UPS shutting down during generator test

[alan mcneil]

I am an electrician at a very large facility with multiple buildings and emergency generators for each building.
Recently we have had reports that the ups systems have been shutting down during generator test days in one particular building.
We have the same generators with the same computerized equipment in other building at this facility and they have no problem with the ups.
At this point in time I have no particular information about this problem.
I am going to start trouble shooting, any idea's, insights or past experiences with similar problems would be helpful to me before I begin my troubleshooting.

 

[tom baker]

Re: UPS shutting down during generator test

The ups and the generator are not getting along.
What I would start with is to find out if the UPS has monitoring software you can run on a laptop. check the configuration and then run the generator, see why the UPS is shutting down.

 

[catchtwentytwo]

Re: UPS shutting down during generator test

A few questions to ask:

1. What is being done for the generator test, is it a utility failure test?

2. What size and brand of UPS? Static or rotary?

3. Is there any interlocking between the generators and the UPS system? Usually there is.

4. Did this just start happening after the system worked "correctly" for a while? If it did, what has recently changed? Did the load increase?

5. Was the building/system commission tested? Is there any start-up documentation from the UPS manufacturer?

[ September 13, 2005, 08:44 PM: Message edited by: catchtwentytwo ]

 

[ron]

Re: UPS shutting down during generator test

Do you get the same results if the UPS is lightly loaded or heavily loaded?
Tell us the sizes in kW of the UPS' and Gens

 

[dereckbc]

Re: UPS shutting down during generator test

Very common problem, and most often very expensive to correct and is a result from a lack of engineering design as Ron has eluded too with his questions. In order to work together you need to have at least two of the following design criteria, preferable all 3

1.The generator to UPS KW ratio should be 2-to-1.
2. The UPS should have a rectifier walk-in capability or soft start capabilities.
3. The generator and UPS need to have the capability to talk to each other.

 

[hurk27]

Re: UPS shutting down during generator test

If this just started happening check the battery's you might have a bad one and does not show up until loaded.

 

[charlie tuna]

Re: UPS shutting down during generator test

alan,
if you have a ups -- you must have some important equipment for it to supply! and i am assuming this generator is designated for this equipment also. usually, a ups unit will accept trashy power without too much of a problem. from your question there must be some portion of the electrical power (voltage-frequency-rotation-grounding) different between the power company's power and the generator's power. this is easy to find --------- if you have a data logger!! or even better -- two data loggers. if you do not have them i would suggest hiring a contractor who has them, to set them up and give you the readings to interpet.

 

[petersonra]

Re: UPS shutting down during generator test

I note you used the phrase "ups systems" implying to me that there are more than one systems doing whatever it is you are seeing.

It is not uncommon for small UPS systems to go to battery power if it does not like the incoming power. they are designed that way. some of them will not charge while on battery power, even if there is power coming in, if it has decided the incoming power is not "good".

Larger UPS systems are usually more sophisticated, and can deal with these type of problems better.

 

[catchtwentytwo]

Re: UPS shutting down during generator test

Another thing you should check is what non-UPS loads are supplied by the generator(s) and in what order are they added to the bus when there's an outage (planned or not).

We had problems with centrifugal chillers being effected by harmonics created by a 6 module rotary-hybrid UPS system operating in inverter mode. There was an factory option for the chillers that fixed that interaction.

On another system, the UPS battery recharge current bogged down a generator that was marginally sized. The UPS tech used an recharge current limit feature activated when the generators were on line and carrying load.

I realize that these examples are not the same issue, but they point out the complexity of the interaction between generators and UPS systems. That's why it is good to know who did the start-up of the UPS system, hopefully they were factory authorized and left a paper trail. There's also a possibility that the UPS manufacturer has seen this before and has a fix.

"If you don't ask, they aren't going to tell."

[ September 14, 2005, 11:51 AM: Message edited by: catchtwentytwo ]

 

[kevinware]

Re: UPS shutting down during generator test

Without the size of UPS and Gen. set and the amount of critical that the UPS is supporting it will be kinda hard to give anything but ideals...

1. Is the ups really shut down or going to bypass? Does your UPS system have a bypass mode?If it is going to bypass then I would check my maintenance log first and see when the last battery maintenance was preformed.

2. Here is a big question.. How old are your batteries? We replace our batteries every four years. When you run a Gen. test how much load do you transfer to the Gen.? Or are you doing a no load test? All of this effects battery life.

3. If the batteries all check out good, then are the Gen. and UPS syncing up when you transfer?

4. Do you have DC voltage on your DC buss? If not you may want to look at your rectifier

5. Is there any stepping of the load when you transfer?

6.When was the last time you checked the building load and compared it to your UPS and Gen. set size? Has the building load increased over the years?

I am sure there is a lot more to say but like I said without size information it is kinda hard to give really good information. But that is just an apprentice's opinion. You may want to wait and see what others with more experience have to say..

[ September 30, 2005, 03:00 PM: Message edited by: kevinware ]

 

[catchtwentytwo]

Re: UPS shutting down during generator test

If the batteries are VRLA (sealed Valve Regulated Lead Acid) type, 4 year replacement makes sense.

If the batteries are flooded-cells, maintained per IEEE Standard 450, you're probably good for 10-15 years if the environment is good.