DC Supply

System

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 Presentation outline
•Duties
•DC Loads
•DC system
•Types of Batteries

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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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 Types of Power Supplies
In a Power Plant

• 11KV/3.3KV/415V AC Power Supply

• 415V AC Emergency Supply(DG)
• DC Power Supply
• UPS Supply

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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 Supplies……………Why?

• 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 POWER SUPPLY
SCHEME
1. Earlier concept;
• 1X100% battery bank along with its chargers for each unit with inter-
unit interconnection through high capacity DC bus bar.
• In view of large size of above DC loads of each unit and the large unit
pitch it is necessary to provide a separate DC system (battery
+chargers) to enhance the plant’s overall reliability.
• NTPC earlier plants –Kahalgaon-I, Vindhchachal-I and some other also
have above DC scheme.

2) Present concept;

• In view of the reasons explained above 2x100% capacity DC system is

provided for each unit and switchyard separately.
• Minor DC loads of offsite areas in the plant i.e. WTP, Ash handling are
fed from plant DC system as it is now restricted to limited area
switchgear rooms, as control now no longer relay based.
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PMI Revision 01 11
 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 Charger II

440 V 440 V
220 V DC 220 V DC

Battery Battery
Bank Bank

DCDB

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Feeders Feeders
 Typical UPS System
440 V
AC
Converter

220 V
DC Battery 220 V DC

Inverter

220 V
ACDB AC UPS

All Unit Controls

&
Power supply
Protection
Module
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 DG-1 DG-3 DG-2

X X

X X

DG SWGR-1 DG SWGR-2

X X
X X

UNIT EMER UNIT EMER UNIT EMER

SWGR-1 UNIT EMER SWGR-3 SWGR-4
SWGR-2
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 EMCC
(1) AOP-1 (2) Em. Lighting Trf.
(3) TVDC Reserve Supply (4) UPS Ch.
(5) Scanner Air Fan (6) BVDC Reserve Supply
(7) AC Seal Oil Pump (8) Air Heater Lub Oil Panel
(9) Jacking Oil Pump (10) Stator Water Pump-B
(11) Barring Gear (12) +26 V DC ATRS Ch. ‘B’
(13) -26V DC ATRS Ch.’B’ (14) 26V DC FSSS Ch. ‘B’
(15) 26V DC DDC Ch. ‘A’

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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/V’s
• 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

EMCC

+/-24 V
CHARGER-
A
Batteries
350AH

USS

+/-24 V
CHARGER-B
Batteries3
50AH

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 +/- 24 V DC System
+24 V DC

EHC

ATRS PANNEL for Controls FSSS for Control logics

ALL TURBINE PROTECTIONS SADC

HP/LP BP Servo Valve

TSE ACS CABIN

ATT EXCITATION SYSTEM CARDS

TSE

SPEEDER GEAR/STARTING DEVICE AVR

JOP-3 GRP

LUB OIL TEMP/CONTROL FLUID TEMP/MAL LOAD SHEDDING SOLENOID

TEMP/COLD GAS TEMP

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 UNINTERRUPTED POWER
SUPPLY
• An uninterruptible power supply (UPS),
uninterruptible power source or sometimes
called a battery backup is a device which
maintains a continuous supply of electric power to
connected equipment by supplying power from a
separate source when utility power is not available.

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 CAPACITY
• UPS units come in sizes ranging from units which
will back up a single computer without monitor
(around 200 VA) to units which will power entire
data centers or buildings (several megawatts).
• Larger UPS units typically work in conjunction with
generators.

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 UPS DESIGNS
• The general categories of modern UPS systems
are on-line or off-line, the latter often referred to as
standby.

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 ON-LINE UPS
• ON-LINE UPS SYSTEMS PROVIDE THE HIGHEST LEVEL OF PROTECTION FOR
MOST IMPORTANT EQUIPMENT.

• THESE SYSTEMS USE A COMBINED DOUBLE-CONVERSION(AC TO DC/DC TO

AC) WHICH CONTINUOUSLY POWERS THE LOAD,TO PROVIDE BOTH
CONDITIONED POWER ANDOUTAGE PROTECTION.

• THEY PROVIDE PROTECTION AND ISOLATION FROM ALL TYPES OF POWER

PROBLEMS,INCLUDING POWER SURGES,HIGH VOLTAGE SPIKE,SWITCHING
TRANSIENTS,NOISE FREQUENCY VARIATION ETC.

• THESE SYSTEMS ARE OFTEN USED FOR MISSION-CRITICAL APPLICATION

THAT REQUIRE HIGH PRODUCTIVITY AND SYSTEM AVAILABILITY.

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MAJOR COMPONENTS OF UPS
• CHARGER
• BATTERY
• INVERTER
• STATIC SWITCH
• ALTERNATE SUPPLY

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UNIT UNINTERRUPTED POWER SUPPLY

CHARGER-1 INVERTER-1 STATIC SWITCH

415 V AC
EMCC

Manual
Battery Bypass
switch

CHARGER –2 INVERTER-2 Voltage

stabilizer
USS

Battery

ACDB-1
240 V AC
ALT SSVS
SUPPLY
ACDB-2

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 INVERTER
• Inverters takes an input 210 to 280 V DC from chargers
or battery and converts them to 240V AC.
• First the DC voltage is converted to square wave using
SCRs.
• The SCRs gate pulses can be controlled to slightly alter
frequency.
• In latest UPS inverters IGBTs are being used.

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 SUPPLY FROM UNIT UPS:
1. HMI/ MMI
2. Servers, Printers, CCTV
3. Work station-Large Video Screen (LVS) for operation thru
logic
4. BFP-A & B LCP for instruments, Speed switch)
5. Field Analyzers: O2 ANALYSER, Conductivity mst (CPU).
6. BFP-C SCOOP.
7. H2 PURITY ANALYSER.
8. MDBFP LCP-Scoop tube actuator
9. PA SYSTEM.
10. RECODERS, Indicators IN UCB.
11. Unit Control Desk & Vertical Panel
12. H2/Seal Oil Panel (DP transmitter: 24 V DC & AC I/P to this is
from UPS
13. Hydrastep

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 IF UNIT UPS FAILS:

1. HMI/ MMI WILL NOT BE AVAILABLE.

2. ANNUNCIATIONS WILL FAIL.
3. PA SYSTEM NOT AVAILABLE.
4. HYDRASTEP INDICATION NOT BE AVAILABLE.
5. Field Analysers will not be available

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Battery

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 Types of Batteries

Lead Acid Nickel - Cadmium

Plante Pocket Plate

Tubular Tubular Plate
VRLA Sintered Plate
Pasted 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
Ni-Cd Pocket Plate
Batteries
• Exide Industries
• AMCO Batteries
• HBL NIFE 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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 General Battery Technologies

Popular Secondary Electrochemical Couples used worldwide

LEAD ACID
* NICKEL CADMIUM
NICKEL METAL HYDRIDE
LITHIUM ION
BIPOLAR LEAD ACID

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More Exotic Systems:

POLYMER BATTERIES

FUEL CELLS

FLY WHEELS

ULTRACAPACITORS

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 Application Pattern:

INDUSTRIAL LEAD – ACID

POWER NICKEL – CADMIUM

LITHIUM ION
PORTABLE NICKEL – METAL HYDRIDE
POWER
NICKEL CADMIUM

HIGH END
APPLICATION – SILVER - ZINC
TORPEDOES, SPACE

NICHE POWER FUEL CELLS

GENERATION
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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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The design, in terms of alloys used, as well as the geometry
of the POSITIVE plate of a lead acid battery, determines the
performance as well as life of the product.

A plate comprises of two distinct aspects:

a. The grid – which acts as - support of the „active material‟

- current conductor
b. The „active material‟ itself.

The Lead Acid battery positive plates come in the following

Three basic geometries:
- the ‘Flat Plates’
- the ‘Tubular Plates
- the ‘Plante’ Plates
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Nickel Cadmium Batteries

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 Features
• Unsurpassed resistance to electrical and mechanical abuse

• Exceptionally long and reliable service life

• Wide operating temperature range

• No emission of corrosive gases

• Explosion proof vents

• Minimal maintenance

• Low life time cost

• Quick recharging

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 BATTERY CAPACITY
• Expressed in ampere hour(AH)
• Duration of discharge-10 hr for Plante/5 hr for Ni-Cd
• Electrolyte specific gravity-1.2+-.005 lead acid plante cells

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 MANUFACTURERS IN INDIA
• LEAD ACID PLANTE • Ni-Cd POCKET PLATE
BATTERIES-EXIDE BATTERIES.
INDUSTRIES • AMCO BATTERIES,
• HBL NIFE BATTERIES

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 Cell Designation -
Lead Acid Plante
P 40 P-HDP

G - Glass
Plante - P AH - Capacity H - Hard Rubber
Tubular - T P - Plastic
W - Lead Lined Wood
F - FRP

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 CELL
DESIGNATION-Ni-
Cd POCKET
KPH 150P
PLATE
P-POCKET AH-Capacity P-Plastic
S-SINTERED S-Steel
T-TUBULAR

L-Low Rate Of Discharge

M-Medium Rate Of Discharge
H-High Rate Of Discharge
X-Very High Rate Of Discharge
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CHARGING OF BATTERIES
Lead Acid - Plante Ni - Cd

Nominal Voltage 2.0V 1.2V

Float Voltage 2.1V - 2.25V 1.40V - 1.42V
Boost Voltage 2.3V - 2.7V 1.5V - 1.7V
Float Current 1.4mA / AH 2.0mA / AH

Boost Current 140mA / AH 200mA / AH

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BATTERY CHARGERS

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 FLOAT CUM BOOST
CHARGERS-FCBC
• Voltage
• Current

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 SIZING IN FLOAT MODE

In float mode the charger shall be capable of meeting the

trickle charging of both the battery banks, station continuous
load current and starting current of largest DC drive.

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 SIZING IN BOOST MODE

In boost mode charger shall be capable of boost charging a fully

discharged battery in 8-10 hours.

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 CHARGER OPERATION
• CHARGER-FLOAT/BOOST
• CONTROLLER -AUTO/MANUAL

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 CHARGER OPERATION
• Float mode/controller auto mode-charger supplies
at constant voltage(set),with current limiter in
function.
• Boost mode/controller in auto mode-charger
supplies at constant current(set),with voltage limiter
in function

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 220 V FLOAT CUM BOOST
BATTERY CHARGER
(i) Manufacture UPTRON POWERTRONICS LTD,Sahibabad

(ii) A.C. input 415 V ± 10%, 3 ø, 50 Hz±5%, 69.7 A

(iii) D.C. output voltage Float 220- 250 V
Boost 200- 300 V
Current Float 110A
Boost 80 A
(iv) Ripple 1% peak to peak without battery

(v) Efficiency at full load More than 85%

(vi) Voltage setting range 220 – 300 V

(manual)
(vii) Current setting range 50% to 100% of rated current

(viii) Cooling AN

(ix) Max. ambient temp. 500 C

(x) Response time Less

PMI than 01
Revision 750 mSec 58
THANK YOU

PMI Revision 01 59