Hydrogen cooling system in details……

 Gas system –Function of the gas system • To provided means for safely putting hydrogen in to or

taking it out of the machine • To maintain gas pressure in the machine at the desired

value• To indicate to the operator at all times the condition

of the gas in the machine it’s pressure and purity• To dry the gas in the machine and remove any water

vapor which may get in to it from the seal oil.

• To meet these functions the following sub-systems are provided in the system-

• Circulation system• Gas filling system • Purging system • Drying system • Purity measurement system

• Circulation of hydrogen

• The gas which enters the air gap is sucked out by means of two axial fans mounted on ends of the shafts & is directed to the gas coolers through the end shield.

• The cooled gas, which comes out of the coolers, is collected in the space between the core & the casing of the stator frame thus completing the close circuit.

• Purging system  • The purging system is required to avoid having an

explosive hydrogen mixture in the generator casing when filling the generator initially with hydrogen or when removing the hydrogen

• before opening the casing to atmosphere the air or hydrogen in the casing is first removed with the help of carbon dioxide.

• Carbon dioxide is admitted in to the generator casing by opening the valves of several cylinders.

• A pressure gauge is provided on the manifold for indicating the pressure in the carbon dioxide.

• Syphone type cylinders are normally used in order to avoid freezing at the discharge point.

• Gas filling• For filling hydrogen in the generator, carbon dioxide

is used in order to avoid having an explosive hydrogen mixture in the generator casing.

• This operation is carried out in two stages • Stage 1 – Purging of air by carbon dioxide • Stage 2 – Purging of carbon dioxide by hydrogen

• Gas filling system • Hydrogen is supplied to the generator from a manifold to

which five H2 cylinders are connected .

• Each cylinder is provided with pressure regulator to reduce the cylinder pressure from 150kg/cm2 to 3.5 kg/cm2.

• One pressure gauge having a range of 0-6 kg/cm2 indicate the pressure of the gas in the cylinders opened to manifold .

• One electrical contact pressure gauge is mounted on the hydrogen control panel for giving the signal of low hydrogen pressure in the hydrogen manifold.

• Scavenging operation

• The removal of hydrogen gas from stator casing and filling it by air is called the scavenging operation

• This process is opposite to the filling operation i.e.

• Stage 1 - Purging of hydrogen by carbon dioxide

• Stage 2 - Purging of carbon dioxide by air

• Drying system • A gas dryer is connected to the ventilation circuit of

the generator to ensure and maintenance of a dry atmosphere in the casing at all times

• Sight glass is provided to periodically check the condition of silica gel, which is used as an absorbing agent.

 • Other types of gas dryers are air blower &

refrigeration type dryers

• Purity measurement system  • The hydrogen control panel, which is located on

the turbine-operating floor, carries the filtering and regulating block or the hydrogen purity receiver.

• One flameproof electrical contact pressure gauge 0-6 kg/cm2 for indicating the pressure of 2 manifolds is also located on the control panel.

Stator water system –Distilled water coolers • Two 100% duty coolers are provided for cooling

distillate

Centrifugal pumps • Two 100% duty centrifugal pumps one working and the

other standby are used for cooling water circulation .• The pumps are electrically interlocked between each

other in such a manner that the standby pump automatically startup in case water pressure drops in the circuit .

• Mechanical filter -• Two 100% duty filters are provided one working and

one standby and two pressure gauges are provided across the filters to indicate accumulation of solids in the filters elements.

• Magnetic filter -• Permanent magnet type filter is provided in the inlet

of stator water to filter out the suspended magnetic particles in the stator water.

DMCW O/L

DMCW I/L

TE SIDE EE SIDE

VENT

VENT

VENTVENT

H2 SEAL H2 SEALGENERATOR ROTOR

DRAIN DRAIN

VENT

VENT VENT

I/L LINE OF COOLER O/L LINE OF COOLER

PREPARED BYCHECKED BY

REV. No.

TITLE

PRATIK BOSE P.K.SAHA

GENERATOR COOLING SYSTEM

SLIDE NO - 48

MAIN EXCITER PILOT EXCITER

DMCW O/L FROM GENERATOR

GEN SIDE

RECTIFIER WHEEL

VENT DRAIN

DRAIN

VENT

PREPARED BYCHECKED BY

REV. No.

TITLE

NITYA MONDAL P.K.SAHA

EXCITER COOLING SYSTEM

SLIDE NO - 49

GENERATOR DUPLEX HYDROGENDRIER

GASPANEL

ANALYSER

SAMPLEVENT

FROM HBOTTLE RACK

PR. REG.

VENT

FILTERAIRSUPPLY

FROM COBOTTLE RACK2

2

WWWWWWFLASH

EVAPORATOR

OILFILL W W

..

WOT

To WOT

OIL TRAP

FROM H2 PLANT

W

LLD

SLIDE NO - 47

AIR SUCTION

HEATER

BLOWER

EXHAUST

WET HYDROGEN INLET

DRY HYDROGEN OUTLET

DRIER - A DRIER - B

# DRIER – A IN SERVICE AND DRIER – B UNDER REGENERATION

WOTOIL TRAP

• Expansion tank -

• An expansion tank, which is a hermetically sealed container made of stainless steel is provided in the system for closed loop operation the tank and the stator windings re filled with water before commercial operation of the set.

• The drain from the stator winding is showered in the expansion tank.

• The expansion tank is provided with 

• A gauge glass to indicate the level of water in the tank

• Two transducers for level signaling device to give high and low level alarm signal

• A vacuum gauge to indicate vacuum inside the tank

• A flat operated level regulator to regulate the make up water

• A drain valve to facilitate drainage of the complete tank in case of necessity

• Water jet ejector/vacuum pump - • Water jet ejector is used to create vacuum in

the expansion tank it consists mainly of a nozzle and a diffuser positioned of a set distance from each other

• The air or any traces of oxygen/hydrogen are taken a way by maintaining a vacuum of 200-300 mm of hg column in this compartment by the water jet ejector.

• Gas trap device - • It is used for detecting the presence of

hydrogen gas in the water employed for cooling the stator windings.

• Appearance of hydrogen in the water stream is possible due to loose leak of joints as the water pressure in the winding is kept lower than the hydrogen pressure kept lower than the hydrogen pressure in the generator casing. A drain valve is provided to facilitate drain age of the complete tank I case of necessity.

• Polishing unit -•  Polishing units are provided across the

stator winding as a water treatment plant and it is mixed bed ion exchanger.

• Any of the following water supplies free from oxygen can be used for cooling circuit like –

• Distilled water • Fully dematerialized water from boiler feed

water treatment plant • Condensate