battery sizing calc and sizing of alcad.
- 2. Scope • Battery selection criteria • Electrochemistry • Comparison of Lead Acid vs Nickel Cadmium • Battery Sizing – Understanding load profiles Where and how you can save money
- 3. The Basics – Build a Load Profile • WHERE TO BEGIN When will the battery discharge • LOADS TO CONSIDER Continuous Non-Continuous Momentary • WHAT HAPPENS FIRST Followed by? For how long? • MARGINS Design Aging Effects of temperature Fluff
- 4. NORMAL OPERATION AC Available No Faults 4.160KV Switchgear 12 AMP TRIP CURRENT 6 AMP CHARGER 2 amps for indicating lights, relays etc. 30 mA to float charge battery ~
- 5. Basics 4.160KV Switchgear 12 AMP TRIP CURRENT 6 AMP CHARGER Charger goes to current limit, puts out 6 amps MAX. 0 mA to float charge battery Remaining 6 amps comes from battery. Load requirements exceed maximum charger output ~
- 6. ABNORMAL CONDITION Charger Output Limited Breaker Operating 4.160KV Switchgear 12 AMP TRIP CURRENT 6 AMP CHARGER 1 amps max coming from charger. 0 mA going to the battery Remaining 11 amps comes from battery. Charger output is limited in some way. ~
- 7. ABNORMAL CONDITION AC Failure Charger Output @ Zero 4.160KV Switchgear 12 AMP TRIP CURRENT 6 AMP CHARGER No current available from charger Full load comes from battery. Charger output is lost completely, due to rectifier or AC failure. ~
- 8. Continuous Loads • Loads that are energized for the duration of the duty cycle • Are normally supplied by the charger • Can have a big effect on battery capacity • Examples Continuously operating motors / pumps Relay coils Indicating lights
- 9. Non-Continuous Loads • Energized for only a portion of the duty cycle • Can be turned on or off automatically or by operator action • Special considerations: If inception is known, but end is not, run to end of duty cycle If end is known, and inception is not, consider the load from the beginning of the duty cycle. • Examples Emergency lighting Lube oil pumps Communication
- 10. Momentary Loads • Very short in duration, can be fraction of a second • Lead Acid - IEEE 485 Even though the load may last for only a few cycles, you must treat it as lasting one full minute • Nickel Cadmium - IEEE 1115 Even though the load may last for only a few cycles, you must treat it as lasting one full second • Examples Switchgear operation Engine starting Field flashing
- 11. Dealing with Multiple Momentary Loads • Discrete Sequence Known Load is maximum current at any instant • Sequence Unknown Load is sum of all loads in that period Usually a greater demand on battery
- 12. Dealing with Multiple Momentary Loads • If a discrete sequence can be established, the load for the period shall be assumed to be the maximum current at any instant IEEE States: Example: Duration 1 Trip - 3 breakers 45 amps 0.5 sec 2 Trip - 5 breakers 75 amps 1 sec 3 Trip - 4 breakers 60 amps 1 sec Since we can determine the sequence, the load for the period would be 75 amps for one minute (for lead acid) Nicad can be broken into 3 distinct loads, or, 75A for 3 seconds
- 13. Dealing with Multiple Momentary Loads • IEEE States: If a discrete sequence cannot be established, the load for the period shall be assumed to be the sum of all the loads occurring within that period Example: Duration Trip - 3 breakers 45 amps 0.5 sec Trip - 5 breakers 75 amps 1 sec Trip - 4 breakers 60 amps 1 sec Since we cannot determine the sequence, you must treat the load as occurring all at once 180A for 1 minute - Lead 180A for 1 second - Ni-Cd
- 14. C o n t in u o u s L o a d N o n C o n t i n u o u s L o a d M o m e n t a r y l o a d 1 m in - L e a d A c id 1 s e c - N ic k e l C a d m iu m The Duty Cycle
- 15. Sizing Margins or Making Batteries Bigger • Aging Factor 25% Recommended • Applicable to: • All types of flooded lead acid • VRLA • Nickel Cadmium • Exception is Plante`
- 16. Sizing Margins or Making Batteries Bigger • Low Temperature Correction For operation below rated temperature • High Temperature Improves performance slightly Not normally used in sizing calc’s. Design margin for maximum life
- 17. Sizing Margins or Making Batteries Bigger • Design Margin Normally considered for future equipment or load growth Allows for operation at lower than expected temperature Can cover for less than adequate maintenance • Almost every sizing has one!
- 18. Sizing Margins or Making Batteries Bigger • If the calculation requires a 220 Ah battery, and the next cell size up is 250 Ah - - • The 30 Ah difference is a 13% margin, “designed” in • An additional margin of 10% might not be required
- 19. Knowledge is not only Power • Develop load profile using worst case • Try to determine sequences Not knowing requires conservatism Conservatism can increase required capacity Increased capacity - More $ • Closely review various sizing factors Low temperature increases battery size Aging factors are good ideas - ensure long reliable life Evaluate design margins, especially after sizing a battery It’s Money
- 20. Have we lost anyone
- 21. So far we’ve covered... • Various discharge scenarios Pick the worst case • Various load types Continuous Non-Continuous Momentary • Sizing margins / factors Temperature correction Aging factor Design margins
- 22. Sizing - What’s needed • Load profile Include all prudent margins • Voltage Maximum Minimum • Manufacturers data Yes, you do need us • Capacity rating - Kt factors Amps per positive plate - Rt factors • Battery type Flooded lead acid Nickel cadmium VRLA
- 23. The load profile 15 BREAKERS TRIP - 10A, 5 CYCLES Sim./Brkr CLOSE - 7A, 5 CYCLES Seq./Brkr SP. CHG - 4A, 6 SECONDS Seq./Brkr TWO OPERATIONS, Beginning and end of 8 hr duty cycle 2A CONTINUOUS LOAD EMERGENCY LIGHTING LOAD 1200 Watts - 90 minutes Starts at outage
- 24. The load profile 90 minutes Continuous - 8 HR Trip 15 Breaker 1 min. - Lead Acid 1 sec. - Ni-Cd Close & Spring Charge Loads 1 min. - Lead Acid 92 sec. - Ni-Cd Trip Breakers at End Of Cycle Lighting Load 150 A Trip Load 10A 2 A ? 7A
- 25. Load profile defined • Nickel Cadmium 162A 1 second 19A 92 seconds 12A 88.45 minutes 2A 390 minutes 152A 1 second • Lead Acid 162A 1 minute 19A 1 minutes 12A 88 minutes 2A 389 minutes 152A 1 minute
- 26. Voltage window • Maximum and Minimum values Determined by DC powered equipment • Allow widest possible range Uses maximum number of cells • More cells = lower end of discharge voltage • More efficient capacity utilization • Least expensive battery
- 27. Impact of voltage window • IEEE 485 Example: 140V - 105V window 60 cells, to 1.75 VPC - 1,010.4 Ah req'd • Wider voltage window 62 cells, to 1.69 VPC - 944 Ah req'd 3% increase cell qty, 7% capacity reduction • Narrower voltage window 58 cells, to 1.81 VPC - 1,186 Ah req'd 3% decrease cell qty, 17% increase in capacity • 100Ah High rate ni-cd cell One minute rate To 1.14 VPC 243 amps One minute to 1.05 VPC 406 amps
- 28. No. of cells calculation Max. Volts - Determines number of cells that can be adequately charged. Equalize value is normally used as determining cell voltage Ex 140V max 2.33VPC = 60 cells (lead acid) or 140V max 1.46VPC = 96 cells (nickel cadmium)
- 29. End of discharge calculation Min. Voltage -Lowest value system designed to operate at Min. Volts # of cells = End of discharge voltage / cell Ex. 105 VDC 60 cells = 1.75 VPC Lead Acid Ex. 105 VDC 96 cells = 1.09 VPC Nickel Cadmium
- 30. Sizing factors • Kt factors Based on performance per rated ampere hour Kt factor = Rated ampere hours Amps available for time t • Rt factors Based on performance per positive plate Used primarily with lead acid cells Rt factor = Amps available for time t per positive plate
- 31. Capacity rating factors • Kt factors Determined from tabular data • Examples 160 Ah rated cell 8 hr discharge rate - 20 amperes Kt = 160 Ah / 20 amps 8 Hr rate Kt = 8 • One minute discharge rate - 320 amperes Kt = 160 Ah / 320 amps One minute Kt = 0.5 • Kt factors are multipliers in IEEE worksheets
- 32. Capacity rating factors • Rt Factors Found in plate performance curves Not all manufacturers publish them When not available, use Kt • Rt factors are divisors in IEEE worksheets
- 33. Did you know this? • Most lead acid model numbers indicate number of plates per cell 3CC7 = Seven plates per cell 4JC11= Eleven plates per cell • One more negative plate than positive Seven plates = 4 Neg - 3 Pos Eleven plates = 6 Neg - 5 Pos • 50Ah / positive plate 150Ah cell from above example (3 pos x 50Ah) 250Ah cell for eleven plate cell (5 pos. x 50Ah) • Positive plates are same for the range
- 34. More things you should know • Ampere hour nomenclatures Most nickel cadmium Some VRLA • Pos. plates are not identical thru range • Wider or taller plate = higher capacity • More plates per cell = higher capacity
- 35. Real life • Create a duty cycle • Periods Amps__________ Duration_________ Amps__________ Duration_________ Amps__________ Duration_________ • Voltage window Max__________ MIn__________ • Calculated No. of cells Lead acid___ Nickel cadmium___ • Environment High Temp_____ Lowest Temp_______ • Aging factor _______ (not for Plante') • Design margins _______
- 36. Summing up • Battery Sizing is a science • Building the load profile is an art • Electro-chemistries vary greatly • You have more control over your battery selection than you think
- 37. www.alcad.com Thank you for your attention Alcad: presentation title 37