TURBINE GOVERNING SYSTEM

PRESENTATION BY

M DEENADAYALAN

C M NIKHIL

B VASANTH KUMAR

TOPICS OF DISCUSSION

INTRODUCTION

CONCEPT OF GOVERNING SYSTEM

FEATURES OF KWU GOVERNING SYSTEM

GOVERNING SYSTEM DEVICES

WORKING OF GOVERNING SYSTEM

HYDRAULIC AND ELECTROHYDRAULIC SYSTEM

PROTECTIVE DEVICES IN GOVERNING SYSTEM

QUERIES

WHAT IS GOVERNING SYSTEM ?

Turbine Governing system is meant for regulation of turbine

speed under no load and varying load condition.

To regulate the steam control valve position and hence load

generated.

To control the initial run up and synchronization of the

machine

To assist in matching the power generated to that demanded

by responding to the network frequency changes.

SALENT FEATURES OF 200 MW KWU TURBINE

GOVERNING SYSTEM

KWU 200 MW turbine is a throttle governed machine.

Two governors, electro-hydraulic and hydraulic areincorporated. Both the governors are connected inparallel.

Only one governor can be selected at a time through theprocess of hydraulic minimum selection.

The control valve opening depends on secondary oilpressure and there is a definite relationship between theopening of HP control valve and IP control valve.

Between 40 to 200MW the turbine load is varied bychanging the HP control valve throttling alone.

HYDRAULIC GOVERNOR SALIENT FEATURES

Hydraulic governor is having only one controlloop called speed controller.

Machine speed is measured and indicated asprimary oil pressure.

Range of speed control is 2800-3210 rpm.

Speed regulation range (droop) of HG is 7%.

HG acts as a back-up to the EHG.

HG can not be isolated mechanically like EHGand HG is considered to be the primarygovernor of the KWU turbine

ELECTRO-HYDRAULIC GOVERNOR SALIENT

FEATURES

EHG consists of three control loops for speed, load andpressure.

EHG optimizes the turbine life by conservative operation withthe aid of TSE.

Faster response and precise frequency control.

Actual speed of the turbine is measured by using hall probes

Range of speed control is wider (0-3210) rpm.

Speed regulation (Droop) can be changed from 2.5% to 8% ina step of 0.5% even when the machine runs on load. The usualsetting of droop in EHG is 5%.

EHG can be mechanically isolated by closing the secondary oilline from the local.

GOVERNING SYSTEM DEVICES

Remote trip solenoids

Turbine trip gear

(Main trip valve)

Starting and load limiting

device

Speeder gear

Auxiliary follow-up piston

Follow-up piston

Hydraulic amplifier

Electro-hydraulic

convertor

Sequence trimming device

Solenoid for load shedding

relay

DIFFERENT OILS USED IN KWU TURBINE

Control oil (source oil)

Auxiliary start-up oil

Start-up oil

Auxiliary trip oil

Trip oil

Auxiliary secondary oil

secondary oil

Test oil

Primary oil

Lube oil

Jacking oil

REMOTE TRIP SOLENOIDS

TURBINE TRIP GEAR

Trip gear is the main protection mechanism of the turbine. It diverts

the control oil coming from the RTS in to TRIP OIL and AUX.TRIP

OIL. Aux.trip oil keeps the trip gear spool valve in open condition so

that uninterrupted trip oil pressure is ensured. Aux.trip oil is also

connected to three hydraulic safety devices namely Over speed , Low

vacuum &Thrust bearing Trip Devices.

STARTING AND LOAD LIMITING DEVICE

USED FOR RESETTING THE TURBINE AFTER TRIPPING

FOR OPENING THE STOP VALVES AND RELEASING THE CONTROL

VALVES FOR OPENING

STARTING DEVICE AT 0% POSITION

BELLOWS COMPRESSED (CONTROL VALVE CLOSED POSITION)

AUX STARTUP OIL RESETS TRIP DEVICES

STARTUP OIL RESETS STOP VALVES (ESVs AND Ivs)

PILOT VALVE(STARTING DEVICE) POSITION RAISED

START-UP OIL AND AUXILIARY START-UP OIL CIRCUITS ARE DRAINED

ESVS OPEN AT 42% AND IVS OPEN AT 56% POSITIONS OF THE STARTING

DEVICE

SPEEDER GEAR

ASSEMBLY OF A BELLOW AND A SPRING

BELLOW COMPRESSION CONTROLLED BY

STARTING DEVICE POSITOIN

SPEEDER GEAR POSITION (ALTERS SPRING TENSION)

PRIMARY OIL PRESSURE

OPERATED FROM UCB OR LOCAL

PRIMARY OIL PRESSURE (SPEED FEEDBACK)

AUXILIARY FOLLOW UP-PISTONS

TEST VALVES

HP/IP STOP VALVES RECEIVE TRIP OIL THROUGH

THEIR RESPECTIVE TEST VALVES

PORT OPENINGS FOR BOTH TRIP OIL AND

START-UP OIL

USED IN RESETTING OF STOP VALVES AFTER

TURBINE TRIP

VALVE CAN BE OPERATED WITH HANDWHEEL

WORKING OF GOVERNING SYSTEM

SPEEDER

GEAR

STARTING

DEVICE

AFUP

HYRAULIC

CONVERTER

FUP

TRIP VALVE

AUX START UP OIL

TO RESET TRIP V/V

EHC

FUP

EHC INPUT

IP SECONDARY OIL

HP SECONDAY OIL

TRIP OIL

TRIP OIL

CONTROL

OIL

AUX TRIP OIL

LOW VACUUM TRIP DEVICE

OVER SPEED DEVICE

THRUST BEARING DEVICE

HP/IP

STOP VALVE

RESET

CONTROL

OIL

TRIP OIL AUX

TRIP OIL

CONTROL OIL

FROM RTS

SELECTION BETWEEN HYDRAULIC AND

ELECTRO HYDRAULIC GOVERNING

MINIMUM PRESSURE BETWEEN HP AND IP

SECONDARY OIL

TURBINE STARTUP USING EHC WITH HC

SYSTEM FOR BACK UP

SECONDARY OIL PRESSURE SET HIGHER THAN

THE EHC SYSTEM AND MAINTAINED USING A

TRACKING SYSTEM

ESV OPENING

PROTECTIVE DEVICES IN GOVERNING SYSTEM

TURBINE PROTECTON

Two type of protection

a)Electrical protectionb)Mechanical tripping

Electrical protection(through RTS) Turbine UCB manual trip Stator water conductivity >21 mho/sec Stator water flow <13 cubic m/s Boiler to turbine through UTR Gen to turbine through UTR Lube oil pressure low -low <1.2 ksc(2/3) Fire protection(channel 1&2) UTR manual trip ATRS shut down programme

Mechanical devices TG over speed trip (bolt-1 –3300 rpm,2-3330 rpm) Condenser vacuum low Axial shift high

GOVERNING CONTROL SYSTEM

Governor control systems consist of three basic elements:

These elements are

Sensing elements – fly ball weight etc.

Transmitting elements - mechanical linkage, hydraulic or pneumatic pressure, electrical signals or, as is most common, a combination.

and Correcting elements - the valve or valves that control the

flow of steam to the turbine.

MECHANICAL PROTECTION DEVICES-OVER SPEED TRIP DEVICE OR EMERGENCY GOVERNORS

• The function is to stop turbine when permissible speed is exceeded.

• Two over speed bolts, one acts when speed reaches 110% (3300rpm) of the rated speed and others comes in action at 111% of the rated speed (3330 rpm)

• It is situated in the front end bearing pedestal & consists of eccentric bolt, adjusting screw, spring, pawl and screw plug. .

• The speed is measured with the help of hall probe.

• When the over speed occurs & goes beyond the preset value(s) the bolts fly out due to centrifugal force & strike against the respective pawls. This will lead to the opening of the Drain port through which Auxiliary trip oil will be drained, resulting in the draining of the trip oil & thereby tripping the turbine.

• Below the tripping speed the bolt is held in position by spring and bears against the plug.

• At speed higher than over speed limit, the centrifugal force overcomes the spring force and forces bolt out of turbine rotor. This activates the turbine trip mechanism.

• Before over speed device comes into action, an another term called DROOP should come in action to reduce the speed of the turbine.

• Speed regulation of the turbine is called Droop

DROOP OR PROPORTIONAL BAND

Droop= amount of speed change from no load to full load divided by rated speed

In KWU turbines Droop is in the range from 2.5 to 8%.

Usually it is taken as 5% of the rated speed. This maximum speed is called ‘Dead band’ beyond which Droop comes in action to increase or decrease the speed of the turbine by opening or closing the control valve .

It is necessary in the control system to sense a change in speed & thus to reposition the valves

If droop =5%, it means +2.5% from 3000 rpm.

LOW VACUUM TRIP DEVICE

The function of the device is to trip the turbine on dropping of condenser vacuum below a limit.

Condenser vacuum permissible is -0.9 ksc.

It consists of twin chamber arrangement with a separating diaphragm. Upper side is connected to the condenser vacuum and lower side to atmosphere. Upper side is also subjected to the primary oil pressure through the piston.

Under poor vacuum with sufficiently high machine speed(>600rpm), the net force acting on the upper side is more than the lower side . This causes the opening of the drain port through which the Aux.trip oil will drain.

This protection is not effective during low speed because of the non availability of the primary oil pressure.

For resetting it doesn’t require Auxiliary start up oil.

THRUST BEARING DEVICE

It is used to protect the turbine against high axial shift and high thrust pad wear.

It consists of a two pair of small cams, one set before and another after a pawl are fitted on the turbine shaft 180⁰ opposite.

The pawl is so arranged that whenever the shaft moves horizontally too much (>0.6mm)either in left side or right side, one sets of cam comes in contact with the pawl and thereby thrust bearing trip device’s latch will be released. This will cause the opening of the drain port through which auxiliary trip will be drained.

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