Design Guide -Battery Sizing

16-QSP-05-3A

DESIGN GUIDE FOR BATTERY & BATTERY CHARGER

Word

SIZING

0

01-09-04

Rev.

Date

First issue

Triune Projects Pvt. Ltd. New Delhi

Description

DESIGN GUIDE FOR BATTERY & CHARGER SIZING

IB

ASA

NS

Prpd.

Chkd.

Appd.

Standard Number

Rev.

06-DG-005

0

Sheet 1 of 11

16-QSP-05-3A

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CONTENTS


1.0

PURPOSE

2.0

PROCEDURE

3.0

STEPS FOR BATTERY SIZING

4.0

STEPS FOR CHARGER SIZING

5.0

LIST OF ATTACHMENTS


Standard Number

Rev.

06-DG-005

0

Sheet 2 of 11

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1.0

PURPOSE The purpose of this document is to lay down the guidelines and design procedure for performing the battery & charger sizing calculation.

2.0

PROCEDURE For battery backup time required, the customer’s design basis shall be referred. In the absence of any specific customer requirements, the backup time can be considered as 1 hour. The battery sizing shall be done on the basis of the following loads.

a) b) c)

total continuous load total 1st minute load total 60th minute load

3.0

STEPS FOR BATTERY SIZING

3.1

Step-1 -Calculation Of Total Continuous Load The total continuous load is the summation of the loads mentioned below: a) b) c) d) e)

Continuous load for HT Switchboards Continuous load for LT Switchboards (PCC) Continuous load for MCCs, if applicable DC Lighting loads Other miscellaneous loads

a) Continuous load for HT Switchboards The following loads shall be calculated:i) Total VA load of indicating lamps ii) Total auxiliary load in VA (This includes trip circuit supervision relay, protection relay, timer, undervoltage relay, auxiliary supply supervision relay.) i)

Total VA load of the indicating lamps = (Total number of H.T. Breakers) *(Number of the indicating lamps for each breaker) *(VA load for each indicating lamp) VA load for indicating lamps shall be obtained from manufacturer’s data . If no data is available, then the load per lamp shall be assumed as 2 VA. Total auxiliary load = (Total number of H.T. Breakers) *(Auxiliary load of each breaker) Auxiliary loads of each breaker can be assumed as 50 VA.

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ii)



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b) Continuous load for LT Switchboards (PCC) Same procedure as mentioned for HT Switchboards shall be followed c) Continuous load for MCC’S Same procedure as mentioned above for LT Switchboards shall be followed, if applicable d)

DC Lighting load

The wattage of all the lamps operating on DC shall be added to obtain the total DC lighting load. e)

Other miscellaneous load

The wattage of all other miscellaneous load operating on DC shall be added to obtain the total miscellaneous load. 3.2

Step-2 – Calculation Of Total 1st Minute Load

a) b) c)

The total 1st minute load is the summation of the following loads:1st minute load for HT Switchboards 1st minute load for LT Switchboards 1st minute load for MCC’S a) 1st minute load for HT Switchboards The total 1st minute load is the summation of the following loads:-

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i) ii) iii) iv)

Total VA loads of trip coils of all the breakers Total VA load of Lock out relay Total auxiliary load in VA Total continuous load i)

Total VA load of trip coils of all the breakers =(Number of breakers)*(VA load of trip coil of each individual breaker) VA load of trip coil shall be obtained from manufacturer’s data. In the absence of any data, the load may be assumed as 250 VA.

ii)

Total VA load of Lock out relay of the breakers = (Number of breakers) * (VA load of the relay) VA load of lockout relay shall be obtained from manufacturer’s data. In the absence of any data, the load may be taken as 150 VA. The number of breakers shall be 3 incoming and approximately 3 outgoing feeders.



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iii)

Total auxiliary load i.e. VA, may include load for relay, for auxiliary relays, timers etc. Total auxiliary load = Total number of breakers * auxiliary load for each breaker feeder. Auxiliary load of each breaker feeder can be taken as 15 VA.

iv)

Total Continuous load is obtained in Step-1 above.

b) 1st minute load for LT Switchboards(PCC) Same procedure as mentioned above for HT Switchboards shall be followed. c) 1st minute load for MCC’s The procedure is the same as mentioned above for LT Switchboards, if applicable 3.3

Step-3 - Calculation Of Total 60th Minute Load The total 60th minute load is the summation of the following loads:i) ii) iii)

Total 60th minute load for HT switchboards Total 60th minute load for LT switchboards (PCC) Total 60th minute load for MCCs.

i)

Total 60th minute load for HT switchboards:-

The total 60th minute load is the summation of the following loads:a) Total VA loads of closing coils of the number of breakers which will close at a time. b) Total VA load of Spring Charging motors of all the breakers, if DC operated c) Total continuous load. a) Total VA loads of closing coils =(Number of breakers which will close at a time) *(VA load of closing coil of each individual breakers) Number of breakers which will close at a time will depend on the operating philosophy of the plant (2 Incomer, 1 Buscoupler, & 2 to 4 Outgoing feeders). The VA load of closing coils of each individual breaker will be obtained from manufacturer’s data. b) Total VA load of the Spring Charging Motors =(Number of breakers) *(VA load of spring charging motor of each individual breaker)

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The VA load of spring charging motor of each individual breaker shall be obtained from manufacturer’s data.



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c) Total Continuous load is obtained in Step 3.1 above. ii)

Total 60th minute load for LT Switchboards(PCC) Same procedure as mentioned above for HT Switchboard shall be followed.

iii)

Total 60th minute load for MCC’s The procedure is the same as mentioned above for LT Switchboards.

3.4

Step-4 –Calculation Of Load Cycle Currents Nominal DC Voltage = V Considering ± 10 % voltage variation minimum DC voltage = 0.9 V N = Number of Cells. Therefore, End Cell Voltage = (Minimum DC Voltage) / (Number of Cells) = (0.9 V) /( N )

3.4.1

Calculation of total 1st minute load cycle current Total 1st minute load (in VA ) is obtained in clause 3.2 above. Total 1st minute load current = (Total 1st minute load in VA )/ (Minimum DC Voltage) = (Total 1st minute load in VA )/ (0.9 V)

3.4.2

Calculation of total Continuous load current Total Continuous load (in VA) is obtained in clause 3.1 above. Total continuous load current =(Total continuous load in VA ) / (Minimum DC Voltage ) =(Total continuous load in VA) / (0.9 V )

3.4.3

Calculation of 60th minute load cycle current Total 60th minute load (in VA) is obtained in clause 3.3 above Total 60th minute load current = (Total 60th minute load in VA ) / (Minimum DC Voltage ) = ( Total 60th minute load in VA ) / ( 0.9 V )

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From the above-obtained values for load cycle currents, the load cycle curve is drawn.



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Sheet 6 of 11

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I (in Amps)

T (in min)

0

3.5

1

59

60

Step-5 –Calculation For Battery Sizing The following factors are to be considered for battery sizing: a) Performance factor This factor is considered to estimate the performance of the battery at a discharge rate other than the nominal rate. The performance factor is defined as the ratio of the amperes that can be drawn from the battery for ‘t’ minutes to the rated capacity (AH), for a particular end cell voltage. Performance factor = Amperes ( in ‘t’ minutes) / (Rated AH ) b) Temperature Correction Factor This factor is considered to take care of the variations in performance of the battery at different temperatures. While high temperature results in higher performance, lower than nominal temperature (27°C) lead to lower performance due to sluggish chemical activities. The performance factor is divided by the temperature correction factor to obtain the corrected performance factor. c) Aging factor The performance of a battery comes down with the time of usage. The battery reaches the end of its useful life when it fails to deliver 80% of its rated capacity. In order to deliver its rated capacity even at the end of the estimated life of the battery, a correction factor of 1.25 ( = 1 / 0.8 ) is taken as aging factor. However, customer’s design basis shall also be referred for any specific requirements regarding aging factor. d) Spare capacity factor

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A spare capacity factor shall be considered to take care of any future additional load. Customer’s design basis shall be referred for any customer requirements regarding spare capacity. In the absence of any specific customer requirements, a spare capacity factor of 1.2 ( 20% additional capacity ) can be considered.



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Sheet 7 of 11

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3.5.1

Calculation of Ampere Hour requirement for the first minute i) ii) iii) iv)

Total time duration = 1 min The 1st minute load current is obtained from calculation in clause 3.4.1 above The end cell voltage is obtained in clause 3.4 above. For the value of end cell voltage, the performance factor corresponding to the value of load current shall be obtained from manufacturer’s data. Typically for an end cell voltage of 1.14 volts per cell, corresponding to a load of 212A for 1 min, the performance factor = 212 / 145 = 1.46

v)

Let the minimum ambient temperature = t° C. Corresponding to the minimum ambient temperature, the temperature correction factor is obtained from manufacturer’s data. Typically for a minimum ambient temperature of 10° C, the temperature correction factor is 1.11

vi)

The performance factor is divided by the temperature correction factor to obtain the corrected performance factor Corrected performance factor = (Performance factor ) / (Temperature correction factor ) Here in our case, the corrected performance factor = 1.46 / 1.11 = 1.31

vii) viii)

Ampere Hour Opening Balance = 0 Ampere Hour Capacity Required for the 1st minute shall be calculated from the formula mentioned below. AH capacity required = ( Load current ) / (Corrected Performance Factor )

ix)

Ampere Hour Capacity Drained shall be calculated from the formula mentioned below: AH capacity drained = (Load Current ) * (Time Duration in mins) / ( 60 ) AH Balance = AH Required - AH Drained AH to be added = AH Required - AH Opening Balance. For the 1st minute, AH Opening Balance = 0 Therefore AH to be added = AH Required

x) xi)

3.5.2

Calculation of Ampere Hour Requirement from the first minute to the 60th minute i)

Total time duration = 58 min

ii)

AH Opening Balance = AH balance at the end of 1st minute obtained from calculation in clause 3.5.1 x) above.

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The value of end cell voltage is the same as obtained in clause 3.5.1 above.



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Sheet 8 of 11

16-QSP-05-3A

ii) The load current drawn from the battery during this time duration is the total continuous load current. The value of continuous load current is obtained from calculation in clause 3.4.2 above. iii) For the value of end cell voltage, the performance factor corresponding to the value of load current, shall be obtained from manufacturer’s data. For the determination of performance factor, even through the actual time duration is 58 min, the time duration shall be considered as 60 min. From the attached manufacturer’s data, for an end cell voltage of 1.14 Volts per cell, corresponding to load current of 129A for 60 min, Performance factor = 129 / 285 = 0.45 The value of temperature correction factor is obtained in clause 3.5.1 x) above.

vi) vii)

v) The performance factor is divided by the temperature correction factor to obtain the corrected performance factor. In this case, corrected performance factor = 0.45 / 1.11 = 0.4 AH Capacity required shall be calculated from the formula mentioned in clause 3.5.1 viii) above. AH capacity drained shall be calculated from formula mentioned in clause 3.5.1 ix) above.

AH Balance = AH required – AH drained. AH to be added = AH required – AH opening Balance. AH opening balance is already obtained in 3.5.2 ii) above.

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3.5.3

Calculation of Ampere Hour Requirement for the 60th minute i)

Total time duration = 1 min

ii)

AH Opening Balance = AH Balance at the end of 58th minute as obtained from calculation in clause 3.5.2 x) above.

iii)

The value of end cell voltage is same as obtained in clause 3.5.1 above.

iv)

The value of current drawn from the battery during this period is obtained in clause 3.4.3 above.

v)

The value of performance factor shall be obtained by the method shown in clause 3.5.2 v) above.

vi)

The value of temperature correction factor is already obtained in clause 3.5.1 v) above.

vii)

The value of corrected performance factor is obtained by the method shown in clause 3.5.2vii) above.



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Rev.

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Sheet 9 of 11

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3.5.4

viii)

AH capacity required shall be calculated from the formula mentioned in clause 3.5.1 viii) above.

ix)

AH capacity drained shall be calculated from formula mentioned in clause 3.5.1 ix) above.

x)

AH Balance = AH required – AH drained

xi)

AH to be added = AH Required – AH Opening Balance AH Opening Balance is already obtained in clause 3.5.3 ii) above.

Calculation of Battery AH capacity Minimum AH capacity required = ( AH to be added for 1st minute ) + (AH to be added from 1st minute ) + ( AH to be added for 60th minute )

minute to 60th

Aging Factor = 1.25 or as specified in customer’s design basis Spare Capacity Factor = 1.2 or as specified in customer’s design basis Hence battery AH capacity required = ( Minimum AH Capacity ) * (Aging factor ) * ( Spare Capacity Factor ) The nearest battery AH capacity as per manufacturer’s rating shall be selected. For example, if the calculated value of AH Capacity is 645 AH & the nearest rating as per manufacturer is 690 AH, then 690 AH shall be selected. 4.0

STEPS FOR BATTERY CHARGER SIZING The customer’s design basis shall be referred for any customer requirements regarding battery charger sizing. In the absence of any specific customer requirements, the method mentioned below shall be followed: -

4.1

Sizing Of Boost Charger Battery Boost Charger Current Rating = 1.15 * 0.14 * AH rating of battery ( For lead acid battery ) = 1.15 * 0.2 * AH rating of battery ( For Nickel Cadmium Battery ) AH capacity of battery is obtained from calculation in clause 3.5.4 above.

4.2

Sizing Of Float Charger

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Battery Float Charger Current Rating = 1.15 * Average DC load + float charge current Average DC load = ( Area under the battery duty cycle curve ) / ( Battery duty cycle duration )



Standard Number

Rev.

06-DG-005

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Sheet 10 of 11

16-QSP-05-3A

In this case, Average DC load = (1 / 60 ) * { (Total 1st minute load current ) * 1 + (Total continuous load current ) * 58 + (Total 60th minute load current ) * 1 } Float charger Current = ( Float Charge factor ) * ( Battery AH Capacity ) The value of float charge factor shall be obtained from battery charger manufacturer. However, for preliminary battery charger sizing calculation it can be assumed as 0.01 ( 1 % max.) battery AH capacity. However, the same shall be checked & confirmed with charger manufacture. 4.3

Selection Of Battery Charger Current Rating The battery charger current rating shall be selected based on Boost charge current or float charge current, whichever is higher. A spare capacity factor, on the basis of customer design basis, shall be considered for future use. In the absence of any specific customer requirements, a spare capacity factor of 1.25 (25 % spare capacity) can be considered. Battery Charger rating = (Float charge current or Boost charge current whichever is higher ) * (Spare capacity factor )

5.0

List Of Attachments

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Attachment 1 – Sample Battery & Charger sizing calculation



Standard Number

Rev.

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Sheet 11 of 11

Design Guide -Battery Sizing

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