Why 130VDC in utility/substations? 1

[mcgyvr]

Why are 130VDC battery banks commonly used in the utility/substation industry?
Specifically wondering why the 130VDC? Why not 120V or 48V or whatever.

 

[cranky108]

The common DC voltage is 125 VDC, not 130 VDC, however as the batteries would tend to be fully charged, they would provide a higher voltage. Another issue is the different reactions have different voltages per cell, so an exact DC voltage is not possible. Then there is a tendency to need more capacity, which is measured with a discharge to 80% voltage. So a little higher voltage from the start would provide that capacity.
Another issue is the batteries capacity changes over the life of the battery, so does the cell voltage change over the life, and with the tempeture.

So to speak to the battery voltage, it is a complex chemical reaction, that is managed for the capacity required.

48V batteries are used, but not in large substations due to the long cable lengths, and the higher currents required for 48V applications.

One issue the was a problem, but may have been mostly solved, is contact dirt, which tends to cause an impedance in the circuit. This dirt requires a higher voltage to breakdown the dirt to the point where it conducts. Thus another reason for a higher control voltage.

 

[mcgyvr]

I just keep seeing converters,etc.. and they all state 130V DC and not 125V DC..
Like

http://www.ictcorporate.com/inside/bulletins/pdf/2012_ad04.pdf

 

[davidbeach]

It's like 460V motors on 480V systems. We call it a 125VDC system, install it using 60 cells, and expect a normal operating voltage a bit over 130. Suppliers used to the substation business will refer to 125VDC systems while others will look at the operating voltage and say 130VDC.

 

[mcgyvr]

Thanks gents..
I thought it might be like that but wasn't sure.

 

[PHovnanian]

And 130V (125V) was used in preference to 48V due to the ability to operate things like incandescent lighting from the station service batteries without having to stock special bulbs.

 

[dpc]

During equalization, the voltage goes even higher. If you buy equipment rated for 120 V, there can be failures. In a previous life, a large A/E firm that I worked for started using 59 cell station batteries instead of 60 cells to help deal with an ongoing problem of indicating light failures occurring during equalization.

 

[mcgyvr]

During equalization, the voltage goes even higher. If you buy equipment rated for 120 V, there can be failures. In a previous life, a large A/E firm that I worked for started using 59 cell station batteries instead of 60 cells to help deal with an ongoing problem of indicating light failures occurring during equalization.

Thats partly what brought up my question.. We can no longer get an "up to" 175V UL rated part and the replacement was 125V max (we said NO).. Then the whole "why 130V" just got me curious.