Loadability of line is defined as the extent of load which can flow through the line without exceeding the limitations. Line Loadability is expressed in percentage of Surge Impedance Loading of line. The limiting factor for line loading are: thermal limit, voltage drop limit and steady state stability.
What is islanding ?
Consider the power network as shown in fig.1
Now if we disconnect the line AB from the infinite transmission grid there will be an isolated region . The D1, D2 are power sources (eg : inverter , solar power cells ). The power generated in this region is fed to the island only.
We see that there no longer is any control over the island voltage at the bus X . Also there is no mechanism here for control of frequency.
This state is referred to as islanding.
HVDC (high-voltage direct current) is a highly efficient alternative for transmitting large amounts of electricity over long distances and for special purpose applications.
What is islanding ?
Consider the power network as shown in fig.1
Now if we disconnect the line AB from the infinite transmission grid there will be an isolated region . The D1, D2 are power sources (eg : inverter , solar power cells ). The power generated in this region is fed to the island only.
We see that there no longer is any control over the island voltage at the bus X . Also there is no mechanism here for control of frequency.
This state is referred to as islanding.
HVDC (high-voltage direct current) is a highly efficient alternative for transmitting large amounts of electricity over long distances and for special purpose applications.
Tariff
The electrical energy produced by a power
station is delivered to a large number of
consumers. The consumers can be per-
suaded to use electrical energy if it is sold at rea-
sonable rates. The tariff i.e., the rate at which
electrical energy is sold naturally becomes atten-
tion inviting for electric supply company. The
supply company has to ensure that the tariff is
such that it not only recovers the total cost of
producing electrical energy but also earns profit
on the capital investment. However, the profit
must be marginal particularly for a country like
India where electric supply companies come un-
der public sector and are always subject to criti-
cism. In this chapter, we shall deal with various
types of tariff with special references to their ad-
vantages and disadvantages.
Generation of High D.C. Voltage (HVDC generation)RP6997
Generation of high dc voltage using different methods like half wave and full wave rectifier, voltage doubler circuits, voltage multiplier circuits, cockcroft-walton circuits and van de graaff generators.
High Voltage Direct Current Transmission System ReportNadeem Khilji
The development of HVDC (High Voltage Direct Current) transmission system dates back to the 1930s when mercury arc rectifiers were invented. Since the 1960s, HVDC transmission system is now a mature technology and has played a vital part in both long distance transmission and in the interconnection of systems. Transmitting power at high voltage and in DC form instead of AC is a new technology proven to be economic and simple in operation which is HVDC transmission. HVDC transmission systems, when installed, often form the backbone of an electric power system. They combine high reliability with a long useful life. An HVDC link avoids some of the disadvantages and limitations of AC transmission. HVDC transmission refers to that the AC power generated at a power plant is transformed into DC power before its transmission. At the inverter (receiving side), it is then transformed back into its original AC power and then supplied to each household. Such power transmission method makes it possible to transmit electric power in an economic way.
These slides are all about Phasor Measurement Units (PMUs). An introduction to PMU is presented as a preliminary knowledge for the course 'Distribution Generation and Smart Grid'. Your valuable suggestions are welcome.
Wide area monitoring systems (WAMS) are essentially based on the new data acquisition technology of phasor measurement and allow monitoring transmission system conditions over large areas in view of detecting and further counteracting grid instabilities.
Tariff
The electrical energy produced by a power
station is delivered to a large number of
consumers. The consumers can be per-
suaded to use electrical energy if it is sold at rea-
sonable rates. The tariff i.e., the rate at which
electrical energy is sold naturally becomes atten-
tion inviting for electric supply company. The
supply company has to ensure that the tariff is
such that it not only recovers the total cost of
producing electrical energy but also earns profit
on the capital investment. However, the profit
must be marginal particularly for a country like
India where electric supply companies come un-
der public sector and are always subject to criti-
cism. In this chapter, we shall deal with various
types of tariff with special references to their ad-
vantages and disadvantages.
Generation of High D.C. Voltage (HVDC generation)RP6997
Generation of high dc voltage using different methods like half wave and full wave rectifier, voltage doubler circuits, voltage multiplier circuits, cockcroft-walton circuits and van de graaff generators.
High Voltage Direct Current Transmission System ReportNadeem Khilji
The development of HVDC (High Voltage Direct Current) transmission system dates back to the 1930s when mercury arc rectifiers were invented. Since the 1960s, HVDC transmission system is now a mature technology and has played a vital part in both long distance transmission and in the interconnection of systems. Transmitting power at high voltage and in DC form instead of AC is a new technology proven to be economic and simple in operation which is HVDC transmission. HVDC transmission systems, when installed, often form the backbone of an electric power system. They combine high reliability with a long useful life. An HVDC link avoids some of the disadvantages and limitations of AC transmission. HVDC transmission refers to that the AC power generated at a power plant is transformed into DC power before its transmission. At the inverter (receiving side), it is then transformed back into its original AC power and then supplied to each household. Such power transmission method makes it possible to transmit electric power in an economic way.
These slides are all about Phasor Measurement Units (PMUs). An introduction to PMU is presented as a preliminary knowledge for the course 'Distribution Generation and Smart Grid'. Your valuable suggestions are welcome.
Wide area monitoring systems (WAMS) are essentially based on the new data acquisition technology of phasor measurement and allow monitoring transmission system conditions over large areas in view of detecting and further counteracting grid instabilities.
Bundle conductors in transmission line chandan kumar
Bundled Conductors are used in transmission lines where the voltage exceeds 230 kV.
At such high voltages, ordinary conductors will result in excessive corona and noise which may affect communication lines.
The increased corona will result in significant power loss. Bundle conductors consist of three or four conductors for each phase.
The conductors are separated from each other by means of spacers at regular intervals. Thus, they do not touch each other.
Alternating current (AC) is the main driving force in the industries and residential areas, but for the long transmission line (more than 650 KM) AC transmission is more expensive than that of direct current (DC). Technically, AC transmission line control is more complicated because of the frequency. DC transmission does not have these limitations, which has led to build long HVDC transmission lines over the last 40 years. HVDC technology made possible to transfer bulk power over long distances.
In this PPT you will learn the basics of electrical power transmission and distributuion, Basic components of power system, factors to be considered for erection of Overhead lines, etc.
AC Distribution in Bangladesh (in a nutshell)Ridwanul Hoque
Power System is an integrated network that interconnects the installations for generation, transmission and distribution of electricity. In Bangladesh electricity is generated at 50 Hertz frequency and at a nominal voltage of 11 KV (Kilo Volts) or 15 KV to be stepped up through transformers to 132 kV or 230 kV for feeding to the grid i.e. a high voltage transmission network that transmits the power to grid substation transformers to be stepped down at 33 kV. 11 kV and 0.4 kV for delivery to the consumers of various categories.
In electronics, impedance matching is the practice of designing the input impedance of an electrical load or the output impedance of its corresponding signal source to maximize the power transfer or minimize signal reflection from the load.
Equipment and Stability Constraints : System OperationRidwanul Hoque
There are two types of constraints which limit the capability of a power system: If the overloading exceeds limits, the equipment is tripped out by protection systems. b) Stability Constraints: A power system may not be able to cater to power flows beyond a certain point due to stability constraints.
A power system control is required to maintain a continuous balance between power generation and load demand. Load Frequency Controller and Automatic Voltage Regulator play an important role in maintaining constant frequency and voltage in order to ensure the reliability of electric power.
HVDC stands for high voltage direct current, a well-proven technology used to transmit electricity over long distances by overhead transmission lines or submarine cables. It is also used to interconnect separate power systems, where traditional alternating current (AC) connections cannot be used.
Hydro Power Plants capture the energy of falling water to generate electricity. A turbine converts the kinetic energy of falling water into mechanical energy. Then a generator converts the mechanical energy from the turbine into electrical energy.
There are three main types of conventional hydropower technologies: impoundment (dam), diversion, and pumped storage. Impoundment is the most common type of hydroelectric power plant. An impoundment facility, typically a large hydro-power system, uses a dam to store river water in a reservoir.
The Rankine cycle or Rankine Vapor Cycle is the process widely used by power plants such as coal-fired power plants or nuclear reactors. In this mechanism, a fuel is used to produce heat within a boiler, converting water into steam which then expands through a turbine producing useful work.
The steam-electric power station is a power station in which the electric generator is steam driven.
The steam-electric power station is a power station in which the electric generator is steam driven.
The Rankine cycle or Rankine Vapor Cycle is the process widely used by power plants such as coal-fired power plants or nuclear reactors. In this mechanism, a fuel is used to produce heat within a boiler, converting water into steam which then expands through a turbine producing useful work.
The aim of our presentation is to describe the AC Distribution system in Bangladesh.
Following are the focused points in terms of Bangladesh perspective:
1. Distribution Procedure
2. Primary and Secondary Distribution System
3. Distribution Substation
4. Distribution Companies
5. Distribution in both City and Rural Area
6. Distribution Loss
7. Protective Devices
8. User Variety
8. Billing Procedure
Power system stability is the ability of an electric power system, for a given initial operating condition, to regain a state of operating equilibrium after being subjected to a physical disturbance, with most system variables bounded so that practically the entire system remains intact.
Economic operation of power system. (i) One dealing with minimum cost of power production called Economic dispatch. (ii) Other dealing with minimum loss of the generated power delivery to the loads. For any specified load condition, economic dispatch (i) determines the power output of each plant.
A Strain gauge (sometimes refereed to as a Strain gauge) is a sensor whose resistance varies with applied force; It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured. When external forces are applied to a stationary object, stress and strain are the result. Learn and Enjoy.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
2. Thermal limitations
• Excessive temperature may result in expansion
and resultant sag of conductors causing
decreased clearance to ground. Temperature
extremes also reduces mechanical strength of
aluminum.
• Since thermal time constants are large, it is useful
to distinguish between steady state and transient
thermal ratings.
• Function of i) ambient temperature, ii) Wind
conditions, iii)Condition of conductor, iv)
Conductor type and v) ground clearance.
3. • ACSR (aluminum conductor steel reinforced) Moose
Conductor (520 mm2): For an ambient temperature of
40 degree C, and a maximum conductor temperature of
75 degree C, ampacity is 700 A (approx.). Typically, two
moose conductors form a bundle of 400 kV line so that
the total ampacity is 1400A for such a line.
• For AAAC (all aluminum alloy conductor) of 520 mm2 :
With an ambient temperature of 40 degree C, and a
maximum conductor temperature of 85 degree C,
ampacity is 850 A (approx.) for a 400 kV line.
• Thermal ratings are a strong function of ambient
conditions (wind flows, solar radiation) and absorption
and emmisivity of the conductor material.
• Evaluate the actual ampacity during real time operation
(season to season, day to day or hour to hour).
4. Dielectric Limits
• Exceeding dielectric limits (maximum electric field strength)
results in failure of insulation, causing faults.
• Electric fields may be excessive (due to overvoltage) under
low loading conditions on long ac transmission lines
Ferranti Effect) or during abnormal conditions like lightning
strokes.
• Deviation of voltages beyond certain limits can also be
considered to be an unacceptable compromise on the
quality of power being supplied to consumers. Low or high
voltages can also damage electrical equipments.
• Given a nominal voltage rating, a steady state overvoltage
of about 10% is often permissible. Shunt reactors
(inductors) are often connected in shunt on transmission
lines to prevent overvoltages under low loading. If
permanently connected to a line, however, they may
excessively reduce the voltages during heavy load
conditions.
5. • . Voltages and reactive power demand of transmission
lines are affected by: line parameters, length of line
and power transfer
• Line Parameters: Line parameters are dependent on the
conductor dimensions and relative placement. The
surge impedance of most overhead lines is around 250-
350 ohms whereas it is 30-50 ohms for cables.
• Typical positive sequence inductance and capacitance
parameters for a 400 kV overhead line: L =
1.044mH/km, C = 12 nF/km. For EHV lines , X/R ratio is
large. The resistance per unit length of this line =
0.0296 ohm / km.
• For a 400 kV paper-insulated lead-covered(PILC)
cable, typical positive sequence parameters are: L =
0.78 mH/km, C = 0.95 uF/km.
6. Voltage variation in
AC transmission line
Important results for lossless lines such as EHV lines:
• Voltage profile along the line is flat only if R= Zc is connected at
receiving end (SIL). Under this situation, there is no demand of
reactive power from either sending or receiving ends. Loads are
decided by consumers and not by a system operator. As such, this
exact condition is practically never met although it is ideal.
• If voltage at both ends is maintained at 1.0 pu, the voltage tends to
sag as we move towards the midpoint if Ps > SIL. The line absorbs
reactive power. If Ps < SIL, voltage swells and the line generates
reactive power.
• For a line which has one end maintained at 1.0 pu but kept open-
circuited at the other end, overvoltage will be evident at the open
end. All these effects are very prominent for long lines.
7. • Cables have very high SIL. The current at SIL
usually exceeds the thermal rating of a cable.
Therefore a cable is invariably loaded below its SIL.
Cables, therefore, generate reactive power and
usually voltages can be very high at low loading
levels, especially for long lengths. Besides this,
cables are much costlier than overhead lines and
are more "unforgiving" towards overloads.
Therefore, cables of lengths exceeding 30-40km
are rarely used for ac transmission.
• Due to voltage problems, underwater cable
transmission and bulk transfer over very long
distances is carried out using DC transmission
technology.
8.
9. Line Loadability in AC lines
• For preventing over voltages at light loads, it is necessary to have
devices for absorbing reactive power (e.g. shunt reactors) not only at
either end of a long line but even at intermediate points.
• Generators connected at the ends of the line have limited reactive
power absorption capability as defined by their capability curves. If
transmission redundancy exists (i.e., parallel transmission paths
exist), then a very lightly loaded long line may be tripped to avoid
overvoltage. However, this may be detrimental to system security if
some additional line trippings take place due to faults.
• If shunt reactors are permanently connected, they result in large sags
in the voltage under heavy loading conditions. Moreover, reactive
power demanded by long transmission lines under these situations
may be excessive and may lead to system-wide low voltage
conditions.
10. • Compensation by connecting (lumped) capacitors in series
and shunt effectively reduce the line reactance and
increase the shunt susceptance, thereby decreasing the
surge impedance. Thus the effective SIL of a capacitor
compensated line is higher than an uncompensated line.
This increases the loadability of a long line.
• Since total conductor cross-sectional area for EHV lines is
mainly decided by electric field considerations (corona),
these lines have large thermal capabilities, much in excess
of the SIL. For long EHV lines, one cannot deviate much
from SIL due to voltage constraints. Therefore, the thermal
limit of a long EHV line is not the key limiting factor.
However, thermal limit is the main limiting factor for short
lines (< 100 km) where voltage constraints are not violated
even for large deviations from SIL.
11.
12. Summary
• Power transfer capability of a ac line is
restricted by thermal and voltage constraints.
• Short lines are limited by thermal constraints.
• Long lines are limited by voltage constraints.
Stability constraints are also important for
long ac lines.