100-2SSSPrinciples

7/28/2019 100-2SSSPrinciples

1/22

SPECIFICATION OF STEAM TURBINE

SL. NO. DESCRIPTION DATA

Type of steam turbine

1. Type : Horizontal, impulse, multi-stage, multi valve, axial

flow, condensing, extraction, geared. (Axial exhaust

type)

Operating conditions:

2. Speed (Turbine /

generator)

: 7810 / 1500 rpm

3. Inlet steam pressure : 64 kg/cm 2A

4. Intel steam : 485 deg. C

5. Exhaust steam pressure : .02 kg/cm 2A

6. Max. 1 st extraction

pressure un-controlled

extraction

: 2.96 kg/cm 2A at turbine nozzle

Operation case : 1 2

7. Inlet steam pressure : 64 kg/cm 2A 64 kg/cm 2A

8. Inlet steam temperature : 485.0 deg. C 485.0 deg.C

9. Inlet steam flow : 49.80 t/h 50.20 t/h

10. Exhaust pressure : .18 kg/cm 2A .20 kg/cm 2A

11. Exhaust temperature : 57.41 deg. C 59.66 deg. C

12. Exhaust flow : 43.81 t/h 44.31 t/h


2/22

13. Gland leakage : 0.1 t/h 0,1 t/h

14. Generator power : 12 kW 12kW

Direction of rotation: (Viewed from generator to turbine / axial exhaust steam turbine)

15. Steam turbine : C.W

16. Generator : C.C.W

Lubrication, Governor and control oil:

17. Type of lubrication : Forced lubrication

18. Lubrication oil pressure : 1.0 kg/cm 2(G)

19. Trip oil pressure : 4.0 kg/cm 2(G)

20. Control oil pressure : 10.0 kg/cm 2(G)

21. Normal required lub oil

& trip oil flow

: 440 lpm

22. Normal required controloil flow

: 50 lpm

23. Kind of oil : Turbine oil ISO VG46

Reduction Gear

24. Type : Horizontal, single reduction, Double helical gear type

Emergency stop valve

25. Type : Oil pressure operated type with steam strainer and

limit switch for indication of closed position

Journal Bearing

26. Type : Tilting pad type, forced lubricated

Thrust Bearing

27. Type : Multi segment tilting pad, double side type, combined

with coupling side journal bearing (Kingsbury type)


3/22

Speed Governor

28. Type : Electro Hydraulic Governor

29. Model / Manufacturename

: 505 / Woodward

30. Speed regulation : 4% as droop

Over speed Governor

31. Type : Electric signal from governor & 2 out of 3 voting

electric type ( Woodward protect GII)

32. Tripping speed : 114% of rated speed (Elec. By Governor)

115% of rated speed (electrical 2 out of 3)

Governing valve:

33. Type : Bar lift and multi valve

Coupling

34. Coupling between

turbine and R/gear

: Flexible type

35. Coupling between R/gear

and generator

: Oil contained gear type

Turning Device

36. Type : Electric (AC) motor driven, Combined of Cyclo & Bevelgear or worm gear reduction, automatic engage and

automatic disengagement.

Oil reservoir

37. Type : Steel plate fabricated type

Reservoir is furnished with oil level indicator, drain valve, oil charging nozzle, 1X100% gas vent

fan.

Main lube oil pump


4/22

38. Type : Gear type, driven by low speed shaft of gear box

39. Discharge pressure : 7.5 kg/cm 2G

Auxiliary Lube oil pump

40. Type : Screw type, driven by the AC motor


Main control oil pump

42. Type : Screw type, Mounted


Auxiliary control oil pump

44. Type : Screw type, Mounted


Emergency oil pump

46. Type : Gear type mounted on oil reservoir and driven by DC

electric motor.


Oil cooler

48. Type : Duplex plate type

Lube oil filter

49. Type : Duplex with change over clock

50. Filtration : 40 Micron

Control oil filter

51. Type : Duplex with change over clock

52. Filtration : 10 Micron

Oil pressure adjusting valve


5/22

53. Type : Self acting type

Gland steam condenser

54. Type : Shell and tube, fixed tube sheet type with AC motordriven exhaust fan

Material List

SL. NO. DESCRIPTION DATA

Steam turbine

1. Turbine HP casing part : Cast Alloy Steel

2. Exhaust casing part : Carbon steel

Emergency stop valve

3. Body : Cast Alloy Steel

Governor valve

4. Body : Cast Alloy Steel

Reduction gear

5. Body : Cast Iron

Oil filter

6. Body : Carbon steel

Instrumentation:

Protection Schedule:

SL.NO. Protection device Alarm Trip

1. Over speed of turbine

2. Low lube oil pressure


6/22

3. Low control oil pressure

4. Hand Trip

5. Remote trip

6. High lube oil temperature

7. High bearing temperature

8. Excessive vibration

9. Excessive axial displacement

10. High exhaust pressure

11. Failure, control loop of governor

12. Low oil reservoir level

13. High extraction pressure

14. High extraction temperature

15. High LO/CO filter Different pressure

Steam turbines are prime movers for driving generators in thermal power plants.In steam

turbines the thermal energy of steam is converted to mechanical work. Steam turbines can be

classified into impulse turbine and reaction turbine.If the ratio of heat drop in moving blades

and the total heat drop in moving and stationary blades is less than 40 % then the turbine is

known as impulse turbine. If the above ratio is greater than 40 % the turbine is known as

reaction turbine. Our turbine is of the impulse type.

A steam turbine depends upon the dynamic action of steam. A turbine consists of fixed blades

or nozzles and moving blades.The nozzles create pressure drop in the steam thus increasing its

kinetic energy. The steam from the nozzles after this boost in velocity enters the moving blades

wherein the flow is diverted causing a change in angular momentum resulting in force. This

force rotates the shaft of the turbine thus driving the generator. If there is no pressure drop

across the moving blades the turbine is known as a impulse turbine. While if there is a


7/22

pressure drop across the moving blades then it is known as an impulse-reaction turbine.

If steam is allowed to expand to condenser vacuum in a single row of nozzles due to large

enthalpy drop, the velocity at exit of nozzles is very large resulting in high blade speed leading

to higher centrifugal stressess or high wheel diameters. Therefore the steam is passed through

several stages. Each stage consists of a row of nozzles followed by a row of blades. In that way

the same enthalpy is dropped without the above difficulties. Our turbine has 9 stages and is a

velocity compounded turbine. The pressure drops in the nozzles only. One row of nozzles is

followed by a row of blades where the kinetic energy is absorbed partially by the blades. No

drop takes place in the blades (theoretically).

. The assembly drawing of a steam turbine along with the components are given below:


8/22


9/22

The major parts of the turbine are described below:


10/22

Casing: The casing has two parts , High Pressure and Low Pressure. On the upper casing in the

HP side a governor valve is provided.This valve is controlled by electro-hydraulic governor to

regulate the flow of steam to the turbine.The turbine is axial flow.Hence the exhaust nozzle is

provided axially at the LP end.The casing is of single shell type.The wall of the casing is thicksince the entire pressure drop across the turbine and the hoop stress has to be withstood by

the single shell.

Rotor

The rotor is of disc type with the blades fitted with the disc and is of forged construction.The

rotor houses a magnetic pick up gear for speed detection, a labyrinth packing to prevent

steam leakage from shaft gland. The mechanical overspeed trip is mounted on the rotor shaft

end.This consists of a ball governor which moves apart due to centrifugal force on increase of

speed of the rotor thus actuating reduced flow to the turbine.

Bearing Housing

The turbine bearing housing consists of bearings to support the rotor. There are two bearing

housings one at front and the other at rear end. Due to thermal expansion occurring in turbine

the bearing housing in the high pressure side is provided with sliding support.

Gland sealing

In turbines gland sealings are provided to stop leakage of steam from the cylinder or casing.

The seal used here is of labyrinth type.Labyrinth packing is provided to seal the shaft with rotor

and reduce the leakage of steam from HP side to LP side

Journal Bearing In both HP and LP side bearing housing a journal bearing is housed to

support the ro tor radially. The bearing is designed with respect to the rotors static weight,

steam force and vibration and is lined up for wedge effect with tilting pad.

Thrust bearing-

To withstand all axial forces due to rotor vibration and steam, a thrust bearing is provided to

support the rotor and disk.

Both bearings are coated with white metal. For stable operation of turbine an oil film is

established between the rotor and the bearing to prevent temperature build up on bearing

surface due to friction and high speed.

Emergency Stop Valve:

When the turbine is tripped the emergency stop valve is shut off by the overspeed trip device


11/22

to prevent entry of steam into the turbine.

To explain the emergency stop valve and its actions one needs to understand the trip system of

a turbine.

The emergency stop valve consists of a pilot piston, a cylinder, a liner and a spring. In opening

the emergency stop valve the trip oil at a pressure of 4.4 kgf/cm 2 is supplied, facilitated by the

opening of the two solenoid valves in the trip oil line to the pilot piston in the oil relay. So the

pilot piston moves under the action of trip oil thus unraveling a port on the liner in the

emergency stop valve and admitting control oil through the port into the cylinder at the

bottom of the ESV. When control oil flows into the cylinder the hydraulic pressure will exceedthe spring pressure and the valve is opened. At trip the solenoid valves close thus preventing

the flow of trip oil and in the process, retracting the pilot valve and closing the oil inlet port in

the ESV cylinder. As a result of this the stored energy in the spring gets the better of the oil

pressure and closes the valve.

Turbine Protection System Schematic

TO OILRESERVOIR

MAGNETICSPEED PICKUP

DIGITAL SPEEDGOVERNOR

GOVERNOR

VALVE

TRIP

SOLENOID

VALVE

MANUAL

TRIP

COCK

EMERGENCY

STOP

VALVE

TO OIL

RESERVOIR

TRIP SIGNAL EXTRACTION CHECK VALVE


12/22

TRIP OIL TRIP CONDITION FLOW

TRIP OIL NORMAL OPERATING FLOW

SIGNAL

Trip system of the turbine works due to action of emergency stop valve.The valve is closed due

to the action of a solenoid valve or a manual trip valve which block the trip oil line. The trip

signal is received from the digital governor, Woodward 505. Also Protech GII overspeed trip

system is present which signals the solenoid valve.Two speed sensors receive speed from pick

up gear to transmit signals to the WoodWard 505 Governor.There are three more sensors

meant for the Protech Overspeed Trip System.

WOODWARD

505 GOVERNOR

WOODWARDPROTECH GIIOVERSPEED (2 OUTOF 3 VOTINGSYSTEM)

SAHH SAHH

OR

TURBINE EMERGENCY

SHUTDOWN


13/22

SENSOR

BLOCK DIAGRAM OF OVERSPEED TRIP SYSTEM

Flexible Coupling: The turbine is coupled to a gear box by a flexible coupling which can

absorb the misalignment caused due to thermal expansion due to steam.

Expansion below: Due to large expansion in case of an axial exhaust steam turbine an

expansion bellow is provided. In downflow turbines gland packing is provided to absorb the

thermal expansion.

HP Governor valve

This is actuated by a servo motor. When the hydraulic motor power exceeds spring

force the lifting bar will go up to open the valve. The hydraulic motor receives oil from the

control oil line at apressure of 10.4 kgf/cm 2.

Gland Steam Condenser

This is a shell and tube type single pass heat exchanger with cooling water passing

through the tubes and steam/air passing through the shell. The condenser is provided with a

gland vapour fan drawing steam at 50 kg/h from the glands of the turbine. The steam is

condensed by the condensate of turbine exhaust steam after it passes through the ejector

condenser and before it enters the turbine. The non-condensable gases present in steam is

rejected to the atmosphere while the steam which is condensed gets drained out. Since the

condenser is maintained at vacuum the drain is piped out through a U-seal.The condenser is

designed with a cleanliness factor of 85 %.

Gland sealing system

The purpose of the sealing system is to prevent atmospheric air from entering the

turbine casing. Steam is used to do this sealing. The pressure of sealing steam is 0.1 -0.2

kg/cm 2.At start up an ejector is used to maintain vacuum in the exhaust and the Air Cooled

SPEEDPICK UPGEAR


14/22

Condenser. If air enters the turbine via shaft gland it will be impossible to raise vacuum and

start the turbine. So at start-up the sealing system prevents air from entering the turbine both

from the high pressure and low pressure glands. During normal operation presre in the HP

side of the turbine is much higher than the atmosphere. So no air can enter the turbine fromthat end. The sealing steam therefore seals atmospheric air to enter the turbine casing via the

exhaust glands during normal operation.Also a part of the high pressure steam is also used for

sealing the LP side. The sealing steam is derived from the main steam line. The tapping for

gland sealing steam is taken from the main steam line which is passed through a pressure

reducing and desuperheating system where its pressure and temperature are reduced to 11

kgf/cm 2 and 250 deg C and then finally passed through a pressure control valve which reduces

it to the sealing steam pressure as given above.

Extraction Steam

A part of the steam generated in the turbine is extracted by a bypass line.This is done

from the exit of the 1 st stage nozzles and is delivered to the deaerator for stripping the

condensate of dissolved gases. The bleed is done at a pressure of 2.9 kgf/cm 2 and a

temperature of 161 deg C.

Spray water

Spray water from the discharge of Condendate Extraction pump at 12 kgf/cm 2, a flow

of 0.77 tph and a temperature of 62 deg C is supplied to turbine exhaust if the exhaust

temperature reaches above 80 degC.

Lube Oil System

The turbo-generator has a lube oil system to supply oil for lubrication of turbine,

generator and gear box bearings. Also there is a control oil system for operating the governor

valve and a trip oil system which supplies the pressure to keep the Emergency Stop Valve open.

Lube oil is normally supplied for hydrodynamic lubrication of bearings. The pressure is created

by a main oil pump which is a gear pump driven by the main shaft. The gear pump delivers lube

oil at required pressure only at or above 95 % shaft. Below that speed the oil is supplied by a

AC motor driven Auxiliary Oil Pump. Also keeping in mind emergency conditions like grid failure

an Emergency Oil pump is provided as a partial stand by for the Auxiliary Oil Pump. This pumpgets automatically activated on failure of auxiliary oil pump and is driven by DC motor driven by

a battery. The control oil pump supplies oil to HP governor valve and the port in the liner of the

Emergency Stop Valve. There is also an auxiliary control oil pump which gets automatically

activated on failure of the main control oil pump. All these pumps draw water from an oil


15/22

reservoir. Oil in the reservoir is passed through an oil centrifuge for removal of water in the oil.

Also to maintain the viscosity of oil at desired values the oil in the reservoir is heated by a

resistive element heater if the temperature falls. Both control oil and lube oil are passed

through duplex filters which removes solid contaminants. Downstream of the filter pipes aremade of stainless steel to prevent corrosion. The lube oil system additionally is provided with a

cooler. Also a part of the lube oil is pressurized by a pressure control valve to cater to the trip

oil line for supply of oil to the ESV oil relay. A centrifugal fan is provided for removal of oil

fumes from the oil reservoir and deliver them outside the building.

Gear Box

The turbo-generator is provided with a gear box to reduce the turbine rpm of 7810 to

1500 at the generator shaft.

Turning Gear

During shut down or trip if the turbine is suddenly brought from full speed of 7500 rpm to rest

then the rotor may get bend or distorted due to unequal expansion and thermal stresses. So

the turbine is cooled uniformly by rotating it by a barring gear at a speed of 11 rpm for 24

hours.

During start up also the turbine is rotated at barring speed of 11 rpm for over 8 hrs to warm

up the turbine before steam is injected to it.

The turning gear consists of an electric motor driving a worm gear reducer connected to an

overrunning SSS clutch encased in an oil tight housing. The clutch can be engaged or

disengaged automatically. The initials SSS denote the 'Synchro -Self-Shifting' action of the

clutch, whereby the clutch teeth are phased and then automatically shifted axially into

engagement when rotating at precisely at the same speed. The clutch disengages as soon as

the input speed slows down relative to the output s


16/22

SSS Clutch

A Pawl

B Clutch Teeth E Input Shaft

C Sliding Component F Output Clutch Ring

D Helical Splines G Ratchet Teeth


17/22


18/22

Basic Principle of Operation of Synchro Self-Shifting Clutch

The initials SSS den ote the 'Synchro-Self-Shifting' action of the clutch, whereby the clutch teeth are phased

and then automatically shifted axially into engagement when rotating at precisely the same speed. The

clutch disengages as soon as the input speed slows down relative to the output speed.The basic operating

principle of the SSS Clutch can be compared to the action of a nut screwed on to a bolt. If the bolt rotates

with the nut free, the nut will rotate with the bolt. If the nut is prevented from rotating while the bolt

continues to turn, the nut will move in a straight line along the bolt.In an SSS Clutch the input shaft (E) has

helical splines (D) which correspond to the thread of the bolt. Mounted on the helical splines is a sliding

component (C) which simulates the nut. In the diagram, the sliding component has external clutch teeth (B)

at one end, and external ratchet teeth (G) at the other.When the input shaft rotates, the sliding component

rotates with it until a ratchet tooth contacts the tip of a pawl (A) on the output clutch ring (F) to prevent

rotation of the sliding component relative to the output clutch ring. This position is shown in Figure 1.As the

input shaft continues to rotate, the sliding component will move axially along the helical splines of the input

shaft. When a ratchet tooth is in contact with a pawl tip, the clutch engaging teeth are perfectly aligned for

inter-engagement and thus will pass smoothly into mesh in a straight line path.

As the sliding component moves along the input shaft, the pawl passes out of contact with the ratchet

tooth, allowing the clutch teeth to come into flank contact and continue the engaging travel as shown in

Figure 2. Note that the only load on the pawl is that required to shift the lightweight sliding component along

the helical splines

.

Driving torque from the input shaft will only be transmit- ted when the sliding component completes its

travel by contacting an end stop on the input shaft, with the clutch teeth fully engaged and the pawlsunloaded as shown in Figure 3.

When a nut is screwed against the head of a bolt, no external thrust is produced. Similarly when the sliding

component of an SSS Clutch reaches its end stop and the clutch is transmitting driving torque, no external

thrust loads are produced by the helical splines.

Where necessary, an oil dashpot is incorporated in the end stop to cushion the clutch engagement.

If the speed of the input shaft is reduced relative to the output shaft, the torque on the helical splines will

re- verse. This causes the sliding component to return to the disengaged position and the clutch will overrun.


19/22

At high overrunning speeds, pawl ratcheting is prevented by a combination of centrifugal and

hydrodynamic effects acting on the pawls.

Driving torque from the input shaft will only be transmit- ted when the sliding component completes its

travel by contacting an end stop on the input shaft, with the clutch teeth fully engaged and the pawls

unloaded as shown in Figure 3.

When a nut is screwed against the head of a bolt, no external thrust is produced. Similarly when the sliding

component of an SSS Clutch reaches its end stop and the clutch is transmitting driving torque, no external

thrust loads are produced by the helical splines.

Where necessary, an oil dashpot is incorporated in the end stop to cushion the clutch engagement.

If the speed of the input shaft is reduced relative to the output shaft, the torque on the helical splines will

re- verse. This causes the sliding component to return to the disengaged position and the clutch will overrun.

At high overrunning speeds, pawl ratcheting is prevented by a combination of centrifugal and

hydrodynamic effects acting on the pawls.


20/22

Elements of basic


21/22

SSS Clutch

A Pawl

B Clutch Teeth E Input Shaft

C Sliding Component F Output Clutch RingD Helical Splines G Ratchet Teeth

1 BA

E

C

D

F 2 3

G


22/22

In hydrodynamic lubrication a film of oil separates the shaft from the bearings to minimize wear by

eliminating metal metal contact. The following are the major factors considered.

Oil film formation: The oil forms a wedge whose thickness and pressure depends on the viscocity,

tenacity of the lubricant, the geometry of the moving parts, their relative velocity and the loadsupported by the film.

The gradient between the oil velocity at the moving parts and that at the centre of the fim creates a

shear force.The viscosity is the ability of that oil to withstand the shear force and the energy required

for that resistance is converted to heat.

The most common example of hydrodynamic bearing is the journal bearing (Figure 2 ). The shaft

(journal) rotating inside a circular bush with a thin film of oil separating the two. The gap between the shaft

and the bush is generally about 0.001 to 0.002 times the shaft diameter. Usually a load W (eg. weight of the

impeller in a pump) has to be supported. When the shaft is rotating, position of the shaft with respect to

the bush is shown in Figure 2b. Rotation of the shaft drags in the oil into a narrowing gap (marked A in the

Figure ),bearing pressure develops and this in turn

supports the load. The oil film ensures low wear and low friction. In practice, the design must ensure a

minimum film thickness to prevent breakage of the film and the subsequent contact between the shaft and

the bush surfaces. When the load is high or the shaft speed is low this minimum film thickness cannot be

maintained. In these cases roller element bearings (eg. ball bearings) or hydrostatic bearings are used.

Interestingly even in ball bearings, we have hydrodynamic lubrication at the ball surface.

Journal Bearing

Figure 2 Journal bearing (a) front view indicating shaft, bush and the oil-film. (b) cross-section

in the side view indicating the pressure developed in the oil-film and the relative positions

Documents

100-2SSSPrinciples