Hydroelectric Power Generation Chapter 6 PDF

CHAPTER 6 Hydro design Chapter 6 System Aspect of Protection What is Hydroelectric Power Generation? Design of Micro Hydro Power Plant Protection Protection Against Abnormal System Frequency HVDC/MTDC Protection  PART 1: What is Hydroelectric Power...

CHAPTER 6 Hydro design Chapter 6 System Aspect of Protection What is Hydroelectric Power Generation? Design of Micro Hydro Power Plant Protection Protection Against Abnormal System Frequency HVDC/MTDC Protection  PART 1: What is Hydroelectric Power Generation?  Hydroelectric Power Generation Hydro power plant is an electrical power generation that converts water kinetic energy to be electrical energy. Classification of hydro power plant: 5 Hydroelectric Power Generation 6 Hydroelectric Power Generation Introduction The energy of water utilized for hydro-power generation may be kinetic or potential. Kinetic energy of water it its energy in motion and is a function of mass and velocity while potential energy is a function of the different in level of water between two points (called the head). In either case continuous availability of water is a basic requiement. For this purpose water collected in natural lakes and reservoir at high altitudes may be made by us or water may be artificially stored by constructing dams across flowing streams. 7 Hydroelectric Power Generation Hydrology Process Hydroelectric power uses the kinetic energy of moving water to make electricity. The hydrologic cycle is very important to hydropower. The hydro energy comes indirectly from solar energy. 8 Hydroelectric Power Generation Precipitation This includes all the water that falls from atmosphere to earth surface. It is mainly two types: Liquid precipitation (Rainfall) Solid precipitation (Snow, Hail) Run Off It is that portion of precipitation which takes its way towards streams, lakes or ocean. Run off can be possible only when the rate of precipitation exceeds the rate at which water infiltrates into the soil and after small and large depression on the soil surface get filled up with water. Also losses due to evaporation have to be deducted. Evaporation It is the transfer of water from liquid to a vapour state. 9 Hydroelectric Power Generation Run Off In general run off is given as:- R=P–E Where: R=Run Off : It is that portion of precipitation which takes its way towards streams, lakes or ocean P=Precipitation : All the water that falls from atmosphere to earth surface E=Evaporation : The transfer of water from liquid to a vapour state 0 Hydroelectric Power Generation Factors for Selection of Site Following factors should be considered while selecting the site of hydro power station 1. Quantity of Water Available This is estimated on the basis of a measurements of stream flow over as long a period as possible. Previous records of rainfall are studied and minimum and maximum quantity of water available during the year are estimated. After following for losses due to evaporation and percolation the net volume of water available for power generation can be estimated. 2. Distance Of Power Station Site From Load Centre In case the load centre is away from the site, the cost of transmission line and the losses occurring in the line will increase the cost considerably. 1 Hydroelectric Power Generation Factors for Selection of Site Following factors should be considered while selecting the site of hydro power station ( cont.) 3. Storage of Water Wide variation of rainfall during the years makes it necessary to store water for continuous generation of power throughout the year. 4. Head of Water The available water head depends upon the topography of the area. It has a considerable effect on the cost and economy of power generation. Low falls on unregulated streams are subjected wide variation which effect the net head, and may, in fact, reduce it to an abnormally low value, uneconomical for power generation. 5. Accessibility Of The Site The site should be easily accessible by rail as well as by road. 2 Hydroelectric Power Generation Bernoulli’s Equation Hydro electric power stations converts energy of moving water to electrical energy by means of a water turbine coupled to the synchronous generator. The power can be extracted depends upon its height and rate of flow. From Bernoulli’s equation, the power (P) is given as: 0.736 Q= discharge in m3/sec P= Qwh w= density of water = 1000 kg/m3 75 h=head in meters (Recall that 75 kg-m/sec = 1 metric Hp= 0.736 kW) 3 Hydroelectric Power Generation Bernoulli’s Equation The equation is simplified to:- P = 9.81qh 4 Hydroelectric Power Generation Bernoulli’s Equation Example 1 A river has discharge of 6000 m3/sec with a head of 20 meters. The overall efficiency being 70 %. Find the power generated ? Solution example 1 P = 9.81qh = 9.81x 6000 x 20 x 0.7 = 824040 kW 5 Hydroelectric Power Generation Prime Mover The purpose of prime mover is to convert kinetic energy of water into mechanical energy. Commonly used prime movers are Pelton, Francis, Kaplan and Propeller. 6 Hydroelectric Power Generation Turbine Basically there are two types of turbine:- 1. Reaction The entrance to the runner only a part of the available head is converted into kinetic energy and a substantial part remains in the form of pressure head. The pressure at the inlet to the turbine is much higher than the pressure at the entire flow from head race to tail takes place in closed conduit system and the atmospheric air has no access at any point. The entire wheel or runner of the turbine remains submerged in water throughout the operation of the turbine. Francis, propeller and Kaplan are some of the reaction turbine which are commonly used at present. 7 Hydroelectric Power Generation Reaction System 8 Hydroelectric Power Generation Turbine Basically there are two types of turbine:- (Cont.) 2. Impulse In impulse all the available head of water is converted into kinetic energy or velocity head by passing it through a contracting nozzles provided at the end of the penstock. The water coming out of the nozzles is formed into a free jet which strikes a series of buckets mounted on the periphery of a wheel. The wheel revolves freely in air. Water is in contact with only a part of the wheel at a time and throughout its action on the wheel and its subsequent flow to the tail race it is at atmospheric pressure. Pelton wheel is an impulse turbine often used. 9 Hydroelectric Power Generation Impulse System  PART 2: Design of Micro Hydro Power Plant Protection  Design of Micro hydro Power Plant Protection  Design of Micro hydro Power Plant Protection Design of micro hydro power plant protection: 1. Choice of generator type Generator converts mechanical energy from turbine to be electrical energy. Design of Micro hydro Power Plant Protection In the design of micro hydro power plant, overall efficiency are taken 50 %, therefore electrical power can be calculated using this formulation. Pe= Q x h x g x 0.5 (kW) Q = water debit (m3/s) h = head (m) g = gravity (9.81 m/s2) Difference Between Synchronous Generator And Induction Generator In a synchronous generator, the waveform of generated voltage is synchronized with (directly corresponds to) the rotor speed. The frequency of output can be given as f = N * P / 120 Hz. where N is speed of the rotor in rpm and P is number ofpoles. In case of inductions generators, the output voltage frequency is regulated by the power system to which the induction generator is connected. If induction generator is supplying a standalone load, the output frequency will be slightly lower (by 2 or 3%) that calculated from the formula f = N * P / 120.  Separate DC excitation system is required in an alternator (synchronous generator). Induction generator takes reactive power from the power system for field excitation. If an induction generator is meant to supply a standalone load, a capacitor bank needs to be connected to supply reactive power. Construction of induction generator is less complicated as it does not require brushes and slip ring arrangement. Brushes are required in synchronous generator to supply DC voltage to the rotor for excitation. Therefore, normally synchronous generator will be choose for hydro power plant generation. Design of Micro hydro Power Plant Protection  Design of Micro hydro Power Plant Protection 2. Earthing system Design of Micro hydro Power Plant Protection Earthing cable must have a good connection to the earthing rod Use approved earthing clamps Length of earthing pole depends on the conductivity of the ground Earthing pole must be at least 3m long All reinforced concrete foundations (power house and power equipment) and all electrical equipment must be connected to the earthing ring Lightning conductor to earthing ring must be 1m above ground  Design of Micro hydro Power Plant Protection Value of earthing resistance (R) < 5 ohm R = earthing resistance (ohm) = soil resistivity (ohm.m) L = electrode length (m) D = electrode diameter (m) Design of Micro hydro Power Plant Protection Design of Micro hydro Power Plant Protection 3. Protection system (MCCB/MCB) Rating MCCB/MCB is higher than nominal current. Size of MCCB/MCB in ampere is given by VLN = line to neutral voltage (v) Pf = power factor. Design of Micro hydro Power Plant Protection Design of Micro hydro Power Plant Protection 4. Cable size Cable is used to send electric power from generator to loads. The cable size can be calculated using this formulation Design of Micro hydro Power Plant Protection Design of Micro hydro Power Plant Protection Example: Measurement data of water debit and head are given below Q = 0.10 m3/s h = 18 m Design the micro hydro power plant included its protection system and also draw one line diagram. Assume soil type is clay, line to neutral voltage system is 220 V (pf=0.8). Chapter 6: System aspect of protection River with the water flow rate of Q=0.1 𝑚3 /𝑠 and head, h=18m is required to design a micro hydro power plant. The electrical power house is built above the ground which has a resistivity, p=15Ωm. Assume soil type is clay, line to neutral voltage system is 220 V (pf=0.8). Using the tables below: a) Select a suitable generator b) Select a suitable cable size c) Select a suitable MCCB A) Pe = Q x h x g x 0.5 (kW) =0.1x 18 x 9.81 x 0.5 = 8.829 kW. The type of suitable generator is three phase synchronous generator. Based on the table 3, STC-10, 10kw, 400V generator is selected. B) Pe,one phase = Pe/3=8.829 kW/3=2.943 kw cable size= =1.7x2943/(220x0.8)=28.43 A. Based on the table 4, the suitable cable is squirrel 76A. C) MCCB= =1.25*2943/(220*0.8)= 20.90 Select 25A (EZC100N1025)