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.

Read more>>>Powerplant and calculations

Generator and Turbine intertripping

Case-1

 On tripping of class A trip of Generator

1-Generator breaker opens

2-Excitation switches off

3-Turbine trips on 86 T relay and followed by closing of ESV and all extractions

4-Turbine speed increases a bit by around 2-3% and gradually speed recedes

 Case-2

 On tripping of class-B trip of Generator

 1-Only generator breaker opens and excitation switches off

2-Turbine rotates on rated speed

3-After normalization of problem, generator synchronized with auxiliary power supply unit and later with grid

4-In case of small turbines, STG clubbed with 86GA to trip Turbine also

 Case-3

 On tripping due to Turbine fault

 1-Relay 86 T gets activated to close turbine ESV all extractions

2-Low forward power or Reverse Power Relay activates first which has time delay, during this time entrapped energy gets consumed by generator

3-Subsequently 86 G relay gets activated to open Generator breaker and followed by excitation gets off

4-Turbine speed does not increase in this case

 Trend of rotor speed on tripping of Turbine and Generator

Read>>>>Powerplant O&M reference books

 On tripping of Generator, instantly generator breaker gets opened and Turbine emergency valve closes.So steam entrapped in Turbine casing causes increase in speed initially and later slows down.

On the other hand,when turbine trips first, generator breaker opens after some time delay through Low forward power or Reverse Power Relay.This time delay helps turbine to consume entrapped steam in casing.As a result turbine generates power and does not allow speed to increase more.

 Relays and significance

Sl No.	Type of relay	Used for
1	86-G	Generator lock out relay
2	86-T	Turbine lock out relay
3	59-G	Generator over voltage @110% alarm and 120% trip
4	27-G	Generator under voltage @90% alarm and 80% trip
5	81-U	Generator Under frequency
6	81-O	Generator over frequency
7	32-P	Generator Reverse Active Power  5 % of Active Power
8	32Q	Generator Reverse Reactive Power
9	37	Low forward Power
10	46	Negative Phase Sequence
11	49	Generator Over Load
12	50	Generator Instantaneous O/C
13	64N	Restricted E/F
14	64R	Rotor E/F2nd Stage

Read Powerplant and calculations

Why Turbines go into over speed trips???

Topping cycle & calculations

  Topping cycle & calculations

 

A Co-generation system can be classified as either a topping cycle or a bottoming cycle on the basis of sequence of energy generated & use.

 In a topping cycle, the fuel supplied is used to first produce power and then thermal energy, which is the by-product of the cycle and is used to satisfy process heat requirements.

 In a topping cycle, a primary heat source, such as a gas turbine or an internal combustion engine, is used to drive a generator and produce electricity. The primary cycle typically operates at higher temperatures and generates high-pressure and high-temperature exhaust gases.

 The exhaust gases from the topping cycle are then directed to a waste heat recovery boiler or a heat exchanger, where their residual heat is captured. This waste heat is then used to produce steam, which drives a steam turbine or an organic Rankine cycle (ORC) turbine in the bottoming cycle.

 Topping cycles are commonly used in combined cycle power plants, where they offer improved efficiency and performance compared to standalone gas turbines or internal combustion engines. The integration of a bottoming cycle allows for the utilization of waste heat, maximizing the overall energy output of the system.

 In a bottoming cycle, the primary fuel used produces high temperature thermal energy and the heat rejected from the process is used to generate power through a heat recovery Boiler & Turbo generator.

 Bottoming cycles are suitable for manufacturing processes that require heat at high temperature in furnaces & kiln and reject heat at significantly high temperatures.

 The bottoming cycle operates at lower temperatures and utilizes the waste heat energy to generate additional power. By extracting energy from the waste heat, the topping cycle achieves higher overall efficiency compared to a single-cycle power generation system.

 Topping cycle calculation:

 A Co-generation facility is defined as one, which simultaneously produces two or more forms of useful energy such as electrical power and steam, electric power and shaft (mechanical) power, etc.” The project may qualify to be termed as a co-generation project, if it is in accordance with the definition and also meets the qualifying requirement outlined below:

 Topping cycle mode of co-generation – Any facility that uses non-fossil fuel input for the power generation and also utilizes the thermal energy generated for useful heat applications in other industrial activities simultaneously.

 For the co-generation facility to qualify under topping cycle mode, the sum of useful power output and one half the useful thermal output be greater than 45% of the facility’s energy consumption, during season.”

Read >>>>Powerplant O&M reference books

Following inputs required for calculation of topping cycle:

• Fuel consumption
• Fuel GCV
• Steam given to processes & their heat content
• Power generation

Topping cycle is calculated by using following formula

 TC Eff = (Sum of total heat supplied to process in kcal X 50% + Total electricity generated in kcal) X 100 / Fuel energy

Example

 A 44 MW Co-generation plant is operating at 41 MW load and utilizing bleed & extraction steam for process heating. Calculate the topping cycle efficiency

The inputs required are as below

Sl No	Particular/Parameters	UOM	Value
1	Boiler fuel consumption	TPH	85
2	Fuel GCV	Kcal/kg	2250
3	Process-1 steam flow	TPH	12
4	Process steam-1 enthalpy	Kcal/kg	740
5	Process-2 steam flow	TPH	170
6	Process steam-2 enthalpy	Kcal/kg	653
7	Power generation	MWH	41

 Calculation:

Total heat content in input fuel = 85 X 1000 X 2250 =191250000 kcal

Heat content in process-1 steam = 12 X 1000 X 740 =8880000 kcal

Heat content in process-2 steam = 170 X 1000 X 653 =111010000 kcal

Power generation in kcal = 41 X 1000 X 860 = 35260000 kcal

 TC Eff = (Sum of total heat supplied to process in kcal X 50% + Total electricity generated in kcal) X 100 / Fuel energy

TC Eff = ((8880000+111010000) X 50% + 35260000) X 100 / 191250000

 TC eff = 49.78%

   

Fastrack All Nighters Analog Black Dial Men's Watch-

For more >>>>read powerplant and calculations

Calculation of pressure drop in steam and water lines

 Calculation of pressure drop in steam and water lines

 The pressure drop in a water & steam lines refers to the decrease in pressure that occurs as water/steam flows through a pipe or conduit due to factors such as friction and flow resistance. Several factors influence the magnitude of pressure drop in a water line:

Pipe Characteristics: The diameter, length, and roughness of the pipe impact the resistance to flow and consequently the pressure drop. Smaller diameter pipes and longer pipe lengths tend to result in higher pressure drops. Additionally, rougher pipe surfaces create more friction and increase pressure drop compared to smoother surfaces.

Flow Rate: The rate at which water/steam flows through the pipe affects the pressure drop. Higher flow rates generally result in higher pressure drops due to increased frictional resistance.

Fluid Properties: The physical properties of the water/steam being transported, such as viscosity and density, can influence the pressure drop. However, for water at typical temperatures and pressures, these effects are usually negligible.

 Pipe Fittings and Valves: The presence of fittings, such as elbows, bends, valves, and other obstructions in the water line, can contribute to pressure drop. These components disrupt the flow and introduce additional resistance.

 It's important to note that pressure drop calculations for steam lines can be complex and require a comprehensive understanding of steam properties and fluid dynamics.

 Pressure drop in water line:

Head loss in water line for turbulent flow is given as

Head loss in meter = 4fLV² / (2gD)

 Where, f = Friction loss in pipe, generally varies from 0.005 to 0.007

L = Pipe length

D = Diameter of the pipe

g = Acceleration due to gravity, 9.81 m/s2

V = Velocity of the fluid

 Example:

A Boiler feed pump is delivering feed water flow 50 TPH to the boiler at a distance of 70 meter.The steam drum height is 38 meter from pump suction.Calculate the pressure drop in water line, assume pipe line size is 80 NB, water density 980 kg/m3 & neglect the other losses from pipe line fittings.

 Feed water flow in m3/sec = 50 000 kg/hr / 980 kg/m3 = 51.02 m3/hr =0.014 m3/sec

Area in side the pipe line = 3.142 X 0.08²/4 = 0.05 M²

Feed water velocity,V =  Flow / Area = 0.014 / 0.005 =2.78 m/sec

 Then, head loss, H = 4 X 0.005 X 38 X 2.78² / (2 X 9.81 X 0.08)

Head loss, H = 3.75 meter

 Minimum head required to lift the water up to steam drum, considering pressure drop in feed water control valve is 8 kg/cm2

 H = 3.75+80+38 =121.75 meter

 Pressure drop in steam line:

Head loss in meter = 2fLdV² / (500gD)

(Density of water is 500 times more than steam at atmospheric pressure)

Where, f = Friction loss in pipe, generally varies from 0.005 to 0.007

L = Pipe length

D = Diameter of the pipe

g = Acceleration due to gravity, 9.81 m/s2

V = Velocity of the fluid

Read >>>Powerplant O&M reference books

 Example: Turbine inlet steam flow is 100 TPH & the distance between Boiler MSSV & Turbine MSSV is 82 meter.The seam pressure & temperature are 65 kg/cm2 and 490 deg C respectively.Calculate the pressure drop in steam line.

 Density of steam at above parameters = 17 kg/m3

Steam flow in m3/sec = 100 X 1000 kg/hr / 17 kg/m3=5882.35 m3/hr = 1.63 m3/sec

Assume main steam velocity being 45 m/sec

Pipe inside area A = Flow / Velocity = 1.63/45 =0.0362 m2

Now, calculate pipe diameter , A = 3.142 X D²/4

D = SQRT (0.036 X 4/3.142) = 0.214 meter = 214 mm

Now, Pressure drop H =(2 X 0.005 X 82/0.224) X (17/500) X (45²/9.81) =25.7 m = 2.57 kg/cm2

For read>>>>Powerplant and calculations

Men's Fastrack watch