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Case for the Equipment Selection of Axial Flow Hydropower Plant

 1 Summary

      Power station is run-off river power station. Maximal head is 13.66m. Minimal head is 9.01m. Weighted average head is 12.05m. Weighted average head in flood period is 11.59m. Rated head is 11.2m. Installed capacity is 3X6MW. Guaranteed output of power station is 9MW. Annual utilization hours of installed capacity are 4713h. Annual energy output is 226,200,000 kW·h..
      As per head variation range and total installed capacity, 3 units of 6MW movable blade propeller water turbine units are determined to be installed at the power station after selection comparison. Turbine type: ZZ560A—LH—510. Runner diameter is 5.1m. Generator type: SF6—60/780. Rated running speed of unit is 100r/min. Unit oil pressure unit model: HYZK6.0—4. Guide vane adjustment type: DTJ—80/4.0—C. Blade adjustment type: DTJ—50/4,0—C.
Generator rotor is the heaviest component in installation and maintenance of unit. As per its lifting weight, crane of major powerhouse shall be one 80t+80t/30 double-trolley overhead travelling crane, whose span L=15.5m.
 
2 Powerhouse Layout
 
      Powerhouse of power station is a part of dam, which is above ground powerhouse. 3 units of 6MW vertical shaft movable blade propeller water turbine units are set.
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 lower to upper 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 first quadrant of generator layer.
      Pump room is set at lower part of erection bay of powerhouse turbine layer, whose elevation is 6.24m. 4 technical water supply pumps are set in total, among which 2 units are seepage drainage pumps and the other 2 units are repair drainage pumps.
      Medium and low pressure air compressors are also set at the lower part of erection bay of turbine layer. 2 medium pressure air compressors and 2 low pressure air compressors, as well as 3 air containers are set in total.
      To reduce powerhouse size and lower fire hazard level, turbine oil depot, insulation oil depot and its oil treatment room are set outside the major powerhouse. 4 oil tanks are set at the depot separately. 4 10m³ oil tanks are set at the turbine oil depot. 4 12m³ oil tanks are set at the insulation oil depot. Pressure oil purifier and vacuum oil purifier as well as oil pump are set at the oil treatment room separately. For convenience of oil filling of unit, 1 5m³ middle oil depot is set at the lower part of erection bay of major powerhouse turbine layer.
 
2.1   Determination of Major Dimensions of Major Powerhouse as Follows:
      1) Powerhouse Length
      Erection bay and generator layer are at the same elevation. Erection bay dimensions shall be determined as per the 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 27.05m. Unit spacing shall be controlled as per layout dimensions of turbine spiral case, which is determined as 19.50m. Total building length of major powerhouse is 85.56m.
 
      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, generator fan housing dimensions, turbine inspection and maintenance channel request, governor equipment layout shall be considered. Distance from unit centerline to upstream sidewall shall be determined as 8.25m. 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 7.75m. Net width of major powerhouse is 16.0m. Span of overhead travelling crane is 15.5m.
     
      3) Elevation of Each layer of Powerhouse
      Calculating based on 0.0m installation elevation of turbine, elevation of draft tube baseplate is -12.07m. Turbine layer elevation is 6.24m. Generator layer elevation is 11.51m. Top track elevation of overhead travelling crane determined by the request of lifting turbine generator rotor is 24.67m.
      Because that downstream check flood level is 21.77m (calculating based on 0.0m installation elevation of turbine), which is above turbine elevation, a flood wall shall be set outside bent frame column at powerhouse downstream.
 
3 Technical Water Supply System
      Because that cooling mode of power station major 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 consumption equipment of each unit includes: upper guide bearing oil tank, air cooler, lower guide bearing and thrust bearing oil groove, water guide bearing oil groove, main shaft seal etc.
 
      1) Water Source and Water Intake Way
Dam-front water intake way is applied for the power station. 2 water intakes are set. Trash rack and air purge mouth are set on each water intake to prevent ordure blocking.
      2) Technical Water Supply Mode
Operating head range of unit is 9.01-13.66m. Central water supply by water pump pressure is applied after analysis and comparison. 4 IS200—150—250B type (Q=400m³/h,H=20m, N=37KW) horizontal centrifugal pumps are set, among which 3 units work and another standby. 1 rotary water filter is set on general water pipe of pump outlet to filter the water.
      Diameter of technical water supply general pipe is Φ377X6. The pipe goes through the powerhouse and leads to each unit. Electromagnetic distributing valve is set on water inlet valve of each unit. And then the water is led to parts as upper guide oil groove, air cooler, lower guide and thrust oil groove, water guide oil groove, main shaft seal etc. Flow indicator is set on drainage pipe of water consumption equipment to monitor unit water supply. Once cooling water is suspended, alarm signal shall be sent out instantaneously.
      3) Water Consumption of Equipment
      Water consumption of equipment is estimated as per empirical formula. Total water consumption of 1 unit is about 350m³/h as estimated.
      4) Living Water and Fire Water Supply System
      Fire hydrant is set at the major powerhouse. Water spray fire extinction mode shall be applied for 3 generators. In addition, concerning request of living and fire extinction in the power station, 1 living and fire extinction water pool is set outside the major powerhouse. Water comes from quality underground water
      1 DN100 living and fire extinction water supply main pipe is set at the major powerhouse which goes through the whole powerhouse. Water is led to water spray fire extinction control box and fire hydrant of each generator. Manual fire extinction mode of water spray is applied for generator.
      High quality water is required for main shaft seal. Besides technical water supply main pipe, which is applied as major water supply source, clean water extracted from living and fire extinction water supply main pipe is used as standby water source. Lubricating water of deep well pump used for water drainage is also extracted from in-house living and fire extinction water supply main pipe.
 
4 Drainage System
      Water drainage system of power station is divided into two parts of unit repair drainage and powerhouse seepage drainage.
 
1 Unit Repair Drainage System
      (1)    Drainage Mode
      Indirect drainage is applied as the drainage way of unit. Namely water in spiral case, tail water pipe and headrace shall be drained to the repair collecting well by spiral case drainage disc valve, tail water pipe drainage disc valve through whole powerhouse major drainage pipe, and then the water shall be drained to the tail water by 2 vertical deep wells set at repair collecting well.
      (2)    Selection of Water Pump
      Calculation shall be made as per water pump productivity and head calculation formula. 2 350SG34D—14X3 type (Q=340m³/h, H=42m, N=55KW) deep well pumps shall be selected. Its advantage is small floor space. Motor is set at 6.24m elevation of lower part of erection bay of major powerhouse turbine layer to avoid moisture and flood. Prelubrication water shall be supplied before startup. Prelubrication water comes from living and fire extinction water supply main pipe of major powerhouse, which is controlled automatically by electromagnetic valve. Unit repair water drainage is manually operated. Water level signal device is set at the water collecting well to monitor water level.
 
      2 In-House Seepage Drainage
      Seepage drainage system is applied to drain seepage of in-house hydraulic structure, leakage 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.
      Seepage of head cover and main shaft seal of power station shall be drained to downstream by 2 3TC—30 type head cover drainage pumps.
      (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 about 30m³/h.
Available capacity of water collecting well shall be considered as per seepage water volume of powerhouse in 30-60min. Within 60MIN, available capacity of water collecting well is 30m³.
      (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 considered as 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 38m by calculation.
      Calculating as per water pump productivity calculation formula, 2 150SG50—8.5X5 type (Q=50m³/h, H=42.5m, N=11kw) deep well pumps shall be selected. Motor shall be set at 6.24m elevation of turbine layer of major powerhouse erection bay section. Liquid level signal device is set on 2 seepage pumps to automatically control startup and shutdown of the two pumps as per water level change of water collecting well. One pump works and the other standby. Prelubrication water shall be supplied before startup of pump. Lubrication water comes from whole powerhouse living and fire extinction water supply main pipe, whose putting in and cutting off is controlled automatically by electromagnetic valve.
 
5 Turbine Oil System
      Turbine oil system of power station mainly supplies turbine oil to 3 units and oil pressure unit of governor. Turbine oil depot is set outside the major powerhouse.
 
1 Components of Turbine Oil System
      Turbine oil system is mainly determined as per oil pressure unit of unit governor. Oil depot consists of 2 10m³ net oil tanks and 2 10m³ running oil tanks, 1 5m³ middle oil tank, 1 0.5m³ gravity oil tank, 3 2CY—5/3.3—1 type gear oil pumps, 1 ZJB2KY type vacuum oil purifier and 1 LY—100 type pressure oil purifier etc. Please check operation instruction in turbine oil system drawing for main process flow details.
      Oil depot and oil treatment room are connected with governor oil pressure unit by pipe. Oil supply and discharge pipe diameter is DN50.
 
2 Oil Consumption of Unit and Oil Pressure Unit
      Oil consumption of unit is provided by manufacturer. Before manufacturer data is acquired, the value may be estimated as per the oil consumption of the same type unit with similar model and similar size. Oil consumption of each unit of this power station is about 8.0m³.
 
3 Selection of Oil Consumption Device
      (1)    Net Oil Tank
      Volume of net turbine oil tank is determined as per 110% of oil consumption of one unit. Concerning layout, 2 net oil tanks shall be selected with 10m³ 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 10m³ running oil tanks shall be set.
      (3)    Middle Oil Tank
      Because that oil depot and oil treatment room are not inside the powerhouse, concerning convenience of unit repair and improvement of efficiency, 1 5m³ middle oil tank is set. Its volume shall be equal to the oil consumption volume of lower guide bearing, which is the maximal oil consumption component of the unit.
      (4)    Gravity Fuel Tank
      For fueling convenience in running, 1 0.5 m³ gravity fuel tank is set for oil filling of unit.
      (5)    Oil Pump
      Concerning filling 1 unit with oil within 4h, and draining out the oil within allowable shutdown period of oil tanker, 3 2CY—5/3.3—1 type gear oil pumps (one for middle oil depot) shall be selected to be used in receiving new oil, equipment oil filling and oil draining. Its parameters shall be: Q=5m³/h; H=0.33MPa.
      (6) Oil Purifier
      In order to purify impurities and water in turbine oil timely, 1 ZJB2KY type vacuum oil purifier and 1 LY-100 type pressure oil purifier and 1 ZJCQ—3 type purifier shall be selected to complete purification of the oil in 1 unit within 8h.
 
6 Insulation Oil System
      Insulation oil system of power station mainly supplies insulation oil for oil switch and main transformer of power station. Insulation oil depot is set outside the major powerhouse.
 
1. Components of Insulation Oil System
      Insulation oil system, which consists of 2 12m³ net oil tanks, 2 12m³ running oil tanks, 2 2CY—5/3.3—1 type gear oil pumps, 1 ZJB2KY vacuum oil purifier, 1 LY—100 type pressure oil purifier etc., is mainly determined as per oil consumption of main transformer. Please check operation instruction in turbine oil system drawing for process flow details. Oil depot and oil treatment room and main transformer shall be connected by pipes. Oil switches shall be connected by pipes. Diameter of oil supply and discharge pipe is DN50.
2. Oil Consumption of Equipment
      Oil consumption of main transformer shall be checked and got from manufacturer or respective sample, which is 20m³.
3. Oil Consumption Device
      (1)    Net Oil Tank
      Volume of net turbine oil tank is determined as per 110% of oil consumption of one main transformer. Concerning reasons like layout etc., 2 net oil tanks shall be selected with 12m³ 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 12m³ running oil tanks shall be set.
      (3)    Oil Pump
      Concerning filling 1 main transformer with oil within 6h, and draining out the oil within allowable shutdown period of oil tanker, 2 2CY—5/3.3—1 type gear oil pumps shall be selected to be used in receiving new oil, equipment oil filling, oil draining and purifying. Its flow Q=5m³/h. H=0.33MPa.
      (4)    Oil Purifier
      In order to purify impurities and water in turbine oil timely, 1 ZJB2KY type vacuum oil purifier and 1 LY-100 type pressure oil purifier shall be selected to complete purification of the oil in 1 main transformer within 24h.
 
7 Compressed Air System
      Compressed air system of this power station is divided into two parts of low pressure system and medium pressure system.
 
1 Low Pressure Air System
      Low pressure air system of the power station supplies air for following purposes: air required for unit braking, air required for repair and maintenance, air required for air valve etc.
      (1)    Air Consumption
      Brake air consumption: brake air consumption of 1 unit is calculated as per formula to be 3.4m³.
      Air consumption of maintenance and repair: 2 pneumatic grinders are set at this power station, among which one grinder diameter is Φ150mm; and air consumption is 1.7/min. Diameter of the other grinder is Φ60mm; air consumption is 0.7/h. 1 pneumatic drill is set with Φ22mm diameter and 1.7/min air consumption. Air consumption of air tool: ∑Q =4.1/min.
      Air consumption of inflatable rubber seal: In repair of unit, inflatable rubber seal is applied for stopping water. Its air consumption is little, which shall be neglected.
      (2)    Air Container
      Special air container is set for unit braking. 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 3.5m³ by calculation as per formula. Air container volume is determined as 4.0 m³.
      (3)    Selection of Air Compressor
      Productivity of air compressor is 5.6m³/min by calculation as per formula. Rated discharge pressure of air compressor is determined as: 0.86MPa. Therefore 2 units of EP50-SB 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 selected, among which 1 unit works and the other standby. 2 air containers are set corresponding to 2 air compressors, among which 1 air container is specially used to supply air to unit braking. The other air container is used to supply air to unit maintenance and repair, and being used as standby air source of unit braking. 2 DN80 air supply main pipes are set at the powerhouse, among which 1 pipe is used for unit braking. The other pipe supplies air to repair and maintenance of air tool. Startup and shutdown of 2 air compressors are controlled by pressure annunciator on air container.
 
2 Medium Pressure Air System
      Medium pressure air system mainly supplies air for the oil pressure units of 3 units. Volume of oil pressure unit tank is 1.5m³. Working pressure is 4.0MPa. Primary pressure air supply mode is applied.
      (1)    Selection of Air Compressor
      Total productivity of air compressor is 1.2m³/min by calculation as per formula. Rated discharge pressure of air compressor is determined as 4.0MPA. 2 air compressors are selected. Productivity of single air compressor: Q=Qk/2=0.6/min.
      2 VF—0.6/40 type air compressors shall be selected as per productivity and discharge pressure of air compressor, among which one is major and the other standby. The discharge rate: Q=0.6m³/min. Discharge pressure shall be 4.0MPa.
      (2)    Air Container
      1 medium pressure air container is set, whose volume is 3.0m³. And working pressure is 4.0MPa.
      (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 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 gas admission device shall be switched on automatically to supply air.
 
8 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.
 
1 Whole Powerhouse Monitoring
      Items of whole powerhouse monitoring are: upstream water level, downstream water level, gross head of power station etc., among which signal of downstream water level is transmitted to the central control room by pressure pickup. While gross head of power station is displayed by water level displayer which is set at the central control room.
 
2 Unit Section Monitoring
      Monitoring items of unit section are: front-to-back pressure difference of trash rack, spiral case entrance pressure, vacuum pressure of tail water pipe, runner upper chamber pressure, cooling water pressure of water guide bearing and main shaft seal water pressure etc.
      Pressure signals of above monitoring items, except for cooling water pressure of water guide bearing, which is displayed on switchboard at turbine layer, are all transmitted to central control room by pressure sensor, monitoring tube and cable.

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