POWER TRANSMISSION

1. Review Notes
Power Transmission
Dr. Lalit K Khurana
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Introduction: Electrical power is normally generated at 11kV in a power station. This generating
voltage is then stepped up to 132kV, 220kV, 400kV or 765kV etc. Stepping up the voltage level depends
upon the distance at which power is to be transmitted.
Electrical Power Transmission System
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a
power plant, to an electrical substation. Electrical power is generated at different generating stations.
These generating stations are not necessarily situated at the load center. During construction of
generating station number of factors is to be considered from economical point of view. These all factors
may not be easily available at load center; hence generating stations are not normally situated very
nearer to load center. Load center is the place where maximum power is consumed. Hence there must be
some means by which the generated power must be transmitted to the load center. Electrical
transmission system is the means of transmitting power from generating station to different load centers.
Fundamentally there are two systems by which electrical energy can be transmitted.
1. High voltage DC electrical transmission system.
2. High AC electrical transmission system.
Why Electrical Power is transmitted at high voltage?
The power generated at generating station is in low voltage level as low voltage power generation has
some economical values. Low voltage power generation is more economical than high voltage power
generation. At low voltage level, both weight and insulation is less in the alternator, this directly reduces
the cost and size of alternator. But this low voltage level power cannot be transmitted directly to the
consumer end as because this low voltage power transmission is not at all economical. Hence although
low voltage power generation is economical but low voltage electrical power transmission is not
economical. Electrical power is directly proportional to the product of electrical current and voltage of
system. So for transmitting certain electrical power from one place to another, if the voltage of the power
is increased then associated current of this power is reduced. Reduced current means less I2R lossin the

2. system, less cross sectional area of the conductor means less capital involvement and decreased current
causes improvement in voltage regulation of power transmission system and improved voltage regulation
indicates quality power. Because of these three reasons electrical power mainly transmitted at high
voltage level.
What is Transmission Line?
Transmission line is the long conductor with special design (bundled) to carry bulk amount of generated
power at very high voltage from one station to another as per variation of the voltage level.
Type of Transmission Line
In transmission line determination of voltage drop, transmission efficiency, line loss etc. are important
things to design. These values are affected by line parameter R, L and C of the transmission line.
Lengthwise transmission lines are three types.
Short Transmission Line
Length is about 50 km.
Voltage level is up to 20 kV
Medium Transmission Line
Length is about 50km to 150km
Operational voltage level is from 20 kV to 100 kV
Long Transmission Line
Length is more than 150 km
Voltage level is above 100 kV
What is the Transmission Efficiency?
Transmission efficiency is defined as the ratio of receiving end power PR to the sending end power PS and
it is expressed in percentage value.
Why Low and Medium Voltage is Used in Distribution Line?
In primary distribution, power is handled at 11 kV or 33 kV. As voltage level gets stepped down from
132kV to 11 kV or 33 kV, current level gets higher valued. But this high valued current distributed among
various local distribution stations (distribution transformers) nearby. These distribution transformers
again steps down the voltage to 415 V. It is because; Power at 415 V is used at the user end. Distance
between these distribution transformers and the primary distribution stations is very short, hence
conductor resistance is not large. Very small amount of power is lost in this section
Transmission Losses
Transmission loss is calculated by taking the difference between total electrical energy received from the
generating plants and the total energy supplied to all bulk supply distribution licensees. It is usual to
express losses as a percentage value rather than an absolute value
The definition of the transmission losses is defined as;
Where; EG = Total Energy Purchased from generation plants (MWh) during reported period ET = Total
Energy Sold to Distribution Licensees (MWh) during reported period

3. Transmission System Power Quality
Quality of a power system service is measured with reference to system voltage and frequency. Power
quality indicators show how the transmission line parameters comply with the defined standards and
limits.
Frequency Standard
The system is normally managed such that frequency is maintained within operational limits of 49.5 and
50.5Hz. Frequency may move outside these limits under faulty conditions, or when abnormal changes to
operating conditions occur. Frequency deviation indices can be found by calculating the number of time
or duration that the system frequency goes beyond the allowable range.
Voltage Criteria
Voltage variation is the deviation of voltage in a certain range. Voltage deviations can be identified by
monitoring the bus bar voltages of the grid substations. According to the defined standards, bus bar
voltage magnitudes must comply with allowed ranges of variation. Voltage deviation indices can be
defined to find the frequency or duration that the bus bar voltages violate above range. By analyzing the
recorded minimum bus bar voltages it could be identified that the allowable voltage limits have been
violated every month during the reported period.
Right of Way Management
The Right of Way in transmission line defined as land set two path of the center of transmission line. Right
of Way is also called as transmission corridor. This corridor can be maintained by private or government
authorities.
Safety is one of the essential factors of transmission line and ROW provides necessary landscape
arrangement. There are several voltage levels of the lines maintained and the width of transmission line
corridor (ROW) changes due to the voltage levels.
For example, 132kV transmission line Right of Way shall nearly 30m which means 15m either side from
the center of 132kV transmission lines. For higher voltages transmission line the width or transmission
line get increased to maintain proper safety clearance. Normally trees which grow higher will cut for
example in generally trees which higher than 3m will cut to maintain proper ROW under transmission line
and trees or plant can grow below3m, The condition and clearance height may different from country to
country.
ROW is one of the major considerations while creating transmission line. Since most of transmission
lines traverse overhead, most of vegetation affect transmission line corridor, therefore social and
environmental study is very necessary while design of transmission lines.
Environmental and social impacts of transmission lines are much less compare to other major
developments but in some cases there transmission line corridor do major impacts in environmental
sensitive areas.
Following are most commonly used ROW parameters for transmission lines
ROW width for 132kV transmission line = 27m
ROW width for 220kV transmission line = 35m
ROW width for 400kV transmission line = 53m
ROW width for 765kV transmission line = 85m
However the maintenance of proper Right of Way (ROW) in Electrical power transmission lines is very
important factor in transmission line
What is Advanced Metering Infrastructure?

4. AMR stands for Automatic Meter Reading. It is an older technology that only collects electrical energy
consumption and transfers that data from the electric meter on the home to the utility (one-way
communication). AMI stands for Advanced Metering Infrastructure. Advanced metering infrastructure
(AMI) is architecture of integrated system of smart meters, communications networks, and data
management systems that enables two-way communication between a smart utility meter with an IP
address and a utility company. The goal of an AMI is to provide utility companies with real-time data
about power consumption and allow customers to make informed choices about energy usage based on
the price at the time of use.
Electrical grids
"The grid," refers to the electric grid, a network of transmission lines, substations, transformers and more
that deliver electricity from the power plant to your home or business. Electrical grids perform two main
functions. They carry electrical current from the power producer to the end-user and they regulate the
electrical current that is being transported through the lines. Current electric grid was built in the 1890s
and improved upon as technology advanced through each decade. o move forward, we need a new kind
of electric grid, one that is built from the bottom up to handle the groundswell of digital and
computerized equipment and technology dependent on it—and one that can automate and manage the
increasing complexity and needs of electricity in the 21st
Century.
What Makes a Grid “Smart?”
The digital technology that allows for two-way communication between the utility and its customers, and
the sensing along the transmission lines is what makes the grid smart. Like the Internet, the Smart Grid
will consist of controls, computers, automation, and new technologies and equipment working together,
but in this case, these technologies will work with the electrical grid to respond digitally to our quickly
changing electric demand.
What does a Smart Grid do?
The Smart Grid represents an unprecedented opportunity to move the energy industry into a new era of
reliability, availability, and efficiency that will contribute to our economic and environmental health.
The benefits associated with the Smart Grid include:
More efficient transmission of electricity
Quicker restoration of electricity after power disturbances
Reduced operations and management costs for utilities, and ultimately lower power costs for
consumers
Reduced peak demand, which will also help lower electricity rates
Increased integration of large-scale renewable energy systems
Better integration of customer-owner power generation systems, including renewable energy systems
Improved security
Today, an electricity disruption such as a blackout can have a domino effect—a series of failures that can
affect banking, communications, traffic, and security. A smarter grid will add resiliency to our electric
power System and make it better prepared to address emergencies such as severe storms, earthquakes,
large solar flares, and terrorist attacks. Because of its two-way interactive capacity, the Smart Grid will
allow for automatic rerouting when equipment fails or outages occur. This will minimize outages and
minimize the effects when they do happen. When a power outage occurs, Smart Grid technologies will
detect and isolate the outages, containing them before they become large-scale blackouts. The new
technologies will also help ensure that electricity recovery resumes quickly and strategically after an
emergency—routing electricity to emergency services first, for example. In addition, the Smart Grid will
take greater advantage of customer-owned power generators to produce power when it is not available
from utilities.
Power Transmission System of India

5. The electricity transmission network sells the electricity transmitted from generation stations, to the
distribution licensees. India's Power Transmission networks constitute the vital arteries of the entire
power value chain. An extensive network of Transmission lines has been developed over the years for
evacuating power produced by different electricity generating stations and distributing the same to the
consumers. Depending upon the quantum of power and the distance involved, lines of appropriate
voltages are laid.
The backbone transmission system in India is mainly through 400 kV AC network with approximately
90,000 circuit kilometers (ckm) of line length. The country has been demarcated into five electrical
Regions viz. Northern (NR), Eastern (ER), Western (WR), Southern(SR) and North Eastern (NER). All the
five regions are interconnected through National Grid comprising hybrid AC/HVDC system. Power grid
Corporation of India Limited (POWERGRID), the Central Transmission utility (CTU) is responsible for
wheeling power of central generating utilities and interstate Mega IPPs, while State Transmission Utilities
are responsible for wheeling of power from State generating units and State level IPPs. The CTU, plays an
important role in the planning of new transmission systems as well as strengthening of existing networks
at the Central level.
As per the Electricity Act, 2003 the functions of the Central Transmission Utility are to
Undertake transmission of energy through inter-State transmission system
Discharge all functions of planning & co-ordination for inter-state transmission system with state
transmission utilities, Central Govt., State Govt., Generating companies, Authority, Licensees etc.
Ensure development of an efficient, coordinated and economical system of inter-state transmission
lines for smooth flow of electricity from generating stations to load centers
Exercise supervision & control over the inter-state transmission system
Ensure integrated operation of the regional grids through RLDCs
Similarly, the State Transmission Utilities are responsible for the development of transmission networks
at the state level.
Power Grid
Powergrid Corporation of India Limited (POWERGRID), a Central Transmission Utilities (CTU) is a
'Navratna' Company operating under Ministry of Power, is engaged in power transmission business with
the responsibility for planning, implementation, operation and maintenance of Inter-State Transmission
System (ISTS). POWERGRID is a listed Company, with 57.90% holding of Government of India and balance
by Institutional Investors & public. As on July 31, 2017, It owns & operates around 1,41,920 ckm of Extra
High Voltage (EHV) transmission lines spread over the length and breadth of the country.
POWERGRID has successfully completed the prestigious NKN (National Knowledge Network) project
devised by Govt. of India, which connects all knowledge centres across the Country such as Indian
Institutes of Technology (IITs), Indian Institute of Sciences (IISCs) etc. As a part of Government of India
plan to connect 250,000 Gram Panchayats (GP) in the Country, POWERGRID one of the implementing
agencies for BharatNet project and has been entrusted with the task of development and maintenance of
the National Optical Fibre Network in states, namely Andhra Pradesh, Telangana, Himachal Pradesh,
Jharkhand and Odisha.
As a part of Government of India plan to connect 250,000 Gram Panchayats (GP) in the Country,
POWERGRID one of the implementing agencies for BharatNet project and has been entrusted with the
task of development and maintenance of the National Optical Fibre Network in states, namely Andhra
Pradesh, Telangana, Himachal Pradesh, Jharkhand and Odisha.
POWERGRID is offering consultancy services to various National clients & International clients, including
many South Asian, African, and Middle East countries.
POWERGRID also acts as 'nodal point' in prestigious "India Smart Grid Task Force" Secretariat for
Government's activities related to Smart Grid.

6. During FY 2015-16, POWERGRID has achieved a turnover of about Rs. 21,281 Crore and Net Profit of
Rs.6,027 Crore. The Company has an excellent credit rating with financial institutions, thereby, is placed
in a comfortable position in terms of resource mobilization.
POWERGRID has emerged as a strong player in South Asia and is playing an active role in formation of a
strong SAARC grid for effective utilization of resources for mutual benefits. Presently, various electrical
interconnections exist between India & Bhutan, India & Nepal and India & Bangladesh
POWERGRID is strengthening its transmission network to establish inter-State and inter-regional links
for enhancing the capacity of National Grid in a time bound manner to ensure optimal utilization of
uneven distribution of energy resources. POWERGRID is strengthening its transmission network to
establish inter-State and inter-regional links for enhancing the capacity of National Grid in a time bound
manner to ensure optimal utilization of uneven distribution of energy resources.
Private sector participation in transmission
Electricity Act 2003 allows non-discriminatory open access to the transmission system with immediate
effect. In order to mobilize resources from private sector, Government of India issued guidelines for
private sector participation in transmission sector in January 2000. Guidelines envisage two distinct
routes for private sector participation in transmission: Joint Venture (JV) Route & Independent Private
Transmission Company (IPTC) Route.
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