BR01B1848

ETDE-BR--0278

Hydraulic and Auxiliary Equipment

Reporter: Mr. Luo Gaorong Deputy Director of International Centre of PCH of ONU in China

.. Power in China

L The Procedures of Small Hydro Power (SHP) Construction

1. The SHP Planning

1.1. The planning of middle and small rivers. Since all SHP stations are built on middle and small rivers, it is necessary to mnduct river planning before the SHP design, which shall be in accordance with multipurpose water resources utilization and cascade optimal development. To be more specific, river planning should take such purposes into account, namely, flood control, water supply, navigation, power generation, environmental protection, natural scene improvement, improvement of surviving conditions of human being, etc so as to develop water resources fully and rationally. At present, most rivers in China have been planned and the planning can be modified annually according to the social and economic development. The planning can be accomplished by water conse~ancy bureaus (departments) at the provincial, prefectural or county level as the river basin varies.

1.2. The planning of rural grid. Most SHP has been incorporated into the rural grid, so the electricity demand of the grid and load forecasting determine the SHP development. At present, most rural SHP grids face such a contradiction, i.e. abundant electricity during the flood season vs. electricity shortage during dry season, which can be relaxed a little bit by exchanging electricity with the national grid. So constructing SHP stations with yearly regulating reservoir has become a priority,

1.3. The SHP planning. If river planning and rural grid planning have been carried out, it is time to conduct SHP planning and feasibility study, which shall be accomplished by design institutions entrusted by project owners. At this stage, project size, type, generator set should be determined, and electricity market analysis, investment estimate and economic appraisal should be conducted for the decisions-making of the project owners. After the feasibility study has been approved, preliminary design can start.

2. SHP design

2.1. SHP design can be devided into two parts, preliminary design and construction detailed drawings. During the preliminary design, the drawing of the main parts of the project and the drawing of overall set-up should be completed, major technical problems be solved, quantity of engineering work be estimated and preparation work before ordering equipments be carried out. Usually, preliminary design can be accomplished within a shoti period of time. After being further improved, the preliminary design forms the bidding design in the bidding document.

2.2. The detailed drawings should be completed by design institutions before the construction for the review of project owners and construction supervisors before they transfer them to the construction contractors to carry out construction. Or design institutions may supply the detailed drawings gradually according to the speed. The turbines with lower specific speed are used at higher heads, while turbines with higher n. are applied at low heads. Only for geometrically similar tucbines operating in kinetically similar renditions the value of the specific speed n. is the same.

Peiton 12-30 TUWO 20-70 b Cross-flow 20-80 Francis 80-300 Propeller and Kaplan 300-1000 \ , The above mentioned figures of the Pelton and Turgo turbines are suitable for single jet, if Pelton turbine with two jets each having a specific speed of 15 can produce double power. This 2 jet Pelton would be equivalent to a tutiine with a specific speed of 15.2 or 21.

1.

Francis turbine is understood as a turbine in which the water flow enters the runner inwards in radial direction, changes its direction gradually and then possesses a direction out axially.

A Francis turbine may be operated over a range of discharge from approximately 40 to 105 percent of rated discharge. Below 40 percent rated discharge, there can be an area of operation where the vibration and power surge occur. The upper limit generally corresponds to the generator rating. The approximate head range for operation is from 60 to 125 percent of the design head. The maximum efficiency of a Francis turbine is established at 90 percent of the rated capacity of the turbine.

This type of turbine is the most common one in use today in China. In the series design of less than 10000 kW turbines, the head range used is from 8-300 m, and the maximum discharge reaches 7.7 m3/second it also can be applicated in high heads even up to 650 m in special design.

The Francis turbine may be mounted with vertical (Fig.2) or horizontal shafts (Fig.3). The vertical arrangement requires smaller area and permits a deeper setting of the turbine with respect to tailwater elevation without locating the generator below the tail-water.

Generator costs for vertical units are higher than those for horizontal units because of the need for a larger thrust bearing. However, the savings on construction costs for medium and large units generally offset this equipment cost increase. 3 ~~ > 3 . The shaft arrangement is of vertical J for runner diameters above 100 cm in Chinese standard. From manufacturing considerations a horizontal one is usually economical for a relatively smaller diameter up to 84 cm. It has the advantage of providing easy access and the runner ● can be dismantled after removal of . . the conical draft tube. . . The runner consists of a band and a -. . crown joined by runner blades. Blade * profiles directly influence the energy > convert and the cavitation performance, therefore high . requirements for the accuracy of the blade shape and the smooth finish of the surface have to be met and the welding construction of the runner has i“ been widely adopted instead of the iron I I one. L The horizontal unit is mostly provided with three bearings, two of them for the generator and the other one for the turbine (see Fig.3). Nowadays a two bearing arrangement (Fig.4) as a simplification of three bearing layout is coming into vogue, especially for the unit up to 3000 kW.

The flywheel is mounted on the shaft in order to stabilize the unit in operation during load rejection.

The expansive joint is used to adjust the clearance of the turbine set during assembling and disassembling.

The spiral casing of the turbine surrounding the guide vanes may be made of cast iron for small-sized low heads, and cast steel for high heads and sheet steel for large-sized high heads. The concrete spiral casing is suitable for large-sized one with low heads.

The guide vane mechanism consists of guide vanes, level, link and regulating ring. Besides there is a breaking link or shear pin which is designed to tail on excessive load, and its adjustment is performed by means of a servomotor through action of regulating ring.

The linkage-mounted control unit is used in turbine series below 500 kW. For high head varieties e.g. HL1 10-WJ the outlet diameter of the runner is small, the control parts can be moved on to the side of the draft tube for mounting and dismounting simply. I

. Bearings are used to maintain alignment of the shaft and to take forces acting upon them. Rolling bearings find use only for the runner diameter less than 35 cm, but sliding ones for large units, above 42 cm in diameter.

As the Francis turbine is of reaction type, the water enters the runner under pressure. This calls for a sealing arrangement to avoid the leakage inside the clearance between the rotating runner and the stationary bottom ring or the head ring which may cause an appreciable amount specially at high heads. A comb configuration is often adopted on the enter of the band and crown by shrinking.

In order to reduce silt wear surfaces of the clearance between guide vanes and the bottom ring or the head cover are covered with replaceable auti-wear plates made of stainless steel.

A braking device is provided for the turbine with a plain bearing, either on the side surfaces or on the outer periphery of the flywheel. As the unit begins to shut down the rotating speed of the main shaft becomes lower and lower. When its speed reduces to about 30?40of the rated value, the device will be actuated to stop the movement of the shaft immediately, othetwise the bearing may be burst out at such low speed.

2. Axial-flow turbine

The future of the axial-flow turbine is that the water ,Z-e, flow passes through the runner in an axial ,. - direction with respect to the shaft. It is suitable for ~- El exploiting of low head and large ~ ‘!!/Y discharge.

The changes of the discharge and the optimum !~ . - . . ~ . . ---00s are..- -r MI la --, . hydraulic performance may be achieved by Fie.5 ~perioon of p~vl 1,~( regulating runner blades and/or guide vanes. runner per fore:. xe

Fig. 5 shows comparative efficiency curves depending on the discharge of various combination. The turbine with adjustable blades and adjustable guide vanes, so called , possesses a better efficiency curve over a wide range of operation, while the turbine with fixed blades and adjusted guide vanes (Propeller turbine) has a sharp efficiency drop at the part load range.

Because of simples construction and easy manufacture, the Propeller turbine is widely adopted in small-sized units. It covers the range of the runner diameter up to 1.4 m in Chinese turbine series. In order to overcome the shortage of the efficiency drop several units are always installed at single site.

The Kaplan turbine is suitable for the site with large changes in head and load. Its head ranges from 0.5 to 1.5 of the designed but the Propeller head from 0.9 to 1.1.

The main hydraulic components consists of a water supply casing, guide vanes, a runner and a draft tube. The following arrangements of the casing are used: open flume, pressure flume and concrete spiral casing. The open flume may be economical for a head up to 7 m and a runner diameter of \ 1.2 m. When the head is over 7 m the shaft length will become excessive causing / disadvantageous with regard to maintenance costs. In this case the pressure case is an alternative to the open flume. The concrete cast with a cross-sectional of rectangular is used for turbines with large sizes and is generally less mstly.

For the fixed blade configuration casting in one piece is common for the turbine with runner diameter less than 0.6 m and low heads. Cast steel is for higher heads. In recent years the blades of cast steel have been machined through a correct shape and profile in a pattern made prior to welding with the hub of the runner so as to improve the quality of blade-processing.

For the Kaplan turbine the shape of the runner chamber is usually cylindrical above the centerline of the motive shaft of blades and spherical below. On the contrary, for the Propeller turbine with small capacity below 500 kW an entire cylindrical chamber is adopted.

The space inside its head cover is so small that the water lubricated guide bearing with simple struction is almost used. In addition a double-skin filtering network on the bearing is supplied to filter out the impurity in water.

=-, --

F’: S.. -m,

FQ.7 Fig.6 ““

A simple inside regulation mechanism (Fig. 6) is normally equipped for Propeller turbines below 500 kW. There is no level, but a link being taken from a pin in the guide vane to the regulating ring, then to the servomotor by a vertical rod, the guide vane mechanism is actuated by a governor, electrical motor or manual. A complicated outside regulation mechanism is placed for large units (Fig. 7).

A Radial thrust bearing lubricated by oil and cooled by water is located on the upper end of the turbine shaft and supports the hydraulical thrust and weight of rotating components. * d 2 - The turbine shaft can be connected to the generator shaft by eithe~ a direct coupling d + or an increase through belt or gear so as to match a cheap generator with high speed.

As a precaution against lifting of the unit due to a A r upward hydraulic thrust of the runner when guide 8 + 1- vanes are suddenly closed, an emergency vacuum * break valve is fixed on the top of the head cover.

\ If water in the river is sandy an auti-waring ring is

4 equipped on the water passage of the bottom ring “. and the hand cover. . -. Fig.0 Coaparimon between . This small-sized Propeller turbine possessing a .TAT and fiplan -a position suction head is always located at positive a setting.

Fig. 8 shows a schematic drawing of Tubular axial turbine (TAT). The dotted line refer an axial-flow unit. Without the complicated spiral casing this construction of . TAT is simple in machining. The intake elbow has a straight geometrically defined shape while the discharge is axial after the elbow bend with guide vanes and its ● efficiency performance is similar to a axial-flow turbine with adjustable blades and fixed guide vanes. . . . 3. Pelton turbine . . . The water flows through the pentock and the . conduit pipe to the nozzle. Out of the nozzle its . pressure energy is transformed into kinetic one, a jet is formed and strikes the runner bucket and . hands over its energy to the runner, finally

. discharges to the tailwater channel. Pelton turbine (Fig.9) has a veryflat efficiency curve and may be effectively operated down to 20?40 rated load, therefore it is , suitable for high heads with heavily fluctuating flow rates.

A deflector is provided. During the emergency shut down, it will deflect the direction of the jet from the bucket to the case so as to avoid a runaway speed for the runner and a strong hydraulic hummer in the penstock.

The runner has to be installed above the highest tailwater level to permit operation at atmospheric pressure and any immersion will cause energy loss by padding. The requirement exacts an additional head loss for an impulse turbine not required by a reaction type of turbine.

The radial central splitter of the buckets divides the water jet and deflects it to both sides so that no axial thrust arises on the runner. In this case the thrust bearing is unnecessary.

The Pelton unit possesses few warning components, which can be protected, therefore it is preferable to other turbines in use of sand-laden water. 2 9

; The load regulation fora Pelton unit is carried out by increasing or decreasing the -i0 opening of the nozzle. A small brake nozzle opposed to the direction of rotation 2 should be equipped. When the turbine unit is shut down, it is opered to bring the > x unit quickly to rest, so the bearing pad will not be burnt away by no oil film in it. The , single-jet Pelton unit is listed up in the product series below 500 kW in China and 4 the two-nozzle Pelton unit is used as a standard size abroad (Fig. 10). 4 4 The following modes of regulation can be applied for Pelton turbines. Nozzle regulation is commonly considered. Double r—--’- . regulation with deflector regulation and nozzle regulation is employed for large-sized turbines.

● 4. \ Turgo turbine is another small-sized free-jet impulse / . turbine. The water from the penstock is transferred into . a high jet through the nozzle but a certain angle is formed between the center line of the nozzle and the rotational plane of the runner. Instead of striking 2710zzle turbine tangentially the center of the bucket and splitting into two as a Pelton turbine, the jet enters the runner at one side and leaves at the other (Fig. 11). Therefore a much bigger jet can be passed than that in a Pelton turbine.

It is suitable for large discharge and higher specific speed possessing an application area between the Pelton turbine and the France one:

Available head range 20-300 m

Capacity up to 2000 kW Fig.ll- T~ Z Specific speed n. =30-70

The inclined-jet turbine can be installed either vertically or horizontally. Its flow regulation is by means of the opening of the nozzle and a jet deflector makes the jet deflect away from buckets to prevent runaway of the turbine and the excessive pressure rise of the penstock is just the same as a Pelton turbine.

Because of the inclined jet the unit is subjected to an axial thrust.

Except the complicated bucket shape other components of the machine are simple in construction. Also the unit is easy to maintenance and reliable to operate and is wear-resisting from sandy water.

Two types of governors are used: the hydraulic type and mechanical-hydraulic type.

— _ ● 5. Cross-flow turbine ✏✌ . Banki tutiine (Fig. 12) is of impulse type. It is named cross-flow because the water ● physically crosses the runner twice, first from the outside towards the center” and then after crossing the open center from the inside outwards.

.

* ,

Fig. fox Iknki turbine

Q c for flankiIunnar divided into 2 part a

The most important property of this turbine is its flat efficiency curve over a wide range of flow. In order to obtain its more flat curve at high variation in flow the guide vane is divided generally in a proportion of 1:2. This means that at low flow only the small section of the guide vane is opened, with medium flow the 2/3 section is opened whereas with full flow both of them are opened.

From Fig. 13 you can see that efficiency even at 15?40of the maximum flow is higher, where the Francis turbine would, in fact, not produce any power.

The turbine is supplied with an intake transition piece between the penstock and the turbine. This is general round to fit the end of the penstock and formed into rectangular shape to be bolted to the turbine housing. Whole unit is completely assembled and mounted to a frame which is bolted the floor.

This type of turbine is suitable for heads from 2 to 170 m. No other type of turbine available today can cover such wide range of heads.

The low head turbine is usually equipped with a draft tube in order to utilize the drop between the turbine centerline elevation and the tailwater elevation. In this case an air inlet valve mounted on the top of the case is needed to control the vacuum inside the case.

The unit capacity of the Banki turbine can be increased by enlarging the unit width even to 2 m, therefore few varieties of runner diameters matching different length of the runners can suit large output range of the turbine up to 1000 kW. 3’ 4.

\

; \ For the runner with large width several intermediate clicks have to be welded and , , the rigidity will be strengthened. The water flow in its secondary action outwards will self-clear runner blades of leaves, grass or other matter which enter the runner. . The runaway speed of the unit is 1.8 times the rated speed. The turbine set is fitted ● with standard governor, speed increases and generator. * The cross-flow turbine is free from cavitation, but is liable to be worn away by excessive silt or sand particles in the water.

In addition to its low cost, the Banki-turbine has features of simplicity, reliability and petiormance combined with low cost civil work as well as little maintenance.

6. Bulb turbine

Straight-flow turbine is essentially classified as axial-flow turbine without a spiral casing and stay vanes. Its hydraulic efficiency is higher than that of Kaplan or Propeller turbine, and it is the same with the optimum unit discharge, optimum unit speed and specific speed.

The table 1 shows the comparison of the power house, among three types of turbines.

Unitcapacity(kVV) 3200 2300 3200 Units 3 4 3 Hmax(m) 4.5 4,6 5.25 Qmzx m3/sec 285 276 240 Lengthof powerhouse (m) 44 31,5 25 VVidth of power house (m) 72 43 24 Excavation depth (m) 16 13 12 Height of power house 18 8 6.5 Excavation volume (m96. 67000 18400 8500

This type of turbine is suitable for low head up to 20 m, the specific speed being 600-1000.

Bulb turbine (Fig.14) is always of horizontal. The generator is enclosed in a \ la n i water tight enclosure located in the center of the upstream water passage and the turbine runner is overhung without the supped of the draft tube.

The simplicity in the hydraulic conduit obviously accounts for the better performance water flow in bulb units features a nearly perfect axial symmetry from the inlet conduit to the draft tube outlet permitting a significant increase in specific speed and eticiency. The bulb turbine is suitable for large as well as medium sized units. If the runner diameter is decreased to less than 3 m the bulb diameter will be too small and hard to accommodate a generator in it.

Because of the low hear hydraulic consideration requires a low speed generator positioned inside a limiting bulb, the only method available to the generator is to increase its core length, but this will result in cooling and ventilating problem which becomes a main constraint for this type of turbine. In general, an auxiliary blower should be used to circulate the air over the active surfaces of the generator.

The bulb turbine can be connected either directly to a generator or through an increaser. Nevertheless, economic factor should be taken into consideration.

A protective device to prevent runaway speed should be equipped. It is normally set to start at 125% of normal speed.

Due to compact design the power house floor and height for the Bulb installations is minimized and maintenance time due to accessibility, however, may be longer than that for either the vertical type or the S-type turbine.

A large unit with a runner diameter of 5.5 m and unit capacity of 10 MW was successfully commissioned in 1984 in China.

Fig. 15 shows a split-flow tubular turbine. Its water passage between the intake and guide vanes is divided into two separate parallel tubes and the turbine shaft can be led to through an increaser upwards to a horizontal generator or through a 90 beveled gear upwards to a vertical generator. ‘he Fig.15 Sketch of the split-type advantage of the former is characterized by good accessibility, and the latter by a very compact design which minimizes the size and the cost of civil works.

This turbine is suitable for small output.

7. S-type turbine

S-type turbine (Fig. 16) is horizontal or shunt mounted unit with fixed or variable guide vanes and fixed or variable blades. The generator is located outside of water passage on the top of the draft tube. This turbine is used for exploiting sites with low head and small capacity. 4 fixed-blade S-type units each with a runner diameter of 2 m and unit capacity of 1250 kW under head of 7 m were commissioned in 1986 in China. Having advantages of compact arrangement and minimum excavation work, the S-type turbine is economically and characteristically better than the vertical Propeller turbine for rebuilding an old hydropower station. Its efficiency will be 1-2% higher than that of the vertical unit.

The turbine shaft is supported outside the draft tube in a plain bearing and connected through a flexible coupling to the shaft of the gear unit, which steps up the low turbine speed to a favorable generator speed.

With the drive of a synchronous generator a flywheel is required for increasing the inertia of rotating parts. The discharge ring surrounding the runner is horizontally split in the center of the shaft to inspect the runner. The turbine can be completely assembled in the workshop and transported to the site as a compact unit.

The S-type tutiine with fixed guide vanes should be equipped with a shutoff valve which possesses shutoff and startup functions.

The draft tube bent downwards in s-shape and brought by the runner shaft will influence the recovery of kinetic energy in it, so the efficiency will be about 1‘A less than that of the bulb turbine.

8. Rim turbine

A rim type of turbine (Fig. 17) is one in which the generator rotor is mounted on the periphery of the runner blades. This turbine has been developed by Escher-wyss and was named Strafe. About 75 units with capacitors from 1000 to 1900 kW and heads of 8-10 m were commissioned during 1940’s 1950’s and are still in proper operation now.

The sealing arrangement between the turbine casing and the rotating outer rim is a very important point of the Strafe. [t must be absolutely reliable to prevent any leakage to the generator. P~&lT

After new hydrostatic seal and hydrostatic bearing were developed, a large-sized turbine with unit capacity of 20000 kW has been operated in Canada since 1984. The rim type of turbine with adjustable blades becomes available. A unit of this type with unit capacity of 8300 kW was installed in Austria.

At beginning, the rim turbine was offered with partial closure guide vanes which required and upstream butterfly valve. After entire closure guide vanes have been designed and produced this valve can be omitted.

The rim turbine gives the unit various advantages:

“ No driving shaft. The hydraulic moment acting on the turbine is directly transmitted to the generator by its blades.

“ Compactness ‘, \\ .. ‘\\ \.\

■ Sufficient space on the periphery to accommodate the generator even for large output.

m Vary large natural inertia ensures stable running and damping of the power fluctuation.

9. Turbine characteristics

Each type of turbine possesses e% hydraulic characteristics different from one another. Fig. 18 shows efficiency 89 curves obtained at optimum unit

speed for various types of turbines. 69 /f/ / “ The best turbine having high and flat I / / efficiency is Pelton turbine 1 or u —. - Kaplan turbine 2. The characteristics .—. —-, ----- of Francis unit 3 is lower its curve is m i sharp at part loads. The Propeller / type 5 exhibits the most unfavorable characteristics. The performance of Fig.18 the Banki turbine 6 has lower efficiency but the curve is adequate flat. Curve 4 shows Tomma turbine.

Furthermore, the efficiency curve on the maximum unit discharge may be traced for individual type of turbine. With an increase in head above the optimum value a decrease in n’, takes place followed by a drop of efficiency.

The reduction of the head results in an increase n“,, the Kaplan turbine possesses a best performance, which efficiency remains high over a wide range of head variation.

The efficiency decreases rather rapidly with decline of the head. For the Francis, Pelton and Turgo turbine, the distinguishing features are their different applications at a hydropower station.

At a site where variation of the load and the head is likely to take place over a wide range it is expedient to use the Kaplan turbine with double control. On the contrary, operation at constant load makes it possible to use uncontrollable turbine with fixed guide vanes and fixed blades. :

● IL Standard Turbine Series in China

● ✌ 1. Symbols of turbine products . . The symbols of turbine products in China is usually made up of there parts as follows: ● .

& 4 rlm-—-clU--Cl m FirstPart Second Part ThirdPart

The first part denotes the types of turbines and runners. The second part denotes the arrangement of the main shaft and feeding conduit form and the Third part indicates the nominal diameter of runners or other required index. . . . The symbols of types of turbines:

. Francis HL ] KaDlan Zz Prooeller ZD Tubular (adjustable blades) GZ (fixed blades) GD I Pelton ICJI TUWO XJ Banki ST

Deriaz XL I

The symbols of main shaft arrangement:

Vertical shaft L Horizontal shall w

The symbols of feeding conduit:

Metal spiral casing J Concrete spiral casing H Open flume M Open flume with pressure My Tube type E

Cylindrical drum type G Bulb type P Siphon type x Single guide vane type D

2. Turbine series less than 500 kW

According to statistics in 1983 there were 73,100 power stations with unit capacity less than 500 kW in China. This means that we need a large quantity of small turbine products and small units have to be mass-produced and to adopt seriation and standardization in order to shorten the period of turbine design, to achieve good quality; to simplify the construction and finally to reduce costs.

The Chart of Turbine Series was set up in’ 1974, then a unified design ‘was completed n 1980 in 1980 for small turbines less than 500 kW. The series (Fig. 19) includes 4 types of turbine types, 8 types of runners and 32 varieties. ;::: i ,.:.:”.,;““:,::,:@*~~-~~~ .Y,:w:ewti@%...... !?%W!W .,:::::::- fi:.::.:;g$ag~stiindks;%?$$...... ,: ...... Francis HL11O w J 30,35,42,50,60 HL220 J 42 H1260 : J 25,30,35,42,50,60 Propeller ZD560 L My 40,60,80 ZD760 L M 40,60,80, 100, 120 ZD760 L My 100, 120 Pelton C22 w 4514.5,5515.5,5517,7019 TUQO XJ13 w 2517,3217,3219 XJ02 W 40/9, 40/11, 50/12.5

3. Turbine series within 500-10000 kW

The turbine series within 500- 10,000kW (Fig. 20) is being standardized as well. It includes 53 turbine varieties with 4 types of turbines and 19 types of runners. The water head ranges 3-450 m, and the flow from 0.26 to 205 m3/sec.

The typical types of turbines are as follows: Francis turbine (Fig. 3), Propeller turbine (Fig. 7), Pelton turbine (Fig. 9) and Tubular turbine (Fig. 16).

\ Francis IHL31O L J 230 HL260 w J 71,84 HL260 L J 100 HL240 L H 120, 140, 180,225 H1230 L J 200 HL220 L J 50,60, 71,84, 100, 120, 140 HUOO L J 100, 140 HL160 w J 50,60, 71,84, 100 HL120 L J 120 HL110 w J 60,71, 100 HL100 w J 65,71,88 Propeller ZD760 L H 180,200,250 I ZD560 L H 100, 120, 140, 180,250 Kaplan ZZ600 L H 330 ZZ400 L H 300 Pelton CJ22 w 70/1 X 7, 70/1 X 9, 92/1 X 11, 110/1 X 12.5, 115/2 xll.5 CJ20 w 115/1 x9 wTubular GDO03 w P 275 GZO03 w P 300 GZO05 w P 250 Ill. Turbine Selection

1. Basic data required for the preliminary design

1.1. Basic data of the power station

Development method of the river, annual run-off regulation of the reservoir.

General layout, hydrological, geological and topographical data.

Hmax, Hmin, H, Qmax, Q, installed capacity q,, water level and discharge relation curves of the upstream and downstream.

Water temperature, penstock, water quality, etc.

1.2. Data of the electric system

Load feature, annual load curve, typical daily load curve and function and location of the power station in the system.

1.3. Data of turbines

Chart of Turbine Series, Application Range of Turbines, general characteristic curves, catalogue, data supplied by the manufacturers and data on operations.

1.4. Condition of transportation and specification of installation.

2. Designing turbines based on general hill model cumes

Based on the max, head, etc, suitable turbine types can be found from the Chart of Turbine Series and main parameters on the hill curves of their model runners (Fig. 21).

Maximum unit flow Q’l M optimum unit speed n’lo Efficiency Cavitation inefficient qti

The procedure of designing turbine is as follows:

2.1. Calculate the runner diameter DI by means of the following formula:

N- D1 = / g.81.~M.Q\~.H~ where:

N= design output of the turbine, given by customers

H= adopt the design head instead

If the maximum head is adopted, the runner diameter will be minimum and the turbine is possible to generate the rated output only under maximum head condition. If the minimum head is adopted the runner diameter will be bigger and the investment will be increased. ?. 3

Generally, the design head is a little smaller than the average head, their relationship is as follows:

For run - off - river Hd = 0.9 Ha

For adjacent the dam Hd = 0.95 Ha

Q,l unit - flow Qi=&

4 For Francis turbines, there is a power limiting line existing in the hill curve of the model runner. It is not recommended to operate the turbines beyond this line -4 because of inefficient and unstable operation. Therefore, the unit flow on the limiting line or a slightly smaller Q’l~ should be selected.

For Kaplan turbines, the power limiting line is not plotted on the characteristic curve, usually an increase of Q’l~ during operation of the turbine is limited by cavitation conditions. At high values of Q’l~ differing considerably from the optimum value the cavitation coefficient rises rapidly. Therefore, in order to suit the operating . conditions of the particular power station, the maximum value Q’l~ is determined by cavitation - free conditions of operation. ~M - hydraulic efficiency of the model turbine.

The efficiency at the intersection point of the optimum unit speed and the power limiting line on the hill curve of the model are selected and listed in the table without modification.

Having obtained the above parameters we calculated the value of the diameter. The diameters of turbine runners have been standardized in China as follows: 25, 30, (40) 42,50,60,71, (80) 84, 100, 120, 140, 160, 180,200,225,250,275, 300 (cm).

The figures in the bracket are only used for axial-flow turbines.

Then, the calculated value is compared with the standard valves, and the nearest standard value is selected as the runner diameter.

2.2. Determine the speed of the turbine:

.=M!@ D1 where: D, = runner diameter selected H= the average head which enables the turbine to operate within efficient ranges for most of the time. If not, use the design head instead. n’q~= the optimum unit speed of the model

After calculating the value of the speed it should be compared with the synchronous speed (refer to the table). Finally, the nearest standard value is selected.

Pole number 2 3 4 5 6 7 8 9 10 12 14 ... rpm 1500 1000 750 600 500 428 375 333 300 250 214 ...

—. 2.3. Calculations for the modification of efficiency

Because the diameter of the prototype turbine is larger than that of the model and the prototype turbine operates at higher head, its efficiency will be higher’_too. Therefore, it is necessary to modify the eticiency according to the following formulas: a) For Francis turbines (H> 150 m):

Aq =1-(1-qM) ~~” b) For Francis tucbines (H< l&)m):

c) For axial - flow turbines: Aq =1-0.3(1-q~)-0.7( 1-q~) /~ & where: H~ = head of model turbine

DlM= runner diameter of model turbine The real value of the prototype turbine efficiency will be q = ?lM+ Aq

2.4. Calculation for the modification of unit speed

Ani-i.(= -0

When Ani~\M (E -’)maynotbemodified

2.5. Check the practical output of the turbine

Use new values of Q“l , n’, and their corresponding efficiency to obtain the output.

Q’t = Q’lM+ AQ’l n-l = n“tM+ n-t

2.6. Determine the suction head Hs

The turbine generator set should be installed at such a height that no cavitation should take place under any operating condition.

For this purpose, each type of turbines can only be selected for a special range of head and power variation. The suction head (Hs) should be calculated at the rated output as foiiows:

i-is <10- &(a+A@

Where: A = station aititude above sea ievei.

a = cavitation coefficient of the design point (Q’l and n“, ) on the hiii curve of the modei.

Aa = safe coefficient of a (see Fig. 22). Ylg.23S%uIof --$- for 4 /’ wriow typ98 of turbines > 2.7. Determine the setting (Hs) of the turbine (Fig. 23).

After the suction head (Hs) has been calculated, the setting of the turbine can be determined by the following formulas:

iis’=tis+ be/2 (m) for vertical Francis turbines

Hs’= Hs (m) for vertical axial - flow turbines

Hs’= HS - D1/2 (m) for horizontal reaction turbines

bo (m) the height of guide vanes

2.8. Plot the operating characteristic curve of the prototype turbine (Fig. 24)

With head (H) and output (N) as coordinates, the characteristic curves on which the q= const. and output limiting line are Plotted show the relation between q and Hs in operation, with these curves, the following technical and economic data can be obtained: average efficiency, long - term average output, investment and costs for unit power. Therefore, ~“ these data are useful for analyzing and comparing the ~~ prelimina~ design and for conducting the operation of c the power station in future.

3. Selection of turbines by the chart of turbine El!!l series and the amangement of application for “ L . — hydraulic turbines am) mu. 24 Opemtion curve or Assuming that the net head H(m), discharge Q (m3/see) prototypeturbinm and output N)kW) are given.

The turbine type may be chosen from the Chart of the Turbine Series.

The turbine product can be determined in the program of application range for this turbine (Fig. 25) in which a lot of parallelograms formed by parallel lines and vertical lines. The corresponding synchronous speeds of the generator are shown in the chart, the nominal diameters of the runners appear on the right hand column and the maximum outputs generated are shown on the left hand column.

The parallelogram can be found by tracing the intersection points of the lines for heads(H) and output of the unit(N) and then the runner diameter (Dl) and the turbine speed (n) can then be found. The suction head at sea level (hs) can be obtained in a figure attached. For every increase of 90 m above sea level, about 0.1 m should be subtracted (-V/900). If the turbine is to be installed above sea level. The practical suction head Hs can be chosen by the following formula:

Hs-hs-&

There is only one curve hs = f(H) in Fig. 26 for Francis turbines. But, for Kaplan turbines the cavitation coefficients vary greatly with change of head or output so . there should be two curves, one for the maximum discharge and the other for the . minimum. It is possible to calculate the suction head by a proportion method with respect to the discharge. *,,

-1 . For each turbine product, the specifications and matching auxiliary equipment have already been listed in the table (see Table 2). After the type and dimension of the . . turbine have been determined, suitable generator, governor and inlet valve can be . . chosen from the table. . In China, the above method is generally used in the selection of small turbine , generator set less than 500 kV.

.- 4’G

Fig.26 hs =- f(H) taa aa

*L...... Iiead it(in) 8- ,*” iaNEEiEll- * Fig.25 -p of application range for HL220 TABLE 2

- - .,..,,...... ~’f%ir ~W* ~ f?b&$fi ${&p; j$~m - 11.6 0.515 750 40 14.0 0.584 750 55 18.0 0.603 1000 75 21.0 0.693 1000 100 125 HU60VW-35 24.0 0.767 1000 1941 X 6 12.0 0.519 720 40 14.5 0.590 720 55 17.8 0.605 900 75 21.0 0.703 900 100 24.0 0.790 900 125 14.2 0.783 750 75 16.5 0.877 750 100 18.7 0.980 750 125 50 21.8 1.080 750 160 26.0 1.140 750 200 26.0 1.050 1000 200 14.0 0.82 720 75 HL260WT-42 )941 X 6 600 16.5 0.90 720 100 19.0 0.99 720 125 22.6 1.02 900 160 26.0 1.10 900 200 13.0 1.19 600 125 17.2 1.34 600 160 19.8 1.46 600 200

4. Design of impulse turbine

Supposing the head and the installed capacity are known:

Design head H = 190 m

Design output N = 350 kW

Only the Peiton turbine can be considered in the diagram of application range for turbine series, the turbine size and other parameters may be determined as follows:

4.1. The runner discharge can be obtained from the following equation ~= N 350 =0.229(m3/ see) 9.81XHTI-9.81X 190X0.82

In which the full load efficiency is about 80- 83°A for small sized Pelton turbine (here we taken 82%). ,’

4.2. Diameter of the jet

It can be written as ~=l’jm;l’jm=’o’(mm)” Where z number of nozzles

In general 1-2 nozzles are suitable for horizontal units,

2 nozzles for small vertical units

and 4-6 for large.

Here we take 1 nozzle.

Standardized jet diameters for small Pelton turbines areas follows: 4.5, 5.5, 7, 9, 11, 12.5 and 14 (cm).

Amount them the value nearest to the calculating result is 70 mm, we should take it as designing value.

4.3. Ditch diameter of the runner (Dl)

According to given head of 190 m the suitable (Dl / DO)and other parameters can be checked our in the following table 3.

, 200-400 CJ22 18-20 10 0.034 40 400-600 CJ20 20-22 12.8 0.027 39 600-800 22-24 15.6 0.022 39

We obtain D, / DO=8, CJ22, Z=16-18, Q’l = 0.45, n’, =40

The ditch diameter of the runner will be D, = 8 x do = 8 x 7 =56 (cm)

In comparison with standard values of ditch diameters 45, 55, 70, 80, 100, 110, 125, 140 (cm). We select the nearest one D1 = 55(cm).

The turbine products will be CJ22 - W - 55/1 x 7

4.4. Synchronous speed of the turbine

n=nl ‘=40gD, = 1002.5(pm) take standard generator speed 1000 rpm.

4.5. Design discharge

Q= (~) 272@= (~)’qlx~ = 0.2257(m3/see)

4.6. Turbine output

N = 9.81 X H.Q.q = 9.81 X 190X 0.2257X 0.82= 345 (kW) I

3 3 5. Some problems on selecting turbine 3 ~ 5.1. Determine the number of turbine units

T With the same design parameters: installed capacity (N) and design lead “(H), ; various number of turbine units can be selected. 3 With different selection of the number of units, the diameter and speed even the type of the turbine will be different, which further affects the investment, efficiency, operation and equipment supply efficiency, operation and equipment supply. ● The more the units are installed at a power station, the smaller the unit capacity of .. each unit will be. The smaller the runner diameter, the lower the efficiency will be. For turbines operating at peak load more power can be generated by using more

. units when the load changes (Fig. 27) and it is evident that too many units are . inefficient. / Generally speaking, the length of the power house depends on the 3 number of units to be installed. ~RW ‘ Z For a power station of low head, it ~ ●-cl- wsch-. b- _bi depends on the width of spiral —Oa. t$- tiu ~ 011 “tt. case and for a power station of high head it depends on the mg. 27 Rehtion curve of the’n=~e;+ dimension of generator as well. All of turbines an.i efficiency of them are related to the diameter of the runner. The more the units, the higher the power house and draft tube and the deeper the excavation will be.

The cost per kW will be expensive as small units are adopted. With the increase of the number of units, more auxiliary equipment, inlet valve, generator and accessories will be needed except the capability of the crane.

The more the units are, the more flexible the operation is. But, the number of operations and probability of fault will be increased. During selection, the aforementioned items must be taken into consideration.

According to he experience gained in China, the following rules apply:

2-4 units for small stations 2 units for Kaplan or Pelton turbines 3-4 units for Propeller turbines

5.2. Comparing types of turbines

There are two or more types of turbines in the overlapping area of the Chart of the Turbine Series (Fig. 28). It means that we can select alternative schemes for the same hydraulic parameters (unit installed capacity and the design head) and it is advisable to list them all up, and find out their main parameters (including efficiency, speed, diameter ●

and suction head). Then, compare their emnomic indices, for example, the average annual electricity generation, the per kW investment and the annual operating cost. These will determine the most efficient scheme.

According to he operating methods the cavitation conditions and operating stability should be analyzed. Besides, equipment delivery, transportation, assembly and civil , engineering need to be mnsidered as well. After comprehensive comparisons a . suitable scheme can be selected. Iv. Hydraulic Turbine Testing

Hydraulic turbine testing includes both prototype turbine tests at the hydropower plants, and model turbine testing in hydraulic turbine laboratories. The former is carried out under actual operating conditions, but it is more mstly and requires a longer testing period. Also because of limitations at the power plant, many parameters cannot be varied over a wide range, therefore, it is impossible to obtain a complete test characteristic.

The latter, on the contrary, has more advantages. A reduced scale model turbine is installed at the test stand in the laboratory. Operation parameters (n, Q) are very easily changed over wide range during the test, so that a complete hill chart of the turbine can be plotted up in a short time.

The model test can be divided into two parts, namely, efficiency test at the performance test stand and cavitation test at the cavitation test stand.

1. Efficiency test

Fig. 29 shows the scheme of a performance test stand used for testing reaction turbines.

Water is supplied by an adjustable flow pump from the reservoir. The water level in the upper tank is kept constant by a weir that serves as a spillway which discharges the overflow directly back to the reservoir. When the guide vanes of the turbine are open, water flows l. Upper tenk 9. L4wer t- 2.screen 10.Spillway device through the model 3. Spillwaydevice 11.SCreen ● passage, transmitting 4.He~ meter 12. Flow otor 5.Dynamometer 13. now muurlag Weti energy from the water to 7.Hodel turbina 14.Re8e~or the model turbine and d. Draft tube 15. suPPIY PJ=P returns to the lower tank where the water level is also kept constant by a spillway weir, or in same cases by a regulating guide vane device. Water then goes over a measurement weir and finally back to the reservoir. Turbine tests are carried out over a wide rangesat different openings (s)of guide vanes andlor different blade positions (q). The following parameters are measured for each test point under steady - state conditions.

The head (H) is usually measured by liquid column manometers, readings are taken directly from the scale of the manometers.

Measurements of discharge (Q) can be cacried out by means of a rectangular calibrated weir on the flow measurement canal. A reading is taken of the height of water over the top of the weir (h), the flow is determined by reference to he calibration curve Q = f(h).

A dynamometer is available for measuring output power. The torque is determined from the measured balance weight applied at the end of the arm.

The speed of rotation of the turbine (n) is recorded by a digital electronic counter. Impulses are transmitted by an electromagnetic vibration pickup fitted on the shaft of the turbine.

The model turbines to be tested may have runner diameters from 250 to 500 mm.

Great care must be taken with measurement of the various parameters. The total error of the testing procedure depends on the accuracy of each individual measurement.

2. Cavitation test

Fig. 30 shows the schematic of a cavitation test stand which is a Exhanatiag vacum out closed circuit designed ..— for testing various types -lwI 1 !. of reaction turbines. II h!Jq Y-i -I-H-+’ I Water is supplied by a 11.1 circulating pumps, and first enters the stilling tank, and by way of the . pipelines up to the high I pressure tank, from where it enters the Ill model turbine. After ///////// //&, -,--- v giving up its hydraulic Fig 30 Sohemo of cavitation teat stand energy, water leaves via l.supply-p 5.W4 turb- 2.stllliag teak 6.~wtria ~*r the tailwater tank and ~.Vmturimter 7.Lo-r preomxe ** finally returns to the inlet 4.Hi# preanura tank 8. ..?!ancmeter of the pumps.

The head (H) across the turbine is usually measured by mercury column manometers, whose readings can be read directly, or by transducers. >..

) The flow (Q) in the test circuit is measured by a venturimeter. The quantity of flow is found by checking the calibration curve Q = f(h) from manometer readings.

The rotational speed (n) of the model is meastired by the same kind of instrument used in performance tests.

By means of a vacuum pump connected to the lower pressure tank, the suction head (Hs) can be varied over a wide limit and extreme cavitation conditions can be studies.

The stilling tank is used to provide for redissolving of air back into the water in order to keep the air content constant.

This stand is equipped with two supply pumps which can be operated either in ,,, ––. –– —...— parallel or m series. This arrangement is able to select test heads to simulate real operating conditions. Regulation of head is done by accurate control of the rational speed of the pump.

3. Test curves

During testing under steady - state conditions, the following parameters: head (H), discharge (Q), rotational speed (n), torque (M) and suction head (Hs) are measured simultaneously and are entered in the following table:

Turbine Efficiency Test 1 Turbine type Runner position Guide vane opening No. Head (H) Speed of Torque Discharge Suction Unit Unit Efficiency rotation(n) (M) (Q) head speed discharge (%) (Hs) (n’,) (Q”,)

Values of unit speed, unit discharge and efficiency have to be calculated before a curve is drawn, such as:

Qi=&

where: D1 - diameter of runner K - a constant

The universal performance curve (hill chart) is drawn by plotting constant q values on cx= const and q = const (when applied) lines on the n“,- Q’l coordinates {Fig. 31).

., Pig. jl After the performance test is completed, a number of operating position on the hill curve will be selected for cavitation testing. The cavitation coefficient (a) is defined as follows:

~ = Hu-Hv-Hs H where: Ha = Atmospheric pressure head

● Hv = pressure head of saturated water vapor

Hs = suction head

For each operating point, the suction head (Hs) is increased by creating vacuum in the lower pressure tank with vacuum pumps. As the cavitation coefficient (a) is progressively reduced, a cavitation break point is found from the q =fla), ~i =flcr), ni =fla) curves. This point is considered to be the critical cavitation coefficient. The a = cost lines are plotted on the hill model curve (See Fig. 47).

If a computer is adopted for calculation, all the transducer output of torque, tachometer discharge and suction head, etc first will be sent to the processing equipment for conversion into digital display and then will be intetiaced with the computer for the required data processing.

v. Speed Regulating Device

The speed regulating device and excitation system are two main auxiliary equipment for hydropower stations.

A turbine generator set functions as energy converter. It converts water energy into electrical energy. The electricity generated must be good quality for user. This means it needs to keep the frequency and voltage of the set constant under any variation of the electrical load.

If the set suddenly removes either water power input or electrical load output, the speed of the turbine will change to its original value. in order to bring the speed back to its normal speed, the governing device should control hydropower input by the moving of the discharge-regulating mechanism or mntrol generating power output by increasing or decreasing the consumer load. A governor is used for the former, while the electronic load controller for the latter.

For a turbine set under isolated operation the governor plays a pole of automatically regulating the speed of the set in a way to keep the frequency constant, but a set with small capacity paralleling in a network has not a capability of regulating frequency of the network. In this case the governor is actuated as a load regulator.

There are two main types of governors, viz: mechanical-hydraulic and electro-h ydrauiic. Usually the latter is adopted for large-sized turbines. The mechanical-hydraulic one is simple and cheap suitable for small turbines. Here we will introduce this type of governor only. 1. Governor

3 1.1. Symbols of governor The symbols of small-sized governors in China are usually made up of 2 partsl as follows: 3

[ 1 I

The first part denotes the type of governor, %, . 1-r Flow-through type of mechanical-hydraulic governor Yr Mechanical hydraulic governor with oil pressure tank YDT Electro-hydraulic governor

The second part indicates its working capacity. For example, lT-75 means the . . flow-through type of governor with wo~ing capacity of 75 kg.m. 1.2. The composition and function of governor

A governor generally consists of the following parts (see Fig.32): Speed or frequency sensor, Amplifier, Feedback system, Actuator, speed adjusting mechanism and safeguard and oil supply device.

Besides the function of speed regulation the governor also can perform:

9 Normally starting or stopping manually or automatically

● Increasing or decreasing load

m Paralleling

■ Emergency stopping When mnnected to the network it can automatically pursue the distribution of the load among turbines operating in the line.

1.3. Small series and main parameters of governors

Its series and main parameters are as follows:

1.4. Choice of governor

Generally the type of governor selected is determined by the wo~ing capacity of its servomotor. Preliminary choice can be made by following empirical formulas: a) For a reaction turbine

W= KQJ=kg.m b) For an impulse turbine the capacity of its servomotor consists of two parts: the capacity of the deflector and the capacity of the nozzles.

W= O.11x1 0-3xZog;do3xHmax+Zo do+ ‘O~Mm- kg.m ( ) where: D, = Runner diameter (m)

Q= Maximum discharge (m3/see)

K= 20-25 constant

M-= Maximum head (m)

do= Jet diameter with rated output (cm)

Zo = The member of nozzles or deflectors

2. Electronic load controller

In order to economically exploit electrical energy out of micro hydropower stations an electronic load controller has been designed.

The block diagram of a stepless ELC is shown in Fig. 33.

Due to economical reason a small turbine in the micro site does not match a discharge-regulating mechanism and operates under constant discharge. Therefore it is unnecessary to install a governor, but an ELC. Fig. 34 shows the connecting of 3

an ELC to a turbine generator set. There are two loads connected, the main load and the ballast load. The main load is the user load consisting of lightning and power supply of motors etc. It is connected across the alternator in usual way. The ballast load is a separate load which consists of water beating and cooking. It Is a fixed dump load capable of absorbing the maximum power that the turbine can produce. The power to it can be controlled and is variable from naught to full power.

Tutiine generator ELC MainLoad set I Ballast load I Fig. 34

The speed of the tucbine generator set is kept constant by sensing the frequency of the generator output voltage and diverting a proportion of the output according to the level of the main load, so as to keep the frequency at the required value. This diverted output goes to the ballast load and is varied steplessly or steeply through thyristors according to changes in the main load demand. The response of ELC frequency is very rapid in about 0.1 -0.2 second, therefore, such governing system is much more precise and responsive than that with a governor. It is also proved to be very reliable and very simple to install and operate.

A further advantage of this method of control is that, the turbine adopted can be largely simplified. Also, because of no sudden change of flow, there is no pressure rise in the penstock so the strain of the penstock will be minimized. These factors further reduce the cost of the installation.

The load controller is mainly adopted in an isolated run-of-the-river power station with installed capacity of 100-200 kW possessing abundant water resource.

Recognizing the importance of ELC for SHP in Asia-Pacific region RN-SHP proposed a project for making use of ELC in the RN-SHP work programme in 1964. According to this an ELC demonstration site with capacity of 60 kW was commissioned in China last year and two others will be operated separately in Nepal and Malaysia in the coming year.

The main features of ELC are as follows:

cheep in cost; its price is half less than that of a governor.

light in weight; a 60 kW ELC weighs about 50450 kg. It is easy to carry to the site.

combinated-type; its electronic components are available on the market.

minimum field adjustment requirement.

less maintenance work.

—. 3. Positioner

A local network generally includes a few hydraulic and thermal power stations. For each station several sets are installed, some are big but most of them “are mmparatively small. For the small turbine generator set it is unnecessary to match a governor, may be a positioner is enough. The positioner is different from the governor. It can not monitor the speed deviation of the turbine and automatically regulate the output of the set. Therefore the function of the positioner only limits:

“ Normally starting and stopping manually or automatically

= Paralleling and operating under a given output

‘ Emergency stopping

There are two types of positioners: Electro-motor and mechanical-hydraulic.

In recent years the mechanical-hydraulic positioner has been developed and applicated in China. Its control system is the same as a governor which is mnverted at hydraulic-manual operation but rather simple.

Its main characteristic of the series varieties is: a) capacity range: 35-3000 kg.m b) closing time: 2 second

Without frequency sensor and amplifier the positioner construction is quite simple, therefore it possess such advances: a) cheap in cost b) easy in maintenance c) safe in operation.

. 4 . .