Lecture 5 - Hydroelectric vs. Thermal Power Flashcards
compare with equivalent plat using other resources; energy over its lifetime at least cost.
Economic justification
(HEP vs TP) Initial Cost
HEP > TP
(HEP vs TP) Tax/ Insurance Rate
HEP < TP
(HEP vs TP) Operational Cost
HEP < TP
(HEP vs TP) Skilled Workers
TP > HEP
(HEP vs TP) Fuel Cost
TP vary with the unit price of fuel and the plant output
(HEP vs TP) Transport Cost
nuclear fuel are quite low
(HEP vs TP) Efficiency
Efficiency drops for TP with age
_____ for power system.
Grid system
defined as the ratio of average load to peak load during a certain period of time
Load Factor
In planning power system, an _____________ is necessary.
estimate of future power requirements
Late afternoon, midday, and summer season are the traditional time of ______ on power systems.
peak load
The load for the peak day of the year determines the required _________
generating capacity
the requirements for the peak week/month dictate the _____
amount of energy
HEP and TP for ______combination
optimum
The _____ for a hydropower plant is the total difference in elevation between the water surface in the stream at the diversion and the water surface in the stream at the point where the water is returned after having been used for power.
gross head
The ______ is the head available for energy production after deducting losses in friction, entrance, unrecovered velocity head in the draft tube.
net or effective head
The ______ of a hydropower plant is the ratio of net head to gross head
hydraulic efficiency
The equal
_______ is to the hydraulic efficiency multiplied by the efficiency of the turbines and generators
overall efficiency
overall efficiency
The of plants hydropower
operating at optimum conditions will usually be between______
60 to 70 percent
The ______ of a hydropower plant is the maximum power which can be developed by the generators at normal head with full flow.
capacity
The unit of electrical power ( rate of energy)
kilowatt = 1.34 HP
The unit of electrical energy (power multiplied by time)
kilowatt-hour (kWh)
_____ is the power (energy) a plant can be expected to deliver 100% of the time.
Firm power (energy)
Hydropower plants may be classified in a number of different ways. They may be classified in terms of capacity as ____________________
microhydro, minihydro, or ordinary hydro.
They may also be classified in terms of head as ___________ or in terms of layout and operative mode as ___________
low head, medium head, or high head
run of river, storage, or pumped storage.
Three Basic Elements for Power Generation
A means to create Head
- dam and reservoir
- intake structures
Conduit to Convey Water
- intake structures
- penstocks
Power Plant
- turbines/generators
- draft tubes
- tailrace
convey water from the discharge side of the turbine to the tailrace.
Draft tubes
maintains a minimum tailwater elevation below the power plant and keeps the draft tube submerged.
Tailrace
For a constant discharge, the energy relation between the forebay and any other section is _________
Bernoulli’s Equation
_________ is a regulating reservoir that temporarily stores water to facilitate____
Forebay
1) low-approach velocity to intake,
2) surge reduction,
3) sediment removal,
or 4) storage.
a free jet of water impinges on the revolving element of the machine, which is exposed to atmospheric pressure. Kinetic to mechanical energy.
Impulse-turbine
flow takes place under pressure in a closed chamber. Kinetic and pressure head to mechanical energy.
Reaction turbine
is also called a tangential waterwheel or a Pelton wheel has a runner with numerous spoon-shaped buckets attached to the periphery and are driven by one or more jets of water issuing from fixed or adjustable nozzles.
impulse turbine
Physical Elements of Turbines: Impulse-type
Jet on bucket is split into 2 parts that discharge at sides of the bucket
One jet for small turbines, many for big
Wheel speed is kept constant under varying load through a governor
Bypass valves or deflectors are provided to prevent water hammer
Can be double overhung Provided with housing to prevent splashing
For efficiency: bucket width is 3-4x jet diameter and 15-20x for wheel diameter
Bucket angle is usually 165o.
nclude Francis turbines, which are constructed so that water enters the runner radially and then flows towards the center and along a turbine shaft axis. Working heads can range between 30 to 450 meters and most economical for 45-450 meters.
Reaction turbines
Physical Elements of Turbines: Reaction -type
Jet enters a scroll case, moves in to the runner through a series of guide vanes
Vanes convert pressure head to velocity head
Vanes are controllable for regulating flows
Relief valves/surge tanks are provided to prevent water hammer
Usually mounted on a vertical axis
From the runner, water enters a draft tube with a gradually increasing cross-sectional area to reduce discharge velocity.
To prevent flow separation, the divergence angle should be less than 10o.
To prevent cavitation, z1 should be limited.
re constructed so that water passes through the propeller blades in an axial direction. Adjustable gates upstream are used to regulate flow. These turbines are typically used in the 3-60 meter head range and are economical for 15-45 meters.
Fixed-blade propeller turbines
are propeller turbines with adjustable pitch blades that operate in the same range of heads. The usual runner has 4-8 blades mounted on a hub, with very little clearance between the blades and the conduit wall. Adjustable gates upstream of the runner regulate the flow.
Kaplan turbines
have a guide vane assembly that is in line with the turbine and contributes to the tubular shape. Economical choice for heads less than 15 meters
Tubular turbines
are horizontal axial-flow turbines with a turbine runner directly connected to a generator or through a speed-increasing gear box.
Bulb turbines
is similar to the bulb turbine with the generator mounted on the periphery of the turbine runner blades. Economical choice for heads less than 15 meters.
rim turbine
Types of Turbine
Impulse-turbine Reaction turbines Fixed-blade propeller turbines Kaplan turbines Tubular turbines Bulb turbines rim turbine
What is stream-flow data?
The most important data for a hydropower feasibility study. It is used to develop estimates of water available for power generation.
stream-flow data is used to develop ______ which show the percentage of time that flow equals or exceeds various values during the period of record.
flow-duration curves
is the head at which a turbine operates at maximum efficiency
Design head
The design head for a run-of-river projects can be determined from a ________as the midpoint of the head range where the project is generating power
head-duration curve
is the head at which rated power is obtained with the wicket gates fully open.
Rated head
the discharge at rated head with the wicket gates fully open
Rated discharge
selected to match the turbine output at rated head and capacity. The head at which a turbine is rated can vary with type of operation.
generator rated output
is limited to the analysis of small hydro projects, particularly run-of-river projects, and for preliminary analysis only of other projects.
flow duration curve
A flow duration curve can be converted to ______ by using the power equation
power duration curve
The following is a summary of the basic steps for computing average annual energy and dependable capacity using flow duration method.
- Develop flow duration curve
- Adjust flow duration curve
- Determine flow losses
- Develop head data
- Select plant size
- Define usable flow range and derive head-duration curve 7
. Derive the power duration curve - Compute average annual energy
- Compute dependable capacity
This method sequentially computes the energy output for each time interval in the period of analysis.
Sequential Streamflow-Routing Method
is used to route the streamflows through the project, taking into account the variations in reservoir elevation as a result of the reservoir regulation
continuity equation
The basic steps for this procedure are as follows: (Sequential Streamflow-Routing Method )
- Select plant capacity
- Compute stream flow available for power generation
- Determine average pond elevation
- Compute net head
- Estimate efficiency
- Compute generation
- Compute average annual energy
defined as a curve, or a family of curves, indicating how a reservoir is to be operated under specific conditions to obtain best or predetermined results.
power rule curve
To determine the energy output of a project, the following steps can be taken: (power rule curve)
- Identify the critical period
- Make a preliminary estimate of the firm energy potential
- Make one or more critical SSR routings to determine the actual firm energy capability and to define operating criteria that will guide year-by- year reservoir operation
- Make an SSR routing for the total period of record to determine average annual energy
- If desired, make additional period-of-record routings using alternative operating strategies to determine which one optimizes power benefits
is one that can be used for flood regulation during part of a year and for conservation storage the remainder of the year.
joint-use storage zone
ordinarily includes a diversion structure, a conduit (penstock) to carry water to turbines, turbines and governing mechanism, generators, control and switching apparatus, housing for the equipment, transformers, and transmission lines to the distribution centers.
hydropower development
serves as a regulating reservoir, temporarily storing water when the load on the plant is reduced and providing water for the initial increments of an increasing load while in the canal is being accelerated.
forebay
direct flows from forebay to the powerhouse.
Penstocks
consists of a substructure to support the hydraulic and electrical equipment and a superstructure to house and protect equipment.
Shasta
Powerhouse
is the channel into which the water is discharged after passing through the turbines.
tailrace
Hydropower Development Planning
- Assemble hydrologic data
- Make preliminary designs for all installations
- make a preliminary evaluation of the social, political, and environmental impacts
- Determine the requirements to be satisfied
- Select feasible projects as close to the load center as possible.
- Compare the best design from the several sites
- Compare the cost of the hydroelectric-power plant with that of an equivalent thermal plant.
- If hydroelectric power is competitive with steam, proceed the detailed design of the hydroelectric installation.
