Notes on Governing System of KWU Steam Turbine:

By K. Venkata Rao,

Chief Engineer (Retired) - APGENCO

General:

The purpose of the Governing System is to regulate the turbine speed till the unit is synchronized and

then to regulate the load on the unit as per the Load Limiter setting after the unit synchronization, these

two functions being called as Speed Governing & Load Governing characteristics.

Before knowing how the Governing System is regulating the unit behavior, we should know about the

normal steam flow path, about the specific valves that are to be operated by the Governing System and

their location in the steam flow path. The Control Oil which is supplied by the AOP/MOP plays a vital

roll in the operation of the governing system which assumes different names and pressures depending

up on its function as per the governing logic.

Steam flow path:

Main Steam from the boiler enters the HP Turbine through the Emergency Stop Valves and the HPT

Control Valves. The CRH steam from the HPT exhaust flows to the reheater in the boiler and the HRH

steam delivered by the reheater flows to the IP Turbine through the IVs & IPT Control Valves. From the

IPT exhaust the steam flows to the LP Turbine, directly through either cross over or cross around pipes

without any valves in between the IPT exhaust and the LPT steam admission point. From the LPT

exhaust the steam flows to the condenser where it is cooled as condensate by the CW System and

collected in the condenser hot well.

About the operation of ESVs, IVs, and the HPCVs & IPCVs of a Steam turbine:

The HP Turbine Stop Valves called as ESVs & the IP Turbine Stop valves called as Interceptor

Valves will either open by 100% or close fully to 0% opening by the action of the servo motor

assembly mounted on each Stop Valve Body when open or close command is initiated.

The HP control Valves and the IP Control Valves will be operated by a common servo motor

called Control Valve Servo Motor (CVSM). A teethed lever with the teeth on its lower side

extending to both sides and connected to the crank levers of the HPCVs & IPCVs will be attached

to the piston of the CVSM. Whenever the CVSM is operated to regulate the opening of the

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Control Valves the Control Valves of both HPT & IPT will be actuated simultaneously to the

required % opening to stabilize the turbine speed as well as load on the unit.

The condensate so collected in the hot well is pumped to the boiler after preheating in the LP Heaters

and HP Heaters.

Functions of Turbine Governing System:

Thus it can be understood that the Stop Valves and Control valves of the HP Turbine and IP Turbine

are to be opened to roll the turbine, and the Control Valves opening is to be varied to regulate the

turbine speed till the unit is synchronized & also to regulate the steam admission to the turbine,

during load raising & load variations to suit the grid demand. All these operations are achieved by the

Turbine Governing System installed.

The working medium of the Governing System Components is the Control Oil supplied by the AOP

initially during the turbine start up and finally by the MOP after rolling the turbine to its rated speed.

Hence the Governing System is called the Hydraulic Governing system. Further the turbine will be

tripped through the governing system only on the initiation of the Turbine / Unit Lock out Relay. After

the developments taken place the Electro Hydraulic Governing System is also installed along with the

Conventional Hydraulic Governing System.

For tripping the turbine on the initiation of the Turbine/Unit Lock out Relay, trip command will be sent

to the Turbine Trip Solenoid Valves and consequent to the actuation of these solenoid valves the ESVs

will close first and then the control valves will close and the Generator Circuit Breaker will be tripped,

thus isolating the unit from the grid. After the unit tripping the unit will coast down to the barring

speeds of 180 rpm and continue to run at this speed where the jacking oil pumps are available to keep

the machine floating on jacking oil pressure.

If the TG set is provided with Barring Gear Motor the turbine will be allowed to come to stand still, after

which the barring gear will be engaged manually and the Barring Gear Motor will be switched on from

the local control panel. The barring speeds for the turbines provided with the barring gear mechanism

will be 3.0 rpm.

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Types of Governing system :

There are two types of Governing Systems called as the Hydraulic Governor and the Electro Hydraulic

Governor. The Hydraulic Governing system will act as a back up for the Electro Hydraulic Governing

System. Function of both types of Governors is the same, the difference in both the systems being only

that:

The Hydraulic Governor operates based on the Auxiliary Secondary Oil signal input received

from the Speeder Gear.

The Electro Hydraulic Governor operates based on the 0-10 Volts supply received from the

ATRS.

All the components of the governing system are common for both systems except that there are

dedicated follow up valves for each system. Hence the HP Secondary Oil & IP Secondary Oil will

be supplied by both sets of Follow up Valves. The main difference between both the systems

being only the input signal whether it is hydraulic or electrical.

Both the governing Systems get the Control Oil supply from the common internal System.

The dedicated follow up valves of each Governing System will modulate as per the signal oil

supplied by the respective Governing Systems and supply the HP secondary oil and IP secondary

oil to operate the respective Stop Valves & Control valves.

The combination of the Starting Device and the Speeder Gear is called the Hydraulic Governor

which provides the input hydraulic signal to the hydraulic converter which in turn delivers the

signal to the follow up valves after amplification of the input hydraulic signal.

Main functions of the Governing System:

The Stop Valves will be opened to 100% opening or closed fully to 0% opening.

The main steam flow or steam admission to the HP Turbine will be regulated by varying the %

opening of the Control Valves for rolling the turbine and also for loading the Turbine.

After synchronization, the load on the generator will be picked up by admitting sufficient

quantity of steam into the turbine to match the load demand.

If the connected load has exceeded the generation, the turbine speed will fall momentarily

which will be brought to normal rated speed by increasing the opening of the Control Valves and

thus admitting more quantity of main steam into the HP Turbine till then the turbine speed is

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brought to the rated speed thus stabilizing the unit at the new level of load demand. The control

valves opening will be increased by the Governing System.

Similarly if the demand on the generator has decreased, the turbine speed will rise momentarily

which will be brought to the normal rated speed by decreasing the opening of the Control

Valves and thus admitting less quantity of main steam into the HP Turbine till then the turbine

speed is brought to the rated speed thus stabilizing the unit at the new level of load demand.

The control valves opening will be decreased by the Governing System.

In case of unit tripping, the turbine trip command will be sent to the Remote Trip Solenoid

Valves of the Governing system by the Turbine / Unit Lock out Relay, consequent to which the

turbine Stop Valves and Control Valve will close in sequence and the generator circuit breaker

also trips thus isolating the TG Set from the grid.

The T.G. Set will coast down and will run at barring speed of 180 rpm till the next unit start up.

Important Components of the KWU Steam Turbine Governing System and their functions:

Sl.

No

Description of

component Quantity Function

1Remote Trip

Solenoids2

When any turbine trip gets initiated, the solenoids get energized and

the Control Oil gets drained through these valves and (actuates)

trips the MTV.

2 Main Trip valves 2

These Valves are also called as the main trip gear. Turbine tripping

takes place through this device. While the unit is in service or under

non trip condition these MTVs will establish Trip Oil & Auxiliary Trip

Oil which will be used for resetting & opening the Stop Valves and

also for producing the HP Secondary Oil & IP secondary Oils.

3 Starting Device 1

As the name of this device denotes, this device is used for resetting

and opening the Stop Valves and Main Trip Valves & Hydraulic Trip

Devices and prepare the Governing System ready to start the

Turbine. This device can be operated either manually by hand wheel

or from remote (MCR) through the motorized actuator.

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4 Speeder Gear 1

This device in combination with the Starting Device forms the

Hydraulic Governor and provides the input hydraulic signal to the

hydraulic converter. This device can be operated either manually by

hand wheel or from remote (MCR) through the motorized actuator.

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Hydraulic &

Electro

Hydraulic

Converter

1 + 1

Amplifies and converts both the hydraulic & electrical signals into

hydraulic signals called the HP Secondary & IP Secondary Oils for the

operation of HP & IP Control Valves.

6Hydraulic Trip

Device1

This device provides the mandatory protections of the turbine by

draining the Auxiliary Trip Oil through it. This device is reset by the

Auxiliary Start up Oil.

Description of various oils in the Governing System:

Sl.

No:Name of the oil Description

1 Control OilIt is the oil taken from the AOP / MOP discharge header fro the Governing

System.

2Trip Oil & Auxiliary

Trip Oil

These two oil circuits are established through the Main Trip Valves under

reset condition.

3

Start up Oil &

Auxiliary Start up

Oil

These two oils are established to their maximum pressure through the

Starting Device at 0% position and their pressures start falling when the

position of the Starting Device is raised.

4Auxiliary

Secondary Oil

This oil circuit is nothing but the output oil of the Hydraulic Governor and

the input oil to the hydraulic converter.

5 Secondary Oil Out put oil of the Hydraulic/Electro Hydraulic converters.

6 Test OilThis oil circuit will be established to test the Over Speed Trip Device while

the turbine is running at rated speed.

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Description of various oils in the Turbine Governing System, their source, pressures and their function:

Sl

No

Name of the

Oil

Its source &

pressure Purpose/Function of the oil

1 Control Oil

AOP/MOP

(7.0 – 8.5 Kg/cm

sq)

To establish the Trip Oil, Aux. Trip Oil, Start up Oil & Aux.

Start up Oil, Aux. Secondary Oil, Secondary Oil Primary Oil

etc.

2 Trip Oil

Main Trip Valve

(4.8 – 6.0 Kg/cm

sq)

To Reset, Open & Trip the Stop Valves

3Auxiliary Trip

Oil

Main Trip Valve

(4.8 – 6.0 Kg/cm

sq)

To trip (actuate) the Hydraulic Trip device.

4 Start up OilStarting Device

(5.5 Kg/cm sq)To assist resetting & opening the stop Valves.

5Auxiliary Start

up Oil

Starting Device

(5.5 Kg/cm sq)To reset the Main Trip Valve & the Hydraulic Trip device.

6Auxiliary

Secondary Oil

Speeder Gear (2.3

– 4.8 kg/cm sq)It is the input signal oil to the Hydraulic Converter.

7Secondary Oil

(HP & IP)

Hydraulic / Electro

Hydraulic

Converter

(0 – 6 Kg/cm sq)

To govern the HP & IP Control Valves opening.

8 Primary OilPrimary Oil Pump

(0 – 2.3 kg/cm sq)

It gives the feed back signal for the Hydraulic Governing

System.

9 Test Oil

Over Speed Test

Device (2.0 kg/cm

sq)

To test the Over Speed Test Device.

10 DrainsAll drains in the

system

By draining the various governing oils from a particular

section, the particular component of the Governing System

will be activated to discharge its function.

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Block Diagram of Governing System: (Slide – 7 of the Power Point Presentation)

The following are the various components of the Governing System:

AOP, MOP, AOP Discharge Header, Remote Trip Solenoid Valves (RSTVs) – 2nos, Main Trip Valves – 2nos,

Starting Device – 1 no, Hydraulic Trip Device – 1 no, Test Valve – 1 no, Stop valve servo Motor – 1no,

Stop & Control Valve Assembly – 1 no, Control Valve Servo Motor – 1 no, Hydraulic Converter – 1 no,

Electro Hydraulic Converter – 1 no, Two sets of follow up Valves each set dedicated to HG & EHG

systems.

The Governing System Hydraulic Oil Circuits showing how the various Governing Oils are generated and

supplied to the Governing System Components and to the Servo Motors of Stop & Control Valves is

explained in this slide as described here below:

When the AOP is started, the pump discharge oil which is called as the Control Oil is supplied at a

pressure of 7.0 – 8.50 Kg/cm sq, through the filter to

a) Main trip Valves 1 & 2 (through the RTSVs)

b) Starting Device & to the

c) Control valve servo Motor.

Main Trip valves 1 & 2 will supply :

a) The Trip Oil to the Stop Valve Servo Motor through the Test Valves, Hydraulic Converter & Electro

Hydraulic Converter

b) The Auxiliary Trip Oil to the Hydraulic Trip Device.

The Starting Device will supply:

a) The Auxiliary Start up Oil to the Main Trip Valves 1 & 2 and also to the Hydraulic Trip Device.

b) The Start up Oil to the Test Valves Turbine Stop Valves.

The Hydraulic Converter and the Electro Hydraulic Converter will supply:

The Secondary Oil to the Control valve servo Motor.

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Starting Device: (Slide – 8 of the Power Point Presentation)

The purpose of the Starting Device is

a) To build up Start up Oil pressure & Auxiliary start up Oil Pressure to reset Stop Valves, Main Trip

Valves & the Hydraulic Trip Device. This can be done by bringing the device to “0” position.

b) To depressurize the Start up Oil pressure & Auxiliary Start up Oil pressure to open the Stop

valves. This can be done by raising device to “100%” position.

c) To produce the Auxiliary Secondary Oil.

Functioning of the Starting device:

When the Starting Device is kept at 100% open position i.e. at MCR position of the unit, Control

Oil enters the middle compartment of the Starting Device.

When the Starting Device is lowered to 0%, the piston of the Starting Device will move

downwards and allows all the three compartments of the Starting Device to be filled with

Control Oil and through the Starting Device, Auxiliary start up Oil at a pressure of 5.5 Kg/cm sq

will be supplied to the Main Trip Valve & Hydraulic trip Device. Start up Oil also will be supplied

to the test Valves of the Stop Valves.

When the Starting device position is raised to 100%, the Starting device piston will close the

entry of Control Oil and the Auxiliary start up Oil & Start up Oil will stop flowing from it.

Main Trip Valve: (Slide – 9 of the Power Point Presentation)

Resetting of MTV for establishing Trip Oil & Auxiliary Trip Oil:

Preconditions:

AOP is in service.

Control oil is being supplied to the MTV.

The Starting device is at 0% position.

Auxiliary Start up Oil & Start up Oil are being supplied by the Starting Device.

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The Auxiliary Start up Oil supplied by the Starting Device and flowing to the Main Trip Valve pushes the

piston of the MTV towards upwards and thus gives the way for the Control Oil to enter into the MTV

compartments. Thus the MTV is reset and it will deliver the Trip Oil & Auxiliary Trip Oil.

The Control Oil which has entered the MTV will be delivered as

a) Trip Oil to Reset / Open the Stop Valves & Follow up Valves etc to produce Secondary Oil at a

pressure of 4.8 – 6.0 Kg/cm sq

b) Auxiliary Trip Oil at a pressure of 4.8 – 6.0 Kg/cm sq flowing to the Hydraulic Trip Device.

Tripping of MTV for killing the Trip Oil pressure:

The ports of the MTV through which the Control Oil is entering the MTV get closed because of

the downward movement of its piston when the MTV is tripped.

The Trip Oil and the Auxiliary Trip Oil get drained through the drain ports of the MTV thus

interrupting the supply of the above two Oils and hence their pressure is killed.

Resetting of Main Trip Valve: (Slide – 10 of the Power Point Presentation)

Precondition:

Auxiliary Start up Oil from the Starting Device to reset the MTV & HTD is already available to the MTV

which has kept the MTV in lifted position giving way for the Control Oil to enter through the Filter and

RSTVs 1 & 2 which are in series. Hence the Control Oil after entering into the compartments of the MTV

will be delivered as Trip Oil to hold Stop Valves and to produce the Secondary Oil and as Auxiliary Trip

Oil to the HTD.

If the auxiliary Start up Oil is drained from the MTV the valve will get closed interrupting the flow of Trip

Oil to the Stop Valves and interrupting the flow of Auxiliary Trip Oil to the HTD.

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Tripping of MTV through RTSVs (Electrical): (Slide – 11 of the Power Point Presentation)

When the RTSVs get the impulse from the Turbine /Unit Lock out Relay the solenoid coils of the

RTSVs will get energized and the RTSVs get closed because of the movement of their plungers

towards upwards.

Since there is no supply of Control Oil to the MTV through the RTSVs and also the drain ports

available in the RTSVs get open because of the upward movement of the plungers, the Control

Oil filled in the MTV compartments gets drained through the drain ports of the RTSVs.

Since the bottom compartment of the MTV is already empty because of the draining of the

Auxiliary Start up Oil, the piston of the MTV is free to move downwards once when the Control

Oil from the upper compartments of the MTV is drained through the drain ports of the RTSVs

and hence it travels automatically downwards.

This downward movement of the MTV piston facilitates opening of the drain port available in

the MTV body through which the Trip Oil & Auxiliary Trip Oils supplied by the MTV will get

drained from their pipe lines.

Tripping of MTV through the Hydraulic Trip Device (Mechanical):

(Slide – 12 of the Power Point Presentation)

Status of the drawing in the slide:

Control Oil supply is available for the MTV and the MTV is shown in the lifted position supplying

the Trip Oil (to hold the Stop Valves & to produce the Secondary Oil) and the Auxiliary Trip Oil to

the Hydraulic Trip devices.

Auxiliary Start up Oil to reset the HTD & the MTV is not available.

Auxiliary Start up Oil to reset the MTV also is not available.

Occurrence when the Hydraulic Trip Device is actuated:

Because of the actuation of the HTD, its plunger moved in side and thus gave way for the

Auxiliary Trip Oil to get drained through the port which was made through in the HTD.

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The Control Oil available in the upper compartments of the MTV also got drained through the

HTD drain port because of which the MTV got closed.

Due to closing of the MTV as said above the Trip Oil available in the circuit holding the Stop

Valves and which is also responsible to produce the Secondary Oil also got drained through the

MTV drain. Due to closing of the MTV as said above through the Hydraulic Trip Device

mechanically, the control oil is prevented entering the MTV even though the RTSVs are in open

position and the AOP is in service.

Resetting of RTSVs, Hydraulic Trip Devices and MTV through the Starting Device:

(Slide – 13 of the Power Point Presentation)

Note: Resetting means the de-energized condition of the device or the status when the device has not

acted while the unit is in service.

Status of the drawing in the slide and the action to be taken to reset the RTSVs, HTD & MTV :

The AOP is in service.

The Control Oil is available up to RTSV-1.

RTSVs are in energized condition with their pistons in lifted position, thus closing the entry of

the Control Oil into the solenoid valves – To reset the RTSVs the trip command to the RTSVs

from the Turbine/ Unit Lock out Relay shall be isolated.

No other oils are available in the system – Hence all the Governing Oils shall be made available

to start the Turbine.

Hydraulic Trip Device is in the acted condition – Hence it shall be brought to the turbine

operating status.

MTV also is in tripped/acted condition – Hence the MTV shall be brought to the turbine

operating status by supplying the Control Oil to it through the RTSVs. The MTV will deliver the

Trip Oil & Auxiliary Trip Oil.

Starting Device is in open (Lifted) condition i.e. at 100% position – It shall be brought to 0%

opening to build up the Start up Oil & Auxiliary Start up Oil pressures.

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Process of resetting the RTSVs, HTD & the MTV through the Starting Device:

The resetting of the Governing System shall be done before restarting the unit after its tripping

or after completion of any works carried out on the unit either because of any major breaks

down in any area of the Plant or overhaul.

The AOP shall be started and its discharge pressure shall be verified to be about 20 Kg/cm sq.

The solenoid coils of the RTSVs shall be de-energized by resetting the Turbine/ Unit Lock out

Relays. Thus the RTSVs are got reset.

When once the RTSVs are de-energized the pistons of the RTSVs will travel down wards thus

giving way for the Control Oil to enter into the RSTVs and from there it flows to the MTV and to

the Starting Device.

The Control Oil enters into the middle compartment of the Starting Device since its ports are

open to receive the Control Oil. The Control Oil entering the Starting Device pushes its piston

downwards.

Because of the downward movement of the piston of the Starting Device it delivers the start up

Oil to Test Valve and also the Auxiliary Start up Oil required for resetting the HTD and the MTV.

Thus the HTD & MTV will get reset.

Because of the reset condition or because of the upward movement of the MTV piston the

Control Oil ports of the MTV will get open and thereby the Control Oil enters the MTV

compartments and the MTV will deliver the Trip Oil (required to hold the Stop Valves and to

produce the Secondary Oil) and also the Auxiliary Trip Oil to the HTD.

Stop Valve operation: (Slide – 14 of the Power Point Presentation)

Status as seen from the slide:

AOP is in service and the Control Oil is available up to the Starting Device and also the middle

compartment is filled with Control Oil. The Starting Device is in raised position to 100%. RTSVs are in the

energized condition with their valves in closed position. MTV is in the tripped condition. In the tripped

condition of the MTV the Control Oil inlet port and the Auxiliary Trip Oil delivery port are found blocked

and the delivery port of the Trip Oil to the Test Valve is in open position. HTD also is in acted condition.

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Auxiliary Start up Oil line from the Starting Device to the MTV and HTD is empty. The Test Valve and the

Stop Valves are in closed position.

Process of resetting the RTSVs, HTD & the MTV through the Starting Device:

The resetting of the Governing System shall be done before restarting the unit after its tripping

or after completion of any works carried out on the unit either because of any major breaks

down in any area of the Plant or overhaul.

The AOP shall be started and its discharge pressure shall be verified to be about 20 Kg/cm sq.

The solenoid coils of the RTSVs shall be de-energized by resetting the Turbine/ Unit Lock out

Relays. Thus the RTSVs are got reset.

When once the RTSVs are de-energized the pistons of the RTSVs will travel down wards thus

giving way for the Control Oil to enter into the RSTVs and from there it flows to the MTV and to

the Starting Device.

The Control Oil enters into the middle compartment of the Starting Device since its ports are

open to receive the Control Oil. The Control Oil entering the Starting Device pushes its piston

downwards.

Because of the downward movement of the piston of the Starting Device it delivers the start up

Oil to Test Valve and also the Auxiliary Start up Oil required for resetting the HTD and the MTV.

Thus the HTD & MTV will get reset.

Because of the reset condition or because of the upward movement of the MTV piston the

Control Oil ports of the MTV will get open and thereby the Control Oil enters the MTV

compartments and the MTV will deliver the Trip Oil (required to hold the Stop Valves and to

produce the Secondary Oil) and also the Auxiliary Trip Oil to the HTD.

Start up Oil & Trip Oils has entered the Test Valve and the Trip Oil has moved to the Stop Valve

Servo Motor and compressed the spring of the Stop Valve Servo Motor. During this process of

the Start up Oil entering into the Test Valve the Test Valve piston has moved downwards and

the Trip Oil also has entered the Test Valve. Thus the Stop Valve is kept pressed or locked by the

Servo Motor and is ready for operation.

Opening of the Stop Valves by raising the Starting Device:

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When the Starting Device is raised to 100% open position, both the Start up Oil to the Test Valve

and the Auxiliary Start up Oil to the HTD get drained from their respective lines through the

ports in the Starting Device.

Because of the draining of the Start up Oil to the Test Valve, the Test Valve piston moves

upwards and allows more quantity of Trip Oil to enter into the Test Valve compartments and

from there it flows to the bottom of the Stop Valve Servo Motor.

Because of the pressure difference in the Trip Oil at the top & bottom of the Servo Motor the

Stop Valve Servo Motor will be lifted upwards thus opening the Stop Valves.

During this process of Stop Valve opening the Trip Oil available at the top of the Servo Motor is

pushed back into the Test Valve’s empty Chamber.

Stop Valve servo Motor: (Slide – 15 of the Power Point Presentation)

In this slide the movement of the Servo Motor internals is shown for different status of the Stop Valve

for detailed understanding of the operation of the Servo Motor and it is also explained how the Trip Oil

is operating the Stop Valve Servo Motor.

In the first figure: Servo Motor internals are shown with description of each part.

In the second figure: Servo mechanism is shown after closure of the Stop Valve.

In the third figure: Servo mechanism is shown with the mechanism in Reset position and the Stop

Valve in closed position

In the fourth figure: Servo mechanism is shown with the Stop Valve in open position.

Resetting of the Stop Valve Servo Mechanism:

Trip Oil was admitted above the piston and the piston was pressed downwards to touch the piston disc

simultaneously draining the Trip Oil below the piston disc. Thus the Piston and the piston disc are

brought together which is described as Resetting of the Stop Valve Servo Mechanism.

Opening of the Stop valve:

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Trip Oil was admitted below the piston disc. The piston disc pushes the Servo Mechanism upwards thus

opening the Stop Valve simultaneously draining the trip Oil above the piston.

Tripping of the Stop Valve:

The trip Oil below the piston disc is drained causing the Stop Valve to collapse, leaving the piston away

from the piston disc. Bringing the piston to the piston disc is called Resetting of the Servo mechanism to

enable the Stop valve to be ready fro the next operation.

Turbine over Speed Trip Device – Operation & Resetting:

(Slide – 16 of the Power Point Presentation)

Status of the System in the slide:

The Servo Cylinder was filled with Auxiliary Trip Oil.

The Oil line of the Auxiliary Start up Oil to reset this device is empty.

Fly Bottle is not touching the fulcrum which is connected to the mechanism of the device.

Drain port of the device is in blocked condition.

When turbine over speed occurs and reaches the preset value,

The fulcrum will be pushed by the Fly Bottle because of the eccentricity developed in the turbine

shaft.

Because of this movement of the fulcrum the piston of the over speed Trip Device moves

forward.

Because of the movement of the piston, the drain port in the Servo Cylinder is made through

and the Auxiliary Trip Oil gets drained.

After completion of the draining of the Auxiliary Trip Oil the Auxiliary Start up Oil will enter the

Over Speed Tripping Device and push the piston to its normal position and thus resetting the

device to be ready for the next event of Over Speed.

Turbine Thrust Bearing Trip Device: (Slide – 17 of the Power Point Presentation)

15

Status of the System in the slide:

Auxiliary Trip Oil is available for the device.

Auxiliary Start up Oil line is empty.

The Test Oil line also is empty.

The Trip Device lever is found pressing on the Turbine Shaft.

Operation of the Thrust Bearing Trip Device:

When the axial movement of the Turbine Shaft exceeds the preset limit, the mechanical lever resting on

the turbine shaft will be pushed away, consequent to which the Thrust Bearing Trip device mechanism is

activated causing the unit tripping.

For resetting the device mechanically, the Auxiliary start up Oil will enter into the device and does the

function.

Resetting of Low Vacuum Trip device: (Slide – 18 of the Power Point Presentation)

Status of the device in the slide: Vacuum Trip occurred condition was displayed.

Description of the different pipe lines connected to the Low Vacuum Trip Device:

Vacuum line connected to the Condenser.

Atmospheric line.

Control Oil line.

Drain line.

Auxiliary Trip Device connected to the Main Trip Device with Auxiliary Trip Oil connection and

one drain pipe connection.

Resetting of the Low Vacuum Trip Device:

The Low Vacuum Trip Device is a Self Resetting Device.

16

When the condenser vacuum is pulled to restart the Turbine, the compartment of the Main

Vacuum Trip Device connected to the condenser vacuum system also will be subjected to

vacuum and hence the Trip Device mechanism will be pulled upwards.

Then the Control Oil flows into the Main Trip Device and also into the Auxiliary Trip Device.

The mechanism of the Auxiliary Trip Device will be pushed upwards by the Control Oil till its

stem touches the limit switch such that the limit switch contact is broken while the vacuum

exists in the Condenser.

Auxiliary Trip Oil also flows into the Auxiliary Trip Device thus making the Low Vacuum Trip

Device ready for the next operation.

Thus on completion of the resetting process of the Low Vacuum Trip Device the heading on the

slide – Resetting of Low Vacuum Trip device disappears.

Tripping of Low Vacuum Trip Device:

When the condenser vacuum falls to the preset value, the Low Vacuum Trip Device gets

activated and trips the Turbine on Condenser Vacuum Low indication.

When the vacuum fails in the Condenser there will be no vacuum in the vacuum connected

compartment of the Main Trip Device also and hence its mechanism collapses and moves

downwards.

Consequent to this downward movement of the MTV mechanism, the Control Oil in the

Auxiliary Trip Device gets drained.

Consequent to the draining of the Control Oil from the Auxiliary Trip Device, its mechanism also

collapses and moves downwards.

Consequent to the downward movement of the Auxiliary Trip Device mechanism, the limit

switch shown gets released and thus establishes continuity in the Turbine Trip Circuit which

activates the RTSVs resulting in tripping of the Turbine on Low Vacuum Trip.

Auxiliary Trip Oil also gets drained from the Auxiliary Trip Device leaving the Low Vacuum trip

device in the Turbine Tripped condition.

Hydraulic Governor of KWU Steam Turbine: (Slide – 19 of the Power Point Presentation)

The components of the Governing System of KWU Steam Turbine are as detailed below:

17

1) Starting Device, 2) Speeder Gear, 3) Auxiliary follow up Valve, 4) Speeder Gear Position

Indicator, 5) Starting Device Position Indicator and the 6) Primary Oil Pump with suction from

the Control Oil Header.

Status of the various components of the Governing System in the slide projected:

Starting device is kept at ‘0’ position which is the pre-requisite condition to reset the RTSVs,

MTV & the HTD for commencing the turbine start up operations.

Speeder Gear also is at ‘0’ position.

Trip Oil line from the Main Trip Valve to the out let of Auxiliary Follow up Valve is available in

filled condition.

Auxiliary Secondary Oil line to the Hydraulic Governor also is filled with oil. The Auxiliary

Secondary Oil will be supplied by the Auxiliary Follow up Valve.

Primary Oil line to the Speeder Gear at 0 – 2.3 kg/cm sq is available in filled condition.

Control Oil is available for the Starting Device.

Control Oil is available at the suction of the Primary Oil Pump.

Operational sequence of the Governing System:

When the Starting Device is raised to 100% open position the Speeder Gear internals are

lowered by the connecting link rod between the Starting Device and the Speeder Gear. Auxiliary

Follow up Valve also was operated by the Speeder Gear lever.

Primary Oil Pump shall be started for supplying the Auxiliary Secondary Oil to the Hydraulic

Governor through the Auxiliary Follow up valve.

Then the Speeder Gear shall be operated and kept at 100% open position.

With this it can be said that the Stop Valves and Control Valves of the turbine can be operated to start

the Turbine.

Trip Oil from MTV: (Slide – 20 of the Power Point Presentation)

Status of the drawing in the slide:

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Control Oil is flowing to the Starting Device.

Start up Oil & auxiliary Start up Oil was found flowing out from the Starting Device.

The Starting Device and the Speeder Gear were at ‘0’ position.

When the Starting Device is raised to 100% open position, the Start up Oil and the Auxiliary start up Oils

got drained through the Starting Device and the Trip Oil started flowing from the MTV to the Hydraulic

Governor. The speeder Gear and the Auxiliary Follow up Valve will modulate in auto while supplying the

Auxiliary Secondary Oil to the Hydraulic Governor.

Hydraulic Governing & Electro Hydraulic Governing System:

(Slide – 21 of the Power Point Presentation)

Status of the drawing in the slide:

Hydraulic Converter & the Electro Hydraulic Converter Systems are found with their dedicated

Follow up Valves modulating in auto supplying HP Secondary oil and the IP secondary Oil

through their respective Follow up Valves.

The Hydraulic Converter receives the Auxiliary Secondary Oil from the Speeder Gear and its

Auxiliary Follow up Valve and the Control Oil from the AOP/MOP.

The Electro Hydraulic Converter receives 0-10 Volts supply from the ATRS instead of the

Auxiliary Secondary Oil from the Speeder Gear (as in the case of Hydraulic Converter) and also

the Control Oil from AOP/MOP.

Description of the Governing Systems:

The combination of the Hydraulic Converter or the Electro Hydraulic Converter along with their

dedicated Follow up Valves is called as the HG/EHG Governing System

Here it is to be understood that the Hydraulic Governor will act as per the Auxiliary Secondary Oil

received by it where as the Electro Hydraulic Governor will act as per the signal voltage received from

the ATRS.

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Auxiliary Secondary Oil signal will be taken as reference to regulate the Control Oil in case of HG where

as the 0-10 Volts signal from ATRS will be converted into Hydraulic Signal and will be taken as reference

to regulate the Control Oil in case of EHG which will be amplified in the Converters and conveyed to the

Follow up Valves to regulate the Trip Oil supplied by the MTV and convert it as HP Secondary Oil and IP

Secondary Oil. There are six numbers of Follow up valves for each Governing System, out of which three

valves will be supplying the HP Secondary Oil and three valves will be supplying IP Secondary Oil.

Hydraulic Minimum Selection: (Slide – 22 of the Power Point Presentation)

There are two conditions narrated for the functioning of the Governing System as:

1) If the drains are at 0% open, the Governor output will be 100% to Close / Open – 100%.

2) If the drains are open by 100%, the Governor output will be 0% to Close / Open – 0%.

Control Valve Servo Mechanism (CVSM): (Slide – 23of the Power Point Presentation)

Status of the CVSM in the slide:

The CVSM along with the pilot valve of the HPCV is shown. The pilot valve of the HPCV receives Control

Oil in the upper half and the Secondary Oil at its bottom. There are three drains on the pilot valve body.

Operation of CVSM:

When the Secondary Oil enters into the pilot valve of the HPCV at its bottom, the pilot valve

piston moves upwards thereby opening the Control Oil port and allows the Control Oil into the

pilot valve compartment. The Control oil entered the CVSM and its piston moved forward

because of which the piston of the pilot valve collapsed.

When the secondary oil pressure decreases slowly, the piston of the pilot valve will further

move downwards initially. But the CVSM moves in the reverse direction and pulls the piston of

the pilot valve upwards.

When the Secondary Oil pressure decreases fast, the pilot valve moves downwards and allows

filling of the pilot valve compartments by the Control Oil which pushes the pilot valve upwards

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to the maximum position and thereby pushing the CVSM to the extreme position in the reverse

direction. The entry

Automatic Turbine Test: (Slide – 24of the Power Point Presentation)

Notes was not written for this slide.

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