power plant genrator cooling methods
TRANSCRIPT
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INTRODUCTION TO
GENERATOR COOLING SYSTEM
STATOR WATER SYSTEM
HYDROGEN COOLING SYSTEM
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HYDROGEN COOLINGSYSTEM
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WHY HYDROGEN RATHER THAN AIR FOR
GENERATOR COOLING
Hydrogen is used for cooling in most large
generators rather than air for several reasons.
The use of gaseous hydrogen as a coolant is
based on its properties, namely low density, high
specific heat, and highest thermal conductivity.Of all gases; it is 7-10 times better coolant than
air. Other advantage of hydrogen is its easy
detection by hydrogen sensors. A hydrogen-
cooled generator can be significantly smaller,and therefore less expensive, than an air-cooled
one.
http://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Specific_heat_capacityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Hydrogen_sensorhttp://en.wikipedia.org/wiki/Hydrogen_sensorhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Specific_heat_capacityhttp://en.wikipedia.org/wiki/Density -
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The main advantages of using H2 cooled Generators
are:
Lesser Windage & friction losses-
One of the main factors contributing to the heating of the
medium is the windage loss. The lesser the density of cooling
medium the less will be the loss. Also due to low density fan power
will be reduced.
Reduction in size of machine-
Due to high thermal conductivity H2 will extract more heat per
unit volume per minute. It is estimated that at 2.109 kg/cm2 m/c
rating is increased by 35%.
Increase in life of m/c -
Enclosed construction which keeps dirt & moisture out fromwinding & ventilation passage.
No deterioration of armature insulation due to corona. During
corona discharge ozone, nitric acid& other chemical compounds
are formed whish attack organic bounding material of insulation.
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Relative properties of coolants
Coolants Specific
Heat
Density Thermal
conductivity
Heat Transfer
Coefficient
Air 1.0 1.0 1.0 1.0
Nitrogen 1.0 0.966 1.08 1.03
CO2 1.27 1.52 0.64 1.13
CH4 1.22 0.55 1.29 1.43
Helium 5.25 0.138 6.4 1.18
H2 at1 ksc 14.35 0.14 6.69 2.65
2 ksc 14.35 0.22 6.69 3.65
3 ksc 14.35 0.30 6.69 4.4
4 ksc 14.35 0.375 6.69 4.85
Oil 2.09 848 5.45 21
Water 4.16 1000 21.0 50
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In additional to the hydrogen, a separate supply system
is required for CO2 to purge the generator of hydrogen
during filling and de-gassing. CO2 is used because it isinert and will not react with the hydrogen. If hydrogen in
the generator were to be purged with air, this would
encroach upon both the upper and lower explosive limit
due to combustible nature of a hydrogen/oxygen mixture.Hydrogen at high purity will not support combustion
above 90%, and at this level there is no danger of
explosive since the explosive range of a
hydrogen/oxygen mixture is 4 to 75% hydrogen in air at500-571 C.
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Hydrogen
Rated pressure
0.3 MPa (Max. 0.35 Mpa)
Purity 95 %
Dew point
14 C ~2.5 C
Cold H2temperature 35 ~ 46 C
Hot H2temperature 70 C
H2consumption
14 m3/day
H2 volume in generator
72 m3
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Hydrogen cooling water
No. of cooler 4
Inlet water temperature 20 ~ 38 C
Outlet water temperature 43 C
Water flow required (including
terminal 3 TPH)
4 x 100 TPH
Inlet water pressure 1 ~ 2.0 kg/cm2
Water pressure drop 0.24 kg/cm2
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Hydrogen is circulated inside generator inclosed circuit by one multistage fanarranged on rotor at turbine end.
Hot gas is drawn by the fan from the airgap and delivered to water coolers whereit is recooled and the divided into variousflow path.
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Index
Working Principal
Main Technical Parameters.
Equipments and Arrangements.
Operation.
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Working Principal.
Flow Path 1 Water passes through a manifold on the exciter end of the generator
and from there to the stator bars via insulated hoses.
Each individual bar is connected to the manifold by a separate hose.
Inside
The bars the cooling water flows through hollow strands. At the
turbine end, the water is passed through similar hoses to another
water manifold and then returned to the storage tank.
Since a single pass water flow through the stator is used, only a
minimum temperature rise is obtained for both the coolant and thebars.
Relative movements due to different thermal expansions between
the top and bottom bars are minimised.
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Working Principal.
FLOW PATH II
Flow path II cools the phase connectors and the bushings. The
bushings and phase connectors consists of thick walled copper
tubes through which the cooling water is circulated.
The six bushings and the phase connectors arranged in a circlearound the stator end winding are hydraulically interconnected.
The secondary water flow through the primary water cooler should
be controlled automatically to maintain a uniform average generator
temperature level for various loads and cold water temperatures.
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Main Technical Parameters.
Water pressure at the inlet: 0.10.2MPaWater temperature at the inlet: 453CReturn water temperature: 80C
T0tal water flow: 45t/hConductivity: 0.5-1.5 s/cm (20C)PH value: 7-9Hardness: 2 microgram equivalent litter
Whole volume of the system 3m3.Circulating water flow required: ~160t/hCirculating water pressure required: 0.1 5-
0.3MPa
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Equipments and Arrangements.
Water Tank
Water Pumps
Water Coolers Water Filters
Demineralizer
Arrangements
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Water Tank
900mm
0mm
850mm
460mm
150mm
Level High
Level Normal
Level Low
Stator Water
Tank
Level High1 Make up valve auto Close
and Annunciation LEVEL HIGH
Level Low - 1 Make up valve auto open.
and Annunciation LEVEL LOW
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Demineralizer
Nos 1
Operating Pressure 0.72 MPa
Design Temperature 65 C
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Operation
Hydrogen pressure in the generator shouldbe about 0.1~0.2MPa higher than waterpressure.
Water inlet pressure should be around0.2MPa.
Water inlet pressure can be increased to0.23MPa in order to increase the flow.
Inlet Water temperature should not be higherthen 55C
Discharging water temperature from statorwinding should not be higher than 80C.
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Heater
DemineralizerF F
Cooler
Cooler
Operation
1
Back Flush
F
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Heater
DemineralizerF F
Cooler
Cooler
Home
2
F
Normal Operation
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Home
Heater
DemineralizerF F
Cooler
Cooler 3
F
Back Flushing
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