battery ventilation

[dave_asdf]

i work for a company with a few data centers and had a question for you. in one of our power rooms we have about 96 2.15 volt vlra batteries backing up a 2400 amp, 48 volt DC plant. the manager was complaining about all the breakers supplying the rectifiers tripping when the weather was bad. turns out there was a damper switch on the room's exhaust plenum that would trip the breakers unless there was a pretty good exhaust flow. i came up with a rig that's working fine for now, but the paper plates i'm using as a check valve wont last forever heh. either way do you guys know of any reason a lack of ventilation would trip the rectifier breakers? if anything i think this would increase gassing if it was caused by excessive discharge. i know vlra batteries are susceptible to thermal runaway but i've got no clue how that would link to ventilation, figured that would be a temp sensor around the batteries. you guys think im good to cut the wires going to the rectifier breaker shunt trips?

 

[ron]

Re: battery ventilation

Typically a battery room is ventilated to the outside. We generally provide for hydrogen detection to activate a backup exhaust fan (or at least local alarm) upon detection of higher levels of hydrogen.
If you do the math, it would take a lot of "unventilated" days to build-up enough hydrogen for a problem, and then the backup fan would turn on.
I would reconnect the circuits connected to the shunt trip, to a local alarm to cause an investigation. There is no code requirement to shunt trip the breakers.

 

[dereckbc]

Re: battery ventilation

First I design DC battery plants for Telcos as a background. I do not understand why rectifiers would trip in bad weather, or while being ventilated, Can you elaborate?

If commercial power trips off and comes back, then the breakers trip indicates a really poor design like the breakers are all undersized. I hope the rectifiers are all served on a dedicated panel with no other loads served and properly sized. I know of many instances where commercial power failed and the site went on batteries. When power was restored service transformers and service entrance equipment burned up b/c they were never sized to battery recharge current.

My next observation is there is no requirement for ventilation using VLRA technology. That is one of the reasons to use them along with no spill containment.

True VLRA are susceptible to thermal runaway, but trust me you would know if that was happening. All the rectifiers would be in current limit, the batteries to hot to touch, and all the equipment using battery power would be off-line

 

[charlie tuna]

Re: battery ventilation

sounds to me that the original design of the room was for constant ventilation. without ventilation a hydrogen buildup situation could occur and so the rectifiers were interlocked with the supply breakers.

 

[dave_asdf]

Re: battery ventilation

dereck, to explain it a little better. 4 breakers on a MDP supply 4 transformers. the 4 transformers supply 4 distribution panels which have individual breakers for all of the rectifiers.
there is an exhaust damper switch which closes when ventilation is lost (or in this case reverse flow is caused by wind blowing outside). when the switch closes it shunt trips the 4 breakers at the MDP which removes ac power to the rectifiers.
i think charlie tuna is right. i think the room was originally designed to prevent hydrogen build up by providing constant ventilation. I had looked into h2 detectors as ron said and i think that's probably the way i'll go, just wanted to make sure there wasn't some requirement i was missing that would require the rectifiers to trip w/o ventilation. thanks a lot guys.

 

[dereckbc]

Re: battery ventilation

Dave, Charlie is probable right about the use interlocked breakers. However it really strikes me as misapplication. As I stated VRLA batteries are designed to never vent unless extreme conditions exist like an overcharge or thermal runaway.

It just blows me away that someone would design the AC system to trip the breakers if ventilation was lost. Especially for VRLA batteries which do not require such a system. Normally I would install the detectors to turn on a exhaust fan in the event hydrogen was detected, or the ME folks just design the air system to exchange the air so many cycles over a given time.

IMO it is one of those no-no?s like battery disconnects or fused links, the thought of using them would never cross my mind. The whole point of a battery plant is to never loose power.

 

[charlie tuna]

Re: battery ventilation

the threat of hydrogen still exists with these batteries -- before changing the design of the ventilation system i would run it past the ahj in that area. i have only had one battery explode on me and it left a lasting idea of the force that can be created!!! i have seen many installations of ventilation verification circuits in battery rooms that have the vlra design batteries.....