2.2.5 Failure of VRLABatteries Mostnormal explanations behind disappointment of VRLA batteries are : i. Positivegrid corrosion · Eachtime battery releases, Pb2 of the positive plate gets changed over intoPbSO4there is an extensive increment in its volume, which puts weight on theglue.
More profound the released, more is the expansion in the volume of theglue of the positive plate and more is the weight on the matrix. Amid chargethe glue of the positive gets converter once more into PbO2 the glue getscontracted. This extension and constriction brings about relaxing of thedynamic material in the framework, over a timeframe. These outcomes in loss ofcontact of the dynamic material with the positive plate and increment in thecell resistance. This is a continuous procedure and under ordinary conditionsis an indication of maturing, which might just happen when the battery hascarried on with its stipulated life. Notwithstanding maturing there aredifferent components which quicken the procedure and prompt untimely maturing.
Some of them are : · Largernumber of charge/release cycles speedier the maturing procedure. · DeepDischarge, further the release speedier the maturing. · Fastrate of Charging.· Fastrate of Discharging.Corrosionis un-recoverable and indicates the end of cell life ii.
SulphationSulphationof the cells plates because of drawn out under charge, cheat or delayedstockpiling may likewise expands the cell resistance. This is a recoverableharm unless it is sufficiently hard to expel and can be recuperated viawatchful and controlled charging of the cell. On the off chance that thesulphation is delicate (not thick), the same might be recuperated by accusingthe cell along of the battery.
The medium kind of sulphation can likewise beevacuated by drawn out charging, which might be finished or part contingentupon hardness of the sulphation. In both the above cases a couplecharge/release cycles are required for the ideal recuperation. This might beaccomplished by cycling the cell inside the battery or expelling the cell frombattery bank and reconditioning, exceptional treatment of charging and so forthat the plant by the producer at his premises.
Now and again sulphation turnsout to be too difficult to overcome. In such a case cell should be harmedunrecoverable. iii.
Dryout (loss electrolyte) · Thereis a misguided judgment that these batteries are completely fixed and no escapeof gasses occurs. Be that as it may, the gasses escape through the wellbeingvalve to keep up the weight inside cells in endorsed limits and in this manner,most normal method of disappointment of the cell/battery is dry out. This mayoccur due the intemperate escape of gasses from the cell, which leaves the cellwith next to zero electrolytes. This may occur due to :· Fastcharging · Operationof the battery at a high temperature· Leakagethrough splits in the compartment or fixing. Theindications for above failure are: a) The first sign for thedisappointment is increment in the inward resistance of the cell or resistanceof the battery.b) Sometimes the increase in resistanceof the battery may not be an indication of the failure of cell or the batterybecause it may be due to rusted terminals, loose connection etc.
, this,therefore is very essential that it shall be checked periodically that neitherthe terminal is rusted or the terminal is loose (for this it shall be ensuredthat the torque of the terminal is as per manufacturers’ instructions. Because,if allowed to remain loose may cause premature failure of the cell/battery. iv. AbruptFailure : · Becauseof absence of legitimate observing timetable, the cells with high resistanceare not deducted in time.
In such cases, when the battery is put on load, itneglects to take the heap. The two fundamental reasons in such cases are: · Improperor Loose between cell associations Inthe event that the between cell connectors are under appraised will getunreasonably warmed and may influence the fixing, bringing about to splits,which thus prompt escape of gasses and dry out. · Increasein the interior resistance of the cell/cells Thismight be brought on by sulphation or eroding of the plates, combining orterminals.
Sudden disappointment will just happen, when the eroding will getexceptionally extreme i.e. at the skirt of breaking.
v. Lowcapacity FailureThisdisappointment may primarily be credited to maturing. As the battery agesbecause of any reason it begins loosing its ability. On the off chance that thebattery limit fall underneath the 80% of its unique limit, it is attempted tohave carried on with its life.
Maturing is moderate process in starting phasesof rot and picks up speed just when it nears 80% of its appraised esteem. In theevent that the limit of any cell/battery is moving toward it requires promptsubstitution. It might be specified here that both of the above Abrupt and Lowlimit disappointments can be identified, well ahead of time ( unless the cellsairs out or fixing gets because of supported high terminal temperature), bywatching a couple of pointers, which can caution well ahead of time about thedisappointment inclination in a cell or the battery, in light of the fact thatrotting of cell or battery is a steady procedure and can be distinguished muchahead of time. vi. ThermalRunaway :Batteriesare extremely temperature delicate.
The compound response expands/diminishes ingeometric movement with the increments or lessening in temperature. TheTemperature in the event of VRLA Batteries is noteworthy on account ofconstrained volume of electrolyte which limits warm conduction. In the light ofthis reality, the best possible temperature is basic for the advancement ofbattery life. The recombination of gasses inside a VRLA cell can just happen ata specific rate.
On the off chance that the rate is surpassed, gas weight willdeveloped past the wellbeing valve level, and gasses/water will be vented outand for all time lost.The most noteworthy buoy voltage at which a cell stillrecombine all the gasses driven off the plates is roughly 2.30Volts. In theevent that the cell temperature expanded while holding the voltage consistent,the cell would dry out and potentially go into warm runaway. Warm runawayprompts a softening down of the container and under most dire outcomeimaginable, will prompt a blast and fire. In the underlying phase of VRLAbattery advancement of warm runaway was viewed as one of the disappointmentmode, however in India it has not been seen till date and in addition atpresent it is not considered disappointment mode.
Warm runaway is calliopes ofthe battery because of high temperature created inside the battery. 2.2.8 Float Voltage Skim voltage is another essential parameter onwhich the life and execution of the battery depends. The buoy voltage might beso set the relating voltage at 27 degree Centigrade should be 2.
25V/cell forbuoy voltage and 2.3V/cell for charge voltage taking the alteration element or3mV/cell/degree centigrade. Besides in the event that glided parallelstrings, the buoy current in each string will rely on upon the inwardresistance of the string.
Consequently it is basic to guarantee that theparallel strings are legitimately coordinated for conductance and resistance.The float voltage is vital for the battery andmust be within the limit set by the IEEE standard to compensate for thetemperature. An accurate digital multimeter must be used to measure the voltageof the battery to ensure the reading gives a correct indication of the battery.The pilot cell is the cell that is selectedrandomly from the battery bank.
The voltage of the pilot cell must be measuredmonthly using accurate measurement instrument. 220.127.116.11 Float VoltageMonitoring i. Mid-point Voltage Measurement : Some battery screens measure the midpoint voltage of every batterystring.
This is exceptionally straightforward way to deal with identify voltagedeviations inside string. In this technique screen will make an alert whenthere is an adequate lopsidedness in the two half string voltages. Thistechnique has its own constraints on the grounds that as the framework voltagebuilds the midpoint observing loses its determination and all things consideredadditionally loses its capacity to perceive a freak cell. ii. Individual Cell Monitoring : To accomplish the ideal advantage of voltage observing it is basicthat the voltage checking is done at cell level.
In this procedure the voltageof every cell is measured and deviation in any of the cell can be identifiedrapidly and effortlessly and therapeutic move required can be made. 2.2.9 InternalResistance Internal Resistance is a good representation of the state of chargeand substitute for the specific gravity reading of the Flooded Lead AcidBattery. The measurement is required to detect to main failures which are dryout and grid corrosion. The datasheet of the battery from the manufacturerusually lists the normal expected value for the measurement.
Internal Resistance can be checked by using the steps below: i. Check and record the voltage and current when the battery is fullycharged and operating on the float. ii.
A normalload is applied across the cell. iii. Recheckthe voltage and current of the cell iv. CalculateInternal Resistance by using the formula: Vb = Va * R /(R+r) , r = internal resistance 2.
2.10 Safety Precaution The following precautionsare highly recommended to be exercised:i. Do not load the battery in airtight environment as it may causes aburst and injury ii. Avoid direct contact of the battery with metallic elements theleakage of battery in the absence of insulator might release fumes and ignitesflare. iii. Do notplace the battery near a device that may cause a spark such as a fuse. iv.
Avoid placing the battery near heat generating source that cancause overheating and lead to flame. v. Do notcharge the battery with opposite terminal of the charger. Battery Type Typical Warranty (Years) Life Expectancy Hydrogen Gas Evolution Approximate Number of Deep Discharge Initial Comparison to Lead Calcium (%) Lead Calcium-VRLA 10 5 None 200 30-50 Nickel Cadmium-Wet Cell 20-25 20-25 Low 1000 200-300 Lead Calcium- Flooded Cell 20 20 Low To Moderate 100 100 Lead Antimony- Wet Cell 15-20 15 High 400 100 Table 2.2: Properties of Different Types of Battery No Year Government Agencies/ Private Firms Description of Items 1 1997 CSI SAAG Sdn.Bhd For PETRONAS DC UPS 24-42 c/w SLA Battery 2 2009 Tenaga Nasional Berhad MS 12-200 SLA Batteries 3 2009 KVC Connectors Sdn.Bhd MS 12-55 SLA Batteries 4 2009 Sabah Electricity Sdn.
Bhd MS 12-260 SLA Batteries 5 2009 Add Value Electrical Sdn.Bhd MS 12-150 SLA Batteries 6 2010 Tenaga Nasional Berhad Generation Division SLA Battery MS 2-200 7 2010 Pacujaya Sdn Bhd SLA Battery MS 2-300 Ultra 8 2010 SEIE Engineering Sdn Bhd MS 12-230AH SLA Battery MS 2-400AH SLA Battery MS 2-500AH Ultra SLA Battery MS 12-200AH SLA Battery MS 2-1500AH Ultra SLA Battery MS 2-300AH SLA Battery MS 2-2000AH SLA Battery MS12-125 SLA Battery 9 2011 MK Construction and Communication Sdn Bhd Sealed Lead Acid Battery Model MS 2-12 AH (Ultra) Table 2.3:Existing UPS System That Used SLA Battery as Their DC Supply 2.3 VoltageMonitoring One of the methods to monitor the voltage ofthe battery is by using the voltage divider circuit. Since a microcontrollersuch an Arduino cannot take an input of a voltage more than 5V, the circuit isused to reduce the voltage that acts as an input to the microcontroller. Thevoltage read by the microcontroller act as an indication of the real voltagethrough mapping. Figure 2.
4 shows the voltage divider circuit in which the inputvoltage passed through a resistor to produce an output voltage that is in therange for the input of the microcontroller.