Turbine governing steam turbines

WHAT IS GOVERNING SYSTEM ? Turbine Governing system is meant for regulation of turbine speed under no load and varying load condition.. GOVERNING SYSTEM DEVICES Remote trip solenoids 

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 are incorporated Both the governors are connected in parallel.

 Only one governor can be selected at a time through the process of hydraulic minimum selection.

 The control valve opening depends on secondary oil pressure and there is a definite relationship between the opening of HP control valve and IP control valve.

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

HYDRAULIC GOVERNOR SALIENT FEATURES

 Hydraulic governor is having only one control

loop called speed controller.

 Machine speed is measured and indicated as

primary 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 EHG

and HG is considered to be the primary

governor of the KWU turbine

ELECTRO-HYDRAULIC GOVERNOR SALIENT

 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% in

a step of 0.5% even when the machine runs on load The usual setting of droop in EHG is 5%.

 EHG can be mechanically isolated by closing the secondary oil line from the local.

GOVERNING SYSTEM DEVICES

 Remote trip solenoids

 Turbine trip gear

(Main trip valve)

 Starting and load limiting

 Sequence trimming device

 Solenoid for load shedding relay

DIFFERENT OILS USED IN KWU TURBINE

 Control oil (source oil)

 Auxiliary start-up 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

WORKING OF GOVERNING SYSTEM

SPEEDER

GEAR

STARTING DEVICE

AFUP

HYRAULIC CONVERTER

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 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 GDEVICES-OVERNORS

• 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.

THANK YOU