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BRIEF DESCRIPTION
of
DC SYSTEM OF NTPC, TANDA
BYJK SAHU
SR. ENGR (OPN)
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Combination of cells iscalled a battery.
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Two electrodes kept in electrolyte
forms a cell, one electrode having +ve
charge is called Anode & other havingve charge is called
Cathode.
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* Battery Voltage may vary as per
connection of cells.
* One cell has normal operative voltage -
2v. Therefore required voltage can be
obtained by 2x Number of cells connectedin series.
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Capacity can be increased by-
*Number of cells connected in parallel.
* By increasing the plate (electrode) area.Capacity is denoted
in Ampere hour (AH).
For example- A battery of 150 AH
capacity will supply 15Amp current for10 hours only.
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It is the measure of concentration of Electrolyte.
S.G.= Density of Electrolyte
Density of water
Normal S.G. of Battery electrolyte is
12005 at27C.
Correction of S.G.- Add7 to the reading for every increase
of10C
temperature.
Subtract 7 for every decrease of10C temperature.
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Parts of the battery are:1. Container
2. Terminal
3. Connector
4. Vent play
5. Float / Level Indicator
6. Electrode / Plates & Seperators7. Electrolyte
8. Mud rib
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20AH TO 150AH CELL
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300AH TO 600AH CELL
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1. Boost charging / Quick charging / Constant Current
charging
Charging current= Capacity x 0.6 Amp
10
2. Float charging / Trickle charging / Constant Voltage
chargingCharging current- Negligible
3. Equalizing charge Boost charging of battery (once in a
Month)
Indications of full charged Battery1. Freely gasing
2. Voltage 3 hourly readings are constant.
3. S.Gravity 3 hourly readings are constant
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Rated discharging Current is Capacity
10
At this Rated discharging current Voltage of anycell should not
fall below 1.85V
NOTE-In any case battery should not discharge
after 1.8V/cell and battery should be put in
boost charging immediately after complete
discharging.
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Equipments used:-
1. Hydrometer
2. Thermometer
3. Apron
4. Gloves
5. Gum boots
6. Protective Goggles
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Following things are to be checked
daily
Cell Voltage
Cell Specific Gravity and Temperature of
electrolyte.
To be checked for leakage.
Cleanliness and corrosion of the connectors.
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1.Battery terminals is to be cleaned and
Petroleum jelly / any conductive anticorrosiveagent should be
applied on terminals.
2.Electrolyte level should be maintained.
NOTE :- Electrolyte level to be topped up with
distilled water only if there is no leakage of
electrolyte.
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Normal DC load is fed from float charger
only through DC DB and Battery is on
floating. Battery only takes load in case of
failure of float charger
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BOOSTCHARGER
110 Cell
88 Cell
1ST Cell
Battery
LOAD
Float Charger In
ON Condition
3O AC Supply
3oAC
Supply
(In Service on cc mode)
Contactor C4
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BOOSTCHARGER
110 Cell
88 Cell
1ST Cell
Battery
LOAD
Float Charger In
OFF Condition
3
O AC Supply
3oAC
Supply(In Service
on CV mode)
Contactor C4
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Inter unit ConnectionMDB - II
Fdr5a
U # 4 BatteryU # 3 Battery
MDB - I
Fdr35B
U # 2 Battery
Fdr5A
U # 1 Battery
Fdr 5
SwitchyardBattery
MDB - III
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BATTERY CHARGING CIRCUIT
Proposed Suggestion
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Important suggesions
If float charger is not in service, do not ON
Boost charger in cc mode. DC Voltage low
may cause problem in the system.
Precautionary Quick charger should alwaysbe left in cv mode if
not in use.
One switch of appropriate rating with a
blocker diode in series should also be
incorporated, in battery to load circuit across
contactor C4 to avoid 220V DC failure in the
system, If Contactor C4 fails suddenly.
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Suggestions are
heartily welcomed.
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