Telecom room with UPS

[acuariost]

Hello!

I have full time in line 30KW UPS for a Telecom room, I'm experiencing some kind of AC interference or noise on my PC monitors (video and audio), 21" LCD Viewsonic and a Synelec video wall. Also we have about 14 PC's in that room.
It could be possible that my UPS have a bad grounding?
It works in 480vac delta sys input voltage, 480vdc battery bank, and 480vac to 208-120 Y sys output for Telecom. My plant system is 480vac close delta with B phase grounded.
It is a problem if the plant ground and UPS output ground are connected together?

Tx

 

[alehman]

That's hard to diagnose on such limited information. Does the interference effect all of the monitors? Are there any other symptoms?

480V grounded B-phase systems are unusual. Have you consulted the UPS manufacturer to be sure that is an acceptable input? Is the UPS output neutral isolated and separately grounded?

 

[acuariost]

Thank alehman...
Yes it does, all the monitors are affected by the interference, normally we use video extenders, but we used a normal video cable and it doesn't change anything. Other symptoms are, RF and Public Adress (PA)interference.

I'm looking in the Tec Specs provided by the vendor.

The UPS output neutral is not isolated it is grounded to the system ground.

Thanks!

 

[SteveFehr]

It depends on the design of the UPS. The surge supressors and static switch may not function properly if it's designed for ungrounded delta. I'd imagine problems with either of these would have been obvious before now, though. The manufacture should be able to tell you, though.

You say in-line, but I'm not used to seeing in-line UPS as large as 30kVA; is this online double conversion UPS?

 

[ScottyUK]

Ensure the UPS neutral has a good connection to a low impedance ground. Ensure this ground path is not shared with anything else. My initial thoughts are the static switch, if fitted, won't like the input supply at all. Most require a bypass supply similar to the UPS output, usually 3ph 4W with a grounded neutral, even though the rectifier is able to accept a 3ph 3W supply.

UPS modules are often sources of magnetically coupled interference which can be really tricky to shield out. How close physically is the affected equipment? Does the problem lessen with distance, or is it fairly constant whether the equipment is close to the UPS or remote from it?


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