CHAPTER 6 DESIGN FOR MECHANICAL AND ELECTRICAL STRUCTURES

Transcription

1 CHAPTER 6 DESIGN FOR MECHANICAL AND ELECTRICAL STRUCTURES 6.1 Fundamental Structure of Equipment for Power Plant The fundamental equipment and facilities are briefly shown above and the details of each kind of equipment and facilities are explained in each clause after clause 6.2. However, the summary of micro-hydro power generating equipment for rural electrification is shown hereinafter for easy and quick reference. More details shall continue in the following clause from 6.2. Summary of Micro-hydro Power Generating Machinery for Rural Electrification in Indonesia 1. Fundamental Conditions The following conditions are required and essential for rural electrification in Indonesia. 1) Stable operation for long term 2) Easy operation by semi-skilled operator(s) or villager(s) 3) Local made machines in Indonesia for easy future maintenance and repair (except small parts) 4) Cheaper cost of equipment including installation 5) Enough and acceptable technical guarantees of machinery with reliable test data and supply records 2. Recommendation According to the above conditions and the survey results on development of micro-hydro power plant for rural electrification in Indonesia, the following two types of hydropower generating machine only are recommended by JICA Survey Team at present stage in Indonesia. 1) Synchronous generator with cross flow type turbine with dummy load and controller (ELC) 2) Asynchronous generator (induction motor with capacitors) with reverse pump type turbine with dummy load and controller (IGC)

2 Description Merits & Demerits Merits Table Recommended Micro-hydro Power Generating Equipment Synchronous Generator with Cross Flow type Turbine *Very reliable power source with stable frequency & voltage for independent network. *Machine suitable to any actual site condition can be designed and manufactured. Asynchronous Generator with Re ve rse Pump type Turbine (PAT) *Lower cost if a pump with motor suitable for site design condition is found. *Construct ion of machine is simple. Demerits *A little higher cost than PAT *Difficulty to select a suit able pump wit h motor at market *No control of voltage * Short life time of capacitors for this system Te chni cal aspect Net head H n 4 50 m 4-20 m Water flow (discharge) Turbine output at turbine shaft Power transmitter Dummy load type governor Generator output at generator terminal Q P t m 3 /s (Discharge is a little variable) kw P t =0.98 x H n x Q x η t (η t = 0.7) Belt coupling for speed matching between turbine and generator η m : Efficiency of transmitter ELC controller with thyristor P g kw P g = P t x η g x η m (η g = 0.88, η m =0.97) (coupled with transmitter) P kva P kva > P g /0.8 (PF= 0.8) The generator with rated output of more than P g /0.8 shall be selected m 3 /s (discharge shall be kept always constant ) 2 7 kw P t =0.98 x H n x Q x η p (η p = η t =0.65) As pump efficiency (η p ) is too much variable due to change of discharge, the pump with induction motor of nearly same head and same discharge shall be selected. Direct coupled without transmitter IGC controller with transistor kw P g = P t x η g (η g = 0.75) Rated output of The induction motor originally generator (kva) to be applied coupled with the pump shall be used as induction generator by adding separate capacitors Rotation speed 1500 rpm rpm due to speed of induction motor as generator Voltage 380/220V, star connection St able wit h AVR on generator 380/220V, star connection Voltage control cannot be made without AVR Frequency 50 Hz, Stable Hz Not so stable Dummy P d Air heat ers (Pd = P g x SF), SF=1.3 Air heat ers (Pd = P g x SF), SF=1.3 Inlet valve Butterfly valve (It is not provided for cost saving sometimes, but it s better to be provided for complete stop of turbine) Same as left, but it is neglected in case of small capacity. Note: η t, η m, η g and SF are fixed only for brief checking. In case of detail design, it is recommended to check the efficiency of each machine and facility

3 The following equipment and facilities are to be required as fundamental structure for the power plant, details of which are shown in Table Equipment & Facility Purpose & Function 1. Inlet valve: To control the stop or supply of water to turbine from penstock. 2. Water t urbine: To change the energy of wat er to t he rotat ing power. 3. Governor of turbine: To control the speed and output of turbine 4. Power transmission facility: To transmit the rotation power of turbine to generator. 5. Generator: To generate the electricity from turbine or its transmitter 6. Control and protection panel: To control and protect the above facilities for safe operation 7. Switchgear (with transformer): To control on/off operation of electric power and step-up the voltage of transmission lines (if required) Note: The above items 3, 6 & 7 may sometimes be combined in one panel as a sort of equipment in case of micro power plant. Table Composition of Fundamental Equipment for Hydraulic Power Station Equipment Type Control Method Inlet valve Butterfly valve Bi-plane butterfly valve Sluice valve Needle valve Hand operated type Motor operated type Counter weight type Turbine Power transmission facility (Speed increaser) Generator Control & Protection panels Power Transformer Cross flow Reverse Pump H-shaft Pelton Turgo-Pelton Propeller H-shaft Francis Tubular Fixed coupling Flexible coupling Belt coupling Gear coupling Synchronous Induction Self-excitation Induction Wall mounted Self stand open type Self stand sealed type Oil immersed, self cooling, single or 3-phase, pole transformer Dummy load type Oil pressure type Motor operated type Manual operated type Non-controlled type Manual AVR APFR Control switches, Main switches IC panels Relays

4 Figure (a) Discharge Q [l/s] Applicable of Crossflow and PAT at Turbine Ne t Head (m) kw 3 kw 7 kw 6 kw 5 kw 4 kw Discharge (l/s) Figure (b) Applicable limit of PAT at Turbine Shaft (in Indonesia at present stage)

5 6.2 Turbine (Water turbine) Type and Output of Water Turbine Water turbines are mainly classified into two types with some additional classification as follows: 1 Impulse turbine Pelton turbine Crossflow turbine Turgo-impluse turbine 2 Reaction turbine Francis turbine Propeller turbine Kaplan turbine Diagonal mixed flow Tubular turbine Straight flow turbine (package type) Note: 1) Impulse turbine: Turbine construction that rotates the runner by the impulse of a water jet having the velocity head which has been converted from the pressure head at the time of jetting from the nozzle. 2) Reaction turbine: Turbine construction that rotates the runner by the pressure head of flow. Shaft arrangement: The arrangement of turbines will be also classified into two types, i.e. horizontal shaft (H-shaft) and vertical shaft (V-shaft) Referring to the required output, available net head and water flow (discharge), the following types of turbine may be applicable for micro or small hydraulic power plant in rural electrification. (1) Horizontal Pelton turbine (2) Horizontal Francis turbine (3) Cross flow turbine (4) Tubular turbine S-type tubular turbine Vertical tubular turbine Runner rotor integrated turbine Vertical propeller turbine Horizontal propeller turbine

6 (5) Turgo impulse turbine (6) Reverse pump turbine Vertical propeller type Horizontal propeller type Submerged pump type The output of turbine is calculated with following formula: P max = 9.8 x He x Q max x η t P max : Maximum output (kw) He : Net head (m) Q max : Maximum discharge (m 3 /s) η t : Maximum turbine efficiency (%) Please refer to chapter The brief characteristics, explanation and drawing of each type are shown in Table The applicable range of each type of turbine is shown in Figure Referring to this table and figure, the customer can select the type of turbine, which is most suitable to the actual site condition including the total cost of civil work and equipment. At present, however, it is recommended to apply cross flow turbine, which is designed and manufactured in Indonesia, because the proper design of cross flow turbine can be achieved by applying available model test data and the cost is comparably low. The reverse pump may also be used as reverse pump turbine by reversing the direction of rotation, if the characteristics of water pump, which is available in market, is matched almost strictly to those of the turbine required from the site condition (head, water discharge, output, efficiency, rotation speed etc.). However, as the site condition of each power plant is not always the same and the matching of characteristics of pump and proposed turbine is difficult, the selection of standard pump for turbine shall be made carefully and circumspectly. In case the characteristics are well matched between pump and turbine, the application of reverse pump turbine is recommended and the cost of such machine will be cheaper. In future the other types of turbine will be selected widely because other type turbines may also be manufactured with proper design and fabrication ability in Indonesia in the near future

7 Figure Applicable Type (Selection) of Turbines

8 6.2.2 Specific Speed and Rotational Speed of Turbine The specific speed is the ratio between the rotational speed of two runners geometrically similar to each other, which derived from the conditions of the laws of similarity, and specific speed of similar runners in a group by the rotational speed obtained when one runner has effective head H = 1m and output P = 1kW. It may be understood that the specific speed is a numerical value expressing the classification of runners correlated by three factors of effective head, turbine output and rotational speed as follows: Ns = (N x P 1/2 )/ H 5/4 N = (Ns x H 5/4 )/ P 1/2 Where, Ns; Specific speed (m-kw) N; Rotational speed of turbine (rpm) P; Output of turbine (kw) = 9.8 x Q x H x η H; Effective head (m) Q; Discharge (m 3 /s) η ; Maximum efficiency (%, but a decimal is used in calculations) η = 82 % for Pelton turbine η = 84 % for Francis turbine η = 77 % for cross flow turbine* η = 84 % for S-type tubular turbine Note: * 70% should be applied for cross flow type turbines in Indonesia at present because the efficiency of present turbines in Indonesia is not so high due to fabrication quality. The specific speed of each turbine is specified and ranged according to the construction of each type on the basis of experiments and actual proven examples. The limitation of specific speed of turbine (Ns-max) can be checked in the following formula. Pelton turbine: Ns-max 85.49H Cross flow turbine: Ns-max 650H -0.5 Francis turbine: Ns-max (20000/(H+20))+30 Horizontal Francis turbine: Ns-max 3200H -2/3 Propeller turbine: Ns-max (20000/(H+20))+50 Tubular turbine Ns-max (20000/(H+16)) The range of specific speed of turbine is also shown in Figure

9 0 Specific speed (m-kw) Pelton turbine 1 2 Ns Francis turbine 60 Ns 300 Cross flow turbine 40 Ns 200 Propeller turbine 250 Ns 1000 Figure Range of specific speed by turbine type

10 Table Kinds and Characteristics for each Type of Water Turbine page

11 Table Kinds and Characteristics for each Type of Water Turbine page

12 6.2.3 Design of Cross Flow Turbine Brief design of cross flow turbines T-13 and T-14, which are designed and manufactured in Indonesia according to the proper design data, is shown hereunder. The detailed design shall be referred to from the manufacturer s design sheet. The design shall be conducted in the following procedure: Basic data of T-13 and 14 are available from the model test. Diameter of turbine: 300mm No. of runner blades: 28nos. Unit speed: 133 rpm 1 To get the basic data for rated water flow (m 3 /s), elevations (m) of water level at forebay and turbine center (or tailrace water if designed as special case) from civil design. 2 To calculate net head from gross head by deducting head loss of penstock (friction and turbulence). 3 To calculate the net hydraulic power and turbine shaft output from water flow, net head and turbine efficiency. 4 To calculate width of turbine runner according to manufacturer s recommendation. 5 To calculate the mechanical power to generator from efficiency of power transmitter (speed increaser) 6 To calculate rated electrical output of generator (kw) Maximum output of electricity 7 To calculate the rotational speed of turbine from specific speed, turbine shaft output (Item 3) and net head. 8 To select suitable generator available at market and its output (kva), frequency, voltage, power factor and rotational speed (frequency), referring to catalogue of generator manufacturer. 9 To calculate the ratio of rated rotational speed of turbine and generator. 10 To select the width and length of belt referring to belt manufacturer s recommendation. 11 To calculate the capacity of dummy load and suitable ELC (Electronic Load Controller) or IGC(Induction Generator Control) in case of induction generator. 12 To calculate the diameters of pulley of turbine and generator. For detailed design, refer to Design Manual for Cross Flow type Turbine attached hereinafter

13 6.2.4 Design of Reverse Pump Type Turbine (Pump As Turbine) As a water pump is to be used as turbine by reversing rotation of pump, the selection of type of pump is very important. 1 To calculate and get the effective head (net head), water flow (discharge), and net hydraulic power using the same method as item 1, 2 and 3 of the above cross flow turbine in To check a suitable pump is available in the market, considering the maximum efficiency point of pump, rotation speed of motor (generator: 2, 4 or 6 poles) because the direct coupling between turbine and generator is usually adopted for this kind of turbine. See Table for the rotation speed. In case of induction generator, the speed of turbine shall be a little higher (i.e. 2-5 %) than that of generator at rated frequency. (1,550 rpm from 1,500 rpm) 3 To select and finalize the pump as turbine, referring to maximum efficiency point of pump, applicable efficiency for actual output of turbine shaft because the range of high efficiency point of pump is very narrow. 4 See the Design Manual for Reverse Pump Turbine for the selection method

14 6.3 Generator Type of Generator Two kinds of generator can be adopted for generating the electric power from energy of water turbine. 1. Fundamental classification of AC generator (DC generator is not used usually for power plant) (1) Synchronous generator Independent exciter of rotor is provided for each unit Applicable for both independent and existing power network (2) Induction generator No exciter of rotor is provided (squirrel cage type) (Asynchronous) Usually applicable for network with other power source. Sometimes applicable for independent network with additional capacitors for less than 25 kw but not so recommendable for independent network due to difficulty of voltage control and lifetime of capacitors except cost saving. Shaft arrangement Either vertical shaft or horizontal shaft is applied to both type of above generators. (Mainly horizontal high-speed type in case of micro/small plant except reverse pump turbine) 2. Another classification is also applied to AC generators as follows; 1) Three-phase generator Star (λ) connection For 3 phase 4 wire network Delta(Δ) connection For single phase 2 wire network 2) Single-phase generator This type is not used in power network system because it is difficult to purchase the generator with capacity of more than 2kW in market. In this case three-phase generator with delta connection is applied as shown above

15 The winding connections of generator (Star and Delta) are shown in Figure as follows R R each winding Star connection S T Star connection S T Figure Connection Diagram of Generator The characteristic (advantage & disadvantage) of both type generators is shown in Table Table Comparison of Synchronous Generator and Induction Generator I. Advantage of Synchronous generator Item Synchronous generator Induction generator Independent operation Independent operation is possible No independent operation is possible since excitation from other system is required Power factor adjustment Operation at desired power factor in response load factor is possible Operation power factor is governed by generator output and cannot be adjustable Excitation current DC exciter is employed. The lagging current is taken as the exciting current from the system so that the power factor of the syst em decreases. The exciting current increases in low speed machines. Voltage and frequency adjustment Synchronizing current Adjustment is possible as desired in independent operation Transient current and voltage drop in t he syst em are small since the paralleling is made after synchronization. Voltage and frequency adjustment is not possible. The generator is governed by the voltage and frequency of the system. Connection to the system to be made by forced paralleling by which a large current is created, resulting in a voltage drop in the system

16 II. Advantage of Induction generator Item Synchronous generator Induction generator Construction The rotor has exciting winding The rotor is the same as a outside the damper winding synchronous generator but the which is equivalent to the bars rotor is of the squirrel cage type. of squirrel-cage of induction Thus, the construction is simple generator. This is more and sturdy. It can easily complicated correspond to operation under adverse conditions and is the best suited for small or medium Exciter and field regulator Synchronization Stability High harmonic load Maintenance capacity. Required This is not required since exciting current is taken from the system Required. Thus, synchronism detector is necessary Pull out may be occur if the load fluctuates suddenly Allowable output is required by the thermal capacity of the surface of the magnetic pole when there is no damper when there is a damper In addition to the items for induction generator, maintenance and inspection is required for field windings and brushes if employed. No synchronizing device is required since forced paralleling is made. Rotating speed is detected and making is performed almost at synchronous speed. Stable and no pull out due to load fluctuation Heat capacity of rotor bars is large and they are relatively strong against higher harmonic load Maintenance is required for stator, cooler and filter but not required for the rotor of squirrel-cage type Output of Generator The output of generator is shown with kva and calculated with following formula: Pg (kva) = (9.8 x H x Q x η) / pf Where; Pg; Required output (kva) H; Net head (m) Q; Rated discharge (m 3 /s)

17 η; Combined efficiency of turbine, transmitter & generator (%) = turbine efficiency (η t ) x transmitter efficiency (η m ) x generator efficiency (η g ) pf; Power factor ( % or decimal), this figure is decided from kind of load in network. If inductive load, such as electric motor, low power factor lamps, is much in network, the figure becomes low i.e. the generator capacity should be larger according to above formula. However, 80% is usually applied for convenient purpose of selection. In case of micro-hydro power plant, the rated output of generator is selected from the standard output (kva) with allowance from the manufacturer s catalogue in the market Speed and number of poles of generator The rated rotational speed is specified according to the frequency (50 or 60 Hz) of power network and the number of poles as shown in following formula For synchronous generator P (nos.) = 120 x f / N 0 N 0 (rpm) = 120 x f / P Where, P: Number of poles (nos.) N 0 : Rated rotational speed (rpm) f : Frequency of network (Hz), In Indonesia 50Hz is standard For induction generator The speed is a little higher than that of synchronous generator for excitation with slip. N (rpm) = (1-S) x N 0 Where, N: Actual speed of induction generator S: Slip (normally S= -0.02) N 0 : Rated rotation speed As the rotational speed is fixed with number of poles, the speed and pole number of generator are shown in Table hereunder. As the frequency in Indonesia is 50 Hz, the speed shall be selected from 50Hz in the table

18 Table Standard Rotational Speed of Generator Unit: rpm (min -1 ) No. of pole 50Hz 60Hz No. of pole 50Hz 60Hz 4 1,500 1, ,000 1, Note: As the frequency in Indonesia is 50 Hz, the speed of 50Hz shall be selected from the table. The size and cost of higher speed generator is smaller and cheaper respectively than that of slow speed one. Referring to the original turbine speed and the rated generator speed, either direct coupling or indirect coupling with power transmission facility (gear or belt) is selected so that the suitable ratio of speed between turbine and generator can be matched. The total cost of turbine, transmitter and generator shall also be taken into consideration. For micro power plant, 4 8 poles are selected to save the cost

19 6.4 Power transmission facility (Speed Increaser) There are two ways for coupling between turbine and generator. One is a direct coupling with turbine shaft and generator shaft. The other is indirect coupling by using power transmission facility (speed increaser) between turbine shaft and generator shaft. Rated turbine speed is to be fixed by the selected type of turbine and its original design condition of net head and water flow (discharge) and can not be changed. On the other hand, generator speed is to be selected from frequency as shown in the above table. Therefore, if the speeds of both turbine and generator are completely the same, turbine and generator can be coupled directly. However, such design of direct coupling is sometimes not applicable due to high cost of turbine and generator, especially in case of micro or small power plant. Therefore, the power transmission facility (speed increaser) is adopted usually in order to match the speed of turbine and generator and save on total cost Two kinds of speed increaser are adopted for coupling turbine and generator as follows 1. Gear box type: Turbine shaft and generator shaft are coupled with parallel shaft helical gears in one box with anti-friction bearing according to the ratio of speed between turbine and generator. The lifetime is long but the cost is relatively high. (Efficiency: 97 95% subject to the type) 2. Belt type: Turbine shaft and generator shaft are coupled with pulleys (flywheels) and belt according to the ratio of speed between turbine and generator. The cost is relatively low but lifetime is short. (Efficiency: 98 95% subject to the type of belt) In case of micro-hydro power plant, V-belt or flat belt type coupling is adopted usually to save the cost because gear type transmitter is very expensive

20 6.5 Control Facility of Turbine and Generator Speed Governor The speed governor is adopted to keep the turbine speed constant because the speed always fluctuates according to change of load and water head and water flow. The change of generator rotational speed results in fluctuation of frequency. The governor consists of speed detector, controller and operation. There are two kinds of governor to control water flow (discharge) through turbine by operation of guide vane or to control the balance of load by interchanging of actual and dummy load as follows: 1. Mechanical type: To control water discharge always with automatic operation of guide vane(s) according to actual load. There are following two types. Pressure oil operating type of guide vane(s) Motor operating type of guide vane(s) 2. Dummy load type: To control the balancing of both current of actual load and dummy load by thyristor i.e. to keep the summation of both actual and dummy load constant always for the same output and speed of generator. The speed detection is made by PG (Pulse Generator), PMG (Permanent Magnet Generator) or generator frequency. In case of the mechanical type, many ancillary equipments, such as servomotor of guide vane, pressure pump, pressure tank, sump tank, piping etc. or electric motor operating guide vane with control system are required. It means the cost of power plant increases a lot for such ancillary equipment. In case of motor operating type, power source, motor and operating mechanism are also required. Therefore, in case of micro hydro-plant the dummy load type governor is cheaper and recommended. Dummy load type governor can be controlled by IGC (Induction Generator Controller) or ELC (Electronic Load Controller), which have been developed and fabricated in Indonesia and have a supply record for more than 30 power plants. Two types of dummy load are adopted with heaters of air cooling and water cooling. In Indonesia, the air cooling method is usually applied instead of water cooling type due to life time and simple construction of heater

21 The capacity of dummy is calculated as follows: Pd (kw) = Pg (kva) x pf (decimal) x SF Where Pd: Capacity of dummy load (Unity load: kw) Pg: Rated output of generator (KVA) pf: Rated power factor of generator (%, a decimal is used for calculation) SF: Safety factor according to cooling method ( times of generator output in kw) in order to avoid over-heat of the heater according to climate Note: Maximum output of turbine (kw) may be applied instead of Pg (kva) x pf (decimal) because maximum generator output is limited by turbine output even if the generator with larger capacity is adopted Exciter of generator In case of synchronous generator an exciter is necessary for supplying field current to generator and keeping the output voltage constant even if the load is fluctuated. Various kinds of exciter are available, but at present two kinds of exciter are adopted mainly as follows: 1. Brush type: Direct thyristor excitation method. DC current for field coil is supplied through slip ring from thyristor with excitation transformer. 2. Brush-less type: Basic circuit consists of an AC exciter directly coupled to main generator, a rotary rectifier and separately provided thyristor type automatic voltage regulator (AVR). The typical wiring diagrams for both brush type and brush-less type are shown in Figure and as follows:

22 PT CT Ex. Tr AVR Pulse Generator (Speed Detector) Slip ring G Figure Wiring diagram of brush type exciter PT CT Ex. Tr AVR Pul se Generator (Speed Detector) Rotating section DC100V G AC Ex Figure Wiring diagram of brush-less type exciter For micro-hydro power plant the brush-less type is used mainly due to easy maintenance and the generator with brush-less type is available in Indonesia. Therefore, this type is recommended

23 6.5.3 Single Line Diagram The typical single diagram for both plants with 380/220V and 20kV distribution line are shown in Figure and Magnet Contactor NFB Fuse Turbine Tr ansmi tter if required Figure Hz H G Generator V A x3 ELC (with Hz Relay) V x3 x3 La mp Indicator Dummy Load Single Line diagram of Power Plant with Low Tension Distribution Line To Custmer Magnet Contactor NFB Fuse M. Transformer 380V/20kV Disconnection Switch Turbine Transmi tter if required Figure Hz H G Generator V A x3 ELC (with Hz Relay) x3 Lamp Indicator V x3 Dumm y Load Single Line diagram of Power Plant with 20kV Distribution Line Circuit Breaker or Fuse Switch

24 6.6 Control, Instrumentation and Protection of Plant The general evaluation of those potential sites extracted by the above-described study is then conducted from the viewpoints described below to examine their suitability for hydropower development Control Method of Plant There are many control methods for power plant, such as supervisory control, operation control and output control 1. Supervisory control method is classified into continuous supervisory, remote continuous control and occasional control. 2. Operational control method is classified into manual control, one-man control and full automatic control. 3. Output control method is classified into output by governor only for independent network, and water level controlled, discharge controlled and program controlled for parallel operation with other power sources. However, in case of micro power plant for independent network in rural electrification, the occasional control, manual control and governor control with dummy load is usually adopted because no person can attend the plant full time and the cost of equipment is saved. It means that any operator attends occasionally to start and stop the plant and the machine is operated by governor control and when some trouble occurs the operator inspects the plant to take some necessary measure Instrumentation of Plant Though much instrumentation is considered for supervision of the hydro power plant during operation, the following instruments shall be furnished as minimum requirement for micro power plant in rural electrification. 1. Pressure gage for penstock 2. Voltmeter with change-over switch for output voltage 3. Voltmeter with change-over switch for output of dummy load (ballast) 4. Ammeter with change-over switch for ampere of generator output 5. Frequency meter for rotational speed of generator

25 6. Hour meter for operation time 7. KWH (kw hour) meter and KVH (Kvar hour) meter, which is recommended in order to check and summarize total energy produced by the power plant if there is some allowance in budget Protection of Plant and 380/220V Distribution Line Considering the same reason mentioned for cost saving in instrumentation, the following protection is required as minimum protection for micro power plant in rural electrification. 1. Over speed of turbine and generator (detected by frequency) 2. Under voltage 3. Over voltage 4. Over current by NFB (No Fuse Breaker) or MCCB (Molded Case Circuit Breaker) for low tension circuit. When above item 1, 2 and 3 are detected by IGC or ELC (adjustable by screw), MC (Magnet Contactor) operates and trips the main circuit of generator Protection of 20kV Distribution Line Normal protection system of line (pole mounted type lighting arresters and fuses or fuse switches) is to be provided throughout the line. However, the following two kinds of system are to be installed as protection of 20kV outgoing facility at power station. 1. The following facilities are to be installed at 20kV switchgear of power station in case 20kV switchgear for large capacity and long outgoing line is required. 1) 1 no. 24kV circuit breaker, driven by AC operated closing and tripping system of capacitor trip power supply device (3-phase, 200A for MHP ) 2) 3 nos. 24kV fuse switches with fuse, hand operated type (3-phase) 3) 1 no. 24kV earthing switch, hand operated type (3-phase gang operated) 4) 3 nos. 20kV lightning arrester (more than 27kV, 5kA) 5) 1 no. 20 kv voltage transformer(3 phase, 22kV/110V )

26 6) 3 nos. 20kV current transformer (1-phase, ratio to be fixed by the actual capacity of MHP) 7) 1 set 20kV bus bar system 8) 1 no. Control and protection panel In case 20kV cubicle is applied, all the above facilities are to be installed in the cubicle. 2. The following facilities only are to be installed by connection from 20kV terminal of 20kV/380V transformer on the terminal pole at power plant, in case only 20kV/380V transformer is installed for step-up purpose due to small capacity distribution line. In this case, protection panel for 20kV line is not required. 1) 3 nos. 24kV fuse switches with fuse, hand operated type (3-phase) 2) 3 nos. 20kV lightning arrester (more than 27kV, 5kA) 3) 1 lot 20kV line connection materials (insulators, support structure, wires)

27 6.7 Inlet valve Referring to water quantity and head of plant, suitable inlet valve is applied between penstock and turbine for tight stopping of water supply for safety and maintenance. However, it may sometimes be omitted for purpose of cost saving in case of low head power plant if the stop log or gate at forebay can almost stop the water leakage from forebay into penstock or separate discharge pass-way is provided at forebay The inlet valve for micro and small power plant is classified into three (3) kinds as follows: Type Applicable head Applicable diameter Head loss Leakage 1.Butterfly valve; Not exceeding 200m Medium (up to 2.5m) Medium Medium 2.Bi-plane valve; Not exceeding 350m More than 500mmm Little Medium 3.Sluice valve; Exceeding 200m Small Almost zero Very less More details are shown in Table For micro or small power plant, butterfly valve is adopted due to simple construction and low cost

28 Table Kinds and Characteristics for Each Type of Inlet Valve