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Sunday, 28 September 2014

Emerging power conductors for Transmission lines

The rapid increase in electrical load, remote generation and system interconnections have made it necessary to transmit more power over longer distances efficiently and easily to keep pace with the development. The approach includes increasing the power flow on existing lines. 


Conductors used in Power Transmission:

The various conductors available for use in power transmission lines are:

·         ACSR (Aluminum Conductor Steel Reinforced)
·         AAAC (All Aluminum Alloy Conductor)
·         HTLS (High Temperature Low Sag)

ACSR Conductor:

ACSR is the most widely used conductor worldwide for power transmission. These conductors have a certain current carrying capacity because of the temperature limitation (up to 80 oC) and this limitation is partly due to the fact that aluminum anneals at about 100 to 110 oC and thus becoming weaker and less secure. The second reason is that aluminum conductors expand at a greater rate than the steel core provided inside for enhancing the mechanical strength. The aluminum literally pulls on the steel forcing it to elongate and hence increasing the sag at elevated temperatures.

AAAC Conductor:

AAAC conductors are well established in European countries because of their lower losses (or greater efficiency) as compared to ACSR conductors, but they cannot be operated at higher temperatures and are therefore not suitable for countries like India where the ambient temperature reaches nearly 50 oC.

HTLS Conductor:

HTLS conductors are specially introduced to double the current carrying capacity of the existing grid to meet the load demand. Lately the revolutionary Aluminum Conductor Composite Core (ACCC) conductor of the HTLS family was introduced. They have increased the current carrying capacity of existing and new lines and that too at higher efficiency. 

ACCC uses carbon fiber (as replacement of steel) which provides a stronger, lighter and smaller core. This in turn permits a design of conductor that contains 30 % more aluminum material than an equivalent ACSR conductor. Because of the increased conductive material, ACCC conductors are more efficient at all operating temperatures. The ACCC conductors use the annealed HTLS technology and therefore, permit the transmission operator to increase the current carrying capacity while keeping the losses to a minimum.

The low coefficient of thermal expansion of the high strength and light weight composite core material ( of carbon and glass) allowed the ACCC conductor to carry approximately twice the current of a conventional conductor; of course with reduced sag. The added aluminum content and superior conductivity decreased the electrical resistance of the conductor which substantially reduces the line losses ( I2R losses are reduced by nearly 30%) compared to other conductors of same diameter and weight. The additional strength and dimensional stability permits the use of these conductors for greater span length and thereby reducing the capital cost.

ACCC conductors were initially developed to increase the capacity of transmission lines below 400 kV. The additional merits of ACCC conductors can be used to enhance the efficiency, reliability and capacity of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines
In 2013, the American Electric Power re-conductored it’s heavily loaded 345 kV transmission line in South Texas with ACCC conductors. It was a live-line conductor replacement project, the largest in the live-line conductor replacement category. 


Use of ACCC conductor in India:

In 2012, Torrent Power Ltd., for the first time in India used ACCC conductors of 318 mm2, Lisbon size conductors to double the current capacity of an existing 132 kV line in Ahmedabad, Gujarat. The line earlier used ACSR “panther” conductor and this was a live-line re-conductoring project without disrupting the normal supply. 

Recently in March 2014, the Maharashtra State Electricity Transmission Company Ltd. (MSETCL) up-graded it’s 132 kV line in Nasik city by ACCC, 273.6 mm2 “Casablanca” conductor capable of carrying 1200 A under emergency conditions. In both the projects, the ACCC conductors were supplied by Indian company Sterlite Technologies Ltd. 

Saturday, 27 September 2014

Polymer Insulators for reduction in Infrastructure cost

Porcelain Insulators:

Porcelain has enjoyed a virtual monopoly; as an insulating material for electrical equipment such as transformers, switchgears etc and in transmission lines. The advantages of porcelain are its high insulation strength. But it has a low strength to weight ratio and are prone to fragmentation under stress.

Polymer materials, on the other hand, have high insulation value at par with porcelain and acceptable strength both under compression and tension. It has a better water and sleet shedding properties and is therefore more useful in contaminated and polluted environment. Although the cost of both porcelain and polymer material are the same but polymer is more favoured because of its better handling. It has a better strength to weight ratio i.e. it is much lighter in weight than porcelain. 

The weight of suspension type polymer insulator for the 138 kV class is only 8% of the porcelain insulator of the same voltage level. This vital property of polymers permits the use of lighter supporting structures, more compact design, narrow Right of Way (ROW) requirements and thus significant reduction in cost.   
  
In the polymer insulator a fiberglass insulation rod or shaft serves as the internal structure and around which the polymer insulator is attached usually in the shape of petticoats or rainsheds. The fiberglass rod has a high compression and tensile strength. The metal fittings at both the ends are crimped directly to the fiberglass rod. Proper sealing is done to avoid ingress of moisture or contamination into the fiberglass rod. The petticoats, as in porcelain insulators, provide a longer leakage path between conductor and the support, so as to keep the leakage current to a minimum value. A variety of polymer insulators are shown in Figure1 .

Fig.1: Polymer Insulators for different voltage range.

The rate at which the petticoats or rainsheds dry up is crucial and depends on a number of factors such as the contamination level of the area, temperature, humidity and wind velocity following the cessation of the rough weather. In areas with extreme contamination; for example near an industrial area or power plant, insulators with various petticoat sizes are used, so as to obtain a greater distance between outer edges of petticoats, eventually to avoid a flashover.

The polymer suitable for High Voltage (H.V) applications are Ethylene Propylene (EP) and Silicon Rubber (SR). Ethylene Propylene polymer has high resistance to corrosion and better physical properties whereas Silicon Rubber shows better performance under contamination and offers higher resistance to Ultra Violet (UV) sun rays. A combined EP and SR polymer has better hydrophobic (water repellent), electro-mechanical properties and high resistance to industrial pollution. Table 1 shows typical properties of Polymer insulators used in distribution and transmission lines of voltages ranging from 11 kV to 400 kV.

Table 1: Properties of Polymer Insulators

Sr. No
Nominal System Voltage kV
Sectional Length mm
Mechanical Strength kN
Creepage Distance mm
Impulse Withstand Voltage kVp
Type of Metal Fitting
1
11
260
5
320
80
Pin
2
33
375
10
980
210
Pin
3
132 Suspension type
1344
70-90
4495
650
B&S
4
132 Tension type
1536
120
5016
650
B&S
5
220 Suspension type
2119
70-90
7595
1050
B&S
6
220 Tension type
2256
120
7975
1050
B&S
7
400 Suspension type
3335
120
13020
1550
B&S
8
400 Tension type
3910
160
14500
1550
B&S

These insulating materials are also used in bushings of transformers, reactors, switchgears, capacitors, instrument transformers, lightning arresters etc.     

Wednesday, 24 September 2014

Specific Design of Converter Transformers for HVDC Transmission System

What are Converter Transformers?

"Converter transformers used in High Voltage Direct Current (HVDC) system are specially designed power transformers of high MVA rating connected between AC bus bar and converter valves."
The windings of the converter transformer on the AC line side are called “line winding” and the windings on the converter valve side are called “valve winding”. These transformers may be a 1-phase unit with two or three windings or may be a 3-phase two winding unit.

Main Difference between Conventional Power Transformer and Converter Transformer:

The main difference between the conventional power transformer and the converter transformer is the DC voltage appearing on the valve winding, harmonics and commutating short circuit pulse currents of rectangular waveform flowing through the windings of the converter transformer.  The harmonic content in the current produced because of converter operation causes additional leakage flux in the transformer. It produces eddy current losses and hot spots in the winding and the transformer tank. Thus, a converter transformer is subjected to higher electrical and thermal stresses, and hence the insulation issue is more prominent.

Due to the said limitations and requirements, certain special features are necessary in the design of a converter transformer. They are:

·         Higher short circuit strength,
·         Special design for windings and insulation,
·         Special design of magnetic circuit,
·         Specially designed on-load tap changers,
·         Close control of leakage flux.

In this transformer, the gap between winding and the core is larger, resulting in higher leakage flux and higher eddy current losses. The end turns of the windings near core need special design with respect to cooling, hot spots and insulation.

During commutation process the valve side windings are short circuited for a short interval. The role of commutating reactance is very significant in limiting the short circuit (S.C) currents. The inductive reactance of the converter transformer controls the short circuit current and its rate of change. The reactance of the converter transformer should be finely matched with the requirements of commutation process so as to have better commutation, lesser harmonics and lesser transients. This is achieved by precise design of core winding and leakage paths.

The windings of converter transformer experience axial and radial forces because of the flow of S.C. currents. Therefore, the windings should be strong enough to withstand the forces thus produced, in addition to the thermal stresses. The cross section of the core is so selected to avoid magnetic saturation in extreme conditions because of DC and AC component flux.

The on-load tap changers (OLTC) for converter transformers are also specially designed to give a wide range of regulation (say +17.5% to -12.5%) in multi-steps of 24 steps or so. These transformers are normally forced cooled i.e. Oil Forced Air Forced (OFAF).  

Saturday, 20 September 2014

Extra High Voltage measurement using Capacitor Voltage Transformer

In power sub-stations, and testing laboratories, it is necessary to measure the extra high voltages with accuracy. While measuring these enormous voltages, it is essential to ensure the safety of working personnel and related equipments. 
  
Capacitor Voltage Transformer (CVT) or Capacitance Coupled Voltage Transformer (CCVT) is typically single-phase devices used for measuring voltages exceeding 100 kV and where the use of Potential Transformers (PT) becomes uneconomical. 

CVT or CCVT convert the transmission class voltages for the purpose of metering and protection or in other words these devices isolate the measuring instruments, meters, relays etc from High Voltage (HV) or Extra High Voltage (EHV) circuit or transmission line and provide a low value replica of the original voltage. CVT also serves as coupling capacitors for coupling high frequency Power Line Carrier (PLC) signals to the transmission lines.

Construction of Capacitor Voltage Transformer:

CVT consists of series connected capacitor elements housed in a hermitically sealed porcelain or silicon rubber shells. These capacitors acts as potential dividers and steps down the voltage to be measured to an intermediate value of about 5 to 12 kV. This voltage is fed to an electromagnetic circuit consisting of an auxiliary transformer which gives the final reduced secondary voltage (say 110 V). 

The dielectric of the capacitor is made up of polypropylene film or paper impregnated with synthetic fluid. Stainless steel bellows are provided in each capacitor section and these bellows allow for the expansion and contraction of the insulating fluid taking place because of the change in the operating temperature.

CVT has at least 4 terminals; one connected to the HV or EHV terminals, second to the ground terminal and two secondary terminals which are connected to the measuring instruments or protective relays as shown in the figure below. 

Many renowned manufacturers including Siemens make an entire range of Instrument Transformers from 72.5 kV to 800 kV class consisting of Current Transformers (CT), Potential Transformers (PT), Capacitor Voltage Transformer (CVT) and Combined CT and PT units.


The main advantages of CVT are:
·         High accuracy because of highly stable capacitance.
·         Maintenance-free performance throughout the life.
·         Robust and reduced size.
·         Reliable ferro-resonance suppression system.

The 1200 kV test station at Bina (M.P.) has installed 1200 kV CVT manufactured by Siemens at its Aurangabad plant. 

Friday, 19 September 2014

Rural Electrification Corporation: Financing the Indian Power Infrastructure

Last Updated: January 20, 2017 

Inadequate Fuel Supply for Power Plants:

The thermal power plants in India, whether coal or gas fired, are struggling with inadequate supply of fuel and are operating at low Plant Load Factor (PLF). Country has the fourth largest coal reserves in the world, and despite of this, its domestic coal production has been unable to keep pace with the increase in coal demand posed by power plants. Under such situations the coal imports for power plants is expected to rise. There has been an unprecedented growth in renewable energy production causing a significant change in the fuel mix for power generation in the country.


Envisaged Generation Capacity Addition:

The targeted generation capacity addition in the 12th Five Year Plan (FYP) is 88,537 MW for which the fund requirement is INR 14 lac crore. For the 13th FYP (by the year 2022) the envisaged generation capacity addition, expecting a GDP growth of 9%, is 94,000 MW . Such a boost in generation capacity needs matching transmission and distribution capacity.

Transmission line addition of nearly 1,00,00 circuit km and sub-station capacity addition of 2,70,000 MVA has been planned in the 12th FYP. 


Funding the various needs of infrastructure developments in Indian power sector:

The estimated fund requirement during the 12th FYP for the Indian power sector alone is about 14,00,000 Crore INR. Rural Electrification Corporation (REC) is one of “Navratna” public sector companies in India and is funding the various needs of infrastructure developments in Indian power sector. REC has been financing power generation, transmission, and distribution projects along with rural electrification and irrigation pump energisation. 

The Corporation has been actively involved in the infrastructure development and improvement in the power sector with special emphasis on expansion and strengthening of existing transmission and distribution networks by financing investments in energy efficient transformers, energy meter, power factor improvement capacitors, High Voltage Distribution Systems (HVDS) etc. The company is also involved in sanctioning loans for Renovation and Modernization (R&M) of the existing power plants, grid connected renewable energy projects and village electrification.


Skill development and Up-gradation programmes by REC:

REC is also regularly conducting various skill development and up-gradation programmes, promoting non-conventional energy by installing solar PV smart mini-grids/solar lanterns, providing health care, potable water and sanitation. The company is further strengthening its activities in allied fields such as power equipment financing, energy efficiency promotion activities etc and providing significant contributions in the development of power sector and the society.              

Thursday, 18 September 2014

India suffers Billions of Dollar every year due to Road Accidents

India suffers more than 50 billion USD every year due to road accidents. The cost include medical expenses, legal fees, property damage, insurance cost and loss of revenue due to death.

The vehicular population in India is only 1% of the global number, yet there is massive cases of injuries and loss of life in road accidents each year in the country. The estimated fatalities due to road accident are 10%. In fact, the death to injury ratio is high in developing countries. Nearly 3% of the India's Gross Domestic Product (GDP) is lost annually in the country due to road accidents.

There have been a few efforts to estimate the cost of road accidents in India. Reports also suggests that the number of injuries and the associated financial damages in the country are highly underestimated. There are certain issues, related to road crashes, which are either omitted or beyond the scope of the studies. These special problems faced by road crash victims, particularly poor victims, are:

  1. Inappropriate medical treatment leading to complications and extended treatments,
  2. Loss of job even the victim survives,
  3. Loss of property, financial savings, household goods to the victim,
  4. Poor condition of surviving family members,
  5. Re-location and reduced income of the victim's family etc.  


Major causes of Road Accidents: 

Engineering is one of the major drawbacks for Indian roads. Many a times, engineers are unable to find the right geometrical symmetry for the needed road. Road safety experts feel the sloppy attitude of the road owning agencies, whether it’s the National Highway Authority or the State Highway Authority, behind this large quantum of national loss. There is also lack of “political will” to tackle the menace. 
"The best example is the photo shown below (clicked on 17th Sep. 2014) in which a truck loaded with goods has met with an opposite to the People’s Medical College, Bypass road, Bhopal."



Each year, at the same spot a good number of trucks receive the same fate because of the ill-planned road divider, causing a huge loss to the nation in terms of damage to the vehicle, goods, road, and off course to the human life (record can be verified). But our concerned government agencies are not at all bothered after all it’s the common man who is going to bear the heat      
  

Need of the Hour:

High rate of road accidents despite of lesser vehicles call for better road safety management, better policies, safer roads, safer vehicles, advanced post-accident relief mechanism, and above all better enforcement of regulations.  

Wednesday, 17 September 2014

Failure of Distribution Transformers in India

Transformer industry in India:

Transformer industry in India has evolved over a period of time and is now a matured industry capable of manufacturing a wide range of power, distribution and special type of transformers for different applications. Recently it has manufactured a UHV 1200 kV class transformer for the test station at Bina in Madhya Pradesh. 

The power transformer market in India is well organized and their customers are large entities like Central Transmission Utility (CTU) and the State Transmission Utilities (STU) whereas the distribution transformer market is dominated by un-organized players.

The number of distribution transformers currently in service is nearly 4.3 million and the number is adding at an annual rate of approximately 10%. Distribution transformers of 11/0.4 kV class usually come with both aluminium and copper winding. 



Failure rate of Distribution Transformers in India:


"The failure rate of distribution transformers in India is as high as 25 to 30% which is the highest in the world."
Reports say that every year distribution transformers worth rupees 200 Crores fail; which is a great financial loss to the nation and which can be avoided. 


Causes of Failure of Distribution Transformers:


Substantial failure rate of distribution transformers in India is mainly due to:

i)   the design criterion, 

ii)  the material used in manufacturing, 
iii) maintenance practice, 
iv) material used in maintenance, and
v)  Un-authorized electrical loads.

The operating conditions, particularly in rural India, like weather conditions, overloading, through or passing faults, inadequate protection, public interference, poor maintenance of LT and 11 kV lines often results in distribution transformer failure.


Distribution transformers installed in rural areas form the bulk of these transformers. They are very much exposed to vulnerable weather conditions particularly lightning. These transformers feed lengthy Low Tension (LT) lines which are more prone to faults because of these atmospheric conditions. 

Majority of the transformers have poor efficiency because of improper or unbalanced loading conditions. It is common practice to connect additional electrical load on these transformers on the basis of maximum demand recorded at some point of time or on the basis of assessed maximum demand without considering the seasonal variations and the actual diversity factor. 

Un-authorized electrical connections also result in overloading. Wide variation in load and ambient temperature make undesired ingress of moisture, particularly in rural areas, which weakens the dielectric strength of transformer oil, forms sludge and deposits on the winding which on passage of time may obstruct the ducts in the winding provided for oil circulation. 


The routine maintenance of LT and 11 kV lines and protective equipments associated with these transformers are also poor. Figure 1 shows a badly maintained LT fuses on one of the distribution transformers.




Fig. 1: Badly maintained LT fuses

Prolonged operation of distribution transformer under abnormal operating condition such as faults, overloading or unbalance load deteriorate the insulating materials; ultimately leading to failure. Figure 2 below shows the damaged High Voltage (HV) winding of  a 11/0.4 kV distribution transformer.



Fig. 2:  Damaged High Voltage winding of  a 11/0.4 kV distribution transformer.

Repair rate of Distribution Transformers:

The repair rate of distribution transformers is also high in India. Each distribution transformer is repaired 2 to 3 times in its whole life span of 25 years (due to fund paucity) reducing the efficiency further with each repair. The direct economic impact of distribution transformer failure is in terms of cost of repair or replacement whereas indirect economic impact comes in the form of revenue loss due to supply interruption and increased losses.     
  

How to reduce Failure of Distribution Transformers:

This significant failure rate of distribution transformer in the country can be curbed to some extent by employing Complete Self-Protection (CSP) scheme which enables the transformer to protect itself from faults. 

In the CSP scheme, transformers are equipped with primary fuses, secondary side circuit breakers and lightning arresters. The primary side fuse is mounted inside the primary bushing and is in series with the primary winding to isolate the transformer in case of faults inside the transformer or on its LT side. Secondary circuit breakers and lightning arresters are there to protect the transformer from overloads, LT side faults and lightning strokes respectively.  

Sunday, 14 September 2014

Do we need the World’s largest single location Solar Electricity Power Plant?


Ambitious target of  Solar Power:

The country is set to become a global leader in solar electric energy production and has an ambitious target of installing 22000 MW of capacity by 2022. This target has been revised to 1,00,000 MW. 

Ministry of New and Renewable Energy (MNRE) has envisaged setting up of large scale Solar Power Plants in India in the 13th Five Year Plan (FYP). These solar power plants will be known as Ultra Mega Solar Power Plants (UMSPP) and will be set up in the desert and wastelands of Sambhar (Rajasthan, 4000 MW), Kharaghoda (Gujarat, 4700 MW), and Leh/Kargil (J&K, 2400 MW).

Sambhar Ultra Mega Solar Power Plant:

The solar plant at Sambhar Lake, is the first of the four UMSPP projects conceived by MNRE and Ministry of Power (MoP) in the year 2013. MoU has been signed for setting up the Solar Power Plant, with a total installed capacity of 4000 MW, near Sambhar Lake, in Rajasthan (India). The plant is proposed to be set up in a time span of 7 years. When fully commissioned, this would become the largest single location solar electricity generation in the world. The plant is expected to generate 6,000 million kWh of electricity each year and with a life span of 25 years, it is set to offset nearly 4 million tonnes of Carbon Dioxide annually. 

The proposed site has plain surface and the required basic infrastructural facilities such as road approach etc. Also the transmission and distribution system is very much there as claimed by the Solar Energy Corp. of India (SECI).

This solar Photovoltaic (PV) power plant is a joint venture of 6 companies and requires about 9000 hectares of land which is to be provided by Sambhar Salts Ltd. (SSL) whereas the equipments are to be provided by Bharat Heavy Electricals Ltd.(BHEL). The arrangement for evacuation of electrical energy, to be produced from this UMSPP, is the responsibility of POWERGRID whereas sale of energy is proposed through SECI. The project manager is Satluj Jal Vidyut Nigam Ltd. (SJVNL) and the operation and maintenance is to be done by Rajasthan Electronics and Instrumentation Ltd. (REIL). The first phase of 1000 MW was to be set up by 2016.

Ecology around the Sambhar Salt Lake: 

Sambhar Salt Lake is declared as a protected site of international importance. Experts say that the wetlands support large biological diversity, provide groundwater recharge, and help to control erosion and flood. The proposed Solar Power Plant is expected to cover nearly 40% of the Sambhar Salt Lake, the lake which attracts 70 species of migrant birds and is the second largest breeding ground of Flamingo birds in India. In the year 1982-83 nearly 5,00,000 flamingo birds visited the lake. Flamingo are tall birds, come in flocks and require large area for feeding and breeding. 

This proposed project could be seen as a step ahead in this direction and can be seen as a great success if it is completed without disturbing the fragile ecology around. Promoters of the project believe that the solar power plant can coexist with wetland ecology. 

Several experts are against the decision. If the growth in solar energy capacity addition is at the cost of polluting and damaging this wonderful ecology around, then, do we need such projects?  

Saturday, 13 September 2014

TRANSMISSION EXPANSION PLANNING

A transmission system connects the various generating power plants to major electrical load centres and thus forms a vital link to the economic and technical development of any country. 

What is Transmission Expansion Planning?

Transmission planning or transmission expansion planning is the process of designing future transmission network configuration that meets the predicted future needs of loads and generation. 

Fundamental objective of transmission planning:

The fundamental objective of transmission planning is to develop the system as economically as possible and to maintain an acceptable reliability level. 

Transmission planning may include:
·         Construction of new lines,
·         Determination of voltage level,
·         Network enhancement,
·         Substation configuration,
·         Selection of new technologies such as FACTS, EHV-DC etc

A transmission or network expansion may be concerned with one or more of the above mentioned tasks and each task require technical, economical, environmental and social assessments. 

The technical assessment includes load forecast, power flow calculations, contingency analysis, voltage and transient stability analysis, short circuit analysis and reliability evaluation.

Factors that call for the development of a Transmission system:

There are many factors that call for the development of a transmission system and these are:

·         Load growth,
·         New power plants,
·         Aging of equipment or Technology,
·         Commercial opportunities,
·         Reliability requirements, etc.

The first three factors account for most of the transmission expansion.

Classification of Transmission Planning:

Transmission planning can be divided into:
i)    long term, 
ii)   medium term, and 
iii) short term planning based on the duration involved. 

Long term planning involves a long planning period usually of 20 to 30 years; whereas medium term planning can be of 10 to 20 years. 

The problems and issues considered in long term planning are preliminary and often requires significant and repeated changes because of uncertain input data and information, change in technology etc. Considerations of long term planning are modified and corrected in the medium term planning according to the actual information obtained in later stages. Short term planning deals with the issues that have to be resolved within 10 years.

Regulated and Vertically  Integrated Utilities:

The electric power industry, over the years, has been dominated by large utilities that had an overall authority over all activities in generation, transmission and distribution of power. Such utilities are called as Vertical Integrated Utilities (VIU). 

They serve as the only service provider in the area and are obliged to provide electricity to everyone in the area. Transmission expansion in a regulated power industry is a centralized affair well coordinated with generation expansion planning. All the necessary information is available to the network planner. 

The main aim of transmission expansion planning in this regulated environment is to minimize the expansion cost while satisfying certain technical and economical constraints.

Restructuring and Deregulation of Power Sector:

Different countries have restructured and deregulated its power industry and many more are in the process. India too have restructured and deregulated its power sector. 

The introduction of deregulation has brought several new entities. One of the first steps in the restructuring process of power sector has been the separation of the transmission activities from the generation activities. It has redefined the scope and role of many of the existing players in the power sector and envisaged to some form of electricity market inducing competition at various levels of electricity related transactions.    

Transmission Expansion Planning in Restructured era:

The restructuring and deregulation have introduced new complexities to the transmission expansion planning. Stakeholders have different desires and expectations from the performance and expansion of the transmission system. 

Providing non-discriminatory access, facilitating competition, minimizing the cost of installation and operation, minimizing the environmental impacts are the desires of different stake holders of the power system. These participants of the electricity market take their decisions independently and also change their strategies frequently to maximize their benefits. 

Consumers of electricity change their load and hence consumption according to the price signals. Availability of independent power producers (IPP) is uncertain because of the changing scenario. Wheeling power are time varying and affect the nodal prices. Therefore, there is no specific pattern of load and the dispatched power in the deregulated electric sector.

Thus, restructuring and deregulation of power industry have changed the objectives of transmission expansion planning and increased the uncertainties.