13 March 2013 1

DC Supply

System

13 March 2013 2

Duties

DC Loads

DC system

Types of Batteries

Presentation outline

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DC SYSTEM IS

DESIGNED

To supply high standard of reliable & secure dc power

To provide continuous & quality power as and when required

Under normal & abnormal operating conditions

Ultimate & final dc back-up power to equipment and dc drives when total ac supply fails

Hence they are battery backed

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DUTIES

To supply equipment which requires dc during normal conditions

To supply standby equipment/dc drives

To supply starters of various equipment

To supply equipment when ac supplies have been lost

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DC Power Supply

Various Critical Drives

Emergency DC Lighting

Switchgear Control Supply for closing & tripping

Control, Protection And Interlocks

Indication, Annunciation & Alarm System

Public Address System

DAS And Communication System

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DC SuppliesWhy?

Emergency Lube Oil Pump

Emergency Jacking Oil Pump

Emergency Scanner Air Fan

Emergency Seal Oil Pump

Breaker/Unit Protections

Emergency Lighting

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The Ultimate Backup

In case of unit tripping / grid failure, either station

changeover takes place / DG would start.

Normally, grid supply would be restored in minimum

possible time and DG would shut down.

In case of DG failure, the DC backup comes in to

service to facilitate safe shut down.

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Selection of voltage -DC

POWER SUPPLY

In power plant D.C. pumps, lighting require comparatively high voltage due to their high power requirement. Hence as a standard these applications are designed with 220V level.

It is desirable to have comparatively lower voltage- 24V/48V/110V for control/indications/annunciation due to safety reasons. However to avoid multiplicity of DC supplies (particularly we require two control supplies), we have adopted uniform 220V DC voltage for plant electrical systems for switchgear control, protection and interlock operation.

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DC System

Battery

Battery Charger

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DC SYSTEM

BATTERY CHARGERS [TWO/THREE]

BATTERY BANKS [ONE/TWO]

DC DISTRIBUTION BOARDS [ONE/TWO]

DC FUSE BOARDS

UN EARTHED SYSTEM

CHARGER TROUBLE, DC EARTH FAULT AND DC VOLTAGE ABNORMAL ALARMS IN UCB

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220 V DC SYSTEM

Charger I

440 V

220 V DC

Charger II

Battery

Bank

Battery

Bank

Feeders

440 V

220 V DC

Feeders

DCDB

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Typical UPS System

Module

Power supply

440 V

AC

220 V

DC Battery 220 V DC

220 V

AC UPS

All Unit Controls

&

Protection

48 V, 15V, 24 V, DC

Converter

Inverter

ACDB

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220 V DC

FSSS HT Breakers Vacuum Breakers HOTV/HORV Deaerator Overflow Valve GRP HP Heater Protections DC Fans & Pumps Extraction FCNRV V/Vs SADC Trim Device Load Shedding Relay Scanner Air Fan Outlet & Emergency Damper All DC Lights

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220 V Supplies

EMCC USS

MAIN CHARGER RESERVE CHARGER

UPS CHARGER-1 UPS CHARGER -2

DAS UPS CHARGER 1 DAS UPS CHARGER-2

+/- 24 VA DC CHARGER +/- 24 VB DC

CHARGER

DG SET BATTERY

SYSTEM

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+/- 24 V DC System

+/-24 V

CHARGER-

A

+/-24 V

CHARGER-B

Batteries

350AH

Batteries3

50AH

EMCC

USS

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+/- 24 V DC System

+24 V DC - 24 VDC

EHC LPBP

ATRS PANNEL SPEEDER GEAR/STARTING DEVICE

ALL TURBINE PROTECTIONS EHC

LPBP ATT

TSE ACS CABIN

STARTING DEVICE TSE

LUB OIL TEMP/CONTROL FLUID TEMP/MAL

TEMP/COLD GAS TEMP

LUB OIL TEMP/CONTROL FLUID

TEMP/MAL TEMP/COLD GAS TEMP

EXCITATION SYSTEM CARDS AVR

JOP-3 GRP

LOAD SHEDDING SOLENOID

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Battery

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Types of Batteries

Lead Acid Nickel - Cadmium

Plante Tubular VRLA Pasted Plate

Pocket Plate Tubular Plate Sintered Plate

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Applicable Standards

Lead Acid Plante Batteries IS:1652

Vented Ni-Cd Batteries IS:10918, IEC:60623

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Manufacturers In India

Lead Acid Plante

Batteries

Exide Industries

Ni-Cd Pocket Plate

Batteries

AMCO Batteries

HBL NIFE Batteries

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Basic Electrochemistry

Lead Acid Battery:

Discharge

PbO2 + 2H2SO4 + Pb ===== PbSO4 + 2H2O + PbSO4 (POS) (NEG) (POS) (NEG)

Water is discharge reaction product and has a very important role in helping assess state

of charge of a cell, at any point of time.

Nickel Cadmium Battery:

Discharge

2NiOOH + 2H2O + Cd ==== 2Ni(OH)2 + Cd(OH)2 (NEG) (POS) (NEG) (POS) KOH is present as electrolyte, in very dilute form, which essentially functions as ion

conductor. Although water gets consumed on discharge, the change in concentration of

the dilute solution is minimal, and hence cannot be used as an indicator of state of charge.

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Whilst lead-acid system has overwhelmingly dominated the

industrial application worldwide, the nickel-cadmium system too,

has served niche applications because of a few of its intrinsic

characteristics which suit such applications very well.

Some of these are:

Excellent charge-discharge cycling capability

Excellent recovery from deep discharge

Compact, low weight

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The Lead-Acid Technology

The lead acid battery comes in two basic configurations;

a. The Flooded Electrolyte version

Towards the end of charge, a large part of the energy supplied

to the cell is dissipated in breaking of water and evolution of

gases, oxygen and hydrogen at the positive and negative

electrodes respectively.

This loss of water through electrolysis is unavoidable and hence

replenishment has to be made periodically to ensure life as well

as performance of the product.

The rate of loss of water is a function of grid alloys, charging

voltages, temperature, age of battery.

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The Lead-Acid Technology

b. The sealed Maintenance Free version. This is more popularly

known as Valve Regulated Lead Acid (VRLA) battery

This again comes in two basic forms:

** The absorptive glass mat (AGM) technology

** The Gel technology with flat or tubular plates.

In essence, the oxygen gas liberated inside a lead-acid cell

diffuses towards the negative electrode and recombines to

reform water. There is no net depletion of water and

hence these versions are popularly known as maintenance

free batteries.

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Battery Capacity

Expressed in ampere hour(AH)

Duration of discharge-10 hr for Plante/5 hr for Ni-Cd

End cell voltage-1.85 volt for Lead acid plante/1.0 volt for Ni-Cd

Ambient temperature-27 deg cent.

Electrolyte specific gravity-1.2+-.005 lead acid plante cells

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SELECTION OF BATTERY

TYPE IN POWER PLANT

Power plant batteries standby duty require high discharge performance with continuously connected on float mode operation.

Expected Life of lead acid tubular is of the order of 8-10 years so in a power plant life of 25 years minimum two replacement would be

required.

Lead acid PLANTE and Ni-Cd (alkaline) have expected life of 15-20 years hence only one replacement would be required in whole plant

life.

In addition lead acid plante have much better discharge performance than tubular type for the specified emergency duration.

In view of above plante type lead acid or Ni-Cd high discharge batteries are specified for power plant applications.

Wherever there is space constraints VRLA batteries may be an option however this has also expected life of 8-10 years.

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THANK YOU