Generator vs UPS vs A/C

[dbuckley]

But after the A/C reaches its running amps the UPS still switches back and forth from normal to battery.

Next guess must be that the genset frequency is unstable, possibly with it being borderline low frequency for the UPS. Is this a mechanically governed genset? Does the genset sound like its running true or is it hunting?

The genset seems large for the load; 60KW@240 is about 300A, and the load is stated at 60A - if thats the case I'd rent a loadbank and get the genset up to 70%-ish load and see what happens then.

 

[ceb58]

Next guess must be that the genset frequency is unstable, possibly with it being borderline low frequency for the UPS. Is this a mechanically governed genset? Does the genset sound like its running true or is it hunting?

The genset seems large for the load; 60KW@240 is about 300A, and the load is stated at 60A - if thats the case I'd rent a loadbank and get the genset up to 70%-ish load and see what happens then.

There was a problem with the gen set fuel regulator (LP) but after replacing the same problem exists. The gen set has an electronic gov. Watching the gen set readings on the lap top and the sound of the engine (6.8L v10 ford) it is running smooth. Freq. staying 59.1 to 60.3, rpm running 1797-1802 volts are +/- 3 of 240v. The gen set seems large but there will be more radio equipment and another UPS installed in building later. The A/C units are 6ton and they can run at the same time.

 

[dbuckley]

Freq. staying 59.1 to 60.3

If thats a change in frequency over a fair period of time, then thats OK, if the frequency meter updates once a second and you're getting those sorts of variance of readings then I'd expect the UPS to be upset. The UPS inverter has to phase lock to the input waveform, and phase lock means "exactly in step". If the frequency varies from say 59.9 to 60.1 in a second, thats a fair rate of frequency change, and may be outside of what the UPS is willing to track.

So I'd suggest contacting the UPS manufacturer, and finding out what rate of change of supply frequency is acceptable.

I still think that loading the generator hard with a loadbank will improve matters.

Otherwise, you're rapidly running out of places to go.

 

[ceb58]

If thats a change in frequency over a fair period of time, then thats OK, if the frequency meter updates once a second and you're getting those sorts of variance of readings then I'd expect the UPS to be upset. The UPS inverter has to phase lock to the input waveform, and phase lock means "exactly in step". If the frequency varies from say 59.9 to 60.1 in a second, thats a fair rate of frequency change, and may be outside of what the UPS is willing to track.

So I'd suggest contacting the UPS manufacturer, and finding out what rate of change of supply frequency is acceptable.

I still think that loading the generator hard with a loadbank will improve matters.

Otherwise, you're rapidly running out of places to go.

The freq. is changing slowly nothing rapid. The parameters of the UPS have been expanded to compensate for "dirty" power. I think as you we need to load the gen. and see what happens. But I personally think we will find the problem in the UPS. It's just now trying to get the boss from having tunnel vision about the gen. set having a problem. If we do load the gen. set and it clears up it is still not the gen. fault that it was over sized and there is no real load on the building. My boss still swears the 12kw UPS will pull 12kw worth of power even though it only has a 4kw load on it

 

[dbuckley]

It's just now trying to get the boss from having tunnel vision about the gen. set having a problem. If we do load the gen. set and it clears up it is still not the gen. fault that it was over sized and there is no real load on the building.

This is a compatibility issue; there is no "fault", just things that don't work together. It happens, and its always a right royal pain in the arse, as everyone really wants a finger to be pointed, someone to take responsibility, but the vendors are all pointing at something that isn't theirs.

Changing either the genset or the UPS may fix the problem.

My boss still swears the 12kw UPS will pull 12kw worth of power even though it only has a 4kw load on it

He is indeed

Ask him where the other 8KW is going.........