Generator / UPS Trouble

Status
Not open for further replies.
T

teslagood

Member
Hello All,

I know a lot of smart people visit this site so I'm gonna pitch this one out there hoping to solicite some help...

Some history -
I am working on a power upgrade for a communication facility which has been piece mealed by God only knows who over the years which involves replacing an 800A generator ATS ( existing mounted outdoors in a NEMA 1 enclosure with extensive water damage ) as well as adding a new 800A main distribution panel. We are also replacing two small -48 vdc power plants with a 1000A plant. There are two 200KW diesel gensets to provide emergency power that are connected in a redundant configuration, not connected in parallel, as well as a 60KVA three phase UPS system for the AC loads.

This has to be accomplished with zero downtime.

To the present -

We tested and had to replace the UPS battery string prior to the transition-

We have replaced the DC plant and swung all DC loads - 500 amps worth without any issues and have decommissioned the old plants.

Replaced the damaged generator ATS, reconfig'd both generator ATS's to operate in a redundant fashion, & installed the new main distribution panel.

Now my issue -

During the transition we had to run on generator power for approx. 30 hours.
I noticed during the transition that on one genset (the newer one - an Onan diesel) that every time an air handler came online the UPS would cycle to battery. The HVAC units are not on the UPS but are connected to the generator. This only occurs with the newer Onan genset. The old Onan genset ( around 15 years ) it doesn't occur. Both generators have electronic govenors and are not undersized for the loads and should have no issues with the inrush of the HVAC compressors.

I connected a Fluke 43B during the transition and didn't see any abnomalies
(I don't have a 3P PQA)

We increased the generator output frequency to 60.1-61.0 Hz and noticed the problem seemed to decrease but the power factor went to *&^%

The generator maintenance company checked the generator and found no problem. I spoke with the UPS company FE who said we should all meet, put facility load on the system and make some adjustments ( coordination ) between systems.

Any suggestions / similar experience would be appreciated.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
How many HVAC units?
Do all the HVAC units hit the line at one time?

If there is more than one HVAC unit you could install time delays to minimize multiple start up.

Are you saying you saw no voltage or frequency deviation during this UPS to battery issue?
 
N

nakulak

Senior Member
no monitoring software for the ats/gensets ?

ups doesn't have monitoring/logging software ? (didn't tell you it was low voltage event /low freq/ whatever?)

can't imagine its not a pq issue, you need to run through the event with a pqa and rub the manufacturer's nose in it so they will diagnose the unit and repair/adjust it as warranty item.
 
T

teslagood

Member
There are eight five ton units on lead / lag controllers. Installed cooling capacity exceeds operating requirements for redundancy.

I didn't see multiple start ups at one time.

This is an old Best Power Unity 360 (since Powerware, then Eaton)
No monitoring software at this time, trying to get the manufacturer (the folks who purchased them) to send me instructions on how to pull info off the front panel display as well as a quote for a network card to pull SNMP traps.

The only thing suspect on the monitoring was a slight dip in frequency when a HVAC unit started up - down to about 59.5 minimum.

Apparently this was enough to cause the UPS to go to battery.

It creates a vicious demand on the generator, UPS going to and from battery as well as multiple HVAC units cycling on and off.

My biggest concern is if the site had to operate for an extended time the on/ off cycling of the UPS battery string might not allow for adequate charge time betwen events whch would lead to an outage for the UPS protected equipment.
 
chaterpilar

chaterpilar

Senior Member
Location
Saudi Arabia
Just my two cents....

a) UPS goes to bypass mode when it sees a change in generator frequency,..and obviously the change in frequency occurs due to the sudden load (inrush) on the generator.

b) I suggest changing the Bypass settings ( span) in UPS from 57 hz- 63 hz.

c) Check the droop setting in Electronic governor of new generator ( Make it zero) i.e isochronous.

If this does not help use softstarters to start the HVAC units.

cheers.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
It is the BEST UPS, I cannot tell you why, but Best UPS systems in the 12-50 KVA range have this issue. Well at least 3 of them I have worked on for abnormal operation on generator.

I have worked with Best field techs opening up the frequency window and voltage window, still the unit would not operate properly on generator, we tried quite a few fixes with no avail. The PQA basically showed nothing out of the ordinary, I subbed to an electrical engineer that was with the utility doing PQ he had gone out on his own. In the end the two of us the gen techs and the UPS tech scratched our heads. We could not figure out how or why. Because of the age of the one of the UPS's the end user finally replaced the unit and no issues.
 
Status
Not open for further replies.
Top