The head losses in the penstock

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

Head 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)
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)]

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

Head loss due to the installation of the bend
hb= Kb * V^2 / (2 * g)
Kb= depends upon the shape of the bend and the condition
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:

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

Calculation of flood spillway

By Ahmad Suhendra

Flood spillway was designed based on the excess water and high water in the channel carrier (head race)

Example :

Flood Spillway will be made on a channel that has a water depth of 0.691 m, with a normal discharge (Q normal) of 0.6 m^3/sec. What is the length of Flood spillway?

Spillway length (L spillway) is obtained by using the equation of calculating Weir and must be able to pass through if the flow (Q spillway) in a state of excess but not based on the flood peak.

Dicharge Coefficient (Cd)
Profile of Crest Weir	μ- factor	Cd=2.953 μ
Board, sharp edge	0.49-0.51	1.44 - 1.51
Board, round edge	0.50-0.55	1.48 - 1.62
Round overfall	0.65-0.73	1.92 - 2.16
Sharp edge,	0.64	1.89
Rounded	0.75	2.21
Roof Shaped	0.79	2,33

Standard Weir equations:
Q = Cd * L weir * (h over the top )^1.5
In this case :

• L spillway = L weir
• Q spillway = Q minor flood - Q normal = Cd * L spillway * ( h over the top)^1.5

There are some values of  Discharge Coefficient  (Cd) and in this calculation the value of Cd was taken 1.6 (Board, the round edge)

Then :

• L spillway = (Q minor flood – Q normal) / (Cd * ( h over the top)^1.5 )

To increase the water on the head race taken a number of around 20% of normal conditions and is considered as a minor flood (small flood).

• Q minor flood = 1.2 * 0.6 = 0.72 m^3/sec
• h minor flood = 1.2 * h = 1.2 x 0.691 = 0.829 m
• h over the top = 0.829 - 0.691 = 0.138 m
• Q spillway = 0.72 - 0.6 = 0.12 m3/sec
• L spillway = ( 0.12) / (1.6 * 0.138 ^1.5) = 1.46 m

Loss coefficients for pipe bends are commonly used in MHP

The losses in figure as shown left , vary according to the R/D ratio and the deflection angle of the bend. An R/D ratio of six results in the lowest head loss, although only a slight decrease is indicated for R/D ratios greater than four. As the fabrication cost of a bend increases with increasing radius and length, there appears to be no economic advantage in using R/D ratios greater than five.

Ref:
BURIED STEEL PENSTOCKS SECOND EDITION 1998
Published by Construction Marketing Committee, AMERICAN IRON AND STEEL INSTITUTE
In cooperation with and editorial collaboration by STEEL PLATE FABRICATORS ASSOCIATION, INC

Generator Selection

Generators must be sized to handle their load based on the continuous KW, kilowatt load, and KVA, kilovoltamp load, and the worst case starting load KW + KVA. They must be derated for temperature and elevation. They are sized also on whether they are continuous or standby use. The following steps are used to obtain information:

Read More


ref:

• http://www.fs.fed.us/database/acad/elec/greenbook/24_generator_selection.pdf
• http://www.teachnet.ie/torourke/Physicswebsite/electromagnetism.htm

The using of Electronic Load Controller (ELC) to replace governor in MHP

By Achmad Hasan

The using of Electronic Load Controller (ELC) to replace governor in Microhydro Power Plant (MHP) can hopefully manage the enormous changing of load by giving a quick system response and lower price than governor. Because of providing power for electricity require high cost and the geographic condition of Indonesia also the unbalance spread of load, so the MHP is the most economic energy resource. MHP is the right plant for providing energy especially for remote area with a low load crowd and far from PLN (Indonesian state electricity company) network.

Read more (in the Indonesian language)

Manning coefficient (n)for several commercial pipes

By European Small Hydropower Association (ESHA)
Over the years many empirical formulae, based on accumulated experience, have been developed. They are, in general, not based on sound physical principles and even, occasionally, lack dimensional coherence, but are intuitively based on the belief that the friction on a closed full pipe is:

1. Independent of the water pressure
2. Linearly proportional to its length
3. Inversely proportional to a certain power of its diameter
4. Proportional to a certain exponent of the water velocity
5. In turbulent flows it is influenced by the wall roughness

One of these formulae, widely used to estimate the flow in open channels, but also applicable to closed pipes, is that developed by Manning

Q= (1/n)* A^(5/3)* S^(1/2)* P^(-2/3)

Where n is the Manning roughness coefficient, P is the wetted perimeter (m), A is cross-sectional area of the pipe (m^2) and S is the hydraulic gradient or head loss by linear meter.

Applying the above formulae to a full closed circular cross section pipe:
S= 10.29 n^2 * Q^2 *D^(-5.333)
S= hf / L (head loss)
hf = Head loss (m)
Q = flow in penstock (m^3/s)
D = inside diameter of penstock (m)
L= lenght of pipe
Manning coefficient n for several commercial pipes

Types of Pipe	n
Welded steel Polyethylene(PE) PVC Asbestos cement Ductile iron Cast iron Wood-stave(new) Concrete (steel forms smooth finish)	0.012 0.009 0.009 0.011 0.015 0.014 0.012 0.014

Ref : ESHA (European Small Hydropower Association),”Layman’s Handbook on How To Develop a Small Hydro Site,”2nd ed, 1998. http://www.scribd.com/doc/8885765/Layman-Handbook-for-hydro-electric-power-plants

The Number of Blades for Crossflow Turbine

By Ahmad Suhendra

Example :

A crossflow turbine is designed with blade angle β1=30 0 (angle between the relative velocity and tangential velocity) and α1=16 0 (angle between the absolute velocity and tangential velocity). The turbine have a rotation speed of 750 rpm on the net head 10 m, flow 100 lt / s, what is the specific speed, absolute and tangential velocity , outside diameter of the disc, blades spacing and number of baldes?

Crossflow turbine requirements are :

• ns = 42 – 170 (classical based on metric HP)
• Ns = 0.86* ns (True metric specific speed)
  
• Nt = 100 -1000 rpm (nominal speed)

1.Specific Speed

ns (rpm) = 3.65 x Nt (rpm) x Q(m^3/s)^ 0.5 / H_netto(m)^ 0.75

= 3.65 * 750 * 0.01^ 0.5 / 10^ 0.75

= 48.7 rpm ----> Ok, Crossflow

2.Absolute Velocity of water

kc = 0.967 Coefficient dependent upon the nozzle

C = kc * (2 * g * Head)^ 0.5

= 0.967 (2 * 9.8 * 10 )^0.5

= 13.54 m/s

3.Tangential velocity

U1 = ( C * Cos α1) / 2

= ( 13.54 * Cos 16 )/ 2

= 6.51 m/s

4. Outside diameter of disc

D1 = 60 * U1 / (phi * Nt)

= 60 * 6.51 / 3.14 * 750

= 0.166 m

Then :

S1 = k * D1----> k = 0.075 – 0.1 (respectively)

Taken k = 0.087

S1 = 0.087 * D1

= 0.087 * 0.166

= 0.0144 m

5. Spacing of blades in disc

t = S1 / Sin β1

= 0.0144 / Sin 30

= 0.0288 m

6.Number of Blades

Z = phi * D1 / t

= 3.14 * 0.166 / 0.0288

= 18 blades (20 were used for design)

Ref : Mockmore C.A and Merryfield Fred " The Banki Water Turbine " , Bulletin Series No:25 Oregon State College Corvallis

What is the blade length (bo) limits on crossflow turbine ?

By Ahmad Suhendra

Crossflow turbine blade has a length limit that must be met in the design, for the turbine at an angle α1=16 o, nozzles coef. kc = 0.98 and k = 0.075 to 0.10 are as follows:

1). C (m/sec) = kc.(2.g.H)^0.5
2). Phi.D1.Nt / 60 = (C. cos α1)/2

Then:
The diameter of blade is :
3). D1 (m) = 39.85 H ^ 0.5 / Nt

Blade length (bo) is obtained from the following equation(4)
4). Q(m^3/sec ) =(So.bo)[ kc ( 2.g.H )^0.5 ]
5). So(m) = k D1

By entering the equation (5) and (3) into equation (4) is obtained :
The blade length (bo) limits is :

6). bo = ( 0.058 Q.Nt / H ) to ( 0.077 Q.Nt / H )

Where:

• g is the constant of gravity 9.8 m/s^2
• C is the absolute velocity of water (m/sec)
• Phi is 3.14
• Nt is the nominal turbine speed (rpm)
• D1 is the diameter of Disc (m)
• So is the thickness of the water jet (m)
• H is the net head (m)

Ref : Edy Sunarto , dkk,” Pedoman Rekayasa Tenaga Air (Hydropower Engineering Guidelines) ”, UPT Hidro Elektris BPPT, Jakarta 1991

What is the maximum performance of crossflow turbine?

By Amad Suhendra

Sonnek (1923) modified the banki theory assuming a constant angle of the blade equal to 30 , so that the expression resulted in maximum performance:

ηmax = 0.863-0.264 *(D / H)

D is the diameter of turbine (disc) and H is the net head

Ref : Ariel R.Marchegiani , "Turbina de Flujo Transversal O Michell-Banki", Universidad Nacional Del Comahue

The Future of Microalgae in Clean Technologies

By Jean VanderGheynst (jsvander@ucdavis.edu)

"There is no magic- bullet fuel crop than can solve our energy woes without harming the environment, says virtual every scientist studying the issue. But most say that algae....comes closer than any other plant"

Green Dreams- National Geographic, october 2007

Read more

IMIDAP - Guide books for MHP feasibility study in Indonesia

IMIDAP
(Integrated Micro-Hydro Development and Application Program)

The overall objectives of IMIDAP are:

1. To enhance interest among the Indonesian private sector in the micro-hydro power business;
2. To increase the number of community-based micro-hydro projects as a result of effective institutional capacity building;
3. To improve the availability, and local knowledge, of micro-hydro technology applications in the potential locations of micro-hydro development;
4. To increase private sector and rural community joint implemen-tation of micro-hydro projects.
   

DOWNLOADS FS Guide books for MHP

1. Pedoman UMUM Penyusunan Studi Kelayakan PLTMH [BUKU UTAMA]*

2. Pedoman Studi Potensi (Pra Studi Kelayakan) [BUKU 1]*

3. Pedoman Teknis Standarisasi Peralatan dan Komponen PLTMH*

4. Pedoman Studi Kelayakan Hidrologi [BUKU 2 A]*

5. Pedoman Studi Kelayakan Sipil [BUKU 2 B]*

6. Pedoman Studi Kelayakan Mekanikal Elektrikal [BUKU 2 C]*

7. Pedoman Studi Kelayakan Ekonomi / Finansial [BUKU 2 D]*

8. Pedoman Studi Kelayakan Sosial Budaya [BUKU 2 E]*

9. Pedoman Studi Kelayakan Lingkungan [BUKU 2 F]*

10. Pedoman Studi Komprehensif Berkelanjutan [BUKU 2 G]*

11. Pedoman Penyusunan Laporan Studi Kelayakan Teknis [BUKU 3]*