HEAD & FLOW MEASUREMENTSHEAD & FLOW MEASUREMENTS

CLASSIFICATION

Based on Installed Capacity

Micro : Upto 100 kW

Mini : 101 kW to 2000 kW

Small : 2001 kW to 25000 kW

Unit size :1001 kW to 5000 kW

Based on Head

Ultra low head : Below 3 meter

Low head : 3 meter to 20 meter

Medium : 20 meter to 80 meter

High head : above 80 meter

POWER EQUATION

Pth = 9.81xQ x H

Pth is Theoretical power output in kWQ is Usable flow rate in m3/sH is Gross head in m

MEASURING HEAD

Head is the vertical distance that water falls from the fore-bay or intake to the turbine.

The head must be measured accurately because it is one of the most important considerations in the hydropower system’s design and costing.

The proposed location of the powerhouse and penstock intake structure should be used as reference points in measuring the head.

METHODOLOGIES FOR MEASURING HEAD

Maps

Detailed topographic maps are useful for locating potential sites and for obtaining a rough estimate of head levels.

WATER-FILLED TUBE AND ROD METHOD

This method is suitable for low-head sites. It is reliable, reasonably accurate and inexpensive.

PRESSURE-GAUGE METHOD

This method can be used for high heads. The head is measured according to the static pressure of water.

ALTIMETERS

Altimeters can be useful when undertaking high head pre-feasibility studies

DISCHARGE MEASUREMENT

By current meters

By weirs

The following points should be observed:

  Rectangular or trapezoidal gauging sections.

The channel should be rectilinear with a constant cross-section and the bottom shall be as horizontal as possible.

  The axes of the current meters shall be parallel to the direction of flow and the measurement section shall be perpendicular to this direction.

  Number of measurement points.

10 Daily Discharge Data

Month/Year   2007 2008 2009  I 9.04 7.14 9.15January II 8.98 7.18 8.55  III 8.63 6.89 7.50  I 8.56 7.14 6.95February II 8.24 7.35 7.33  III 8.02 7.02 7.10  I 8.33 7.30 7.86March II 7.84 7.03 8.36  III 8.15 9.32 9.40  I 8.43 7.76 9.93April II 8.63 11.09 10.64  III 9.27 14.61 9.81  I 9.72 14.01 11.68May II 10.75 15.05 12.67  III 11.91 14.15 10.39  I 11.01 13.89 11.94June II 11.91 12.38 12.42  III 17.45 21.98 12.30  I 17.95 45.82 33.77July II 22.41 53.83 34.50  III 31.33 50.32 66.57  I 32.74 68.45 78.94Aug. II 65.95 65.36 59.47  III 74.48 58.59 67.32  I 50.27 46.12 49.96Sept. II 24.30 32.94 28.27  III 19.95 29.20 18.70  I 15.95 18.97 11.73Oct. II 13.85 11.84 9.40  III 11.45 9.70 8.96  I 10.00 9.95 9.63Nov. II 9.70 9.92 9.62  III 8.02 8.97 6.62  I 7.78 8.59 5.98Dec. II 7.70 8.47 5.71  III 7.41 8.62 5.69

Table 2 : Flow Duration, Power Potential and Energy Generation

% of time equalled or exceeded

Discharge in Cumecs   90% of Power Power      Av.Discharge Potential Available

          for power gen. in kW in kW

2007 2008 2009 Average        2.78 74.48 68.45 78.94 73.96   66.56 17120.70 2000 3000 4000 5000 6000 7000 80005.56 65.95 65.36 67.32 66.21   59.59 15327.38 2000 3000 4000 5000 6000 7000 80008.33 50.27 58.59 66.57 58.48   52.63 13537.14 2000 3000 4000 5000 6000 7000 800011.11 32.74 53.83 59.47 48.68   43.81 11269.24 2000 3000 4000 5000 6000 7000 800013.89 31.33 50.32 49.96 43.87   39.48 10155.75 2000 3000 4000 5000 6000 7000 800016.67 24.30 46.12 34.50 34.97   31.48 8096.20 2000 3000 4000 5000 6000 7000 800019.44 22.41 45.82 33.77 34.00   30.60 7870.88 2000 3000 4000 5000 6000 7000 787122.22 19.95 32.94 28.27 27.05   24.35 6262.75 2000 3000 4000 5000 6000 6263 626325.00 17.95 29.20 18.70 21.95   19.76 5081.35 2000 3000 4000 5000 5081 5081 508127.78 17.45 21.98 12.67 17.37   15.63 4020.32 2000 3000 4000 4020 4020 4020 402030.56 15.95 18.97 12.42 15.78   14.20 3653.01 2000 3000 3653 3653 3653 3653 365333.33 13.85 15.05 12.30 13.73   12.36 3179.22 2000 3000 3179 3179 3179 3179 317936.11 11.91 14.61 11.94 12.82   11.54 2967.78 2000 2968 2968 2968 2968 2968 296838.89 11.91 14.15 11.73 12.60   11.34 2916.08 2000 2916 2916 2916 2916 2916 291641.67 11.45 14.01 11.68 12.38   11.14 2865.93 2000 2866 2866 2866 2866 2866 286644.44 11.01 13.89 10.64 11.85   10.66 2742.46 2000 2742 2742 2742 2742 2742 274247.22 10.75 12.38 10.39 11.17   10.06 2586.59 2000 2587 2587 2587 2587 2587 258750.00 10.00 11.84 9.93 10.59   9.53 2451.55 2000 2452 2452 2452 2452 2452 245252.78 9.72 11.09 9.81 10.21   9.19 2362.81 2000 2363 2363 2363 2363 2363 236355.56 9.70 9.95 9.63 9.76   8.78 2259.40 2000 2259 2259 2259 2259 2259 225958.33 9.27 9.92 9.62 9.60   8.64 2223.14 2000 2223 2223 2223 2223 2223 222361.11 9.04 9.70 9.40 9.38   8.44 2171.44 2000 2171 2171 2171 2171 2171 217163.89 8.98 9.32 9.40 9.23   8.31 2137.48 2000 2137 2137 2137 2137 2137 213766.67 8.63 8.97 9.15 8.92   8.03 2064.18 2000 2064 2064 2064 2064 2064 206469.44 8.63 8.62 8.96 8.74   7.86 2022.51 2000 2023 2023 2023 2023 2023 202372.22 8.56 8.59 8.55 8.57   7.71 1983.15 1983 1983 1983 1983 1983 1983 198375.00 8.43 8.47 8.36 8.42   7.58 1949.20 1949 1949 1949 1949 1949 1949 194977.78 8.33 7.76 7.86 7.98   7.19 1848.11 1848 1848 1848 1848 1848 1848 184880.56 8.24 7.35 7.50 7.70   6.93 1781.75 1782 1782 1782 1782 1782 1782 178283.33 8.15 7.30 7.33 7.59   6.83 1757.83 1758 1758 1758 1758 1758 1758 175886.11 8.02 7.18 7.10 7.43   6.69 1720.79 1721 1721 1721 1721 1721 1721 172188.89 8.02 7.14 6.95 7.37   6.63 1706.13 1706 1706 1706 1706 1706 1706 170691.67 7.84 7.14 6.62 7.20   6.48 1666.77 1667 1667 1667 1667 1667 1667 166794.44 7.78 7.03 5.98 6.93   6.24 1604.27 1604 1604 1604 1604 1604 1604 160497.22 7.70 7.02 5.71 6.81   6.13 1576.49 1576 1576 1576 1576 1576 1576 1576100.00 7.41 6.89 5.69 6.66   6.00 1542.54 1543 1543 1543 1543 1543 1543 1543              Av. Power = 1920 2414 2715 2966 3190 3392 3583              Energy 16.82 21.15 23.78 25.98 27.94 29.71 31.38                  4.32 2.64 2.19 1.97 1.77 1.67

Net Head = 30 m Load factor 0.96 0.80 0.68 0.59 0.53 0.48 0.45Turbine Efficiency = 92% 2000 3000 4000 5000 6000 7000 8000Generator Efficiency = 95%