Characteristic curves of a Turbine

These are curves which are characteristic of a particular turbine which helps in studyingthe performance of the turbine under various conditions. These curves pertaining to anyturbine are supplied by its manufacturers based on actual tests.The data that must be obtained obtained in testing a turbine are the following:

1. The speed of the turbine N2. The discharge Q3. The net head H4. The power developed P5. The overall efficiency o6. Gate opening (this refers to the percentage of the inlet passages provided for

water to enter the turbine)The characteristic curves obtained are the following:

a) Constant head curves or main characteristic curvesb) Constant speed curves or operating characteristic curvesc) Constant efficiency curves or Muschel curves

Constant head curves: Maintaining a constant head, the speed of the turbine is varied byadmitting different rates of flow by adjusting the percentage of gate opening. The powerP developed is measured mechanically. From each test the unit power Pu, the unit speedNu, the unit discharge Qu and the overall efficiency o are determined. The characteristiccurves drawn are

a) Unit discharge vs unit speedb) Unit power vs unit speedc) Overall efficiency vs unit speed

Constant speed curves: In this case tests are conducted at a constant speed varying thehead H and suitably adjusting the discharge Q. The power developed P is measuredmechanically. The overall efficiency is aimed at its maximum value.The curves drawn are

P vs Qo vs Qo vs Puo max vs % Full load

Constant efficiency curves: These curves are plotted from data which can be obtainedfrom the constant head and constant speed curves. The object of obtaining this curve is todetermine the zone of constant efficiency so that we can always run the turbine withmaximum efficiency.This curve also gives a good idea about the performance of the turbine at variousefficiencies.

N is constant

N is constant

N is constant

100% GO

75% GO

50% GO

25% GO

Nu

Qu

100% GO

75% GO50% GO

25% GO

Nu

o

100% GO

75% GO

50% GO

25% GO

Nu

Pu

Main Characteristic curves of a Pelton turbine

100% GO

75% GO

50% GO

25% GO

Nu

Qu

N is constant

N is constant

N is constant

100% GO

75% GO50% GO

25% GO

Nu

Pu

100% GO

75% GO

50% GO

25% GO

Nu

o

Main Characteristic curves of a Kaplan turbine

N is constant

100% GO

75% GO50% GO

25% GO

Nu

o

100% GO

75% GO

50% GO

25% GO

Nu

Pu

100% GO

75% GO50% GO

25% GO

Nu

Qu

Main Characteristic curves of a Francis turbine

% Full load

o

N is constant

P

o

N is constant

Q

P, o

o

P

N is constant

Operating Characteristic curves of a turbine

P for full gate opening

N

P

Constant Efficiency curves for Reaction turbine