Marc2lastnames
The company I work for just picked up the service contract for all of the local fire department generators-lots of deferred maintenance- I was sent out on a troublecall generator not starting during power outage. The unit is a Generac 75KW 3 phase unit. The incoming power is 120/240 with a stinger. When I got there I started the unit in manual, fired up no problem, so I started to measure the voltage at the unit it was set at 212VAC but the hertz read 180.18. Though my meter had died so went down to the ATS to read the utility power, that read 245 @ 60.01htz. Went back up to the unit was able to adjust the voltage up to 245 but the hertz stayed at 180. The unit is running at 1800RPM and everything else seems fine. Where do I start to narrow down the problem so it can be fixed?
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Skip Douglas SkipD
What sort of meter are you using that shows the 180 Hz? There are many multimeters that will not read the frequency from generators very well because of the "noise" on the output waveform from most generators that have voltage control electronics.

In order to actually be producing 180 Hz power, the generator's engine would have to be running three times the normal RPM.
Skip Douglas
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douglas123
I have seen this scanario on several occasions. Crappy sine wave from gen end. Even my Fluke 179 meter sees this on occasion. If you were reading phase to phase this is where I see the erratic HZ reading. Try reading phase to neutral or possibly phase to ground. If they will let you put the genset online take a reading with the generator with some load on it. Tell me about deferred maintenence. City is broke,county is broke, taxes are going up, maintenace is overlooked and forgotten until the unit is called into service and does not work. Go figure. Is the generator wired for 120/240 Delta? curious as to why the voltage was low. What is your phase to neutral reading now at the generator? If your are in fact running Delta configuration make sure your STINGER legs at the transfer switch are on the same phase. Just thought generator might be wired 120/208 LOW WYE.
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Marc2lastnames
let's see, my meter is a Fluke 867B GMM have since used it on 3 other generators. On the maintenance issue the old contract lapsed about 6 years ago so only the firemen have been looking after the units which means topping of fluids and weekly exercise, no inspections or servicing. I got the 180htz reading both phase to phase and phase to ground lug on unit. Both incoming and the genset are Delta with stinger on C leg. Don't know why the voltage was so low could have been that way from the install or drifted over the 6 year no maintenance period. Still waiting for approval to install a temporary generator to make sure they don't lose the dispatch computers. Thought I would take a suitcase loadbank to do some testing
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Skip Douglas SkipD
Marc2lastnames;11282 wrote:
let's see, my meter is a Fluke 867B GMM have since used it on 3 other generators.
I looked up that meter on the web, and I saw that it has Selectable True-rms or Average Sensing. You really need true RMS readings to be able to read the frequency of a generator. This is because of the fact that the output is probably not a clean sine wave. Check pages 1-12 and 2-2 in the user's manual for the meter for how to switch the selection.

Can you use that meter as an oscilloscope and see a calibrated TIME scale along the horizontal axis? That would prove what the frequency really is. If the meter cannot substitute for a real oscilloscope, then get an oscilloscope to verify the truth.

My old Fluke 8060A meters do a great job of reading the frequency of generator outputs.

You could also use a tachometer to measure engine RPM, of course. 1800 RPM should be measured when the power frequency is 60 Hz. The engine would have to be running at 5400 RPM to produce 180 Hz power.
Skip Douglas
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bucdup
I will generally use a Hertz Splitter in a case like this. You can get them on e-bay.
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Skip Douglas SkipD
bucdup;11301 wrote:
I will generally use a Hertz Splitter in a case like this. You can get them on e-bay.
Do you know what you get if you Google the term Hertz Splitter? It's a log splitter rented out by Hertz.

I do hope your post was a joke. :confused:
Skip Douglas
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bucdup
SkipD;11304 wrote:
Do you know what you get if you Google the term Hertz Splitter? It's a log splitter rented out by Hertz.

I do hope your post was a joke. :confused:


Who me joke? I am 100% serious all the time.

Now, did you Google Hertz splitter just to see what would come up? Or to see if this miracle product actually exists? :cool:
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Marc2lastnames
When I use the meter I always have it set on RMS. I think I can use it as an oscilloscope have to look through the manual and get back to the station to take some more measurements.
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