Publication: Electrical World
New York, NY, United States
German 50,000-Volt Transmission System.
T0 supply the city of Munich with additional electrical energy, and to run in parallel with the several existing municipal steam and hydraulic plants, a new municipal hydro-electric plant has recently been completed.
It utilizes the water of the river Isar in Moosburg, where three 1887-hp, double twin turbines are installed. Energy is generated at 5000 volts, but the e.m.f. is increased to 50,000 volts for transmission over two parallel circuits to the substation near the city of Munich, where the e.m.f. is decreased to 5000 volts for distribution.
This plant, known as the Uppenborn station, being the latest of German hydro-electric undertakings, possesses many novel features, particularly on the electrical end.
Thirty-three miles below the city of Munich the river Isar makes a bend, which is cut off by a head and tail race canal about 2.5 miles in length, giving a net fall of 28.1 ft. at low water and 24.8 ft. at high water. Permission was given to draw 2500 cu. ft. of water per second during 207 days, while during the remainder, including the dry season, only 1070 cu. ft. is available.
Just below the junction of the head race and the river a dam was thrown across the river at about right angles. For this purpose the width of the Isar was increased from 225 ft. to 619 ft. On the opposite end from the intake is a spillway, 328 ft. long. Adjoining the spillway is a fish passage 6.5 ft. wide, built up in steps. Next to this are the sluice gates for regulating the head. They are divided into four sections, each 55.7 ft. wide, three of which are separated by concrete pilasters, while the fourth is separated by a lock 26.25 ft. wide for passing boats, etc. This lock, having two mechanically operated swinging gates on the up-stream end, is about 150 ft. long. The bottom has a slope of about 2 per cent. It is made of concrete covered with planking.
The sluice gate passages adjoining the lock are subdivided into two sections by a removable guide, for the purpose of giving free passage for floating debris, etc. The two passages near the intake are divided into three sections, and the guides here, for the sluice gates, are stationary.
Each sluice gate is divided into two sections, one upper and one lower. They are, however, not of the same size, the lower being the smaller, thus enabling the sections, due to the hydrostatic head, to be operated by the same amount of power. Two such sections, or one gate, can be lifted by a three-phase, 10-hp motor in 10 minutes. When operated by a hand windlass with a ratio of 1:2800, 50 minutes are required to lift one section. On the down-stream side of the gates, resting on the concrete piers, is an operating gallery of structural steel.
The bottom of the intake to the head race is about 7 ft. above the bed of the river, thus preventing foreign material, such as gravel and sand, from entering the head race. As this provision cuts down the depth of the water to 4.9 ft., the width of the intake was made 125 ft., thus giving a velocity of 3.9 ft. with a friction or head of loss of 4 in.
This intake passage is divided up by a massive concrete pier, and in order to further reduce the size of the sluice gates they are subdivided into four sections by structural steel sluice guides. Each gate is divided in two parts and operated in the same manner as those described above. At the side of the dam and intake is an attendants' house, which contains also a transformer for supplying energy to gate motors. On the other side of the intake is a lock, similar to the one mentioned, for passing boats into the head race.
The head race canal is 1.3 miles long, and is built with a slope of 1 in 3000 for a calculated velocity of 4 ft. per second. It is 54.5 ft. wide on the bottom, with side slopes of 1-to-1.5. Under ordinary conditions the depth of the water is 9.2 ft. Throughout the greater part the sides of the canal are finished off in embankments, which, at the highest point, are 16.5 ft. above the natural ground.
At a low point the head race crosses a creek which is passed underneath through two culverts.
The power house lies across and at right angles to the head race, which is here 175 ft. wide. At one end of the power house is a lock for passing boats and a fish way, similar to those at the dam. At the other end is a sluice gate and passage for letting off the head race water into the tail race; the latter is 1.1 miles long. Some difficulty was encountered during the excavating, because part of the work runs through marshy land.
At an angle of 72 deg. to the flow of the water to the turbine chamber, and in front of the sluice gates, are racks built up of 2.25-in. x o.25-in. bars, spaced with a clearance of 1 in. The sluice gate for each turbine is 11.5 ft. high and 24 ft. wide. It is divided vertically into three sections, which can be interconnected for motor operation.
The sluice gate seen foremost in Fig. 1 is 14.8 ft. high and 13.1 ft. wide, and its purpose is for emptying the head race as above indicated. On the other end of the sluice gates is the gate for the lock; it is 26.25 ft. wide and 16 ft. high, and is lowered when the water is left off. All sluice gates, with the exception of the latter, can be motor-operated. On the down-stream side of the gates is a gallery from which they are operated by hand.
The turbine chambers are located between the gates and the generator room, the roof being flush with the street and made of reinforced concrete. There are installed three twin inward-flow Voith turbines, mounted on a horizontal shaft, each having an output, with a water consumption of 785 cu. ft. and a head of 26 ft. of 1887 hp at 150 r.p.m. Each twin turbine has its own draft tube; the two of a complete unit join into a single draft tube, which is part of the foundation and discharge into the tail race.
During the greater part of the year there is surplus water, to utilize which a 224-hp twin turbine, consuming too cu. ft. of water per second, making 300 r.p.m., has been installed. The generator of this turbine is a three-phase, 5000-volt, 50-cycle machine, designed for an output of 210 kw at a power factor of 0.9. To the unit there is coupled a 110-volt exciter. The operation of this set is kept independent from the remainder of the plant, as it supplies energy for the city of Moosburg. However, provision is made so that in case of emergency it can be joined in parallel with the rest of the plant, as will be seen below.
The regulation of each of the main turbine sets is accomplished by an oil-actuated, hydraulic governor, located in the generating room. The oil is supplied at 295 lb. pressure by pumps operated from the turbine shafts. The oil piping of the different pumps is interconnected so that one may assist another. For synchronizing the generators the governors are equipped with small motors controlled from the main switchboard.
The turbine shafts are rigidly coupled to the shafts of the three-phase alternators, which are of the revolving-field, 5002-volt, 50-cycle type. With unity power factor the output of each generator is 1400 kw. Overhanging on each shaft is mounted