Unit Quantities of a Turbine | Power, Discharge, Speed, Application

What are Unit Quantities of a Turbine?

Unit Quantities of a Turbine are certain quantities related to a turbine, which are obtained when the turbine operates under unit head (i.e. H = 1m).

It is assumed that efficiency of the turbine remains same in both the cases (i.e. when turbine is working at unit head and when turbine is working at full head).

While studying turbines it is important to understand following three unit quantities.

• Unit Power (P_u)
• Unit Discharge (Q_u)
• Unit Speed (N_u)

What is Unit Power (P_u) of a Turbine?

Unit Power of a Turbine is the power generated by a turbine working at unit head.

P_u = P/H^3/2

Where:

H = Available head to turbine

P = Power generated by the turbine at the given head i.e. H

What is Unit Discharge (Q_u) of a Turbine?

Unit discharge of a Turbine is the discharge of turbine working at unit head.

Q_u = Q/H^1/2

Where:

H = Available head to turbine

Q = Discharge of the turbine at the given head i.e. H

What is Unit Speed (N_u) of a Turbine?

Unit speed of a turbine is the speed of turbine working under unit head.

N_u = N/H^1/2

Where:

H = Available head to turbine

N = Speed of the turbine at the given head i.e. H

Application of Unit Quantities of a Turbine

The values of unit quantities of a turbine remain constant for a particular turbine. Hence some vary useful relations can be obtained from them.

Relations obtained from unit quantities of a turbine

P_u = P₁/H₁^3/2 = P₂/H₂^3/2

Q_u = Q₁/H₁^1/2= Q₂/H₂^1/2

N_u = N₁/H₁^1/2 = N₂/H₂^1/2

Also read:

What is draft tube of a turbine?

Dimensionless numbers in fluid mechanics

Types of notches and weirs

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