power plant instrumentation

1. UNIT 5
Instrumentation of
Power Plant

2. Measurement of smoke and dust
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Photocell type smoke meter
The exhaust gases passes
through chimney
A focused light beam through
chimney is passed on photocell
at the receiver
The variation in signal of photo
cell circuit is measured .
The indicator is scaled in
percentage obscuration.
Alarms and recorders fitted
for continuous record of
smoke .

3. Photocell type smoke meter
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Light absorbed by particles is measured
The major problem is fouling of projector and
receiver lenses by smoke and dust.
It is experimentally determined that the dust will
not be deposited if the ratio of length to
diameter is min 4:1 for coarser particles and 16:
1 for fumes and smoke.

4. Reflected light dust monitor
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The reflected light from dust
particles is measured
Lamp and photo cell are
mounted side by side.
Light from lamp is beamed
into dust through a suitable
opening .
The light reflected by dust
particles fall on photocell
The indication of reflected
light varies with dust quantity
in gas.

5. Measurement of moisture in carbon
dioxide circuit
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The infrared gas analyser is commonly
used to measure moisture in carbon
dioxide.
A continuous supply of CO2 obtained by
connecting analyser across gas
circulators.
The analyser detects the difference in
infrared radiation intensity passing
through reference tube and sample tube.
Reference tube consist dry CO and
sample tube consist carbon dioxide
drawn from gas circuit.

6. Measurement of moisture in carbon
dioxide circuit
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Nichrome twin heaters are source of
infrared radiation which are directed by
electrically driven fan so that reflgular
discrete amount of radiation directed into
two tubes through calcium fluoride .
pressure retaining windows depending
upon moisture content in the gas .
For unequal infrared heating of condenser
unit gas, a pulsed pressure difference is
created across diaphragm .
This pressure difference measured by
voltmeter and recorder decide moisture
content.

7. Measurement of Water purity
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Impurities in water cause corrosion, excessive
sealing of tubes in boilers, scale formation and
cracking of metallic parts .
Impurities may enter into feed water circuit through
condenser .
The electrical conductivity of water used to
measure the content of salt in feed water, steam
and condensate .
Pure water is highly resistant to the passage of an
electric current .

8. Measurement of Water purity
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Conductance is measured in mhos.
One mho is the conductance of substance through
which one ampere of current flows at potential
difference of one volt .
It has been recommended for 100 bar power plants
conductivity of water should not exceed 0.3 micro
mho/ cubic cm at 20°C.
Distilled water have conductivity of about 6 micro
mho / cubic cm .
Conductivity meter used is basically an electric
measuring device, Wheatstone Bridge .

9. Measurement of Water purity
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The conductivity cell is
immersed in water sample
forms the unknown
resistance in one leg of the
bridge .
The change in solution
conductivity changes its
resistance Rx.
The amplifier then actuate a
balancing motor which
immediately move slider on
R4.
This gives impurity value of
water.

10. Measurement of pH (Potential of hydrogen ) value of
water
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pH of solution shows alkalinity and acidity of
solution .
For neutral solution pH=7, alkalinr when 14>pH>7
Acidic when 7>pH >0.
Concentration of H ions represented in moles per
litre .
The scale formations and corrosive tendency of
water are influenced by pH value.
Low pH cause corrosion while high pH precipitate
calcium carbonate .

11. Electrometric method of pH measurement
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Every metal when dipped into the solution of its
own salts it goes in the form of positive ions.
The pressure causing flow of positive ions in
solution called electrolytic solution tension .
The metallic ions in solution also exert osmotic
pressure .
Hence potential difference between metal
electrode and solution depend upon electrolytic
solution tension and osmotic pressure .

12. Electrometric method of pH measurement
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Measurement of pH of water is carried out by means
of glass electrode and reference electrode which are
dipped into solution and e.m.f is measured by pH
meter.
pH meter has two electrodes ,a measuring element
potential of which depend upon concentration of
hydrogen ions and comparison element whose
potential is always const.
Two such elements are electrically connected to form
galvanic system .
By measuring e.m.f we can find H ions concentration.

13. Electrometric method of pH measurement
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When glass surface dipped in solution containing hydrogen ions, it
develop Electropotential Proportional to hydrogen concentration .
The circuit is combination of Electrometer and potentiometer .
The potential of glass electrode is adjusted to equilibrium by
potentiometer circuit.

14. Nuclear Measurement
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The fissile fuels used in nuclear reactors necessarily
canned in materials which have structural stability
Due to fault occurring in the canning material due to
structural defect or corrosion ,a leak of fission products
may occur which cause contamination and health hazard.
Methods used to detect nuclear radiation .
1. Detection by Gamma activity of fission products
Presecence of fission products in coolant detected by
measuring gamma activity of the coolant. .
Not satisfactory because required high degree of sensitivity

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2.Detection by Gaseous fission product activity
A no. Of radioactive gaseous fission product are
produced during fission process .
Large no of isotopes of krypton and xenon occur as
result of radioactive decay. These are solid products.
Krypton and xenon further decay into isotopes of
rubidium and caseium with β emissions.
So β activity is measured to detect fission products in
coolant circuit .
The gaseous fission product from stream of coolant are
first removed and allowed to enter precipitation chMber.
Nuclear Measurement

16. 2.Detection by Gaseous fission product
activity
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Precipitation chamber
consist of a metal cylinder
with thin metal wire
passing through its centre
and insulated from cylinder.
Cylinder potential is kept
positive 4KV.
Gas from each sample
passed through
precipitation chamber for
25 seconds.

17. 2.Detection by Gaseous fission product
activity
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The daughter products positively
charged rubidium and casesium
are collected on wire in solid form.
At the end of sampling period
wire is passed out of precipitation
chamber and into a hole in
phosphorus and photomultimeter
system.
A phosphorous is beta sensitive is
used and photo multiplier output
is amplified to rate meter.

18. 2.Detection by Gaseous fission
product activity
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A typical cooled reactor will
have nearly 3200 fuel
channels.
It is uneconomical to
monitor each channel for
the presence of fission
products .
So small pipe is attached at
the top of each channel in
such a way that gas sample
is picked up from each
channel .

19. 2.Detection by Gaseous fission
product activity
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Sampling pipes are brought out
of the reactor vessel and
shielding are connected together
into groups.
The combined gas sample
passed to selector valve
controlling no of channels.
The valve select each group of
channel in sequence and allows
gas to pass through precipitation
chamber.
Gas again recirculated to main
gas circuit.