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Battery Sizi ng & ©1996-2010 Operation Technology, Inc. – Workshop Notes: Bat tery Sizing & Dischar ge

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Battery Sizing &

©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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When does a battery kick in?

• Load in DC System exceeds the battery

• ower s os genera y e wors case

scenario]

Slide 2©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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IEEE 485- Definitions

• Battery Duty Cycle

 

specified period of time (sum of all individual loads)

• Cell Size

 – Rated capacity of a lead acid battery or number of

positive plates in a cell

• Period

 – Time interval for which the load is assumed to be

constant

• Vpc

Slide 3©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 – Volts per cell (individual cell voltage)

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Duty Cycle Classification

• Continuous Load (Non-Random)

 – on-ran om oa s

 – Normally carried by the battery charger 

 – Includes lighting, converters, indicating lights,

communications systems, continuously operating motors

• on- on nuous oa an om or on- an om

 – Emergency pumps

 – MOV operations

 – Critical ventilation system motors

Slide 5©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 – Fire protection systems actuators

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Duty Cycle Classification

• Momentary Loads (Random or Non-Random)

 – oa s w ura on a o no excee more an

one minute

 – MOV with stroke of less than a minute

 – Field flashing of generators

 – Motor starting currents

 – nrus curren s so eno s, re ay co s, e c

Slide 6©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Individual Load Duty Cycles

• Static Loads

• Motor loads

• DC Lump Loads

• Elementary Elementary Diagram

• DC to AC Inverters

Slide 7©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Guidelines for Battery Duty

yc es

 

be higher or equal to one minute

• First identify the non-random load battery

duty cycle

• Find worst case scenario

• Include the random load duty cycle

Slide 8©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 

conservative combination of the two

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Duty Cycle Example A

Slide 9©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Duty Cycle Example B

Slide 10©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Battery Modeling

• Battery voltage based on manufacturer

• Enter batter characteristic curves in batter

library

• nterpo at on extrapo at on s per orme to

obtain battery size and discharge voltage

pro e

Slide 11©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 

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Characteristic Curves

Battery Characterist ic Curves

1000.00  1.5

1.6

1.67

100.00

  e   (  m   i  n .   )   1.75

1.78

10.00   T   i  m

  .

1.84

1.88

1.00

10.00 100.00 1000.00

1.92

1.96

Slide 12©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 Amps per Positi ve Plate

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Interpolation Methods

Slide 13©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Battery Sizing Study Case

• Load Summation

 – s a e oa u y cyc es

 – Generally more conservative for systems with more

• Load Flow Method – Adds all the load duty cycles, but performs a load flow

calculation at every time step to account for systemlosses more realistic results

 – Generally more conservative for systems with moreconstant power loads

Slide 14©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 – Load model type based on load type or duty cycle type

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• Load Duty Cycles

 – eren sys em u y cyc es

• Correction factors

 – Battery minimum temperature

 – Aging compensation

 – Initial capacity

 – Design margin

• Voltage Requirements

 – Maximum system voltage deviation (charging voltage)

 – Minimum system voltage deviation (depends on finalVpc)

Slide 15©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 – Battery minimum discharge voltage (final Vpc)

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Battery Discharge Page

• Vd Calculation Parameters

 – Time step and maximum voltage limit• Correction Factors

 – Same as battery sizing (no design margin)

• Load Flow Parameters

 – 

 – Precision

Slide 16©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

 – Initial conditions and motor load handling

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Displayed Results

• Tabulated results for battery voltage, bus

system

• One-line diagram displayed results (similar

to DC load flow)

• Complete set of plots that include battery

, ,flows

Slide 18©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

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Things to Consider 

• Obtain as many battery characteristic curves

• Obtain specific curves for battery model and

type

methods

• Use most conservative approach for yoursystem (load flow method or load

Slide 19©1996-2010 Operation Technology, Inc. – Workshop Notes: Battery Sizing & Discharge

summation)