequency, as well as percent regulation and droop percentage.

MikeL.

 

[waross]

If there is a 50Hz/60Hz jumper there is probably UFRO.
I have been away from new generators for a few years now.
The first electronic governors that I saw used droop to facilitate parallel operation.
61.8 Hz at no load was the tip-off.
(Speed droop, not voltage droop)

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

 

[catserveng]

Bill,

That may not even be a good tell anymore, more and more AVR's out there today, even in smaller units are digital. The jumper has been replaced with a digital switch you enable or disable in the software. Some AVR's use the global rated settings to set a lot of parameters on everything else.

Now several engine/generator manufacturers are going to "field control modules" and the actually controlling is done by the generator control panel.

Not much use for the old "pot tweaker" on a lot of newer units these days.

MikeL

 

[waross]

Thanks Mike.

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

 

[Rectified]

Lots of great hands-on field experience being relayed here. I am not an engineer, just an electrical contractor slightly out of my element (which is why I came here looking for answers). Over 40+ years, in this rural area of Northern California, I have installed quite a few residential standby generator systems, but have tried to work in conjunction with reputable dealers with factory trained techs. Now, with the spikes in numbers of fires and rolling blackouts, generators are being marketed like TV sets to consumers, and electricians -- who have no clue that a "calibrated" DMM is even a thing -- are becoming defacto dealers/installers/techs. Really, I'm just trying to keep people's wells running without blowing up their computers, but this knowledge gap has developed.

In the process, I have become a lot more informed about the field of power generation, and the tools available. Thanks for not only the practical tips, but for helping me understand (or look up) terms I didn't before: droop, AVR, UFRO, resonant reed frequency meter, etc. My job, I have learned, is not to know everything, but when, and how, to get help to get the job done right. Much appreciated.

 

[crshears]

Not that I added to the thread, but I'm in much the same boat, Rectified; I'm not an engineer either, but I've been operating generating stations of various vintages and types, as well as transmission and distribution systems and their ancillaries for 40+ years, and have found this site in general and many of its contributors in particular to have been an information source of practically incalculable value.

I've learned over the years that sometimes the most primitive technologies have proven to be the most immune to things like power system harmonics and other altered wave forms; being one-trick ponies, they simply ignore all that other chaff. By way of example, mechanical governor systems [ at least in my view ], if well maintained and properly calibrated, will outperform those with electronic/digital components, and also seem to be much more robust and able to tolerate a great deal more abuse. Similarly, magnetic amplifier technology, although not as flexible and readily modifiable [sp?]; unfortunately, both of these not only seem to have fallen out of favour, but the knowledge of how to design, build, install, commission, calibrate and operate them is rapidly being or has already been lost...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

I miss the old Ward Leonard drives and the various applications of Amplidynes.
I was in on the commissioning of one of the first electronic replacements for Amplidynes.
It used hockey-puck SCRs in place of the Amplidyne.
Our factory wizz went through more hockey-pucks than the NHL playoffs.

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

 

[FreddyNurk]

Happy to defer to catserveng's experience, but a lot more manufacturers are providing electronic engines these days, which removes all chance of mechanical governing.
I'd imagine that it would also relate to not running stand alone sets in droop either, as there's no real means or reason to configure them for speed droop in that case. Of course, it can be done with an external controller, but its the controller that allows the droop, not the engine.

Certainly from the sites I used to be involved with, all engines for generation sites above 100kW were electronic injection and control. The rest of the sets all had electronic actuators and governors, admittedly analog rather than digital, and they were very reliable.

The big downfall with electronic stuff is diagnosis when it all goes wrong, I had a Caterpillar (Perkins) set that threw a fan belt once, and the remnants of the fan belt managed to take out the engine's speed reference. Engine diagnostic tools were non-existent in Australia, and it was only by chance that the fitter who changed the fan belt found it. Would have been obvious in 5 seconds if we had the gear.

EDMS Australia

 

[waross]

Generator governors have developed from industrial instrumentation.
Electronic instrumentation was coming in back in the 60s and 70s. (I think, you know what they say about the 60s. grin)
Different names for the same functions.
Gain or proportional band is called droop on a governor.
3% droop is 3% proportional band plus 3% offset in instrumentation jargon.
Reset or integral on a PID controller is called isochronous on a generator governor.
Pre-act or derivative on a PID controller is not used on governors.
The dynamics of an engine speed control system do benefit from derivative control.

You can add a tach-generator that is configured for a 4-20 ma output to an engine and send the signal to an off the shelf electronic PID controller. The PID controller may sent a signal to a fuel valve or actuator to control the speed of the engine.
Nothing new here.
Basic instrumentation and control theory teaches us that it is extremely difficult to control a system without some proportional band or droop.
How about reset, integral or isochronous control? (different names for the same function)
The controller responds to any change in load, positive or negative with droop.
The integral or isochronous section detects the error resulting from the droop action and biases the setpoint to eliminate the error.
Isochronous gives a steady frequency only with a steady load.
Any change of load results in a droop response that is then corrected back to the desired frequency.
Given the history of instrumentation and control over the last 50 years, I have a hard time believing that the new electronic governors no longer use droop for stable control.
Do you have any links to accurate information on electronic governors, Mike?



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

 

[FreddyNurk]

In terms of the terminology outlined, you're correct waross, they would still use both proportional and reset on electronic engines. When I stated that they don't run speed droop, the units I've seen are isoch with an external interface for whatever purpose.

To put it another way, the units obviously have internal control loops, but the sets I'm used to seeing all sit at 50Hz at no load, including the odd larger standby unit.

EDMS Australia