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UMKC Substation125 VDC Battery System Sizing
Revision 4
prepared for
Burns & McDonnell
April 2, 2014
prepared by
UMKC Senior Design (Substation) Group
UMKC Substation 125 VDC Battery System Sizing Table of Contents
Table of Contents
1.0 INTRODUCTION...................................................................................................1
2.0 SYSTEM DESIGN CRITERIA...............................................................................22.1 Battery Cells.............................................................................................................22.2 Assumed Derating Factors.......................................................................................3
3.0 LOAD CLASSIFICATIONS...................................................................................4
4.0 BATTERY SIZING.................................................................................................64.1 Battery Capacity & Duty Cycle:..............................................................................64.2 Battery Postive Plates..............................................................................................7
5.0 BATTERY CHARGER SIZING..............................................................................9
6.0 CONCLUSION....................................................................................................10
7.0 REFERENCES....................................................................................................11
8.0 APPENDIX A.......................................................................................................12
UMKC Substation Group TOC-1 UMKC
UMKC 125 VDC Battery System Sizing
1.0 INTRODUCTION
The substation DC system provides a continuous source of power for operating circuit
breakers, protective relaying, SCADA system, and other critical systems.
The station battery is a critical piece of equipment on our system. Batteries provide a
reliable source of DC power required for switching, relaying and communications. They provide
power for the line and transformer protection systems, circuit breakers and other equipment. The
batteries are used to provide an emergency source of DC power needed to aid in safe shutdowns
and in station restoration. The battery must accommodate the initial switching load during a
disturbance and have enough reserve for restoration at some time in the future. Our battery
chargers are sized to provide the continuous station load, maintain a fully charged battery and
recharge the battery within 24 hours after a discharge. The chargers are not capable of fully
handling switching or restoration loads. The battery is used to provide these high current needs.
Poor battery system integrity can result in damage to substation and generating facilities.
After reviewing the layout and the one line diagram of the substation the worst case
tripping scenario can be: if a 69 kV line should fall on the 138 kV bus, then one would need to
evaluate a simultaneous 69 kV line fault and a 138 kV bus fault. As there might be a bus tie
breaker failure, then two simultaneous bus faults would occur. As there is backup relaying, it is
assumed that both primary and backup relays will pick up. We have been informed not to
consider future expansion in our substation design. Emergency lighting will pick up in the first
minute of duty cycle and will be on during the 8 hours period.
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UMKC 125 VDC Battery System Sizing
2.0 SYSTEM DESIGN CRITERIA
2.1 BATTERY CELLS
The number of cells (ncells) for the battery can be calculated by the following equation where Vmax is the
maximum system voltage specified to be 140VDC, and Vcharge is the maximum charge voltage per cell of
2.33VDC.
ncells=V max
V charge
The number of cells equates to 60; with this value, the minimum cell voltage (Vcell) is 1.75V/cell which is
calculated by the following equation where Vmin is the minimum battery voltage specified to be 105V.
V cell=V min
ncells (V/cell)
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2.2 ASSUMED DERATING FACTORS
When sizing a battery, various factors used in the calculations account for the lowest possible
temperature, the age, and a design margin; these factors are shown in the following table.
Table 2-1 Battery Correction Factors
Correction Factor Multiplying FactorTemperature (Assuming 55oF is the lowest) 1.15
Age (Accounts for battery instability 80% of life) 1.25Design Margin (Accounts for unexpected future loads) 1.10
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3.0 LOAD CLASSIFICATIONS
Table 3-1 Load Classifications
Loads Amps
Trip coil 1 12
Trip Coil 2 12
Close Coil 1.9
Emergency Lighting 1.536
MOAB 20
Relays 2.5
Communications 10
Announciators 0.144
Intrusion Alarm 0.8
Table 3-2 First Minute Loads (Load L1, Time = 1 minute)
Breakers Tripping = L2Load Amps Quantity Total Amps Duration (hr) Amp Hours
Trip Coil 1 12 4 48 0.016666667 0.8Trip Coil 2 12 4 48 0.016666667 0.8MOAB 20 1 20 0.016666667 0.33333333
Total 116 0.016666667 1.93333333
The continuous load is primarily made up of relay loads and devices to be continuously energized
throughout the eight hour interval. The table below shows the continuous current.
Table 3-3 Continuous Loads (Load L2, Time = 480 minutes)
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Steady State Loads = L1Load Amps Quantity Total Amps Duration (hr) Amp Hours
Relays 2.5 1 2.5 8 20Communications 10 1 10 8 80Intrusion Alarm 0.8 1 0.8 8 6.4Emergency Lighting 1.536 1 1.536 8 12.288Annunciator 0.144 1 0.144 8 1.152
Total 14.98 8 119.84
The following table assumes that the transformer fault and failed breaker issues have been resolved and
the affected part of the substation can be re-energized. Following the re-energization, it’s assumed the
station AC service issue is resolved and the eight hour period concluded.
Table 3-4 Closing the breakers
Closing Breaker = L4Load Amps Quantity Total Amps Duration (hr) Amp Hours
Close Coil 1.9 4 7.6 0.083333333 0.63333333Breaker Motor 43.5 4 174 0.083333333 14.5
Total 7.6 0.083333333 15.1333333
4.0 BATTERY SIZING
4.1 BATTERY CAPACITY & DUTY CYCLE:
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To calculate the total number of amp-hours required of the battery, the 480 minute time frame can be
divided into periods where each one can be expressed as a function equal to the total amperes consumed
in that time frame. The integral of these piecewise functions over the entire time frame yields the total
amp-hours. The following table represents this.
Total ampere hour is the sum of all the tables on the previous pages.
Total Amp Hours136.90666
7
From the previous Table 4-1, a duty cycle can be shown as the following figure.
Figure 4-1 Load Profile
4.2 BATTERY POSTIVE PLATES
IEEE Standard 485 goes into detail on how to calculate the number of positive plates
required of the battery. To do this, the load profile shown in Figure 4-1 used in conjunction with
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the current per positive plate required to bring the batteries’ voltage to 1.75 per cell in a specified
amount of time are required. The latter is provided by the battery manufacturer and is shown in
Appendix A.
We can calculate the positive number of plates using IEEE method. The spread sheet
below will give us the number of positive plates and we can use this formula to find the total
number of plates. We look at at the latter provided by the battery manufacturer, and based on that
we can understand how much AmpHour this certain battery will produce.
total number of plates=1+(2∗number of positive plates)
The total number of plates equates to eleven. The Enersys battery EC-11M will be able to
supply the substation considering that the rated capacity of the battery is 470Ah, and the required
amount should not exceed 136.906Ah
Battery Sizing Spreadsheet
Project: UMKC Substation
1 2 3 4 5 6 7
Change Duration Time to End Capacity @
Load in Load of Period of Section T Min. Rate
Required Section Size
Period (amps) (amps) (min) (min)(6A)
Amps/Pos (Rt)
(3) / (6A)= Positive Plates
Section 1 - First Period Only - If A2 is greater than A1, go to Section 2.
1 A1= 129.44 A1-0= 129.44 M1= 1 T=M1= 1 126.5 1.02324110
7Sec 1 Total
1.023241107
Section 2 - First Two Periods Only - If A3 is greater than A2, go to Section 3.
1 A1= 129.44 A1-0= 129.44 M1= 1 T=M1+M2= 240 21.5 6.02046511
6
2 A2= 14.98 A2-A1= -114.46 M2= 480 T=M2= 475 13.5 -8.47851852
Sec 2 Total -2.4580534
Section 3 - First Three Periods Only - If A4 is greater than A3, go to Section 4.
1 A1= 129.44 A1-0= 129.44 M1= 1 T=M1+M2+M3= 475 13.5 9.58814814
8
2 A2= 14.98 A2-A1= -114.46 M2= 480 T=M2+M3= 479 13.5 -8.47851852
3 A3= 196.58 A3-A2= 181.6 M3= 5 T=M3= 5 108.25 1.67759815
2Sec 3 Total
2.787227782
Section 4 - First Four Periods Only - If A5 is greater than A4, go to Section 5.
1 A1= 129.44 A1-0= 129.44 M1= 1 T=M1+M2+M3+M4= 480 13.5 9.58814814
8
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2 A2= 14.98 A2-A1= -114.46 M2= 239 T=M2+M3+M4= 479 13.5 -8.47851852
3 A3= 14.98 A3-A2= 0 M3= 235 T=M3+M4= 240 21.5 0
4 A4= 196.58 A4-A3= 181.6 M4= 5 T=M4= 5 108.25 1.67759815
2Sec 4 Total
2.787227782
Section 5 - First Five Periods Only - If A6 is greater than A5, go to Section 6.
1 A1= 170 A1-0= 170 M1= 1 T=M1+M2+M3+M4+M5= 480
2 A2= 25 A2-A1= -145 M2= 239 T=M2+M3+M4+M5= 479
3 A3= 25 A3-A2= 0 M3= 235 T=M3+M4+M5= 240
4 A4= 25 A4-A3= 0 M4= 5 T=M4+M5= 5
5 A5= A5-A4= -25 M5= T=M5= 0
Sec 5 Total 0
Section 6 - First Six Periods Only - If A7 is greater than A6, go to Section 7.
1 A1= 170 A1-0= 170 M1= 1 T=M1+M2+M3+M4+M5+M6
= 480
2 A2= 0 A2-A1= -170 M2= 239 T=M2+M3+M4+M5+M6= 479
3 A3= 0 A3-A2= 0 M3= 235 T=M3+M4+M5+M6= 240
4 A4= 0 A4-A3= 0 M4= 5 T=M4+M5+M6= 5
5 A5= 0 A5-A4= 0 M5= 0 T=M5+M6= 0
6 A6= A6-A5= 0 M6= T=M6= 0
Sec 6 Total 0
Random Equipment Load Only (if needed)
R AR= AR-0= 0 MR= T=MR= 0 0
Maximum Section Size 2.787228 Uncorrected Size 2.7872277
8
+ Random Section Size (9) 0 x Temp. Corr. 1.15
= Uncorrected Size 2.787228 x Design Margin 1.1
x Aging Factor 1.25
= Positive Plates 4.40730393
Positive Plates (rounded up) 5
total number of Cells 11
5.0 BATTERY CHARGER SIZING
When sizing the battery charger, the capacity (A) in amps can be found by the following equation where
L is the continuous load being 13.44 Amps, C is the ampere hours emergency discharge which is the 470
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Ah battery rating of the Enersys (EC-11M), H is the number of hours recharge time assumed to be 24
hours, and the 1.1 constant is an factor accounting for the efficiency of lead acid cells.
A=L+ (1.1∗C)H
The charger capacity is calculated to be 34.98 Amps, and therefore, the next larger size will be provided
by Hindle power or equal capable of handling 40Amps will be sufficient for this substation. So, we will
use two 40 Amp battery chargers with a transfer switch feeding each charger from the two AC sources.
6.0 CONCLUSION
Battery sizing is based on the worst case cenario which can happen in the substation. In
our case the worst case scenario is when all 4 breakers trip, and both primary and backup relays
will pick up. After classifying the loads, we should make our duty cycle which is a period of 8
hours. Then based on the IEEE method we should find the number of total plates which will give
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UMKC 125 VDC Battery System Sizing
us the Amp Hour capacity that battery manufacturers can provide. From there we can easily find
the charger ampacity. For UMKC substation we are going to use 11 plate battery which has the
AmpHour capacity of 470, and two chargers with 40 Amperes.
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7.0 REFERENCES
1) IEEE Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications, IEEE Standard 485-1997 (R2003)
2) Siemens SPS2 SF6 Breaker Nameplate
3) EnerSys Type EC-M Battery Datasheet
5) Schweitzer Website, www.selinc.com
6) Southern State Website Part Number: VM-1-104125 (MOAB electrical characteristics)
7) SEL Inc. Website. (Relays electrical characteristics)
8) Hindle Power Inc. Website. (Battery Charger electrical characteristics)\
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8.0 APPENDIX A
ENERSYS EC-M BATTERY DISCHARGE CURRENT
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