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Welcome To Newly Recruited Assistant Engineers

B.PARAMESWARA RAO ASST.ENGINEER TSGENCO

2X 250 MW TURBINE INTERLOCKS & PROTECTIONS

What is an Interlock?An interlock is a feature that makes the state of two mechanisms or functions mutually dependent. It prevents incorrect operation to avoid possible damage of equipment.Interlocks can be considered as start permissives of any equipment.

What is Protection?The state of action to prevent possible damages of any equipment or system. It is necessary to safeguard the equipment against abnormal deviation of process parameters to unacceptable values .

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TURBINE PROTECTION SYSTEM

HYDRAULICProtectionELECTRICALTrip SystemGenerator Mechanical Protection

The function of the turbine protection system is to trip the turbine by instantly closing stop & control valves of HP & IP turbine thereby cutting of the steam supply.

Trip circuit mainly consists of the following itemsMain Trip valves MAX 51 AA005 & MAX 51 AA006 Two solenoid valves for trip initiation MAX 51 AA001 & MAX 51 AA002

TURBINE PROTECTION SYSTEM

During the trip initiation The pistons of Main Trip valves MAX 51 AA005 & MAX 51 AA006 move to downward by the spring force. There by trip oil circuit is connected to drain and Trip oil pressure is falls to zero, causing the stop valves and control valves to close by spring force.TURBINE TRIP INITIATION

Turbine Trip Gear

Remote Trip Solenoid ValvesMAX51 AA 001,002

Main Trip ValvesMAX51 AA 005,006DrainTrip oilTrip oilDrain

1.Bearing Lube Oil Pressure very Low (225mm)

The protection acts if Drum Level raises to > 225mm.

carryover of silica in to the turbine causes scaling on turbine blades.

The trip signal is initiated by drum level transmitters in 2-out-of-3- logic with a time delay of 10sec.

3.MS Temp Very Low (< 460 Deg C)

Sudden drop of MS temperature leads to serious thermal shocks which in turn induces surface stresses on HP turbine thereby reducing the life of the turbine. The protection gets armed after the MS temp crosses 510 Deg C.The trip is acted when MS temp. drops to 460Deg C.

3.MS Temp Very Low (< 460 Deg C)The temperature is measured by means of Six thermocouples and protection criteria is derived in 2 out of 2 logic.

MS TEMP-LEFT(>510)MS TEMP-RIGHT(>510)&PROTECTION ARMING

3.MS.TEMP V. LOW TRIP LOGIC

MS TEMP-LEFT(510 Deg C)

5.Fire protection Operated or M.O.T Level LowTripping of the turbine during the fire hazard can be initiated either manually by means of fire protection push buttons 1 &2. or M.O.T level Very low (- 115 mm) .The trip signal is initiated from 2 out of 3 level transmitters mounted on Main Oil Tank.

5.Fire Protection Push Buttons on BTG

5.Fire protection Operated or M.O.T Level Low

Emergency Shut off valve

Gate Valve5.Fire protection Operated or M.O.T Level Low

6.AXIAL SHIFT HIGH/LOW ( 1 MM) TRIP The Measurement is used to monitor the position of the shaft in the Thrust Bearing as Axial Shift. The turbine is tripped in case, the permissible limit exceeds beyond 1 mm to avoid the surface rubbing between stationary and rotating components.The Measuring Range Is -1.5 To + 1.5 MM.Towards GeneratorThrustBearing TowardsHPTPositiveNegative

6.AXIAL SHIFT HIGH/LOW ( 1 MM) TRIP 3 Nos Axial Shift Sensors At Bearing No.2

7. Low Vacuum Electrical Trip (< -0.7Kg/cm2)The protection acts if the Condenser pressure falls to -0.7Kg/cm2 .

it is provided to protect the condenser against a non-permissible pressure increase.

The trip signal is initiated by three Vacuum switches in 2-out-of-3- logic.

Condenser Pressure (S-1)Above -0.7 kg/cm2PROTECTION ARMING

2/3 LogicCondenser Pressure (S-2)Above -0.7 kg/cm2Condenser Pressure (S-3)Above -0.7 kg/cm2Low Vacuum Condenser Electrical Trip Arming

Condenser Pressure (S-1)Below-0.7 kg/cm2Trip To turbine

2/3 LogicCondenser Pressure (S-2)Below -0.7 kg/cm2Condenser Pressure (S-3)Below-0.7 kg/cm2Low Vacuum Condenser Electrical Trip Protection

8.H2 Cold Gas Temp Very HighIf the cold gas temperature of the Generator increases, it will increase the stator winding &core temperatures.

The possible reasons : Loss of BCW water to the H2 coolers.

The temperature is measured by means of four RTDs and protection criteria is derived in 2 out of 2 logic.

8.H2 Cold Gas Temp Very High-Logic

TEMP SIGNAL AT COOLER-CANDTEMP SIGNAL AT COOLER-DNORMAL VALUE 35 to 40 DEG CALARAM VALUE > 45 DEG CTRIP VALUE > 50 DEG CTEMP SIGNAL AT COOLER-AANDTEMP SIGNAL AT COOLER-BORTRIP TO TURBINE

9.Hot Air Temp After Main Exciter Very HighIf the Hot air temperature of the Exciter increases, it will lead to damage of Diode Wheels located in the main exciter.

The possible reasons : Loss of BCW water to the coolers.

The temperature is measured by means of Two RTDs & Two Temp. Switches and protection criteria is derived in 2 out of 2 logic.

9.Hot Air Temp After Main Exciter Very High

TEMP SIGNAL (SWITCH)ANDTEMP SIGNAL (SWITCH)NORMAL VALUE 50 to 55 DEG CALARAM VALUE > 75 DEG CTRIP VALUE > 80 DEG CTEMP SIGNAL (RTD)ANDTEMP SIGNAL (RTD)ORTRIP TO TURBINE

10.Liquid in Terminal Bushing HighLiquid in Generator Terminal Bushing high signifies entry of oil or water due to generator cooler leakage.Due to entry of oil or water, insulation value may go down and earth fault or stator winding failure may occur.The liquid level is measured by means of Three level Switches and protection criteria is derived in 2 out of 3 logic.

10.Liquid in Terminal Bushing High

Arrangement of Level DetectorsLevel DetectorSight GlassShutoff Valve

Generator Mech. Trip to Turbine (Logic)

Cold Gas Temp High >50 DegHot Air Temp After M.Exciter >80 DegLiquid in terminal Bushing Top High (2 sec Delay)ORgateGenerator Mechanical Trip to Turbine

Unit Trip Interlock Block Diagram

Generator TripTurbine Trip

Low Forward power Relay

Reverse Power RelayBoiler MFT11.Master Fuel Trip (M.F.T)12.Generator Electrical protection Operated

Turbine Interlocks & Protections13.Emergency Turbine Trip From Control Room.

Hydraulic Trip Devices

Over Speed Trip Device

When ever a preset over speed is reached, the eccentric fly bolt(8) activates the piston(4) and limit switch(10) via a pawl(7).This connects the Auxiliary Trip oil to drain thereby depressurizing it(X to C).The loss of Auxiliary Trip medium pressure causes the Main Trip valve to drop, which in turn causes the trip oil pressure to collapse.

TURBINE OVERSPEED TRIP DEVICE

FLY BOLTAux Trip OilAUX START-UP OIL TO RESET

AUX TRIP OILDrain

TURBINE OVERSPEED TRIP DEVICE

Low Vacuum Trip deviceThe purpose of the low vacuum trip is to operate the trip valve by draining the aux. trip fluid whenever the condenser back pressure increases beyond the permissible limits.In the hydraulic low vacuum trip device, a compression spring set to a specific tension pushes downwards against diaphragm, the topside of which is subject to the vacuum.Deterioration of vacuum inside condenser causes the pilot valve in the low vacuum trip to be moved from its upper position downwards by the pretension spring, resulting in depressurization space of below right hand valve.The right hand valve is moved to the lower end position by spring, hence opening auxiliary trip fluid circuit. This causes a reduction in the pressure of fluid below differential pistons of main trip valves, and their tripping by the springs. When tripfluid circuit is open to drain, all stop and control valves close.

DrainControl Oil

AtmosphereVacuum

Aux Trip OilDrain

LOW VACUUM TRIP DEVICEResetting Of Low Vacuum Trip DeviceTripping Of Low Vacuum Trip Device

Low Vacuum Trip Device

Turbine Trip Gear

Remote Trip Solenoid ValvesMAX51 AA 001,002

Main Trip ValvesMAX51 AA 005,006

Generator TripTurbine Trip

Low Forward power Relay

Reverse Power RelayBoiler MFT

Turbine Trip Conditions Discussed AboveMFT Trip

Tripping Conditions Due to GT & UAT faults

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