TURBINE CHARACTERISTIC CURVE

Introduction

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

ž1. The speed of the turbine N
ž2. The discharge Q
ž3. The net head H
ž4. The power developed P
ž5. The overall efficiency n
ž6. Gate opening (this refers to the percentage of the inlet passages provided for water
to enter the turbine)

CONSTANT HEAD CHARACTERISTICS CURVES

• žHead and gate opening are kept constant. 
• žSpeed is varied by changing water flow through inlet opening.
• Overall efficiency and unit quantities are calculated and plotted against speed as abscissa.

PELTON TURBINE

FRANCIS TURBINE

KAPLAN TURBINE

Significances of main characteristics curve

• žDischarge of pelton wheel depends only on gate opening. 
• žDischarge decreases and increases respectively for francis and kaplan turbines with increase in speed. 
• žPower is max at a particular speed and so is efficiency. 
• žMax efficiency of pelton wheel occurs at same speed irrespective of %of GO.

Constant speed characteristics curves

• žIn this case tests are conducted at a constant speed varying the head H and suitably adjusting the discharge Q. 
• The power developed P is measured mechanically. 
• žThe overall efficiency is aimed at its maximum value. 
• žThe curves drawn are 

P vs Q

no vs Q

no vs Pu

no max vs % Full load

Significances of constant speed characteristics curves

• žAt 100% full load overall efficiency is near about maximum efficiency .
• žThe max. overall efficiency of all turbines is same.
• žA min discharge is required to set turbine runner into motion.
• žOutput power is directly proportional to discharge for constant head.
• žOverall efficiency remains nearly constant beyond a particular value of discharge.

Constant efficiency curves

• žThese curves are plotted from data which can be obtained from the constant head and constant speed curves. 
• žThe object of obtaining this curve is to determine the zone of constant efficiency so that we can always run the turbine with maximum efficiency. 
• žThis curve also gives a good idea about the performance of the turbine at various efficiencies.

Reference:

A text book of fluid mechanics and hydraulic machines; RK RAJPUT