Training report:

Generator Cooling and Sealing System

Mohd Basid AzmiB.Tech(Electrical)

Generator Specifications

KVA Rating :247MVA

KW Rating : 210MW

Voltage : 15750 V-

Stator,310 V - Rotor

Amperes : 9050 A- Stator,2600 A -

Rotor

Rated Power Factor : 0.85 Lag

Phases: 3RatedFrequency

:50 Hz

Connection: Star-Star

Coolant:Water And Hydrogen

Gas Pressure:3.5 Kg/Cm3

Insulation: Class B

Type: Thw-210-2Maker & Year:

BHEL (Haridwar) 1986-87

Rated Speed:3000 Rpm

Phase Connection:Double Star

Rating of Turbo Generator

NEED FOR GENERATOR COOLING SYSTEM

Large no. of conductors

high currents

flowing in the windings

• insulation blisters: conductors grow and elongate

• generation of large amount of heat.

Hydrogen Cooling

Minimize drag - “windage”

Keep generator internals clean

Maximize generator output

Minimize electrical, mechanical and corrosion problems

better heat transfer

increase breakdown voltage

Rotor cooling system

.

Gap Pickup Cooling

gas flow maintained by pressure

difference between the inlet wedge and

outlet wedge

Flow directed along the ventilating

canals made on the hot zone of the

rotor.

Hydrogen gas in the air gap is sucked

through the scoops on rotor wedges

This method gives uniform distribution of temperature and

eliminates the deformation of

copper due to high temperatures

Specifications:

A) H2 Pressure : 3.5kg/cm2

B) Purity : 97%

C) Gas Volume : 66 m3

Stator cooling system

• The stator winding is cooled by distillate,

which is fed from one end of the machine by

a Teflon tube and flows through the upper

bar and returns back through the lower end

of the other slot.

• The stator winding is cooled by circulating

the dematerialized water.

• DM water used for the cooling of the stator

winding calls for the use of very high quality

of cooling water. For this purpose DM water

of specific resistance is selected.

• The system is designed to maintain a

constant rate of cooling water flow to the

stator winding at a normal inlet water

temperature of 40°C.

Specifications:

A) Water Pressure : 3.5 kg/cm2

B) Qty. Of Water :130 m3/Hr

Generator Sealing system

• Sealings are employed to prevent leakage of hydrogen from the stator at the point

of rotor exit.

• The seal oil is a portion of the lube oil, diverted from the lube oil system. It is then

fed to a separate system of its own with pump, motor, hydrogen detraining or

vacuum degassing equipment, and controls to regulate the pressure and flow.

• A continuous film between the rotor collar and seal liner is maintained by the

means of oil at a pressure, which is about O.5 atm above the casing of hydrogen

gas pressure.

• The thrust pad provides a positive maintenance of the oil film thickness.

Generator Seal Oil SystemSystem functions:

• supplying the generator shaft with seal oil with hydrogen.

• permanent monitoring and differential pressure

regulation of hydrogen and oil,

• oil seal maintenance

– air and hydrogen separation,

– oil filtration,

– temperature regulation,

• removing oil vapors and hydrogen from the hall.

Generator Seal Oil System

• This system follows the following path:• Main Oil Tank• Main Oil Pump• Seal Oil Cooler• Seal Oil Filter• Damper Tank• DPR (Differential Pressure Regulator)• Hydrogen Seal• Seal Oil Fans• Main Oil Tank

• This system has two more pumps:• AC Seal Oil Pump• DC Seal Oil Pump

Generator Seal Oil System

• The pressure of seal is 4.2kg per sq Cm. while the pressure of hydrogen is 3.5 kg

per sq. cm. The purpose of this system is to provide seal to the hydrogen used for

cooling of stator. If the seal breaks, the system also breaks down.

• MOT(main oil tank):- It contains 28000ltrs of turbine oil. It supplies oil to all

bearings and seal.

• MOP(main oil pump):-It takes from the main oil tank and supplies further.

• Seal oil cooler:- It contains clarified water and distilled mineral water. The outer

covering area is called housing. It covers an assembly of about 200 tubes

assembled on plates. Air gaps are found between the tubes (25mm above, below

and on each side of each tube).These gaps are filled using hydrogen which cools

the stator.

Generator Seal Oil System• Seal oil filters:- These are rounded mesh like structures kept over each

other. There are about 34 filters present.

• Damper tank:-It is kept at 14mtrs of height above the ground. If MOP

fails A/C or D/C pump works and if these fail then damper pump comes

into action. Here the hydrogen pressure is .7% to .9% less than the oil

pressure because if the hydrogen pressure increases, the seal would

break down.

• DPR(differential pressure regulator):- The function of DPR is to

regulate the pressure of the oil and balance it. Whenever main oil

pump fails, the AC seal oil pumps starts automatically .DC seal pump

fails but it can supply the oil up to an hour. The generator is kept at a

height of 8meters so that oil is supplied by pressure.

Generator Seal Oil SystemSealing Data:

A) Seal Oil Pressure :4.1 To 4.4 Kg/Cm2

B) Quantity :80 Lt/Min

C) Type :Radial Flow, Double Chamber Thrust Type

AC Seal Oil Pump:

A) Type :Multistage Vertical Split Centrifugal Type

B) Capacity : 3.34 Lit/Se At 12kg/Cm2

DC Seal Oil Pump:

A) Type : Multistage Vertical Split Centrifugal Type

B) Capacity : 4.16 Liters At 12 Kg/Cm2

Line Charge Capacity :75 MVAR

References

• Kothari, D. P. , Nagrath, I. J. " Electric Machines" (2012)• Mehta, Rohit, Mehta, V. K., “Principles Of Electrical Machines,”(2006)