Niagara Falls 100.000-Hp. Development

Niagara Falls 1 00,000 Hp. Development [9 With this ideal constantly in mind each contractor has put into the work the best design, material and work- manship of which he was capable, and more than the expected efficiency has been attained. Provision for testing the wheels in place was macle by building a testing chamber around the base of the slope tunnels so that Pitot tubes or other equipment might be readily installed. While tests of the wheels may be made by using Pitot tubes and chemical gagings, it has not been possible to have such tests carried out up to the present time. However, complete efficiency tests have been made by a new indirect method of water measurement recently invented by the writer. This method, sometimes called the “pressure-time process,”* utilizes the relation between velocity change and rise of pressure, and by means of specially designed appa- ratus* there is produced a diagram, called the pressure- time diagram, from which the mean velocity in the conduit may be calculated. The apparatus, which is attached to a small piezometer tube tapped into the wall of the penstock at any convenient point, records on a sensitized film or paper the changes of pressure that occur in the penstock with respect to time. The changes of pressure are produced by the simple process of closing the turbine gates, or in some cases the Johnson valve. The procedure for a test by this method may be briefly described as follows: The turbine gates are put on hand control, and steady conditions of load on the unit are maintained for several minutes until the flow in the penstock has become as uniform as possible. Reading's of headwater and tailwater elevations are taken in the usual manner, and the pressure head at the entrance to the turbine casing is observed by gage or piezometer, so that allowance may be made for the loss of head in the penstock. Measurements of the generator output are taken by calibrated wattmeter and auxiliary instruments, and, if the unit is separately- excited, ammeter and voltmeter readings of the exciting ♦Patents applied for by N. R. Gibson. FIG. 11—HORIZONTAL CROSS SECTION THROUGH THE THREE NEW WATERWHEEL FOUNDATIONS current are also obtained. When conditions have been steady for several minutes the turbine gates are closed gradually by operating the hand-control of the governor. During the closure the load thrown off the generator is taken up by the other units operating in synchronism with it. At the same time the Gibson apparatus makes its record of the changes of pressure that occur in the penstock. From this record may be calculated the mean velocity of the water in the penstock prior to the shut- down. Having determined the velocity, the discharge is readily computed, and after allowing for the known efficiency of the generator the turbine efficiency is cal- culated in the usual manner. From these tests it has been determined that the turbine efficiencies are in excess of 90 per cent from half gate to full load, reaching in each case a maximum of 93 per cent. The average combined efficiency curve, including losses in penstock, Johnson valve, turbine and generator, is shown in Fig. 3. It will be noted that at normal load the efficiency from forebay to switchboard is 90 per cent. At the top are ice diverters which have been anchored near canal intake to keep the waterway free of ice. Below, at the left, are the intake racks for the new units. The racks are removed when slush ice is flowing. The flaring mouthpiece of one pen- stock shown in the middle view looms up like a cavern back of the man shown. At the right is a view from the draft tube looking up toward the outlet of one wheel. FIG. 10 PROVISIONS FOR HANDLING LARGE VOLUMES OF WATER USED BY STATION NO. 3 WHICH, WITH EXTENSION, HAS RATING OF 250,000 HP.