HYDRAULIC TURBINES

 

HYDRAULIC TURBINES

Hydraulic Turbine is device which converts hydraulic energy in to mechanical energy.

• For Turbine Inlet energy is greater than Outlet energy.
• Hydraulic Power Plant is a cheap procedure of generating Electrical power.

GENERAL LAYOUT OF HYDRAULIC POWER PLANT:

Fig.1 | General layout of hydro Electric Power Plant

HEADS & EFFICIENCIES:-

1.   Gross Head (H_g): - It is the difference between Head Race Level (H.R.L.) and Tail Race Level (T.R.L.).

2.   Effective Head or Net Head(H_net): -

H_net = H_g – h_L

If minor losses is neglected –

H_net = H_g – h_f

 

Where, h_L = Total Head Loss

h_f = Head loss due to friction

 

Measure Frictional Head Loss -

h_f = fLV² / 2gD [Darcy-Weisbach equation]

OR

h_f = 4f’LV² / 2gD 

 

EFFICIENCIES OF TURBINE:

1.   HYDRAULIC EFFICIENCY(η_H): -

 

2.   MECHANICAL EFFICIENCY(η_M): -

 

3.   VOLUMETRIC EFFICIENCY(η_V): -

4.   OVERALL EFFICIENCY(η_O): -

CLASSIFICATION OF HYDRAULIC TURBINE: -

1.   ACCORDING TO THE TYPE OF ENERGY AT INLET: -

A.   IMPULSE TURBINE: -

• Available Inlet Energy is only Kinetic Energy.
• Pressure is Atmospheric Pressure.
• Nozzle converts available total head into Kinetic Head.

     Examples: - Pelton Wheel

B.   IMPULSE REACTION TURBINE: -

Available Inlet Energy is both pressure and Kinetic Energy.

Examples: - Francis Turbine

C.   PURE REACTION TURBINE: -

Available Inlet Energy is only pressure Energy.

2.   ACCORDING TO THE DIRECTION OF FLOW THROUGH RUNNER: -

A.   TANGENTIAL FLOW TURBINE: -

Direction of flow is Tangential.

Examples: - Pelton Wheel

B.   RADIAL FLOW TURBINE: -

Direction of flow is radially inward or outward.

Examples: - Old Francis Turbine

C.   AXIAL FLOW TURBINE: -

Direction of flow is parallel to the axis of shaft.

Examples: - Kaplan, Propeller

D.  MIXED FLOW TURBINE: -

Direction of flow is radially at inlet and axially at outlet.

Examples: - Modern Francis Turbine

  

3.    ACCORDING TO AVAILABLE HEAD AT INLET: -

A.   HIGH HEAD TURBINE: -

Head > 260 m

Examples: - Pelton Wheel

B.   MEDIUM HEAD TURBINE: -

260 m > Head > 60 m

Examples: - Francis Turbine

C.   LOW HEAD TURBINE: -

Head < 50 m

             Examples: - Kaplan, Propeller

4.   ACCORDING TO SPECIFIC SPEED OF THE TURBINE: -

A.   LOW SPECIFIC SPEED TURBINE: -

Specific Speed = 30 to 60

Examples – Pelton Wheel

B.   MEDIUM SPECIFIC SPEED TURBINE: -

Specific Speed = 60 to 300

Examples – Francis Turbine

C.   HIGH SPECIFIC SPEED TURBINE: -

Specific Speed =300 to 1000

Examples – Kaplan (300-600), Propeller

SPECIFIC SPEED OF TURBINE: - It is the speed of an imaginary turbine, identical with actual turbine (in shape, geometrical dimension etc.), which develops unit power under unit head.

N_s = (N√P)/ (H_net)^5/4

SL. NO.	SPECIFIC SPEED	TURBINE USED
1	10 - 60	PELTON WHEEL
2	60 - 300	FRANCIS TURBINE
3	300 – 600	KAPLAN TURBINE
4	600 - 1000	PROPELLER TURBINE

 

 

UNIT QUANTITY:

1.   Unit Speed: - It is the speed of the turbine, working under unit head.

N_u = N/ (√ H_net)

2.   Unit Discharge: - It is the discharge through turbine, working under unit head.

3.   N_u = N/ (√ H_net)

4.   Unit Power: - It is the power developed by the turbine, working under unit head.

5.   N_u = N/ (√ H_net)

 

MODEL RELATIONSHIP:

1.   Head Co-efficient(C_H):

N²D² ∝ H_net

C_H = [H_net/ N²D²]

 

2.   Capacity or flow Co-efficient(C_Q):

Q ∝ ND³

C_Q = [Q / ND³]

 

3.   Power Co-efficient(C_P):

P ∝ N³D⁵

C_P = [P/ N³D⁵]