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Tuesday, March 29, 2011

Low Specific Gravity of cells of 125 VDC Battery Bank

I. Background of the Problem:
March 24, 2011
a. The Substation Engineer-on-duty conducted monthly testing of station batteries. Our 125 VDC Battery Bank is composed of sixty lead acid battery cells. Battery testing include voltage, temperature and specific gravity measurements for the 125 VDC, 48 VDC and 12 VDC battery cells.
b. He noticed that the specific gravity of some cells of 125VDC battery bank 1 were below the normal value which is 1.215. He then put 125 VDC Battery Bank 1 to equalizing charge for 24 hours.

c. The specific gravity of the 125 Battery Bank 1 was measured again and the specific gravity of cell nos. 1, 2, 48, and 52 were still below normal value while the specific gravity of cell nos. 13, 17 and 38 were 1.215 which barely reached the passing limit.
d. Other data:
Year Commissioned 125 VDC Battery Bank 1: 2002
Battery Bank Specification: Leadline, 300 AHrs, d=1.25, 20 deg. C
Date of last testing and maintenance:
Battery load capacity Test:
March 29, 2010 (Test and maintenance section group)-yielded satisfactory
results
Voltage/ Temperature/ specific gravity measurements per cell:
February 25, 2011 (SS Engineer-on-duty)-yielded satisfactory results

II. ACTIONS TAKEN

1. The hydrometer of other substation was borrowed to verify if the hydrometer at Bantay SS is defective.
2. We equalized Battery Bank 1 again for 12 hours to make sure that the battery bank is charged well.
3. Re-tested the specific gravity of the battery bank 1 on March 26, 2011 and same results were obtained.

III. ROOT CAUSE OF THE PROBLEM
There are four possible causes of low specific gravity of station batteries. These include but not limited to the following items:
a. Leaving station batteries in discharge state for a long period of time. Lead acid batteries should be charged periodically to prevent sulfation;
b. Only one battery bank is being used for substation loads. Loads of battery bank is shifted periodically to allow the other battery bank to be charged in full state;
c. Electrolyte levels of station batteries is not maintained on its minimum limit. If the electrolyte level is not maintained at minimum level, there is a possibility that the plates will be exposed to air which will result to oxidation. Oxidation of plates leads to damage of exposed portion of plates that will lead to loss of capacity, and;
d. Service age of station batteries has been reached.

The root cause of the problem is the service age of the station batteries has been reached already. Typically, station batteries have service life of 15-20 years. However, service life of station batteries can be greatly reduced due to various factors. One factor is high operating temperature. Ideal operating temperature for lead acid batteries is at 20 degrees Celcius and their recommended operating temperatures ranges from 10-30 deg Celcius. For Leadline station batteries, printed on each cell its operating temperature which is 20 degrees Celcius.

The first three possible causes for low specific gravity of station batteries are not applicable for SS station batteries because of the following reasons. First, the chargers for battery banks are online therefore the battery banks are always charged. The connected loads for 125 VDC System are also minimal thus the battery banks are not fully loaded. The battery banks are also use regularly and loads are shifted from one bank to another every week. Lastly, the electrolyte level for each cells are always monitored and maintain by the SS engineers on duty.

IV. RECOMMENDED ACTION PLAN
1. Replacement of the battery cells with low specific gravity if replacements are available.
2. Formulation of monitoring logbook for electrolyte level for station batteries.
3. Installation of ACU for Battery Room.

V. ANNEX A:History of 125VDC Station Batteries at the substation

125 VDC BATTERY BANK  1125 VDC BATTERY BANK 2
1996-Substation was commissioned
1996-VARTA Station Batteries were used for
          Battery Bank 1
1996-Substation was commissioned
1996-VARTA Station Batteries were used for
          Battery Bank 2
2002- Leadline Station Batteries replaced
           VARTA Station Batteries.
           *6 years-useful life for VARTA Station
           Batteries
2006- Hoppecke Station Batteries Replaced
           VARTA Station Batteries.
           *10 years-useful life for VARTA Station
           Batteries
March 28, 2011- Leadline station batteries    
           shows signs of deterioration.
           *Cell numbers 1, 2, 48 and 52 have low
           specific gravity values
           *approximately 9 years of operation
.

6 comments:

  1. The Online charger stays connected and always charge the battery. This may not be good for the battery unless the charger automatically shifts to trickle mode when the battery is fully charge.

    ReplyDelete
  2. Good day! I forgot to mention that the online charger connected is at trickle mode (float charge). Also, our charger, SAFT NIFE model 125 TPR 150, has the capability to automatically shift to float or trickle mode when the battery bank is full-charged. Thanks for sharing.

    ReplyDelete
  3. Bite 3 (by Megger) is also good instrument in battery testing..the one thing it does is it measures the impedance of the battery and the strap(jumper)..although it has a high price.. fyi

    ReplyDelete
  4. its better to use motolite batteries.. convincing! or hire thai boxers the 3K battery.

    ReplyDelete
  5. hmmm... I was an OJT on Battery Load Capacity Testing. The Bantay SS was a problem since 2007. Bakit hindi pa napapalitan ang battery cell na iyon?

    ReplyDelete
  6. Just a querry sir, are the batteries that put to equalizing charge are also online/onload?

    ReplyDelete

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