Why do turbines go into over speed trip???

 

A turbine rotor can go into over speed when its rotational speed exceeds its designed or safe operating limits. This can occur in various types of turbines, such as steam turbines, gas turbines, or even wind turbine.A turbine rotor can go into over speed when its rotational speed exceeds its designed or safe operating limits. This can occur in various types of turbines, such as steam turbines, gas turbines, or even wind turbine.

 Now a days steam turbines are designed for rotation speed more than 10000 RPM.For low capacity turbines the speed is generally more than that of high capacity turbines.

 Following are the most relevant reasons for Turbines to go into high speed or over speed.

 Sudden Load Loss: If the load on the turbine suddenly decreases, the turbine may accelerate beyond its design limits due to the reduced resistance. This can occur, for example, if there's a sudden disconnection of the load or if a generator or other equipment connected to the turbine experiences a fault.

Malfunctioning Governor: Turbines often have governors that control the amount of steam input to the turbine in order to maintain a specific rotational speed. If the governor malfunctions, it might not be able to regulate the turbine's speed properly.

Sudden cut off of extraction steam:Sudden cut off or closure of extraction steam valve may leads to over speed of Turbine.

Control System Failure: The control systems that regulate the speed of a turbine may malfunction, leading to an inability to control the turbine's speed effectively. This can occur due to electrical failures, software glitches, or other issues with the control system.

Loss of Blade Load: Turbine blades are designed to extract energy from the fluid (steam, gas, or water) passing through them. If there's a sudden drop in the fluid flow rate or pressure, the blades might not experience enough load to keep the turbine's speed in check, leading to over speed.

Read >>>Practical approach to power plant operation and maintenance

Failure of Throttle valves: Damages to the any of the throttle valve lead to over speed of the Turbines

Stuck up of throttle valves: Stuck up of throttle valves due to burs, scoring marks or due to dust and dirt may lead to over speed of the Turbines

Looseness in linkages:Looseness in HP or KP valve linkages may lead to mal-operation of the throttle valves leading into more steam flow and hence over speed of the Turbine

 To prevent overspeed and its potentially catastrophic consequences, turbines are equipped with safety measures such as mechanical overspeed protection systems, which may include centrifugal force-based devices that trip and reduce the flow of fluid into the turbine when a certain rotational speed is exceeded. Regular maintenance, monitoring, and adherence to operational guidelines are essential to ensure the safe and reliable operation of turbines.

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Droop and isochronous mode operation of steam Turbine

 Droop and synchronous modes are two operating modes commonly used in turbine control systems, particularly in the context of electrical power generation. These modes help regulate the speed and power output of the turbine to maintain stability in the electrical grid.

 Droop Mode Operation:

In droop mode, the turbine operates with a speed or frequency droop characteristic. Speed droop refers to the decrease in turbine speed as the load increases, while frequency droop refers to the decrease in electrical frequency. This mode allows multiple turbines or generators to share the load in a grid.

 In droop mode, the turbine's governor control system adjusts the fuel supply to the turbine based on the difference between the actual speed/frequency and a reference speed/frequency. As the load on the turbine increases, the speed or frequency decreases slightly, which causes the governor to open the fuel valve and increase the steam flow, compensating for the increased load. Similarly, when the load decreases, the speed or frequency increases, resulting in a reduction in fuel supply.

 Droop mode operation allows for load sharing among multiple turbines or generators. Each unit operates at a slightly different speed or frequency, which helps balance the load in a grid. The speed or frequency difference between units is known as the droop setting, and it determines how the load is shared between them.

 Key features of droop mode operation:

 Speed Control: The turbine's speed is adjusted to maintain a stable power output as per the grid's load demand. As the load increases, the turbine's speed decreases.

 Frequency Regulation: The frequency of the electrical output from the turbine is dependent on the load. As the load increases, the frequency decreases, and vice versa.

 Load Sharing: Multiple turbines operating in droop mode share the load in proportion to their capacities. Each turbine adjusts its speed based on the droop characteristic to contribute its fair share to the overall power demand.

 Load control in droop mode

 While STG is connected with grid this mode becomes active.If, STG is connected to other STG, but without grid paralleling then also this mode can be made active.

Generally 4 to 6% of droop is set for electro hydraulic control system.

By taking 4% droop as an example, 1% droop corresponds to 25% load, 2% droop is equivalent to 50% & 4% refers to 100% load.

In such controllers mode,load will be input & based on it speed will be adjusted.

 For example:

A 25 MW turbine has 8500 RPM and has droop set 4%.If Turbine is operating at 12.5 MW then controller speed set point is

 8500 + 2% X 8500 = 8670 RPM

 If it is operating on full load, then speed setting will be

 8500 + 4% X 8500 = 8840 rpm

 Isochronous mode operation:

 In isochronous mode, the turbine operates at a constant speed or frequency regardless of the load variations. In this mode, the governor control system works to maintain a steady speed or frequency by adjusting the fuel supply to the turbine.

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 The governor closely monitors the speed or frequency and makes minute adjustments to the fuel valve to counteract any changes caused by load fluctuations. As a result, the turbine operates at a constant speed or frequency, providing a stable power output.

 Isochronous mode is typically employed when maintaining a constant frequency is critical, such as in certain industrial applications or when connected to a sensitive electrical grid that requires precise frequency control.

 Key features of isochronous mode operation:

Read Generator and Turbine inter tripping

 Speed Control: The turbine's speed is regulated to remain constant, regardless of the load demand. As the load increases or decreases, the turbine adjusts its power output while maintaining a constant speed.

 Frequency Regulation: The turbine's output frequency is maintained at a constant level, typically the nominal frequency of the electrical grid. The turbine adjusts its power output to match the load demand while keeping the frequency stable.

 Load Balancing: In isochronous mode, each turbine connected to the grid contributes to the load based on its power capacity. The turbines collectively adjust their power outputs to meet the total load demand while maintaining a constant speed and frequency.

 It is to be noted that,when STG runs in parallel mode, it remains in droop mode.If the STG is connected to to grid, as soon as STG comes out from grid (Island mode), auto changeover occurs from droop mode to synchronous mode.Then STG controls speed only

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Why do turbines go into over speed trip???

Effect of moisture content in steam Turbines

Effect of moisture content in steam Turbines

 When steam passes through a turbine, it undergoes expansion and releases energy, which is harnessed to generate power. However, if the steam contains water droplets or moisture, it can have detrimental effects on the turbine blades. As the steam expands and flows through the turbine stages, the droplets can impinge on the blades, leading to erosion, pitting, or damage.

 The churning effect typically occurs in the last few stages of the turbine, where the steam is at lower pressure and velocity. At these stages, any remaining liquid particles in the steam are prone to separation from the gas phase and can cause erosion on the turbine blades.

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 Moisture content in steam  leads into the following problems:

 Erosion: The high-speed impact of liquid droplets on the turbine blades can cause erosion, leading to damage and reduced efficiency over time. Erosion can wear down the blade surfaces, affecting their aerodynamic shape and performance.

 Vibrations: The churning effect can induce vibrations in the turbine rotor and other components. Excessive vibrations can cause mechanical stress and fatigue, leading to increased wear and potential failures.

 Loss of efficiency: The presence of liquid droplets in the steam reduces the effective energy transfer from the steam to the turbine blades. This can result in a decrease in overall turbine efficiency and power output.

 To mitigate the this effect and protect the turbine blades, several measures can be implemented:

 l Proper design of steam Turbine & blading to ensure proper expansion of steam in blades.Blade Design: Turbine blades can be designed to minimize the impact of churning. This can include using erosion-resistant materials, shaping the blades to minimize droplet impingement, and providing protective coatings.

 l Drainage Systems: Proper design and implementation of drainage systems within the turbine help remove condensed water and moisture effectively

 l Proper operation of the Turbine & maintaining steam parameters as per design

 l To mitigate the moisture content in steam and its negative consequences, steam turbines are equipped with various mechanisms and components, including steam separators, moisture separators, and steam dryers. These devices help remove or reduce the moisture content in the steam before it enters the turbine, ensuring better steam quality and minimizing the chances of churning.

 Proper design, operation, and maintenance practices, such as regular inspection and cleaning of turbine components, are essential to prevent or minimize the churning effect and maintain optimal turbine performance and longevity.

How do you calculate the work done & specific steam consumption of a back pressure steam turbine?

 

In back pressure turbines, steam just inters through HP valves & exists through exhaust, no any bleed or condensation is done.

The efficiency of the back pressure turbines is more as compared to condensate & condensate cum extraction steam turbines. However specific steam consumption of back pressure turbines is very less as compared to above both type of Turbines

 How do you calculate the work done per kg of steam?

 Let us assume 1 kg/sec of steam is entering into Turbine whose enthalpy is H1 kcal/kg & existing from turbine at enthalpy H2 kcal/kg

Then, work done per kg of steam is given as =(H1-H2) kcal/s

Or 4.18 X (H1-H2) KW, since 1 KJ/sec = 1 KW

 How do you calculate specific steam consumption of a back pressure Turbine?

 Specific steam consumption is defined as the amount of steam consumed to generate 1 KW of power

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

 i.e 860 / (H1-H2)

 A back pressure turbine is operating at pressure & temperature 64 kg/cm2 and 490 deg C respectively, the exhaust steam at pressure 2 kg/cm2& temperature 140 deg C is being used for process.Calculate the work done and specific steam consumption?

 Enthalpy of inlet steam at pressure & temperature 64 kg/cm2 and 490 deg C  = 809 kcal/kg

 Enthalpy of inlet steam at pressure & temperature 2 kg/cm2 and 140 deg C  = 660 kcal/kg

 Work done = (809-660) = 149 kcal/sec

Or 4.18 X 149 = 622.82 kJ/kg or 622.82 KW

Specific steam consumption SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / 149 = 5.78 kg/kw or MT/MW

 A back pressure turbine having inlet steam enthalpy and exhaust enthalpy 780 kcal/kg & 580 kcal/kg, then calculate the specific steam consumption of that Turbine?

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / (780-580)

SSC =4.3 MT/MW

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Steam Turbine standard operating procedures (SOPs)

 

Lube oil system operation

Pre-checks

• Ensure lube oil tank level is normal
• Ensure lube oil pumps are healthy to operate
• Ensure lube filter & cooler are in service
• Ensure lube oil inlet and outlet valve provided at filters & coolers are open
• Ensure cooling water inlet & outlet valves provided for oil coolers are in closed condition
• Ensure suction & discharge valve of the pumps are in opened condition

Operation

• Start the oil pump (AOP)
• Ensure no abnormal sound & vibrations
• Observe the discharge pressure
• Ensure header pressure is normal, if not adjust with PRV or recirculation valve
• Check the oil filter DP, if high change over the filter
• Check overhead oil tank is getting filling
• Ensure lub oil is supplying to each bearing & adjust the oil pressure to each bearing as per desired requirement
• Maintain the oil temperature by adjusting cooling water inlet & outlet valves.

Note: Keep open cooling water inlet valve 100% open & adjust the temperature by adjusting outlet valve

• Ensure the over head oil tank is full
• Keep stand by lube oil pump & EOP ready

Barring gear operation

• Ensure lube oil system is in service and oil is circulating at the bearings at a desired pressure
• Ensure barring gear motor is healthy to start & its all interlocks are in place
• Engage the barring gear clutch
• Start the barring gear motor
• Observe the rotor is rotating at barring speed without increase in bearing vibrations & temperature
• Ensure there is no any abnormal sound

Cooling water system operation

Pre-checks

• Ensure the cooling tower level is normal
• Ensure cooling water pump is healthy to operate & their protections & interlocks are in place
• Ensure cooling water pump (MCWP) suction valve is open & discharge valve is closed
• Ensure all the field instruments are healthy & inline
• Ensure surface condenser inlet & outlet cooling water line valves are open
• Ensure Condenser water box vents are open
• Ensure cooling tower inlet cooling water line valves are open

 15-Emergencies in Power plant

Operation

• Start the pump from DCS at 70% RPM
• Open the discharge valve slowly
• Observe discharge pressure is increasing gradually
• Ensure the pump’s vibration & bearing temperatures are normal
• After venting air from condenser water box close the vent valves
• Observe cooling water is falling in cooling water
• Increase the pump’s speed as per requirement
• Note down cooling water inlet & outlet water temperature of condenser
• Start cooling tower fans one by one as per requirement

 SOP Lube oil & Oil cooler change over

Condensate system operation

• Ensure the hot well level is adequate. Otherwise make the hot well level with DM water
• Ensure the CEP is healthy & its all interlocks are in place
• Ensure pump’s suction & discharge valves are open
• Ensure ejector & gland sealing steam condenser inlet & outlet cooling water line valves are open
• Start the pump, ensure the water will flow from ejector & Gland steam condenser (GSC)
• Ensure gland steam outlet control valve to deaerator is close & cooling water is recirculating through recirculating control valve
• If the hot well level increases, then GSC discharge valve can be opened
• Once the Turbine comes into line,GSC outlet control valve should be kept in auto mode to maintain hot well level
• Vacuum pulling & Vacuum killing
• Pre-checks
• Ensure auxiliary steam is available at desired pressure and temperature
• Ensure vacuum breaker valve fitted on steam condenser is closed
• Ensure cooling water is circulating in the condenser and the turbine gland is charged fully at 0.1 kg/cm2
• Ensure live steam line to ejector steam lines drain are kept open
• Ensure Hogger & main ejectors steam and air valves are in closed condition

Vacuum pulling through hogger ejector

• Charge the main steam line to ejector steam & temperature control valve
• Ensure the rated pressure (10 kg/cm2) and temperature (220 deg C) for ejector vacuum pulling
• Once the rated parameters are reached open the steam valve of starting or hogger ejector
• Observe the steam is vented to the atmosphere
• Then open the ejector airline valve
• Observe vacuum inside the condenser increasing slowly and will reach 60 to 70% of rated vacuum within 20 minutes

SOP to put main ejector into line

• Ensure CEP is running
• Ensure cooling water inlet and outlet valves of main ejector which is to be taken into line
• Vent out air from water box of the ejector
• Then open the drain valve of inter condenser and after condenser of ejector
• Open the steam valve of after condenser ejector
• Open the steam valve of inter condenser ejector
• Observe the condensate is drained out from both the condensers
• Slowly open the air valve & observe the vacuum is increasing
• When vacuum reaches rated, then stop the hogger or starting ejector

Vacuum killing or Taking out of main ejector

• Close the air valve of the ejector
• Close the steam valve of inter condenser
• Close the steam valve of after condenser
• Close the drain valves of after & inter condensers
• Close the cooling water inlet & outlet valve once the ejector is cooled

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Turbine lube oil flushing procedure

 

Oil pipe lines cleaning & flushing:

Generally Steam Turbo Get machineries lube oil supply line & control oil lines are of stain less steel & return oil lines are of carbon steels. The oil pipelines fabricated at site are to be cleaned by acid pickling for CS pipelines and by Caustic Soda for SS pipelines.

Before acid pickling the pipes should be thoroughly flushed with air for removing of loose particles.

Acid pickling pipes should be dummied one end with rubber gasket and filled with acid of 5 to 8% of concentrated HCL acid and keep the pipes filled with acid for 24 hours, so that all loos metal particles will come out. There after remove the acid from pipes & clean the pipes thoroughly with water and neutralize with caustic soda.

Fill the 3 to 4% of concentrated caustic soda solution in the acid cleaned pipelines and keep the pipes for 24 hours, so that all acid contents gets neutralized.

Ensure the time between acid cleaning and soda wash should be kept minimal Also chemical solution should not exceed 60˚C. After that all soda washed pipes are thoroughly cleaned/rinsed with water and dry with Air, Lube oil (ISO VG 46) to be applied inside the pipelines to avoid rusting.

All the passivated pipelines are covered both the ends of pipes with plastics caps / lids so that no dust particles can enter inside. All passivated pipelines are to be fitted immediately in the original position and start the oil circulation / flushing.

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Turbine oil flushing:

Pre-checks or requirements for oil flushing;

• Fire fighting system at MOT and STG area is ready to use.
• Main oil tank should clean thoroughly using sponge/Cloth, diesel and with compressed air
• Ensure AOP suction strainers are cleaned and boxed up properly
• Fill the Oil Tank with flushing oil of Grade ISO VG 46 (refer O&M Manual) through centrifuge by site suitable temporary flexible hose connection. Temporary hose connection one end is immersed in the oil barrel and another end is connected to oil centrifuge inlet point. Centrifuged oil should be send from oil centrifuge outlet to Main oil tank by permanent piping. Flushing oil should be same as per first fill oil. The detailed specification & makes are specified in the operation & Maintenance manual
• Ensure Main oil tank level should be > 65% or as per requirement in local level gauge
• Before start up the LOS system please ensures there is no bypass in protections of motors like-Over load, single phase preventer etc.
• All the Oil Pumps & Main oil tank fans are kept ready for operation. Ensure Emergency local Buttons of all the motors are released condition.
• MOT heaters should on. Also ensure Heaters to be cut of at 65 ˚C of MOT Oil temperature
• Ensure MOT Mist fans power supply panel are in charged condition and Mist fan kept ready to start
• Ensure Aux. Oil pump power supply panel is in charged condition kept ready to start.
• Ensure STG Barring gear motor, EOP motor & ACOP motors power supply is switched off condition.
• Ensure AOP pump suction and discharge Pressure Gauges are working and its isolation valves are in opened condition.
• Ensure any one of the Lube oil cooler is line up i.e the inlet 3 way valves is directed in one cooler only and cooler equalizing valve is in closed position. Also ensure corresponding lube oil cooler vents and drains are in closed condition
• Lube oil cooler inlet and outlet cooling water valves are in closed condition. Ensure cooling water to be charged up to isolation valves during flushing
• Ensure lube oil cooler inlet Pressure Gauge isolation valves are open. Also ensure All PTs (if applicable) isolation valve is closed condition during flushing to avoid entry of any foreign particles.
• Remove the original filter elements (625 mesh) from filters skid & put Temporary made filters element (perforated pipe and rolled with temporary filter screen having sizes start from 50 mesh and fastened by wire) to both filter shell.
• Ensure any one of the Lube oil filter is line up i.e. inlet 3 way valves are directed in single oil filter only and equalizing valve is in closed condition. Ensure Lube oil temporary filters are cleaned and box up properly. Ensure Lube Oil filter drains and vents are in closed condition. Ensure Lube Oil filter line inlet & outlet Pressure Gauges is working and its isolation valves are open.
• Ensure Lube oil header Pressure Gauge is working and its isolation valve is open and PT‟s isolation valves are closed condition during flushing to avoid entry of any foreign particles.
• Turbine front & Rear bearing pedestal flanges oil inlet to out let, Gear box flanges oil inlet to out let, Alternator Front & Rear bearing pedestal flanges oil inlet to out let should be bypassed during oil flushing by suitable temporary hose pipes.

Procedure:

Stage-1

• Start AOP & check any oil leakage from the pipe lines welding joints & flange joints
• Observe lube oil header pressure rising
• Monitor the lube oil circulating through bearings bypass hose pipes
• Observe AOP oil pressure regularly, if discharge pressure is decreasing it means that, pump’s suction strainer is jammed. So stop the pump, clean the strainer & again restart the AOP
• Observe the Lube oil filter DPs if it crosses 0.6 kg/c2 change over the filter to stand by filter
• Raise the lube oil temperature 55 to 65 ˚C by MOT heaters or Temporary heaters. Once the oil temperature raised 55 to 65 ˚C lightly hammer the line with mallet or soft hammer so that all the loose materials will come out with the oil.
• After duration of two to three hours, change over the filter to the stand by one and check for the cleanliness of the mesh and if required replace the same. These processes are to be repeated by changing the filters in line and also mesh if required at intervals of 2hrs, 4hrs, 8hrs durations..
• Every 4 hours reduce the oil temperature by raking lube oil cooler into line. This thermal shock will helpful for expansion & contraction of pipe lines thereby removing scale & clogged particles inside the pipe lines & other system.
• Once 50mesh cleared then change to 100mesh then 150mesh and then 200mesh.This process to be continued up to 200mesh cleanness. Once 200 meshes are cleared then follow the Stage -2 flushing.

SOP lube oil cooler & oil filter change over

Stage-2

• Remove top half of the bearings (Thrust, Front & Rear) of T u r b i n e Rotor and keep them at safe location-Clean the preservatives which applied in the rotor. Re-place the bearing caps and their housing/cover in its position and ensure that oil will not spill out during flushing.
• Turbine front and rear pedestal loop line (flexible hoses) to be removed and normalized the inlet and out let connections as per original. Ensure Loop will be continued in the gearbox & Alternator bearings which are bypassed with flexible hoses.
• Ensure the temporary made filters element filter screen having sizes start from 50 mesh.
• Repeat the procedure as per Oil flushing Stage -1 Continue flushing further till system is clear. Once 200 meshes are cleared Oil flushing is completed.

Stage-3

• Completely drain the oil from MOT, coolers, filters and piping system.
• Once the MOT is drained completely, open oil tank cleaning, Clean the tank internals using site suitable special wipers with long rod along with compressed air. After cleaning, fill fresh lube oil inside the tank, ensure that oil is sprayed throughout inside of the tank (Sprayer-site suitable hose connection). Once the oil fogging is over fix the oil cleaning door with oil gasket and apply the grease on the gasket before tightening the bolts.
• Remove the Turbine thrust, front & rear bottom half the bearings from respective pedestals by small amount of lifting the Turbine rotor (max 0.1mm only)
• Remove the Turbine thrust, front & rear bottom half the bearings from respective pedestals by small amount of lifting the Turbine rotor (max 0.1mm only)
• Completely disassemble and clean the Turbine thrust, front & rear bearings by petrol or site suitable cleaning medium. All bearings pads to be inspect. Clean/polish both top & bottom halves. Ensure their correct fitting. Clean the holes provided in Thrust Bearings Pads holder & Journal Bearing holes also
• Insert the Turbine thrust; front & rear bottom half of the bearings in the respective places. Rest the Turbine rotor on the bearings
• Assemble thrust, front & rear top half of the bearings in the respective places. Ensure required clearances as O&M Manual recommendations
• Position the bearing caps/cover and tightens the cap studs as per torque recommended
• Ensure all pumps (AOP, MOP, EOP & ACOPs) suction strainers are well cleaned and boxed up properly
• Ensure both filters skid temporary filters are removed and filter skid is thoroughly cleaned. Insert the original filters in the respective places.
• Main oil tank – Oil should be filled through centrifuge with first fill oil of OEM recommended Grade 

Do not use: Flushing oil for final filling of MOT, if required get it tested from authorized party or OEM.

• Ensure Loop lines (flexible hoses) to be removed in the gearbox & Alternator bearings and normalized the inlet and out let connections as per original
• Ensure all dummies are removed which installed in PRVs, MOP & EOP discharge piping, control oil line and trip oil line system.
• Ensure all field instruments are fitted properly & they are taken into line
• Take All PRV’s into line
• Ensure all flange joints are fitted correctly
• Ensure all interlocks are in line
• Start the AOP & circulate the lube oil throughout the system

 

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 Why do turbines go into over speed trip???

 

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What do you mean by Turbine supervisory system???

 

What do you mean by Turbovisory or Turbine supervisory system?

Turbovisory or Turbine supervisory system is the monitoring of a Turbine. It supervises the condition of turbine and informs to an operating person. It also ensures the parameters do not exceed maximum allowable limit.

What is the significance of Turbine supervisory system?

Turbines are heavy & high speed machines, failures of machine lead into unrecoverable losses. So in case of any abnormality turbine should stop automatically. This is taken care by Turbine supervisory system.

What are the equipments or systems used in Turbine supervisory system?

Vibration probes: These probes are used for sensing shaft or bearing casing vibrations. Generally two probes are fitted at 90⁰ apart at X & Y-directions to measure the shaft vibrations. These vibrations are measured in microns, mills or mm/sec.

Speed probes: Speed sensors are generally Magnetic Pick up unit (MPU) type. These are fitted at teethed portion of turbine shaft for measurement. Generally 2 MPUs are used to measure the shaft speed, one for speed sensing & other for controlling.

Axial shift probes: This probe is fitted at the turbine front end to measure the axial displacement of shaft. Axial displacement probe of the shaft is generally set between +/- 0.4 to +/- 0.6 mm.

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Bearing temperature measuring sensors: These are used to sense the bearing metal temperature or bearing drain oil temperature. For measuring bearing metal temperature, RTD is inserted into drilled hole & touches the white metal & to measure the oil temperature RTD sensor touches the drain oil only.

Differential expansion probes: During abnormal operation conditions like quick start up, wrong SOP & uninform temperature distribution in casing & turbine rotor there could be the possibility of rubbing among turbine internals. To measure & monitor these gaps differential expansion probes are used & trips the turbine if these gaps increase beyond set values.

Casing temperature measuring sensors: Generally turbine casing thickness is very large around 150 mm &it depends on turbine operating parameters. So it is very much necessary of uniform distribution of temperature throughout the casing thickness.

And also the difference between top & bottom casing temperature of turbine should be very less.

Casing expansion measurement probes/sensors: These sensors are used to measure absolute expansion of casing. During startup &subsequent loading conditions turbine casing thermal expansion is must. Generally LVDTs are used for casing expansion measurement.

ESV opening indication: This is used to indicate the actual position of valves.

Eccentricity: This is very important supervision system. This is used to measure the mechanical bow. This may happen due to sudden trip of turbine & unavailability of barring device. Standstill position of turbine rotor for long time

Why do vacuum breaker valves are provided on steam condensers?

During tripping of turbine due to any of the above reasons like bearing vibration, temperature, axial shift, differential expansion etc, the vacuum breaker valve opens to bring down the turbine rotor speed to zero at the earliest time

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 Turbine oil flushing procedure

 

9-steps for Steam Turbine commissioning

 

1. What do you mean by Turbine commissioning?

Turbine commissioning is the process of start-up of newly installed Turbine auxiliaries & Turbine up to satisfactory level.

2. When and how do one shall conduct commissioning of Turbine?

Turbine & their auxiliaries are commissioned after proper install, checking & trials. And it is commissioned under the guidance of OEM (Original Equipment Manufacturer)

3. Write down the sequential steps involved in Turbine commissioning

• Steam blowing
• Oil flushing
• Cooling water system commissioning
• Evacuation or vacuum pulling system commissioning
• Condensate lines flushing
• Calibration of servomotor, interlocks checking
• Turbine rolling
• Over speed trip setting
• Synchronization & loading

4. Write down the various steps involved in steam blowing

• Hope Boiler is commissioned
• Steam blowing line is installed properly with required supports
• Start to increase Boiler pressure up to 40% of operating or 40 kg/cm2 whichever is lower
• Heat up the line by opening Boiler Main bypass valve, heat up is done at steam temperature around 400 deg C
• Blow the steam line from steam pressure 40 kg/cm2 to 25-20 kg/cm2
• Again steam line is cooled up to 100-150 deg C or 3 hours if main steam line from Boiler to Turbine is insulated & 1 hour if line is uninsulated
• Continue this process for around 20-30 blows
• Then put the target plate aluminium or steel & continue the blow
• Blowing is continued till

For Target Plate Made of Aluminum:

The piping considered clean if there are not more than 3 (Three) pitting of 0.5 mm to 1mm dia. in center area of 25 mm X 25 mm and shall not have any deformed edges. Besides this there shall be no pitting in the rim zone. Pitting below 0.5 mm may be ignored.

 For Target Plate Made of Stainless Steel:

The piping is considered clean if there are not more than five pitting of 0.1 mm dia to 0.5 mm dia. in centre area of 50 mm X 50 mm & shall not have any deformed edges. Pitting below 0.1 mm may be ignored

Then normalize the steam line

Connect main steam line flange to ESV (Ensure MS line flange & ESV flange’s prallelity is done)

What do you mean by Turbine supervisory system???

5. Write down the sequential steps for Steam line charging.

 Following steps shall be followed during steam line charging:

•  Ensure all the maintenance works related to steam lines are finished.
•  Ensure the clearance from process or Turbine side for charging the steam line.
• Ensure all the drain and trap valves are opened. 
• Slowly open the steam line bypass valve and allow for heat up of line.
• After ensuring line proper heat up, cracks open the main valve and allow for condensate drain.
• After ensuring no condensate in drain line, open the main valve gradually and observe the hammering. (If hammering occurs suddenly close the main valve). 
• After opening the valve 100%, wait till line stabilization. 
• After ensuring no condensate in drain lines, close all the drain valves

6. What is the significance of steam blowing?

Steam blowing allows power station boilers and pipelines to ensure that during normal operation no adhering material in the super heaters, reheaters, and steam pipelines will become dislodged, reach the turbine blades, and damage them. The steam blowing operation cleans all the debris in the super heater, reheater and the steam pipe line connecting the turbine.

7. What are the sequential steps involved in Turbine oil flushing?

Following are the steps

• Ensure OEM recommended oil is being selected for oil flushing
• Oil tank is filled with oil
• Flushing loops are prepared as per OEM recommendations
• Ensure return oil line is fitted with OEM recommended strainers
• Ensure oil centrifuge is in place & ready for operation
• Flush oil by starting lube oil pump & ensure oil is circulating through cooler
• Keep oil centrifuge ON with heater ON
• Maintain oil temperature up to 70 deg C for 4-5 hours
• Charge oil cooler & bring down the oil temperature up to 35-40 deg C
• Then hammer the oil lines to dislodge the sludge, bur or any other foreign materials
• Continue oil flushing till return line strainer is clean by 24 microns filter
• Oil flushing shall be deemed as completed, If Lube oil filter does not choke for more than 24 hours

8-What are the steps involved in cooling water system commissioning?

Following activities are involved in cooling water system commissioning

• Ensure all erection activities are completed on cooling water system
• Ensure all instruments are fitted on CW system
• Ensure cooling tower level is filled with required quality water
• Check the Cooling water pumps physical condition, if found ok take no load trial Or Ensure CW pumps are commissioned under the guidance of OEM
• Connect cooling water line with flushing line & leave to open areas (DO not connect return cooling water line to cooling tower)
• Then start the cooling water pumps & flush all the lines
• This activity shall be done -5 times & keep on making up cooling tower level every time

Read Generator and Turbine inter tripping

9-List down the sequential steps involved in condensate line flushing

• Condensate system consists of Condenser, CEP, Ejector, GSC
• Ensure all condensate system is ready for flushing
• Condensate line should be left open at deaerator floor
• Ensure hot well level is normal & provision is made to make up the level of hot well
• Ensure CEP is ready to start or CEP is commissioned under the guidance of OEM
• Then start CEP & flush the line
• This activity shall be dine for 8-10 times & every time up hot well level

10-What are the sequential steps for turbine rolling?

• Ensure Lube oil system is commissioned & is in service
• Ensure cooling water system is commissioned & is being charged
• Ensure condensate system is in service
• Ensure main steam line is charged as per standard process
• Vacuum pulling is done
• Reset turbine protections
• ESV opens & Turbine rolling is done s per OEM guidance

 

 Questions & Answers on steam blowing