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sealed acid battery 5

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sadgol

Electrical
May 24, 2009
19
Hi everybody
Because of special specification of sealed batteries I have never seen that this type of battery used in power substations.But I want to be sure that can we use this type of battery in power substation or not.Do you have any experiance about this?
 
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Sealed lead acid batteries are used in nearly all environments. They have many advantages over wet cells. The two main advantages are they are sold as "maintenance free" (which is not exactly true) and that they have low gassing rates as they recombine the vented gas within the cell.
The downfalls are their shorter lifespan (5-10 years), their dependence on being kept as close to 20 degrees centigrade as possible and the charge voltage has to be more precise.
I work mainly in the oil and gas industry and the majority of batteries, whether it be switchgear tripping and closing or control, UPS for critical loads or 24V telecoms system are now using sealed lead acid batteries.

UPS engineer
 
Flooded cell Ni-Cad or flooded cell lead-acid. Given the choice, flooded Ni-Cad has better life and better temperature performance, but at higher cost.

I would not accept VRLA in a substation: too unreliable. Do the job properly, not cheaply.


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Using four 1500 AH VRLA banks, accept a 10 year life.Wet batteries maybe last longer but with modern day testing the lifecycle cost analysis favours sealed batteries.
ARAMCO used them for years, then switched back to wet. They get damaged by high temperatures during shipment. So not recommended for the middle east.
 
Sealed VRLA batteries are more sensitive to degradation due to temperature. High temperatures severely shorten life.

Some of my former clients bought into the "maintenance free" sales pitch and were severely affected by the short lifespan.

old field guy
 
It's difficult to factor the cost of a ruined transmission substation or a wrecked steam turbine-generator into life cycle cost calculations. Some applications warrant the use of best available technology because the incremental cost of using the best available technology over an inferior type is so trivial compared to the overall cost that economic analysis of the battery itself becomes meaningless when compared to the additional risk posed by using inferior equipment.


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The two main advantages are they are sold as "maintenance free"
It would be more accurate to say that they are "maintenance proof". They need maintenance but cannot be maintained because they are sealed.
 
It would be more accurate to say that they are "maintenance proof". They need maintenance but cannot be maintained because they are sealed.

I agree. That is why the maintenance free was in inverted commas.
Most sites that I deal with do quarterly Cellcorder internal resistance checks and two yearly discharges.
I have also seen more sealed lead acid cells fail before the 10 year mark than last the full 10 years.

I would listen to the guys who have substation experience and project costing experience. They know more about the implications of battery systems in substations.

My concern is that you have stated that the project requires sealed lead acid cells. If you could give more information on why they need to be used then that would probably help.

UPS engineer
 
I have never seen VLRA batteries that lasted longer than 5 years. They ultimately dry out being 'maintenance proof'.

I think the biggest advantage of flooded is that you get to actually see what's happening with them. You actually have to have, hands-on, which keeps a human in the loop. You can see the specific gravity start to shift in some cells not just find the whole stack choking at some point. Sir-prize!
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Keith Cress
kcress -
 
The electrical utility I work for also tried sealed cells for a while and have gone back to flooded cells.
 
Some telcos have started using high quality VRLA batteries, while others use flooded. My experience with VRLA is that cells go bad without warning (sometimes arrive from the factory bad) and leave your whole string as an open circuit. Flooded cells almost never fail suddenly. Telcos nearly always have multiple strings in parallel, so they only loose a portion of the capacity when a cell fails.

Alan
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"It’s always fun to do the impossible." - Walt Disney
 
Unless you specify wet you will get sealed. Most substation applications have two 100% batteries, but sealed batteries do need testing more often. If you want to play it safe, use wet batteries and ni-cads have special features for smaller sizes. Most critical UPS systems for idustrial DCS applications come with sealed batteries part of the UPS. Wet batteries need battery rooms.
 
No critical UPS would use VRLA, the only reason for using them is initial and lifetime cost where they do win over flooded cells. Anything with the word 'critical' in the name should be using flooded cells for reliability; VRLA batteries are for things you can live without in order to save some up-front costs: If it was truly critical then you wouldn't cut corners to save costs.

As an example, the dual-redundant UPS system which went in to the power plant I left a year ago had dual VRLA battery strings on each UPS. A series of cell failures in the space of a week and a DC shoot-through on an inverter left us with one UPS module on one VRLA string. I would have been much happier on a single string of flooded cells - 'nervous' isn't close to how I felt. One more bad cell would have taken the whole site off. An example of a project driven by cost and not how the engineers would have liked to do it.


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