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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.

UMKC Substation Group 1 Burns & McDonnell


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)



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



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)



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:



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



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



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



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



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.



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)\


http://www.selinc.com/


8.0 APPENDIX A

ENERSYS EC-M BATTERY DISCHARGE CURRENT




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