substation battery system 120 voltage 1

[vtb1]

Hi,
For 120V dc battery, most of the times we use 125V or 130V.
Theoratically, we consider 2V/cell. So for 60Cell, it will be 120V.
What is the reason to populate the term 125 or 130V? Which one is correct?

 

[Zogzog]

Those are usually float voltages set on the charger, if I understand your question correctly.

 

[vtb1]

I agree with that zogzog, the charger has 130V float dc V.
But which term is correct for communication and documentation purpose when refer " Battery "? 125 or 130?

 

[stevenal]

125 VDC is the ANSI recognized nominal voltage from the switchgear standards.

 

[dpc]

As stevenal said, in the US, the nominal voltage is almost always 125 V dc and the battery can float at 130V or higher on the charger 99% of the time. During equalization, it will be even higher.



David Castor

http://www.cvoes.com

 

[DLynn908]

Typically battery float charge voltages for a single cell is 2.25 volts. 2.25 x 60 is 135vdc. But like DPC said an equalize charge is higher. Most of the switch gear applications i have seen have utilized 60 cells at 135vdc which is 120vdc nominal. Of course depending on the battery, the voltages per cell can vary.

Good luck

Don

 

[dpc]

Back in the "old country" we actually switched to 59 cells instead of 60 just to keep the voltage a little lower.

David Castor

http://www.cvoes.com

 

[cherry2000]

The tolerance on DC bus voltage is usually 90V to 140V. Now , as correctly specified by DLynn, 2.25V/cell is the correct float voltage. Now 125VDC is the 'nominal voltage' whereas 135VDC is the actual float voltage. You should be more worried of the end cell voltage which typically is 1.75V/cell but can be much higher depending on the voltage window for the counsumer devices and also the voltage drop in the system. One typical application is the DC motor of a MV Breaker which can start running in the last 1 min of the 8hr discharge cycle. Thus after calculating the voltage drop, one can end up with much higher end cell voltage.
DPC, you are correct in saying that many a times we may have lower no., of cells. Some UPS manufacturer's routinely give 54 cells, since the DC link voltage is limited by the lowest voltage that the inverter can tolerate, and also the current carrying ability of the components, since to deliver the same kVA o/p at lower DC voltage, a greater current is seen at the DC link level.