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Case for the Equipment Selection of Francis Hydropower Plant

1 Summary

      Maximal head of power station is 25.7m. Minimal head is 23.3m. Average head is 25.5m. Rated head is 24.8m. Installed capacity is 3×4MW. Operation mode of power station is mainly counter regulation. Generation is also considered. Guaranteed output of power station is 2.87MW. Annual utilization hours of installed capacity are 4491h. Average generated energy for many years is 53,900,000kW·h.
As per head variation range and total installed capacity, 3 units of 4MW Francis turbine generator are determined to be installed at the power station after selection comparison. Turbine type: HLD74-LJ-180. Runner diameter is 1.8m. Generator type: SF4-28/325. Rated running speed of unit is 214.3R/min. Governor type: SKYDT-3000.
Generator rotor is the heaviest component in installation and maintenance of unit. As per its lifting weight, crane of major powerhouse shall be one 50t/10t, single trolley, electrical overhead travelling crane, whose span L=10.5m.
 
2 Powerhouse Layout
      Powerhouse of power station is dam-rear above ground type. Unit’s layout is in a column. From right to left is erection bay section and unit section. Major powerhouse of power station has a three-layer structure. From upper to lower is spiral case layer, turbine layer and generator layer. Main run channel is on the upstream side of major powerhouse. Equipment lifting main channel and auxiliary run channel is at the downstream side. Stair leading to the turbine layer is separately set at powerhouse erection bay and unit section.
      Turbine governor is set at the second quadrant of generator layer.
      Pump room is set at lower spiral case layer of erection bay, whose elevation is 2.19m. Totally 4 water drainage pumps are set, among which 2 units are leakage drainage pumps, the other 2 units are repair drainage pumps. 2 fire pumps are set at 2.95m high gallery of major powerhouse upstream.
      Air compressor room is set at auxiliary powerhouse on turbine layer, which is 2.61m high. 2 medium-pressure air compressors and 2 low pressure air compressors and 3 air containers are set in the room.
      Turbine oil depot and oil treatment room are set at the lower turbine layer of erection bay. 3 oil pipes are set in the oil depot. Pressure oil purifier and vacuum oil purifier and oil pump are set at oil treatment room. Insulation oil depot and oil treatment room are in site area. Oil supply and discharge of main transformer shall be completed by fuel tanker.
 
2.1   Determination of Major Dimensions of Major Powerhouse
       (1)    Powerhouse Length
      Erection bay and generator layer are at the same elevation. Erection bay dimensions shall be determined as per required dimensions of setting 5 major components as turbine head cover, runner, generator rotor and upper, lower frame etc. in installation and maintenance, as well as the required dimensions for working space. Length shall be 12.58m. Unit spacing shall be controlled as per layout dimensions of turbine spiral case, which is determined as 9.60m. Total building length of major powerhouse is 43.29.
       (2)    Powerhouse Width
      Major powerhouse width is determined by composite factors like layout dimensions of turbine spiral case and turbine generator unit, as well as electromechanical equipment layout etc. For powerhouse upstream side width, spiral case dimensions in +y direction, turbine inspection and maintenance channel request, layout dimensions of governor equipment and excitation transformer, auxiliary powerhouse layout etc. shall be considered. Distance from unit centerline to upstream sidewall shall be determined as 6.30m. Powerhouse downstream side width shall be determined by spiral case dimensions in –y direction, which shall meet large component lifting and channel requests in the meantime. Distance from unit centerline to downstream sidewall is 5.70m. Net width of major powerhouse is 12.0m. Span of overhead travelling crane is 10.50m.
      (3)    Elevation of Each layer of Powerhouse
      Calculating based on 0.0m installation elevation of turbine, elevation of draft tube baseplate is -4.29m. Turbine layer elevation is 2.61m. Generator layer elevation is 7.21m. Top track elevation of overhead travelling crane determined by the request of lifting turbine generator rotor shall be 14.86m.
 
2.2 Determination of Major Dimensions of Auxiliary Powerhouse
      Auxiliary powerhouse is located at upstream side of major powerhouse, whose width is 7m. And bus room elevation is 2.61m. 10kV high voltage power distribution room elevation is 7.21m. 35kV high voltage power distribution room elevation is 11.81m. Central control room, house service transformer room and high voltage, low voltage power distribution room, air compressor etc. are all set in the auxiliary powerhouse.
 
3 Technical Water Supply System
      Because that cooling mode of power station main transformer and air compressor in the major powerhouse is air cooling, technical water supply of this power station is applied mainly for the cooling and lubrication of 3 turbine generator units. Water consuming equipment of each unit includes: cooler of generator upper guide bearing, air cooler of generator, lower guide bearing cooler, cooler of water guide bearing, shaft seal cooler etc.
 
3.1 Water Source and Water Intake Way
      Penstock water intake way is applied for the units. 1 water intake is set on each unit. Trash racks are all set on the 3 water intakes. Compressed air purge mouth is also set on each water intake in the meantime to prevent ordure blocking.
 
3.2 Technical Water Supply Mode
      Head range of power station is 23.3-25.7m. Automatic flow water supply mode is applied. Connection main pipe is set also. Water supply of units is mutual standby. After the water is taken from penstock, it shall be supplied to the units automatically controlled by electromagnetic valve through water filter. The main water inlet pipe of the units is DN100 type, which is set at the upstream side of the major powerhouse. Then the water shall be divided into 5 ways and led into generator upper guide bearing, generator air cooler, lower guide bearing and turbine water guide bearing as well as main seal respectively. Hand valve and pressure gauge are set on each water supply pipe. Flow indicator is set on each branch drain to monitor unit water supply. Once cooling water is suspended, alarm signal shall be sent out instantaneously.
 
3.3 Water Consumption of Equipment
      Water consumption of equipment is estimated as per empirical formula. Water consumption of each unit is: water consumption of generator air cooler is 65m³/h; water consumption of cooler of generator upper guide bearing is 22m³/h; water consumption of lower guide bearing cooler is 3 m³/h; water consumption of water guide bearing cooler is 5 m³/h; cooling water of main shaft seal is about 10m³/h. Total water consumption of 1 unit is 110m³/h.
 
4 Drainage System
      Water drainage system of power station is divided into two parts of unit repair drainage and powerhouse seepage drainage.
 
4.1 Unit Repair Drainage System
      (1)    Drainage Mode
      Direct drainage is applied as the drainage way of unit. Namely for repair drainage system, water in flow channel flows automatically to the downstream tail water, and then drainage valve disc shall be opened; water in penstock, spiral case, tail water pipe, and water leakage of upstream & downstream gates in repair process shall be drained to the downstream by water pump. Unit repair drainage pump is manually operated and started by vacuumizing of 1 water ring type vacuum pump.
      (2)    Water Pump System
     Calculating as per water pump productivity and calculation formula of head, 2 units of SB100-100 model (Q=70-130m³/h, h=13.6-11.0m,N=11kW) horizontal type centrifugal pumps shall be selected. Water pump shall be set at -2.19m elevation of lower spiral case layer in erection bay.
 
4.2 In-House Seepage Drainage
     Seepage drainage is applied to drain seepage of in-house hydraulic structure, seepage of valve and piping etc. Seepage is drained through drainage ditch to seepage collecting well. And then it’s drained to the downstream by seepage drainage pump.
     (1)    Available Capacity of Seepage Collecting Well
     Estimated value of seepage water quantity of building is provided by hydrotechnics professional. Seepage water quantity of this power station is 45m³/h.
Available capacity of water collecting well shall be considered by seepage water volume of powerhouse in 30-60min. For this power station, it’s 45 m³ in 60min.
     (2)    Selection of Seepage Drainage Pump
     2 seepage drainage pumps are set, among which one unit works and the other standby. Water discharge time of working pump is 20-30min.
     Head of seepage drainage pump shall be equal to the difference between the lowest water level elevation of water collecting well and the highest tail water level of downstream, plus pipe loss. It’s determined as 20m by calculation.
     As per water pump productivity formula, 2 units of 300SG210-10.5×2 type (Q=210m³/h, h=21m, N=18.5kW) centrifugal pumps with vertical axes shall be selected. Its motor shall be set at the same elevation of water drainage pump of repair water pump. Startup of 2 water pumps shall be controlled automatically by liquid level signal device as per water level change of water collecting well. Lubricating water shall be supplied to the water pump before startup. Water comes from technical water supply main pipe.
 
5 Turbine Oil System
     Turbine oil system of power station mainly supplies turbine oil to bearing lubrication of 3 units and oil pressure unit of governor. Turbine oil tank and oil treatment room are set at the erection bay section of turbine layer.
 
5.1 Components of Turbine Oil System
     Power station turbine oil is mainly used in the unit and oil pressure unit of governor. Turbine oil system consists of 1 4m³ net oil tank, 2 2m³ working oil tanks, 1 leakage oil tank, 2 2CY-3/3.3-1 type gear oil pumps, 1 ZJB-0.6KY type vacuum oil purifier, 1 LY-30 type pressure oil purifier etc.
 
5.2 Oil Consumption of Unit and Oil Pressure Unit
     Oil consumption of unit is provided by manufacturer. Oil consumption of each unit and oil pressure unit is about 3.3m³.
 
5.3 Selection of Oil Consumption Equipment
     (1)    Net Oil Tank
     Volume of net turbine oil tank is determined as per 110% of oil consumption of one unit. 1 net oil tank is selected with 4m³ volume.
     (2)    Running Oil Tank
     Volume of running oil tank shall be the same as the volume of net oil tank. Concerning easy purifying of running oil and improvement of efficiency, 2 2m³ running oil tanks shall be set.
     (3)    Oil Pump
     Concerning filling 1 unit with oil within 4h, and draining out the oil within allowable shutdown period of oil tanker, 2 2CY—3.3/3.3—1 type gear oil pumps shall be selected to be used in receiving new oil, equipment oil filling and oil draining. Its parameters shall be: Q=3m³/h; H=0.33MPa.
     (4)    Oil Purifier
     In order to purify impurities and water in turbine oil timely, 1 ZJB-0.6KY type vacuum oil purifier and 1 LY-30 type pressure oil purifier shall be selected to complete purification of the oil in 1 unit within 8h. When there is little water and many impurities in the oil, only pressure oil purifier shall be applied adequately. When there is much water in the oil, vacuum oil purifier shall be applied to isolate the water from oil; and then pressure oil purifier shall be applied for purifying.
 
6 Compressed Air System
     Compressed air system of this power station is divided into two parts of low pressure system and medium pressure system.
 
6.1 Low Pressure Air System
     Low pressure air system of the power station supplies air for following purposes: air required for unit braking and standstill seal, air required for repair and maintenance by air tool etc.
     (1)    Air Quantity
     Brake air consumption: brake air consumption of 1 unit is calculated as per formula to be 1.68m³.
     Air consumption in repair and maintenance: 2 pneumatic grinders are set in the power station, among which 1 unit diameter is Φ22mm and its air consumption is 1.7m³/min. Total air consumption in repair is: 4.1m³/min.
     Air consumption of inflatable rubber seal and main shaft seal: air consumption of inflatable rubber seal used for turbine main shaft maintenance seal is little, which shall be neglected. And the air shall be extracted directly from air supply pipe.
     (2)    Air Container
     Unit braking air is extracted from air container. Air container volume shall be guaranteed that when 2 units consume braking air synchronously, air pressure in the container shall be remained above the lowest braking air pressure. Acquired volume of air container shall be 1.68m³ by calculation as per formula. Air container volume is determined as 2.0 m³.
     (3)    Selection of Air Compressor
     Productivity of air compressor is 5.2m³/min by calculation as per formula. Rated discharge pressure of air compressor is determined as: 0.86MPa. Therefore 2 units of EP50-S type air compressors are selected, among which one unit is major and the other standby. Its off-air delivery: Q=5.5m³/min. Discharge pressure: P=0.86MPa.
     (4)    Running Mode of Equipment
     2 air compressors are shared by braking air system and repair air system, among which 1 unit works and the other standby. 2 air containers are set corresponding to 2 air compressors, among which 1 2.0m³ air container is specially used to supply air to unit braking, the other 2.0m³ air container is used to supply air to maintenance seal and air tool, and being used as standby air source of unit braking. 1 Φ57×3.5 air supply main pipe is set at the powerhouse for unit braking. The other Φ57×3.5 air supply main pipe is used to supply air to maintenance seal, air tool and purge. Startup and shutdown of 2 air compressors are controlled by pressure annunciator on air container.
 
6.2 Medium Pressure Air System
     Medium pressure air system mainly supplies air for the oil pressure units of 3 units. Working pressure of oil pressure unit tank is 2.5MPa. Primary pressure air supply mode is applied.
     (1)    Selection of Air Compressor
     Total productivity of air compressor is 0.08m³/min by calculation as per formula. Rated discharge pressure of air compressor is determined as 3.0MPa.
As per productivity and discharge pressure of air compressor, 2 units of VF-0.35/30 type air compressors are selected, among which one unit is major and the other standby. Its off-air delivery: Q=0.35m³/min. Discharge pressure: P=3.0MPa.
     (2)    Air Container
     1 medium pressure air container is set, whose volume is 1.0m³. And its pressure is 2.5MPa.
     (3)    Running Mode of Equipment
     2 air compressors are selected in this system, which are mutual standby. At the first time of gas charging after oil pressure unit is installed or repaired, 2 air compressors shall work synchronously. Automatic gas admission mode is applied for the gas admission of oil pressure unit. When oil level of pressure oil tank exceeds upper limit of normal oil level, and oil pressure is lower than normal working oil pressure in the meantime, signal shall be sent out by signaling set composed of oil level annunciator and pressure annunciator. And gas admission device shall be switched on automatically to supply air.
 
7 Hydraulic Monitoring System
     Whole powerhouse hydraulic monitoring system is divided into two parts: the first part is whole powerhouse monitoring, the second part is unit section monitoring.
 
7.1 Whole Powerhouse Monitoring
     Items of whole powerhouse monitoring are: upstream water level, downstream water level, reservoir water temperature.
 
7.2 Unit Section Monitoring
     Monitoring items of unit section are: front-to-back pressure difference of trash rack, spiral case entrance pressure, penstock flow, vacuum pressure of tail water pipe entrance, pressure of tail water pipe outlet etc.
     Water level (pressure) signals of above monitoring items are all transmitted to central control room and turbine hydraulic switchboard by water level (pressure) sensor, monitoring tube and cable.
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