**By Ahmad Suhendra**

**The various head losses which occur between reservoir and turbine are as follows:**

**1. Trashrack (or screen) losses**

**2. Entrance losses**

**3. Losses due to pipe friction**

**4. Bend losses**

**5. Losses in valve and fittings.**

**6. Losses in sudden contraction and expansion**

ht = [Kt* (t / b) ^ (4 / 3)* (Vo ^ 2 * Sin α)] / (2 * g)

V = The average velocity of water in penstock

Head loss due to installation of a trashrackHead loss due to installation of a trashrack

ht = [Kt* (t / b) ^ (4 / 3)* (Vo ^ 2 * Sin α)] / (2 * g)

*Kt= depends upon the shape of the screen**Vo=Approach velocity (m/s)*

**Head loss due to entrance**

he = Ke * V ^2 / (2 * g)he = Ke * V ^2 / (2 * g)

*Ke = depends upon the shape of the intake opening*V = The average velocity of water in penstock

**[Permissible velocity in Penstocks,V(m/s) =0.125 (2 g H)^0.5,**

Ref : USBR (1961) (P J Bier)]

Ref : USBR (1961) (P J Bier)]

**Head loss due to friction in the penstock**

hf = [(10.29* n ^ 2 *Qp ^ 2) / Dp^5.333] *Lp

*n = manning's roughness coefficient depends upon the type of pipe*

hb= Kb * V^2 / (2 * g)

*Kb= depends upon the shape of the bend and the condition*

of the inside surface

of the inside surface

V= The average velocity of water in penstock

**Head loss due to Fitting and Valve**hv = Kv *V ^ 2 / (2 * g)

*Kv= depends upon the type of fitting and valve*

V= The average velocity of water in penstock

**Head loss due to sudden contraction and expansion**

hc = Kc *V ^ 2 / (2 * g)

*Kc= depends upon the type of sudden contraction and expansion*

V= The average velocity of water in small pipe(1.273 Q /Dp^2 m/s)

**Total Head Loss**

h_total = ht + he + hf + hb + hv + hc

Where: - g = constant of gravity 9.8 m/s^2
- Qp = flow in penstock (m^3/s)
- Dp = inside diameter of penstock (m)
- Lp= lenght of penstock (m)

- k = resistance coefficient

- t = screen thickness (mm)
- b = width between bars (mm)
*α*= angle of inclination from horizontal (deg)

Ref:

- http://www.iaa.ncku.edu.tw/~aeromems/Mott/ch10.pdf
*ESHA (European Small Hydropower Association),”Layman’s Handbook on How To Develop a Small Hydro Site,”2nd ed, 1998*

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