1. Multi-Staging in Impulse Turbines
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Improvement in Initial Design - Inspired by Parson….

2. Simple Impulse Turbine

3. Availability of Steam for Condenser Temperature of 450C
Turbine Inlet : 3500 kJ/kg
Turbine Exit
Specific
Available
Jet Velocity
Pressure
Temp
Enthalpy
Work
MPa C
kJ/kg
m/s 1
509.9
2464
1036
1439 2 5
528.4
2232
1268
1592 3 10
549.6
2135
1365
1652 4 15
569
2080
1420
1685 20
586.7
2041
1459
1708 6 25
602.9
2012
1488
1725 7 30
617.7
1989
1511
1738 8 35
631.3
1969
1531
1750

4. Multi Stage Impulse Turbine

5. The most powerful steam turbine-generator in the world at the time of it's construction:1903
Built in 1903, the 5,000-kilowatt Curtis steam turbine-generator was the most powerful in the world. It stood just 25 feet high, much shorter than the 60 feet reciprocating engine-generator of a similar capacity

6. Compounding of impulse turbine
Compounding is done to reduce the rotational speed of the impulse turbine to practical limits.
Compounding is achieved by using more than one set of nozzles, blades, rotors, in a series, keyed to a common shaft; so that the jet velocity is absorbed by the turbine in stages.
Three main types of compounded impulse turbines are:
a) Pressure compounded Steam Turbine : The Rateau Design
b) velocity compounded Steam Turbine : The Curtis Design
c) pressure and velocity compounded Impulse turbines : The Rateau-curtis Design.

7. Multistage Impulse Turbine : GE Product

8. The Curtis Design

9. Pressure compounded impulse turbine : Rateau Design

10. Impulse Turbines with pressure stages
Multistage turbines with pressure stages have found a wide field of usage in industry as prime movers (~ 10 MW).
The number of pressure stages vary from 4 to 5.
The distribution of enthalpy drop in a large number of pressure stages enables the attainment of lower velocities for the steam flowing through the system of moving blades.
As a result more advantageous values of blade speed ratio and blade friction factor are obtained .

11. Selection of Number of Stages

12. Impulse Turbines with pressure stages
Total enthalpy drop available for mechanical power U
Vr1
Va1
Vr2
Va2 b1 a1 a2 b2

13. Variation of Diameter along a stages
Stage Z

14. The Curtis Design

15. A System of Velocity Triangles for Curtis Turbine
Vr1,1
Va1,1
Vr2,1
Va2,1
b1,1
a1,1
a2,1
b2,1 U
Vr1,2
Va1,2
Vr2,2
Va2,2
B1,2
a1,2
a2,2
b2,2 U
Vr1,3
Va1,3
Vr2,3
Va2,3
b1,3
a1,3
a2,3
b2,3

16. The Curtis Impulse Turbine
Total enthalpy drop available for mechanical power

17. Curtis Turbine With 2 Rotors
Total power with similar blading U
Vr1,1
Va1,1
Vr2,1
Va2,1
b1,1
a1,1
a2,1
b2,1

18. ith Reversible Symmetric StageU
Vr1,j
Va1,j
Vr2,j
Va2,j
b1,j
a1,j
a2,j
b2,j

19. Efficiency of Multi Rotor Curtis Turbine
For a three rotor Curtis Turbine:
For a n-rotor Curtis Turbine:

20. The Curtis-Rateau Design