1-List down the applications of auxiliary DC power supply
system in Power plants?
- Protections relays
- Circuit breakers
- DCS
- Trip circuits
- Signaling
- Telephone system & communication
- Emergency lighting
- Transmitters & Positioners
- Emergency oil pumps
- Metering panels
2-List down the various DC voltages & their
applications in power plants
Sl No.
|
Voltage
|
Applications
|
1
|
220 VDC & 110 VDC
|
Protection system
Emergency lighting
Trip & closing coil of circuit breakers
Operating mechanisms
|
2
|
48 VDC
|
Telephone communication
|
3
|
+/- 24 VDC
|
Control circuits
Measuring instruments
Static relays
|
3-What is the power source for DC supply?
Main power source is lead-acid storage battery & AC/DC
rectifier set
4-What are the installation requirements for lead acid
battery ?
- The room should be isolated from other system
- Room should have adequate lighting & ventilation
- The room walls & floor should have acid proof tiles
- Battery cells should be installed on insulated racks
- Racks should be placed on insulator generally porcelain
insulators
- Cables should be acid proof
- The DC bus bars should be of round or flat copper materials
- Bus bars connections are made by soldering or brazing
- The positive terminal of the battery is Red & negative
terminal should be blue
30-selected QnA on power Transformers
5-How do you calculate the maximum discharge current of
batteries?
Maximum discharge current = (Continuous load (W1) + Short
time Load (W2)) / Rated Voltage
6-How do you specify the batteries?
Batteries have following specification:
- Rated voltage
- No.of cells
- AH capacity
- Arrangement of cells
- Details of charging equipment
7-What do you mean by AH of batteries?
AH
(Ampere hour) is the capacity of battery. It is the product of current and
total time required for discharge. It depends on the magnitude of discharge
current.
8-How do you
decide the number of batteries for a particular battery bank?
No.
of battery cells = Bus bar voltage / Voltage of one cell
9-What are the
various charging methods employed for batteries?
- Initial
charging
- Quick
charging
- Trickle
charging
60-Basic questions & Answers on power plant electrical system
10-What do you
mean by trickle charging? & what is its significance?
Trickle
charging is constant charging current that is supplied to battery to compensate
its discharge current.
Batteries
get discharge when not in use. Hence to avoid sulphating, the batteries should
be kept continuous charging by trickle charging.
11-What do you
mean by primary cells (dry cell) & secondary cells?
Primary
cells are non rechargeable cells & Secondary cells are storage batteries
12-What are
anode, cathode & electrolyte in Lead-acid batteries?
- Cathode:
Sponge lead
- Anode:
Lead Peroxide (PbO2)
- Electrolyte:
Sulphuric acid & water
13-What is the
voltage level of lead acid batteries that are generally employed?
It
is 2 V
14-What is the
voltage level of fully charged & fully discharged lead acid battery?
Voltage
of fully charged cell is 2.5 V & 1.75 V for fully discharged cell
15-What will
happen during battery discharge & charging of lead acid battery?
During
discharging process, the lead & lead peroxide het change into lead sulphate.
And during charging lead sulphate gets convert into lead & lead peroxide
16-How do you
check the specific gravity (SG) of electrolyte of lead acid battery?
Specific
gravity (SG) is checked with the help of Hydrometer
17-What is the
SG of fully charged & fully discharged electrolyte
SG
Fully charged electrolyte: 1.28 & 1.12 for fully discharged electrolyte
18-What is the
proportion of Sulphuric acid & water in Lead acid batteries?
Sulphuric
acid: 64% & Distilled water: 36%
19-How do make
up electrolyte level in lead-acid batteries?
Lower
level of electrolyte is due to evaporation of water.
If
the lower electrolyte level is due to evaporation of water, then add distilled
water. And if If the lower electrolyte level is due to spilling over bubbling,
then add acid & water solution.
20-Explain the
charging method of lead-acid battery?
During
charging process current forced into battery from opposite direction to its
normal direction of current flow.
That
is during normal use current leaves from positive terminal & enters through
negative terminal. During charging current enters through positive terminal
& leaves through negative terminal
21-Why do the
lead-acid batteries get discharge when they are not in use?
This
is because internal discharge current due to impurities in the electrolyte
22-What
electrolyte is used in Nickel-Iron batteries?
Potassium
hydroxide
23-What is the
voltage level & density of electrolyte of Nickel-Iron battery?
It
is 1.2 V & 1.2
24-Which
electrolyte is used for Nickel Cadmium batteries?
Potassium
hydroxide
25-What precautions
do you take to avoid over discharging of battery?
- Over
discharging can be avoided by
- Regular
charging of battery
- Avoid
excessive discharge rate
- Avoid
short-circuit currents & leakage current
- Schedule
charging & discharging
- When
not in use, battery terminals should be considered
Basics of power plant instrumentations
26-What do you
mean by sulphated Battery?
Discharge
battery with abnormal hardened lead sulphate on its plate is a Sulphated
battery
27-What actions
you will take if Battery is charging slowly?
- Check
battery connections & rectify if there are loose connections
- Check
charger capacity
- Add
distilled water or acid water solution if electrolyte is low
- Check
sulphatation of battery & rectify it
- Increase
current rating
- Check
connection that is positive lead of charger to positive of battery &
negative to negative
28-What are the
reasons for overheating of battery while charging?
- Poor
ventilation
- High
charging rate
Lower
specific gravity of electrolyte
29- What are
the reasons for overheating of battery while discharging?
High
discharge rate
Separators
between plates have damaged
30-What are the
reasons for cells having unequal voltages?
- Over
discharge
- Lower
electrolytes level
- Foreign
material in electrolyte
- Positive
plate worn out