power plant genrator cooling methods

8/11/2019 Power Plant Genrator Cooling Methods

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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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power plant genrator cooling methods

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