Electrical Power

2.1 INTRODUCTION System : Overview

Overview of Generation, Transmission and Distribution

Three main components of electric power system are :

 Power Generation Station

 Transmission Lines

 Distribution Lines.

Power is among the most capital-intensive infrastructure sectors.

Power has been placed in the list of concurrent subjects under the
Indian Constitution. After independence, the State Electricity Boards
(SEBs)/State Electricity Departments were the sole utilities (except a
few licensees in private sector) responsible for generation,
transmission and distribution of electricity in their respective area. To
supplement the efforts of States in bridging the yawning gap
between demand and supply of power, it was decided, in mid
seventies, to set up generating stations and transmission lines in the
Central Sector. Today, States control about 60 % of the country’s
Generation capacity, 70 % of the transmission network, and almost
100 % of the distribution system.

Figure 2.1 : Typical Electrical Power Supply

 Objectives
After studying this unit, you should be able to

 learn about electrical power system 31

Elementary  understand how electrical power is generated,
Electrical and
Exposure to Tools
 explain the power transmission system,

 describe the power distribution system,

 list the various problems related to generation, transmission

and disribution,

 know the grid management, and

 identify the quality parameters of electric supply.

2.2 COMPONENT DESCRIPTION

In the earlier unit, we learnt the concept of phase difference between

voltage and current in the AC. Now we extend it in the case voltages on
multiple lines. Let us consider the case of two conductors carrying voltage
of equal magnitude. Further, we assume that the frequency of the two is
also exactly the same. Now we look at the third possible parameter, i.e.
the difference of phase between the lines. The argument may be
extended to more than two line. Of interest to us is the case of three lines.
Commonly, commercial power stations produce power for evacuation
using three lines. The angular phase differential between any two lines is
120 degrees. The use of three lines ensures that the overall phase
difference is 120  3 = 360 degree, which represents a full circle, hence
360 degree is same as 0 degree. Such a scheme is named as 3-phase
supply and needs three wires to conduct electricity.

In India, the Electric Supply is generally AC, and is available at many

different voltage levels, depending on the ease of use or technical
requirements. The lowest level, i.e. the retail consumer gets electric power
at 230 volts, this is single-phase, two-wire supply. Barring this and the
occasional HVDC lines, all other supply is 3-wire, 3-phase. The line
voltage stated in these cases is always the voltage between any two
phases. There are many standard values in use. To name a few : 400V,
3.3 kV, 6.6 kV, 11 kV, 33 kV, 66 kV, 110kV, 132 kV, 220 kV and 400 kV.

While there is no hard and fast rule, the voltage levels 132 kV and above
are normally, part of the transmission network, while the lower voltage
levels are used in the distribution system.

Given below are many of the components of a power system.

32
 Component Description Electrical Power
System : Overview
Component Description

Power from transmission network is

delivered to sub-transmission network after
Grid Substation (GSS) stepping down the voltage to 66 kV or
33 kV through 220/132/66/33 kV Grid
substations.

Sub-transmission Network Power is carried at 66 or 33 kV by

overhead lines or underground cables

Power Sub-Transmission Power is stepped down by 66-33/11 kV to

(PSS) 11 kV for distribution.

Power is delivered from PSS through

primary feeders at 11 or 6.6 kV to various
Primary Distribution Feeders distribution transformers.

Distribution Substation Power is further stepped down by 11/0.4 kV

(DSS) transformers to utilisation voltage of 400 V.

Secondary Distribution It carries power from DSS at 400 V (230 V

Network single-phase) to various consumers through
service lines and cables.

It comprises

Generation Units that produce electricity

High Voltage Transmission Lines that transport electricity

over long distances

Low Voltage Distribution Lines That delivers electricity to

Consumers

Substations, which are the part of the electricity transmission

and distribution system where the voltages are transformed to
lower levels for distributing power to end – user.

 Check Your Progress 1

Who is mainly responsible for Electricity Supply system in the country?

33
Elementary
Electrical and  Check Your Progress 2
Exposure to Tools
Which are the three major components of Electric Power System?

2.3 POWER GENERATION

 Power Generation

 Major Players

In India the following players generate electrical power :

 Central Utilities such as NTPC, NHPC, Nuclear Power

Corporation, Damodar Valley Corporation and NEEPCO.

 State Electricity Boards which are state-owned utilities like

Orissa, Haryana, AP, Uttar Pradesh, Karnataka etc.

 Licensees such as BSES and CESC.

 Independent Power Projects (IPPs).

Four basic categories of Electric Power Generation in India

based on the energy source:

 Fossil fuel, such as – coal, oil and natural gas,

 Hydro Power,

 Nuclear Power, and

 Renewable Energy – bio-fuels, solar, biomass, wind and

tidal.

Figure 2.2 : Electrical Power Generation Sources

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 Our country is the world's third largest producer and third largest Electrical Power
System : Overview
consumer of electrical power. ‘The national electric grid in India has
an installed capacity of 368.79 GW as of 31 December 2019’.

As on December 2019, about 55.5% of power generated in India is

from Coal Based Thermal Power Station. The large hydro Electric
Power Plants accounts for about 12.3% of total electricity
generation. Nuclear Power Plants make up about 1.8% and about
23.5% comes from renewable energy resources (Wind, Solar,
Biomass, and Small Hydro).

Coal : 205,344.5 MW (55.5%)

Large Hydro : 45,699.22 MW (12.3%)
Small Hydro : 4,683.16 MW (1.3%)
Wind Power : 37,669.25 MW (10.2%)
Solar Power : 34,405.67 MW (9.3%)
Biomass : 10,001.11 MW (2.7%)
Nuclear : 6,780 MW (1.8%)
Gas : 24,955.36 MW (6.7%)
Diesel : 509.71 MW (0.1%)

Figure 2.3: Share of Installed Generation Capacity from Energy Resources

 Check Your Progress 3

What is the contribution of Hydroelectric Power Generation to the total
Installed generation capacity in the country?

2.4 POWER TRANSMISSION

 Transmission

In India, the power plants typically produce 50 cycles/second (Hertz)

alternating current (AC) with voltages between 11 kV and 25 kV.
Electric power is brought from the power plant to the consumer
through an extensive transmission and distribution (T&D) system
comprising transmission lines, distribution networks, forming the
state and the regional grid.

The various stages are given below:

 At the plant, the 3-phase voltage is generated and

stepped up to a higher voltage for cross-country
transmission, on cables strung on towers.
35
Elementary  High voltage (HV) and extra high voltage (EHV)
Electrical and
Exposure to Tools transmission in the next stage, to transport A.C. power
from the power plant over long distances at voltages like
132 kV, 220 kV, 400 kV and 760 kV.

 For longer distances and higher powers, higher voltages

are economical. By using high voltages, there is a
reduction in line losses. In special cases HVDC (High
Voltage Direct Current transmission + 500 kV DC) is
preferred.

 Sub-transmission network at 132 kV, 110 kV, 66 kV or

33 kV constitutes the next link towards the end user.

 Major Players

Most of the states restructured their State Electricity Boards and

have unbundled them in three entities Generation, Transmission and
Distribution. As such, the state created transmission company (else
the local SEB) remains the dominant player. The central sector
company, Power Grid Corporation of India Ltd (PGCIL) is the owner
of most of the higher voltage transmission lines in the country. A few
private sector player, e.g. Tata Power and Reliance Power have also
entered in this field.

 Check Your Progress 4

What is the full form of HVDC?

2.5 POWER DISTRIBUTION

 Distribution

This segment involves receipt of bulk power from the transmitting

utilities and the supply to the final consumers at lower voltage levels.

Distribution at 11 kV/6.6 kV/3.3 kV constitutes the last link to the

consumers which is connected directly or through step-down
transformers. These transformers bring the voltage levels down to
400 V for 3-phase, 3 or 4 wire secondary distributions. The forth
wire, when present is called ‘neutral’ or the return wire.
36
The single-phase residential lighting load is connected between any Electrical Power
System : Overview
one phase and neutral (230 V) and 3-phase load is connected
across 3-phase lines directly.

 Major Players

Orissa and Delhi are the only states where power distribution
has been entrusted to the private sector. Orissa has been
divided into 4 zones – Wesco, Nesco, Southco and Cesco.
AECO, CESC, NDPL, BSES, Torrent Power are some of the
Private Companies managing Distribution in Cities. In some of
the cities Distribution System has been handed over to
franchisees. Among these are, Kolkatta, Kanpur, Ahmedabad,
Noida, Surat.

 Description of the Power Distribution System

Typically, electricity generated by a power station is carried

over a transmission line at high voltage. Usually, these lines
may run upto hundreds of kilometre and deliver the power into
a common transmission network, called the grid.

The grid is connected to load centres (cities) through a

sub-transmission network of usually 33 kV (or sometimes
66 kV) lines. These lines terminate into a 33 kV (or 66 kV)
substation, where the voltage is stepped-down to 11 kV for
power distribution to load points through a distribution network
of lines at 11 kV and lower.

The power network concern to the end-user is the distribution

network of 11 kV lines or feeders downstream of the 33 kV
substations. Each 11 kV feeder which emanates from the
33 kV substation branches further into several subsidiary 11 kV
feeders to carry power close to the load points (localities,
industrial areas, villages, etc.).

At these load points, a transformer further reduces the voltage

from 11 kV to 400 V to provide the last-mile connection through
400 V feeders (also called Low Tension (LT) feeders) to
individual customers, either at 230 V (as single-phase supply)
or at 400 V (as three-phase supply). The utility voltage of
400 V, 3-phase is used for running the motors for large to
medium industry and agricultural pump sets and 230 V, single
phase is used for lighting in houses, schools, hospitals and for
37
Elementary running small industries, commercial establishments, etc. Very
Electrical and
Exposure to Tools large industries are supplied power at 11 kV or higher.

A feeder could be either an overhead line or an underground

cable. In urban areas, owing to the high density of customers,
the length of an 11 kV feeder may generally be up to 3 km. On
the other hand, in rural areas, the feeder length is much larger
(up to 20 km). A 400 V feeder should normally be restricted to
about 0.5-1.0 km. Unduly long feeders lead to low voltage at
the consumer end. The power supply system, including the
distribution network, is depicted in Figure 2.4.

Figure 2.4 : Typical Electric Power Supply System with Distribution Network

Generate More Reduce AT&C Improve Customer

Power Losses Service

Increase Revenue Adopt Better Use Information

Collection Management Technology

Figure 2.5 : Some Measures that can be taken to Address the Challenges before the
Power Distribution Sector

38
 Electrical Power
 Check Your Progress 5 System : Overview

What is the lowest 3-phase voltage in the distribution network?

2.6 GENERATION, TRANSMISION AND

DISTRIBUTION – PROBLEMS

Generation Transmission Distribution

Inadequate Inadequate Inadequate and aging

power inter- regional sub-transmission and distribution
generation transmission links network leading to frequent power
capacity cuts and local failures/faults,
erratic voltages and low or high
supply frequency.

Lack of optimum Lack of grid discipline Large-scale theft, inefficient use of

utilization of the and poor grid electricity by the end consumers.
existing management Bad power factor.
generation
capacity

Problem with High Transmission Day to day problems of the

availability of the losses consumers like hurdles in getting
source of new connections or enhancement
energy, i.e. Coal of loads, stiff procedures,
for thermal unfriendly commercial policies,
plants, Water for tardy metering, inflated billing and
Hydro plants insufficient collection avenues,
hostile staff, massive churning of
the consumers, poor dispute
resolution mechanism.

 Check Your Progress 6

What problems faced by the Distribution Utility can be attributed to its
consumers?

39
Elementary
Electrical and 2.7 GRID MANAGEMENT
Exposure to Tools

 Grid Management

 What is a Grid?

You know that a power system has a generating unit to

generate electrical energy, which is consumed at the load. This
energy cannot be stored and has to be consumed at the same
instant. But since the load is not concentrated at one place and
in most cases, it is not possible to have a generator very close
to the load centre at all times, we go for transmission lines,
which facilitate transmission of power from generator to load.
To provide redundancy, the transmission lines are also
interconnected. Thus all generation units and load centres are
connected and as a result, a grid is formed

Generation Transmission Distribution Consumers

(Grid as an Intermediary between Generation and Load)

Figure 2.6 : The Electric Power Chain, from Generation till Consumption

The grid is basically a connection of generating stations,

substations and loads through transmission lines, at a voltage
level above the distribution voltage. The distribution voltage,
however, is not strictly defined.

It is different for different areas. In some distribution systems,

power is taken from the grid at 33 kV, in some it is taken at
66 kV and in some, it may even be taken at 220 kV. Therefore,
the grid covers the above mentioned high voltage system down
to the level of connection point of the distribution system.

Definition of Grid

Grid is defined in the Electricity Act, 2003, as : “the high voltage

backbone system of inter-connected transmission lines, substations
and generating plants.”

40 Figure 2.7 : Definition of Grid

 Advantages of a Grid Electrical Power
System : Overview
 Reliability

The system is more reliable since we can serve the load in

more than one ways. As a result, even if one generation unit
fails the rest can share the load.

 Stability

The system becomes more stable as the changes of a fault

disturbing the whole system become less.

 Economy

In a grid, the cost required is lesser than a dedicated system

since lesser installed capacity is required as well as lesser
spinning reserve is involved.

 Check Your Progress 7

What is a grid?

2.8 OBJECTIVES OF GRID MANAGEMENT

 Reliability,

 Grid security,

 Economy, and

 Quality in electric supply.

 Reliability

Reliability comes with integrated grid operation for smooth

evacuation of power from generating stations and its delivery at the
states’ periphery.

 Grid Security

Security comes by maintaining the system parameters like

frequency, bus voltages, line loadings and transformer loadings
within permissible limits. It involves stable and smooth operation of
the grid, i.e. minimum interruptions of power, either through tripping
of single grid elements (like generator, transmission line,
41
Elementary interconnecting transformer, HVDC back-to-back pole) or grid
Electrical and
Exposure to Tools disturbances involving tripping of a large number of grid elements
simultaneously or even a total blackout.

 Economy

Economy comes by merit order generation, optimisation of hydro

resources, minimisation of losses and judicious inter-regional
exchanges. It envisages getting the cheapest power to the
customers through minimization of transmission losses and ensuring
that the cheapest generation is used first, then the next costly
generation and so on.

 Quality in Electric Supply

Quality in electric supply is facilitated by the inertia of a large grid,

which smoothes over variations in frequency and power due to
sudden changes in load.

 Check Your Progress 8

How does a Grid improve reliability?

2.9 QUALITY OF ELECTRIC SUPPLY

QUALITY in electric supply is now gaining importance.

The parameters of quality are frequency, voltage and harmonics.

Quality parameters of Electric Supply.

Frequency is a global phenomenon, i.e. it is the same at all points of a

grid, which is operating in synchronous operation. Frequency is an
indication of the balance between generation and load in a grid. If the
generation exactly matches the load, the frequency would be the nominal
frequency, i.e. 50 Hz. If generation is more than the load in a grid as a
whole, the system frequency would be greater than 50 Hz. If generation is
less than the load, the system frequency would be less than 50 Hz.

Voltage is a local phenomenon, i.e. it can be different at different points of

the grid. Therefore, the grid operator has to ensure that the proper voltage
profile is maintained at all points of the grid. For ensuring proper voltage
profile, capacitors or reactors are installed at different points in the grid. If
42
it is observed that the voltage is low at a particular point in the grid, then Electrical Power
System : Overview
capacitors are installed at that point. Similarly, if voltage is observed to be
high, as per the studies, then reactors are installed at that point. The
basic purpose of these elements is to ensure that the reactive power
requirement of the load or transmission lines is met.

Besides this, there are also other voltage phenomena like unbalanced
voltage in the three phases, voltage dip, etc. Voltage unbalance in the grid
could be caused due to the tripping of one of the phases of a transmission
line or due to unbalanced load in the three phases emanating from the
distribution systems or bulk loads. Voltage dip, on the other hand, is a
transient phenomenon caused by a transient fault or tripping of an
element at a remote location of the grid. Stormy weather could also cause
flashover between arcing horns, resulting in voltage dip.

Harmonics is recently becoming an issue in the modern world, due to a

number of electronic devices connected in the grid as well as in the
distribution system, which converts AC to DC through rectifiers or which
chop an AC wave for voltage or current control. In the grid, harmonics are
caused by HVDC stations, which convert AC to DC and back from DC to
AC.

In the distribution system, harmonics are caused by power supplies and

inverters which are installed to supply emergency power to computers and
all household appliances using digital technology, which have permeated
our lives. For this, standards have been laid down in the Regulations for
Technical Standards for Connectivity to the Grid. As per the provisions of
these Standards, the limits for individual and total harmonics distortion
have been given.

2.10 LET US SUM UP

In this unit, we learnt about the Electric Power System. We now know that
electricity system is organized in three major parts, namely, Generation,
Transmission and Distribution. We have learnt that power is generated
wherever feasible, and the generating plant may not be close to the user
or consumer. Hence power is transmitted over long lines at high voltage to
cover this distance. These lines form the Transmission system and the set
of the lines is named as the grid. Once the power is brought close to the
user, it is converted to lower voltages and over the distribution system,
supplied to the end user.
In regard to Generation, we learnt the various sources of energy, which
are employed to generate electric power. We know now that thermal
power (mainly coal) forms the largest source, followed by hydropower. We 43
Elementary understand that depending on the source, we classify power generation
Electrical and
Exposure to Tools as renewable or not. In general, electric power is generated as AC or
Alternating Current.

Under Transmission we understand that long transmission lines are

required to carry the generated power up to the user location. We have
learnt that transmission voltages generally range from 132 kV and higher.
This helps in reducing power loss. We also know that more
interconnecting lines are usually provided to enable redundancy in the
system. The complete set of these lines is referred to as the Grid. Grid
has high inertia and hence help to reduce variations in the operating
parameters, such as frequency and voltage.

Under distribution system we understand that part of the system, which is

closer to the end user. Hence, we can afford to use lower voltages,
typically, below 66 kV. The residential consumer gets power at 230 V.

We know the difference between single-phase supply (phase to neutral)

and three phase supply (phase to phase). The lowest 3-phase voltage is
400 V. We understand that 3-phase supply is normally provided to
industrial consumers. Against this, the normal residential user gets
single-phase power at 230 V.

We have learnt about the objectives of Grid management, which implies

Reliability, Security, Economy and Quality. We have also learnt that
frequency, voltage and harmonics are the factors that affect the quality of
power supply.

2.11 KEY WORDS

Electric Power System : System that generates, transmits, and

distributes electric power to the end user.

Energy : Capacity to perform work.

Capacitor : A capacitor is a device for storing a large

quantity of electric charge.

Efficiency of Power : Ratio of the power delivered to the power

Transfer supplied by the source.

Alternatively Current : The current where magnitude changes

with time and the direction reverses
periodically is known as alternatively
current.
44
Transformer : It is a device to change low alternating Electrical Power
System : Overview
voltage at high current into high voltage at
low current and vice-versa.

High Voltage Power : Use of voltages greater than 100 kV to

Transmission keep low resistive losses (I2R) on the
transmission lines.

Passive Elements : Element that absorbs energy.

Phase Voltage : Voltage of each phase of a three-phase

system.

Power Factor : Equal to cos , where  is the phase

angle difference between the sinusoidal
steady-state voltage and current.

2.12 TERMINAL QUESTIONS ?

(a) Why do we need Transmission lines?

(b) What voltages are common in a distribution system?

(c) Why is high voltage preferred for transmission lines?

(d) What are the three quality parameters of electric supply?

1.6 ANSWERS TO CHECK YOUR

PROGRESS 
Ans. 1

State Electricity Boards/ Departments.

Ans. 2

Generation, Transmission and Distribution.

Ans. 3

25%

Ans. 4

High Voltage Direct Current.

Ans. 5

400 V

Ans. 6

Theft of Electrical Power and Inefficient use of electricity.

45
Elementary Ans. 7
Electrical and
Exposure to Tools Grid is the total set of Transmission lines, from Generation Plants up
to the Distribution location, including the cross-connect and
redundant lines.

Ans. 8

The Grid is very much larger than any user load or generation plant.
The grid can be said to have inertia to change directed by the failure
of any generator or user load. Since the grid has multiple sources of
power and many loads, any single failure is but a fraction of the total
power available. Hence it leads to only a minor change in the grid
related parameters, such as frequency or voltage.

Electrons are very particles with a unit negative charge, whereas,

Protons have a unit positive charge and are many times heavier than
the electrons. Also, Protons reside in the nucleus of an atom, while
Electrons revolve around it.

2.14 ANSWERS TO TERMINAL QUESTIONS 

(a) As stated, the generating plants are normally not located close
to the load point due to various economic/ operational reasons.
This brings the need to carry power to the load, efficiently.
Such a carrier is the transmission line. Stated otherwise,
Transmission lines are needed to transmit bulk power over long
distances, economically.

(b) The lowest voltage in a distribution system is 230 V, single

phase, or 400 V, 3-phase. The other common voltages are
3.3 kV, 6.6 kV, 11 kV, 33 kV, 66 kV and in some cases, even
132 kV.

(c) As we recall, Power is voltage  current. Hence, by increasing

the line voltage, we achieve lower line current, for the same
amount of power. The lower current causes lower resistive
losses in the line. Hence higher voltage is preferred for power
transmission.

(d) Three main quality parameters are :

 Frequency

 Voltage

 Harmonics
46