Stby Generator Frequency Not Matching RPM

I'm sorry, you say the frequency increases with no engine speed increase?

Not possible in my mind, but I'd love to see a rational explanation from another member if it is possible.

I suspect he's picking up superimposed noise from the load. If he's using a digital frequency meter, it may be sensitive enough to pick up backfeed from the switched power supplies in the broadcast equipment. Another possibility source is the refresh frequency of the video equipment.

The engine speed would not increase because the power frequency (50 or 60 Hz) is essentially a carrier for the higher frequency low power signals. The generator is a pretty good indicator of the power frequency and it would be completely insensitive to any signal too weak to force an RPM change.

"My company installed a small stby generator...."

What does the manufacturer have to say?

Was it recently installed?

The company's tech support staff should be able to help you out.

Thanks for the replies.

I personally never observed the Frequency increase. The two meters it was observed on were a Fluke DMM and the analog panelmeter.

"I" understand the relationship between the physical nature of the generator and the frequency and was leaning to some kind of "noise" being inducted onto the power which the meters were "picking up".

The most common consensus the electricians here were thinking is the neutral of the stby generator not being switched and the "power" from the utility "bucking" the generator on the neutral. Of course to which I don't agree and why I posted the question to people more knowledgeable than myself.

Anyway.....

Check your neutral-to-ground filter network. Most likely your transmitter and house power supply are coupled to the same ground through a capacitor in series with a current limiting resistor. What you are seeing is the unwanted transmission wave noise being filtered off the signal then being reflected additively back through the common ground. Look at it with an oscilliscope and you should be able to separate the waveforms by changing your sampling time and/or frequency range. You may have to use both channels in order to differentiate the signals from each other. The Fluke DMM uses an internal "recirculating remainder" calculation circuit prior to display which sums whatever signals the probes sample into the digital output screen for viewing. The sensitivity is so high the meter cannot/will not screen the low level signal noise and will instead totalize the sensed value. Much like a carrier wave used for "scrambling" military communications.

Hope this helps,

Jim

"i am not so sure that what you heard is what I thought I meant."

Easy answer.. remove the gen set, and run it up well away from the tower and see what results you get!

They did that. They put it on a load bank before the original install 1 yr ago and then at the beginning of this week. Works fine and steady until transferred to the tower.

I think your load consists of "Power Electronics". Switching power supplies, Rectifiers, Thyristors, etc. In that case "Voltage & current Harmonics" may be very high. Measure power harmonics with Fluke 41 or Fluke 434; It is possible to install Harmonic filters and get rid of your problems.

Hang an O'scope on it and see what's going on.

Other replies are good: check the output with an oscilloscope; remove the generator from the tower and see how it operates under another load; use an mechanical reed type frequency meter (Good Olde Days instrument) affixed to the motor frame to detect the real frequency; the solid-state meters are suseptible to trash generated by switching power supplies, etc. Ain't no way in Hades the frequency will increase with increased load. If this is the case, you have breached the Laws of Physics and may have discovered something patentable.

Regards/Jim

I understand. That's pretty much what I've been saying to them all along. The freq CAN'T change without RPM change. So that only leaves something from the tower. So their only answer is the neutral buss not being switched.

Is it possible that the RPM meter is not sensitive enough to pick the increase in speed?

We are all working on the frequency meter but the RPM meter could be the one that is lying.

You didn't say how much the frequency increase.

Like 75 to 80 Hz. The RPM was checked with a handheld also. It's an 1800RPM genset.

That is a lot of frequency variation. You would have at least heard it in the RPM.

Back to the noise on the frequency meter.

Here is another item to look at. Balance.

Your load bank is, ideally, perfectly balanced between the phases. When you swap over to your critical load it may not be "perfectly" balanced. Harmonics will affect the feedback to the mains, in this case, your generators. On the small scale of your genset the feedback affects power transmission.

Load measurement and resultant panel balancing may help your situation. It may be a long road but worth it in the end.

Would the harmonics have more effect on a single phase genset. I have worked on many offshore vessels with 3-phase, both 208wye and 480, and balance has never been perfect and nothing like this has ever come up before.

But we never had HIGH power radio tower on boats. LOL

Thanks again.

We run twin 500kW units for about 600kVA of load. When switching between the load bank and powering the load the output frequency increases to 60.1 Hz from a fairly stable 60 (yesterday it was ~59.955).

Our load is not perfectly balanced, but I do my best. We normally run about .96 PF inside and 1.00 outside the UPS.

There is no balancing of the load for single phase.

You must be having some feedback from all the electronics or the transmission tower, affecting the readings on your meters.

Since they are arguing about switching the neutral, eliminate the doubt and switch the neutral from the mains supply and see if this is going to solve the reading problem (which I doubt). More importantly make sure that the Neutral is grounded properly at the generator panel.

Connect a 3 phase motor with a stamped rpm of ~1800 (nominal) or ~3600 (Nominal) for 60Hz and check their rpm on no-load: 80Hz will pull them to ~2400 and 4800 rpm which are significantly higher and easy to verify (the actual rpm of the motor will be stamped < than 1800 and < than 3600 ).

I am sure, if the readings are interferences, the motor will run as if at 60Hz. the increase being seen will prove parazitic only.

Also, the Genset Governor will keep it at ~60Hz, IF the MAINS supply is going to pull (Buck or BOOSt) the frequency, the Genset will show a speed increase!!!! I don't think that the rpm of the genset has increased in your case (?!).