Summer Training

NHPC - Faridabad

A Training Report On Study of Hydro Power Plants and Detailed Design of Large Hydro Generators

Contents        

Overview of NHPC Design E & M Division Hydro Power Plants Hydro Turbines Power House Hydro Generators Design Study About the Software

About NHPC    

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NHPC (National Hydro Power Corporation) A Govt. of India Enterprise Established in 1975 Started with an authorized capital of Rs. 2000 million, today has an asset value of Rs. 200000 million One of the largest organization for Hydro-Power development in India Has constructed 13 hydro-power projects in India and abroad Total Installed Capacity of 3694.35 MW

Projects completed 

Baira Siul (MP)

3 X 60

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Salal (J&K)

3 X 115

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Chamera (Himachal Pradesh)

3 X 180

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Dhauliganga (Uttaranchal )

4 X 70

Indira Sagar (MP)

8 X 125

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Projects under Construction 

Teesta– V (Sikkim)

510 MW

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Parbati–II (Himachal Pradesh)

800 MW

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Subansiri (Arunachal Pradesh)

2000 MW

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Chamera-III (Himachal Pradesh)

231 MW

DESIGN ( E & M) DIVISION  One of many divisions of NHPC  Deals with the design Electrical &

Mechanical components of power plant

Functions of Design E&M  Planning and preparation of Electrical and

Mechanical design for DPR  Power Potential Studies & Power System Studies  Preparation of Technical specification of E & M equipments  Standardization of Technical specification  Assistance in evaluation of all tenders

Hydro Power Plants       

Reservoir : Holds the water from the river Dam : Civil construction Penstock : Large pipes through which water flows from the reservoir to the turbine Turbine :Turned by the force of water on their blades Power Plant : Power generation and transmission Generator : Converts mechanical energy of turbine into electrical energy Control Gates : Control the flow of water

Types of Hydro Power Plants  Storage Plants  Pumped Storage Plants  Run-of-River Plants

Storage Plants    

Impound and store water in a reservoir formed behind a dam. During peak demands, enough water can be released to meet the additional demand. Water flow rate may change greatly May involve dramatic environmental consequences including soil erosion, degrading shorelines, crop damage, disrupting fisheries and other wildlife, and even flooding

Pumped Storage Plants  Reuse water after it is initially used to

generate electricity.  Water is pumped back to the reservoir during peak-off hours  During peak hours this water is used again for generating electricity

Run-of-River Plants  Amount of water running through the

turbine varies with the flow rate of water in the river  Amount of electricity generated changes with seasons and weather conditions  Since these plants do not block water in a reservoir, their environmental impact is minimal

Hydro Turbines Hydro turbines can be classified on the basis of force exerted by water on the turbine A) Reaction Turbines    

Francis Kaplan Propeller Bulb

B) Impulse Turbines 

Pelton

Hydro Turbines Type of turbine to be used in a plant is decided on the basis of available head Head Range   2m   to      70  m                    Kaplan  30m to    450  m                    Francis  above 300 m                     Pelton Also a turbine is characterized by its specific speed.

Power House POWER HOUSE BUILDING CONSISTS OF THREE MAIN AREAS NAMELY  1. Machine Hall/Unit Bay  2. Erection/Service Bay  3. Control

Room/Auxiliary Bay

HEAD CALCULATION 

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• Avg. Gross Head = MDDL + 2/3(FRL - MDDL) -TWL(4 Units Running) = 203 + 2/3(208 - 203) -184.24 = 22.09 m. • Rated/Net Head = Avg. Gross Head - Head Loss = 22.09 - 0.75 = 21.34 m. • Max. Gross Head = FRL - min TWL = 208.00 - 181.78 = 26.22 m • Max. Net Head = Max. Gross Head-Head Loss = 26.22-0.75 = 25.47 m • Min. Gross Head = MDDL - TWL(4 Units Running) = 203.00 - 184.24 = 18.76m • Min. Net Head = Min. Gross Head - Head Loss =18.76 - 0.75 =18.01 m. # calculations has been done for PARBATI H.E. PROJECT, STAGE-II

Selection of Machine Speed  Economically should have highest

practicable speed  Deciding parameters : • Variation of head

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Silt content Cavitation Vibrations Drop in peak efficiency

HYDRO GENERATORS       

Hydro Generators are low speed salient pole type machines. Rotor is characterized by large diameter and short axial length. Capacity of such generator varies from 500 KW to 700 MW. Power factor are usually 0.90 to 0.95 lagging. Available head is a limitation in the choice of speed of hydro generator. Standard generation voltage in our country is 3.3KV, 6.6KV, 11 KV ,13.8 KV, & 16KV at 50 Hz. Short Circuit Ratio varies from 1 to 1.4.

A typical Hydro Generator

CLASSIFICATION Classification of Hydro Generators can be done with respect to the position of rotor (i) Horizontal (ii) Vertical (two types) a) Suspension Type b) Umbrella Type

Suspended Type Vertical Generator

Umbrella Type Vertical Generator

COMPONENTS OF GENERATOR 1. STATOR Stator Sole Plates  Stator Frame  Stator Magnetic Core  Stator Windings 

2.     

ROTOR Rotor Shaft Rotor Spider Rotor Rim Rotor Poles Ring Collectors

Rotor Spider

Rotor Rim

3.

BRACKETS

 Upper Bracket  Lower Bracket 4. 

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GENERATOR AUXILIARIES Excitation System Air Cooling System Braking And Jacking System Bearings Fire Protection Heaters

Design Study 

Output equation can be derived by the basic emf equation of a hydro generator. This has been taken from Electric Machine Design ,AK Sawhney.

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Output Equation: Q = C0 * D2 * L * Ns

Where, output coefficient, C0 = 11 * Bav * ac * Kw * 10-3 Q = kVA rating of machine Bav = specific magnetic loading ac = specific electrical loading Kw = winding factor Source: (derived from output equation of AC machines) (Pg456,Electric Machine Design, AK Sawhney)

Design Study 

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Calculation of Output Coefficient Is calculated from a graph obtained by analyzing the published data of 40 generators in manufacture in USA, Canada, UK, Japan a Europe. Calculation of Number of Poles using P=120f/N Frequency f is 50 Hz as per Indian Standards Air Gap Diameter Di= (60 * Vr) / (pi * N) Vr is the Maximum peripheral velocity obtained from a graph between Vr and Number of poles

Design Study 

Calculation of Stator core length

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Stator core length is the gross length of the stator and can be calculated by using the formula for output coefficient L t= W/ (C0* Di 2 * N) Where, W = Rated KVA of machine C0 = Output coefficient obtained from curve N = Rated RPM of the machine

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Source :

(Fig 1-1, Page 4, Large AC Machines by J.H. Walker.)

Design Study STATOR DESIGNING  Pole pitch is defined as the peripheral distance between two consecutive poles. It may be expressed as number of slots, degrees .(electrical or mechanical) Calculated as : ψ= pi x Di/P Where Pi (constant) =22/7 Di = Air gap diameter in meters P = No. of poles  Flux per pole Flux per pole (φ) =Mean flux density * Pole pitch (ψ)* Length of core 

Mean Flux density is assumed to be 0.6-0.7 Wb/m2 

Turns per phase = = (1.1 * Vph)/4.44fφ

Design Study 

Calculation of number of parallel paths

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Total current per slot should not exceed 5000 A.

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If I be the rated current per phase and there be p parallel paths then current per conductor is I/p , and current per slot is 2*I/p This should not exceed the limit of 5000 A. 5000 > 2 * I / p

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The value of p greater than or equal to this value, that satisfies other designing constraints is chosen as the appropriate number of parallel paths.

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After the calculation of turns per phase we can calculate the approximate no. of stator slots.

Design Study 

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No. of slots is given by, Ns = (no. of phases) * T ph * (no. of parallel paths) / (turns per coil) Note: Turns per coil = 1 for bar winding Number of conductor per slots = 2 ( for bar winding)

Design Study  Short Circuit Ratio  Defined as the ratio of field current

required to produce rated voltage under open circuit conditions to the field current required to circulate rated current at short circuit.  Short circuit ratio is the reciprocal of synchronous reactance Xd  For salient pole hydro electric generators SCR varies from 1.0 to 1.1.

Design Study   

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Effect of SCR on machine performance Stability : Low value implies lower stability limit, as the maximum power output is inversely proportional to Xd Parallel Operation : Low SCR leads to high Xd, that is small synchronising power.Machines become more sensitive to voltage and torque disturbances. Cost : A high SCR adds to the size of the machine making it costlier. Present trend is to make a machine with low SCR. This is due to the recent advancement in fast acting control and excitation systems.