Nickel Cadmium batteries for station service

[rockman7892]

I’m working with a customer the prefers to use Nickel Cadmium batters over lead acid type for their 125VDC substation batteries.

Every substation I have ever been in has has lead acid type so I don’t have much familiarity with NiCad.

Does anyone have any experience with NiCad for station service and any good reasons for or against its use for station service compared to lead acid?

Are there significant differences in battery size calculations for NiCad vs lead acid for station service applications? I see there is an IEEE standard IEEE 1115 for calcs of NiCad batteries which I’m suspending may have similar info as IEEE 485 for lead acid type?

 

[RRaghunath]

Ni-Cad batteries are alkaline unlike Lead acid.
The Ni-Cad battery cell voltage is 1V against 2V of Lead acid.
Ni-Cd batteries don't suffer problems like sulfation that reduce the life of Lead acid batteries.
Ni-Cd batteries have better shelf life and long service life of 20 years.
Lead acid batteries are sensitive to ambient temperature, their life reduces drastically with increased ambient temperature. Ni-Cad batteries can withstand higher ambient temperatures (and also have better performance at low ambient temperatures).
For the above reasons, Ni-Cad batteries are preferred in critical applications in spite of their higher cost especially in unmanned and difficult to reach places (for routine maintenance).

 

[rockman7892]

Thanks RRaghunath

I did some comparison between the lead acid (IEEE 485) and NiCAD (IEEE 1115) standards and found that the process and calculations for determining required capacity is very similar. Both used same duty cycle, method of calculation (table worksheet) application of capacity factor kt for each period, and application of temp, margin and aging factors to calculated capacity.

Unless I missed something I didn't see any real difference in calculation methodology between the two. The only real difference that I saw was the difference in battery capacity factor kt with the multipliers for NiCAD being larger.

Obviously the voltages between the two are different with Lead Acid having typical minimum discharge down to 1.75V while NiCAD goes down to 1.14 typically. This appears to impact number of cells (60 for lead acid vs 92 for NiCAD) but does not appear to impact capacity calculations.

As a general question I'm curious what calculation worksheets others use and how you typically account for capacity discharge factor kt. This discharge capacity factor is based of the actual battery discharge ratings so this is somewhat of an iterative process between calculating capacity and using specific kt factor in that calculation. Is there a standard table or graph that is typically used to reference kt factor in these calculations?

 

[TugboatEng]

My experience with NiCad is in emergency lighting systems (small cells). Lead acid batteries are damaged by deep cycling. If you have a backup battery system that is expected to function regularly and for long periods of time, lead acid can be a poor choice. If you go the lead acid route you should double the capacity relative to your need and consider using relays that will cut out your batteries when they drop to 50% capacity.

If you choose NiCad you can run the batteries to depletion which means you don't need discharge protection and you need less installed capacity.

 

[rockman7892]

TugboatEng

Related to your last sentence about needing less installed capacity for NiaCAd, I don’t see how this is accounted for in any of the calculations for determining capacity size?

Is there a calculation or factor somewhere in IEEE or other equations that supports the need for less capacity?

 

[TugboatEng]

 

[FacEngrPE]

Tug is referring to the NiCd batteries not being damaged by deep discharge, while lead acid are.

Also consider the minimum voltage for the connected equipment to operate correctly. Allowing battery voltage to drop below the equipment minimum requirements will have undesirable results.

Emergency lighting using incandescent lighting can tolerate a wide input voltage range, but the lamps will become dim quickly once the batteries reach the "cuttoff" point of.

(reference

https://www.semanticscholar.org/pap...59dd79d832c0049c88c8b784d5fb732e4be/figure/8)