Dynamic modelling of full scope power plant

1. By:-
GOVIND KUMAR
MISHRA
ROLL NO. :-
1
STEAM TURBINE
(Dynamic model for full scope power plant)

2. CONTENTS
1. Steam Turbine
2. Principle of Steam Turbine
3. Types of Steam Turbines
4. Compounding in Steam Turbine
5. Thermal and Rotational Inertia Effects in Steam
Turbine
6. A Steam Turbine Dynamic Model for full scope
power plant
7. Failures in Steam Turbine
8. Results and Accuracy
9. References
2

3. What is turbine?
 Turbine ia an engine which
converts energy of fluid into
mechanical energy (i.e shaft
power).
And, Steam Turbine is
steam driven rotary engine.
3

4. 4

5. Types of Steam Turbine:
5
 There are mainly 2 types :
1. Impulse steam turbine
2. Reaction steam turbine

6. Impulse Steam Turbine

7. Single Stage Impulse Turbine:

9. Component of Impulse Turbine:

10. Reaction Steam Turbine:
 A reaction turbine uses a jet of steam that flows
from a nozzle to the rotor.
 Actually, the steam is directed by fixed blades
into the moving blades designed to expand the
steam.
 Consequentially, there is a small increase in
velocity over moving blades.
 It is compounded for better results.

11. Schematic diagram:

12. Compounding in Steam Turbine:
 It is a way of reducing the wheel or rotor speed to the
optimum level.
 It is also defined as the process of absorbing pressure
energy or kinetic energy of steam in several stages by
utilising miltiple sets of movin and fixed blades.
 There are mainly 2 types of compounding:
1. Pressure compounding or Rateu Staging
2. Velocity compounding or Curtis Staging
 Sometime, both compoundings are used in same turbine
and known as Pressure- Velocity compounding

13. Pressure compounding:
 It is simple impulse staging and pressure energy of steam is
absorbed in multiple stages.

14. Velocity compounding:
 In this staging kinetic energy is absorbed in multiple stages.

16. Dynamic Model of Steam Turbine :
16
 For modelling purposes,3 distinct regions have been
identified within safe running of Steam Turbine:
1. Normal operation
2. Start up and shut down
3. Idle operation
 Thermal and Rotational Inertia effects are produced in
start up and shut down condition and it is properly
accounted during ST modelling.
 Casing Temperature is also considered as a key factor in
dynamic modelling of ST as it can cause failure of system.

17. Thermal Inertia Effect:
17
 It is caused due to the heat transfer processes present,for
instance,during warming up of the turbine sections carried out as
part of cold start up process.
 Heat transfer accounted here are only
conduction and convection , radiation is
neglected .
 Energy variation in ST from inner to
outer region is given by:

18.  Heat transfer coefficient involved in this process is computed from
corresponding
Nusselt Number( Nu= h*L/k):
1. Between Steam and Internal Casing: Forced convection takes
place,so Nu is determined by Dittus-Boelter equation,where,
Re=Reynold
Number
Pr=Prandtl Number
2.Between External Casing and Ambient: Natural convection takes
place ,so Nu is determined by :
where, Ra=Rayleigh Number
= Gr*Pr
Gr=Grashof Number

19. Mechanical Inertia Effect:
 It is caused as a consequence of bringing the steam
turbine from low rotational speed (rest or idle) to speed
corresponding to normal operation.
 Regarding this effect modelling is based on
momentum conservation on ST shaft as follows:

20. Casing Temperature:
20
 It is obtained from the ST dynamic model developed .
 Parameters accounted for simulation of dynamic model and obtaining
casing temperature are:
1. Heat transfer area
2.Characteristics length
3.Casing internal diameter
4.Casing wall thickness
5.Casing masses
6. Characteristics time
7. Specific heats
8. Nusselt number constants (m,n)

21. Steam Turbine Dynamic Model:
21
 After simulation of Steam turbine dynamic model casing
temperatue is well analysed as variation with time.
 Both casing temperature and time are in non-dimensional form on
ordinate (Y-axis) and absicca(X-axis) respectively.

23. In this simulation, Highest temperature of HP turbine is taken as
reference temperature for non dimensionalisation of temperature.

24. Failures in Steam Turbine:
24
Blade Failure in ST is most frequent and it is due to :
 Stress corrosion cracking (22%)
 High cycle fatigue (20%)
 corrosion fatigue cracking (7%)
 Temperatue creep rupture(6%)
 Low cycle fatigue (5%)
 Corrosion (4%)
 Other causes( 10%)
 Unknown (26%)

25. Results and Accuracy:
25
 Accuracy of model prediction is very good as there is negligible
discrepancy in model results as compared with operating
data(0.02%- 2%).
 HP and IP internal casing temperature is higher than
corresponding external temperature and LP casings as it is obvious
because steam at higher temperature passes through HP and IP
turbines
 Wheel rotational speed (discrepancy upto 0.02%) and shaft power
outpur (discrepancy upto 2%) suddenly increases in starting period
and gets a constant value.
 Exit Temperature of HP turbine is higher than IP and LP turbine(
discrepancy upto 1%).

26. Reference:
26
1. Journal:Applied Thermal Engineering
Paper: A steam turbine dynamic model for full scope power plant
simulators
By: Cesar Celis, Gustavo R.S.Pinto, Tairo Teixeira, etc.
2.Power Plant Engineering: P K NAg

27. Thank you !
27