Transcript Catalyst 101 - Philadelphia Scientific UK Ltd

Philadelphia Scientific
A Case Study: Four Years of
Performance Data at a Canadian
Rehydration and Catalyst Addition Site
Harold A. Vanasse – Philadelphia Scientific
Robert Anderson – Anderson’s Electronics
© Philadelphia Scientific 2004
Presentation Outline
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Site Description.
Process Description.
The Science Behind the Process.
Site Results.
Financial Impact.
Trends from 10,000 cells.
© Philadelphia Scientific 2004
Site Description
• Central Office site owned by a major
telecom.
• One string of 24 cells.
– “20-Year Design” VRLA Product.
– 900 Ah cells.
– Major US Manufacturer.
• Cells were installed in 1993.
• Temperature controlled at 21 – 27 ºC.
© Philadelphia Scientific 2004
Site Description
• Good maintenance practices followed.
– Dedicated power technicians.
– Annual re-torqing of intercell connectors.
– Semi-annual conductance testing, voltage
measurement and visual inspection.
• About as good as it gets for batteries!
© Philadelphia Scientific 2004
Test Site as found
in 2000
• Slight bulging of jar cover indicating
positive plate growth – not severe at all.
• Capacities near 5%!
• Customer not happy.
© Philadelphia Scientific 2004
Decision Process
Scrap cells and replace with new cells.
OR
Try adding water & catalysts and save the cells.
© Philadelphia Scientific 2004
Decision Process
• Decision: Water and catalysts were
added to each cell as a test of the
process.
• Telecom felt they had nothing to lose.
© Philadelphia Scientific 2004
Philadelphia Scientific
Process Steps
© Philadelphia Scientific 2004
Step 1: Cell Inspection
Cell Inspection
• Cell Leaks: The cell must pass a
pressure test in order to qualify.
• Physical damage: Positive Plate growth
should not be in an advanced stage –
no severely bulging jars or covers.
• Cell voltage measurement.
• Cell temperature measurement.
© Philadelphia Scientific 2004
Process Steps
Continued
2. State of health determined.
– Ohmic measurements.
– Capacity Test.
3. Cells Rehydrated -- Water added to
each cell.
4. Catalyst Vent Cap installed into each
cell.
5. Annual follow-up inspections.
© Philadelphia Scientific 2004
What Happens Inside the
Cell at Each Step?
(This is the technical section!)
© Philadelphia Scientific 2004
What Water Addition Does –
Part 1
• Dry out occurs because oxygen and
hydrogen gas vent from the cell over
time.
• As float current rises dry out process
accelerates.
• The water that was added replaced the
water that was lost.
– Maintains proper electrolyte.
© Philadelphia Scientific 2004
What Water Addition Does –
Part 2
• When glass mat separator dries out it
shrinks.
– Electrical contact between plates is
disrupted (conductance lower).
• Water added is absorbed by glass mat.
• Glass mat swells like a sponge and
restores electrical contact between
plates.
– Conductance higher/better.
© Philadelphia Scientific 2004
What Catalyst Addition Does
• Negative plate self discharge is a
fundamental problem with VRLA cells.
• Too much oxygen reaches negative
plate and causes it to discharge.
• This occurs while battery is on float
charge!
• Polarization of individual plates tells the
story.
© Philadelphia Scientific 2004
What is Polarization?
• A measure of the voltage on the positive
plate and the voltage on the negative
plate.
• Cell over-voltage is divided between
positive and negative plates.
• We want to know how the voltage is
distributed among the plates.
© Philadelphia Scientific 2004
And Now For Some Math …
• An example:
Float Voltage
Open Circuit Voltage
Overvoltage
2.27 Volts
2.15 Volts
0.12 V or 120 mV
• The overvoltage is what overcomes the cell’s
self-discharge.
© Philadelphia Scientific 2004
Polarization of Plates
• Results of a long term
lab test serve as
example.
• Non-catalyst cell: All the
overvoltage is on the
positive.
• Catalyst cell has a
better distribution.
© Philadelphia Scientific 2004
Non-Catalyst Catalyst
Cell
Cell
Neg.
0 mV
-20 mV
Pos.
120 mV
100 mV
The Positive Plate and the
Lander Curve
Optimum
Positive Plate
Polarization
© Philadelphia Scientific 2004
Tafel Curve
• A diagram that relates polarization and
current … among other things.
• The next slide shows:
– The difference between a healthy and nonhealthy distribution of voltage.
– How a decrease in positive plate
polarization leads to lower cell current.
© Philadelphia Scientific 2004
Tafel Curve Series
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Catalyst Addition
• By placing a catalyst into a VRLA cell:
– A small amount of O2 is prevented from
reaching the negative plate.
– The negative stays polarized.
– The positive polarization is reduced.
– The float current of the cell is lowered.
© Philadelphia Scientific 2004
Putting It All Together
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Ongoing Inspections
• Site inspected each September from
2001 to 2004.
• Parameters:
– Visual inspection.
– Conductance.
– Capacity Test.
– Temperature.
– Float Voltage.
© Philadelphia Scientific 2004
September 2004: Positive Plate
Growth Not Progressing
© Philadelphia Scientific 2004
Site
Conductance Change
3500
3192
3257
3153
3191
2 Years
3 Years
3070
3000
Conductance
2500
2306
2000
1500
1000
500
0
Before
© Philadelphia Scientific 2004
4 Days
1 Year
4 Years
Site Load-Test Run Time
Change
(Minutes before 1.90 VPC at 3 Hour Rate)
140
120
120
108
108
1 Year
2 Years
116
Minutes
100
80
67
60
40
20
9
0
Before
© Philadelphia Scientific 2004
4 Days
3 Years
4 Years
Site Run Time Change
(Minutes at Actual 62 Amp Load -- Calculated)
12.0
10.7
11.0
10.3
10.0
9.6
9.6
1 Year
2 Years
9.0
8.0
Hours
7.0
6.0
6.0
5.0
4.0
3.0
2.0
1.0
0.8
0.0
Before
© Philadelphia Scientific 2004
4 Days
3 Years
4 Years
Anecdotal Evidence
• During the August 2003 blackout the
battery string at this site did not drop the
load.
• Site was powered by the battery for 5+
hours until generator arrived and was
on-line.
© Philadelphia Scientific 2004
Test Site Data
Interpretation
• Immediate improvements (within 6
months) result of water addition.
• Long term improvements (6 months to 4
years) result of catalyst addition.
• The improvements are still being
maintained after 4 years.
• Site load being protected for the
required amount of time (8 hours).
© Philadelphia Scientific 2004
Financial Impact
• This string was about to be recycled,
however 4 years later it remains in
service.
• The end user did not need to buy new
cells for this site – this purchase has
now been deferred for 4 years.
© Philadelphia Scientific 2004
Financial Impact
• Based on a financial analysis of actual
work at over 375 sites across multiple
customers in North America:
– For every $1,000 spent on this process
$13,000 has been deferred in battery
replacement costs.
– Typical payback in 4 to 8 months.
© Philadelphia Scientific 2004
Another Way to Look
at the Financials
• Assume:
– Site equipment has 20 year life.
– Batteries have 7 year life.
• 3 strings of batteries will be purchased
throughout the life of the site.
• If batteries can last 10 years only 2 strings
would be purchased.
• Test site is now at 11 years of life.
• The requirement to purchase 1 string of
batteries has been eliminated.
© Philadelphia Scientific 2004
Trends from 10,000
Cells
• Rehydration and catalyst addition
process completed on 10,000 cells so
far.
• Ages range from 1993 to 2001.
• Four trends identified:
1. Cell dry out (or loss of compression) starts
earlier then most people believe.
© Philadelphia Scientific 2004
Trends from 10,000
Cells
•
Trends continued:
2. New cells are not immune to the problems
presented. Negative Plate Self Discharge
begins within the first few years.
3. Ohmic measurements (conductance,
resistance, impedance) are good tools to
identify problems if data is trended.
4. By customizing the amount of water added to
each cell uniform recovery can be obtained
across an entire string.
© Philadelphia Scientific 2004
One Last Bit of Data
• 180 cell UPS Site
• Internal Resistance data trended over
the last 7 years.
• Water and Catalysts added in 2002.
• Improvements seen in resistance
measurements.
© Philadelphia Scientific 2004
180 Cell UPS Site
Average Internal Resistance
(mOhms)
1000
900
800
700
600
500
400
300
200
100
0
856
653
1997
© Philadelphia Scientific 2004
681
1998
708
1999
744
2000
2001
578
602
2002
2003
Conclusions
• VRLA Cells can be recovered from
Negative Plate Self Discharge.
• Water and Catalyst Addition process
can defer replacement of cells that are
“failing”.
• Our test site is still looking good after 4
years.
• Ohmic measurements can provide early
warning if data is trended.
© Philadelphia Scientific 2004