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TRANSCRIPT
Battery Storage Systems
• System Components
• Applications
• How to Size Batteries
Agenda
System Components
Basic battery theory
• Electro-chemical reaction
• Two dissimilar metals– Positive electrodes
– Negative electrodes
• Electrolyte– Capable of conducting electric current
• Suitable container and cover
• Proper connecting Hardware
Purpose of Batteries
• Once AC power is lost, batteries pick up the load until the generator starts or until power is regained
• Batteries provide power for both AC and DC equipment during outages
• Benefits of using batteries– Immediate response (compared to
generator)
– Do not require fuel source to be replenished
– Noiseless (no muffler)
– Only emissions are Oxygen & Hydrogen –no Carbon or Nitrous emissions
Flat pasted plate construction
• Grid– Collects and carries current
– Provides support for active material
– Tends to grow & corrode over time
• Active material (Paste)– Positive = PbO2 (black, when fully charged
and healthy)
– Negative = Pb (gray)
– Primary source of chemical reaction (electricity)
– Tends to degrade (soften) with heavy use or deep cycling
• Plate = Grid + Paste
Lead acid battery internal construction
Lead acid battery construction (cell)
• Positive Plate
• Lead alloy grid and
PbO2 active material
• Negative Plate
• Lead alloy grid and Pb
active material
• Electrolyte
• H2So4
• Separator
• Container
Lead acid battery construction (monobloc)
• Positive plate • lead alloy or pure
lead grid and PbO2
active material
• Negative plate • lead alloy grid and
Pb active material
• Electrolyte • H2SO4
• Separator
• Container
Lead acid battery glossary
• Cell: A unit part of the battery consisting of two dissimilar electrodes immersed in an electrolyte: 1 cell = 2 volts
• Battery: An energy storage unit consisting of two or more connected cells where a conversion of chemical energy to electrical energy takes place – voltage varies depending on application
• String: Series connection of batteries of a required total cell quantity and capacity
Questions to ask
• Rack preference—step, tier?• 2-step, 2-tier, 3-tier?
• How critical is space?
Questions to ask
• Seismic rating – UBC, IBC, IEEE693
• Single string
• Parallel string
• Redundant strings
• Terminal plates / Overhead buss bar
• Plate orientation:– Perpendicular & Parallel configurations
Questions to ask
• Charger requirements? • The person sizing the battery
must also know the charger
limitations, especially if the
existing charger is to be reused
• Charger must be able to meet
the recharge time requirement
and provide the continuous load
• Temperature compensation must
be considered
Questions to ask
• Spill containment?• Is the spill containment required by codes?
• Check with local inspector & fire marshals
• Contains acid spills
Standby applications comparison
3 Major Markets Served: Telecom/UPS/Utility
• Telecom/Broadband - 24/48 volt DC, 4 or 8 hour rate
– Wireless: Mobile Telephone Switching Office (MTSO) and Cell sites
– Wire-line: Central Offices (CO) and Outside Plants (OSP)
• UPS - 480 volt DC, 15 minute discharge
– Computer backup - Inside, clean, controlled installations
• Utility - 120 volt DC with various duration discharge with 1 minute initial and final spikes– Generation plants, transmission & distribution substations
Typical standby battery applications
• Telecommunications
– DC Power backup for local telephone service
providers, long distance, fiber optic
transmission, cellular telephone service
providers and outside plant broadband
(bundle)
Standby applications
• UPS (Uninterruptible Power Supply)
– AC Power backup for a wide-
range of commercial, industrial,
and government facilities
Standby applications
UPS application
• UPS service – factors that affect battery life– High current for shorter reserve time
• High current density
– Battery sized for reserve time closer to actual usage
• Typical outage 2-3 minutes vs. sizing to 15 minutes
– More cells per string
– Exposure to more discharge cycles• Blackouts, Brownouts, Generator testing
UPS application
• UPS applications are more
stressful to batteries than
telecom & Utility applications
– Higher current density due to
typical reserve times of 10-15
minutes vs. 8 hours in
telecommunications
• Less efficient utilization of active
material
• Internal resistance more of a factor due
to higher discharge currents through
each plate and post
• Utilities (Switchgear & Control)
– AC Power backup for Utility companies, generally in generating plants, and substations
– Designed to provide power backup for switches, circuit breakers, motors, monitors and communications equipment used for protecting electricity generation, distribution, and transmission – also known as Utility market
– Other common S&C applications include oil & gas exploration/production facilities, transport, and manufacturing operations
Standby applications
Standby applications
• Switchgear Requirements
– Power for intermittent outages
• 2-20 outages/year
• Not considered a high cycling
application, but must be able to
handle 20 year’s worth of cycles
– Critical uptime issues
• Loss of electricity not tolerated
Standby applications
• Switchgear Requirements– Duty cycle
• Combination of continuous and noncontiguous loads
• Initial and last loads are the most important
• Example:– Initial high rates-1 minute
(Sheds loads)
– Long duration, sustaining rate
– Concluding high rate-1 minute
– Breaker Tripping and
Closing
– Lights and Alarms
– Control Circuits
– Communications Circuits
Duration (8-12 hours)Think duty cycle
instead of nominal Ah
rating!
Typical application differences
Telecom Battery UPS Battery Utility Battery
Standby float application Standby float application Standby float application
Typ. 8hr discharge rates Typ. 15 min discharge
rates
Typ. 1hr discharge rates
Constant current
discharge
Constant power
discharge
Multi-step duty cycle
discharge
Few cycles
<10 cycles/yr
Moderate cycles
10-20 cycles/yr
Very few cycles
2-5 cycles/yr
Long duration, deep
discharges (to 1.84vpc or
1.75vpc)
Short duration, high rate
discharges (to 1.67vpc)
Short & long duration
deep discharges (to
1.75vpc)
Poor high rates Very good high rates Good high rates
CO: temp. OK
OSP: high temp
Typically temp. OK Varying temp environ.
Telecom Battery UPS Battery Utility Battery
Nominal 8 hr discharge
rate
Nominal 15 min.
discharge rate
Combination of long &
short duration rates
Thicker pos plates Thinner pos plates Moderately thick plates
Plates farther apart Plates very close Moderate plate center
High electrolyte to plate
ratio
Low electrolyte to plate
ratio
Moderate electrolyte to
plate ratio
Minimal cycling Improved cycling Moderate cycling
Poor high rates Very good high rates Reliable high rates
Good long rates Poor long rates Reliable long rates
Typical battery design differences
How to Size a Battery
• What is the actual load? (tells you if the same Ahr capacity battery will work)
• Did the operating temperature change? (helps you size the correct battery)
• Did the operating voltage range change? (helps you set the proper charger voltage)
• Do you require spill containment? (helps you meet the latest local codes)
• What are required design and aging margins? (helps you size the battery)
• In most cases, replacing like-for-like will work. However, above questions should be asked in order to get the reliable battery system
What to ask in sizing replacement battery?
• What are you backing up? (tells you the type of application)
• Do you have a space constraint? (tells you if the flooded is applicable or if you need the multi-cell jars)
• What is the max / min voltage the system can handle? (helps you using the correct Amp or KW values)
• What is the load requirement? (tells you capacity required)
• What is the system voltage? (tells you the # of cells required)
• What is the operating temperature? (helps you size the correct battery)
• What are required design and aging margins? (helps you size the battery)
• What is the seismic zone? (helps you choose the correct rack)
• Do you require spill containment? (helps you meet the local codes)
What to ask in sizing new battery?
Battery sizing
• Some customers have internal battery-sizing computer programs
• EnerSys provides an online Battery Sizing Program (BSP) for flooded batteries– www.enersys.com
• IEEE 485 provides guidelines for sizing batteries– Temperature correction
– Design margin
– Aging factors
– Initial capacity vs. Peak capacity
• Battery system requirements typically dictated by equipment in place– Runtime based on Ah rating
– Single Cell (2V) vs. Multiple Cell (4, 6, or 8V)
Standby applications
• Switchgear Requirements– Duty cycle
• Combination of continuous and noncontiguous loads
• Initial and last loads are the most important
• Example:– Initial high rates-1 minute
(Sheds loads)
– Long duration, sustaining rate
– Concluding high rate-1 minute
– Breaker Tripping and
Closing
– Lights and Alarms
– Control Circuits
– Communications Circuits
Duration (8-12 hours)Think duty cycle
instead of nominal Ah
rating!
• Proper Sizing:
– Sizing the battery for the right application is key to
battery longevity and site reliability
– Sizing should take into consideration the
environment, aging factor, potential site growth
(sizing margin)
– Under sizing a battery will lead to:
• Shorter run times
• Deeper depth of discharge (shorter battery life)
• Loss of site reliability
Battery sizing
Questions to ask
• What factors/margins should be applied?• What is the minimum temperature at which the
battery must supply the loads? • See IEEE-485 for cell size temperature correction
factors
• Is a design margin required? • This is a factor engineers sometimes use to
compensate for future growth, less than optimal
service conditions or other reasons – typical design
margin used is 10%
• Is an aging factor required? • A battery is considered to reach the end of life when
its capacity reached 80% of rated capacity
• To assure that the battery can still support the loads at
end of life, a 1.25 aging factor should be applied
Sizing correction
• Must consider temperature effect on capacity
• Lead-acid batteries are typically rated at 25C (77°F)
• Size batteries larger (higher Ahrs) if operated at colder temperatures
• IEEE recommends using the factor of 1, when sizing at higher than 25C (77F)
Temperature correction factor
Source: IEEE485-1997
• Heat
– Accelerates chemical activity
• Increases corrosion rate
– Shortens life
– Increases self discharge rate
– Causes higher gassing rates
– Increases maintenance
– Increases capacity
– Raises charging current
• Accelerates dryout for VRLA
• Increases the watering interval for VLA
• Overall impact is shorter battery
life
Temperature effect
Temperature and float current
• The increase in float current at elevated temperature
impacts the grid corrosion rate and the gassing rate
(almost doubles for every 15F in temperature rise)
• Both the grid corrosion and the gassing rates
significantly impact the life of the battery
• One of the side effects of high level of gassing is
that it may possibly lead to a thermal runaway
condition
• Cold
– Slows the chemical activity
• lowers corrosion rate
– Causes lower gassing rates
– Maintenance is the same
– Results in lower capacity
• If cold temperature is not considered,
the battery may be undersized
Temperature effect
Reduced temperature
• Operating at lower temperatures is less harmful to
batteries than high temperature operation and will
often increase battery life
• However, there are some negative effects
1) Capacity decrease
• Resolved by applying a temperature correction factor
when sizing the battery
• Low temperature will reduce available battery capacity by
approx. 0.5% per degree F
2) Undercharging
• If the voltage is not temperature compensated (increasing
the charging voltage at lower temperatures), it is possible
that the batteries may become undercharged - resulting in
loss of capacity and life
Thank you! Any Questions?