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Saturday, 13 September 2014


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.