Module 1 : Introduction
Lecture 2 : Why make interconnections?
Objectives
In this lecture you will learn the following
Why are power systems interconnected?
What is the concept of reliability? Why is it more economical to interconnect a power system?
Identifying the major elements of a practical interconnected power system.
Reliability and Economy are the main reasons for interconnecting power systems
Reliability implies that with a large interconnected grid, the loss of a system component like a major transmission line or
generator will have minor impact on system. When one device fails, another one makes up for the loss. In a practical grid,
there exists more than one path connecting a load to each generator. Thus the loss of one transmission line or tripping of
one generator does not usually interrupt power to a load.
Economy implies that electricity can be obtained from where it is cheap. It is more economical to operate large
generators 24 hours a day at full capacity (base load stations), catering not to a particular load, but pooling power into the
grid and to be used by many connected loads. A few generators which can be started almost instantaneously can then act
as reserves to cater to sudden increases in load (peak load stations). Generally steam stations are run as base load
stations while reservoir based hydro-stations and gas stations act as peak load stations. The possibility of sharing reserves
in interconnected systems also results in smaller reserve requirements. Different regions in a grid may face peak demand at
different times of the day. Therefore the total system peak demand is smaller than the sum of the individual peaks of
various regions.
However, extensive interconnections also mean that a disturbance in one part of the system may quickly spread to the
entire system, leading to tripping of loads/generators, and may even make interconnected system operation unviable. For
example, some large disturbances may make it impossible for generators to run in synchronism. In case interconnected
system operation becomes unviable, the system must "gracefully" split into smaller systems ( islands). However, if the
control and protection systems are inadequate to face this eventuality, a complete blackout may also occur, leading to loss
of service to millions of consumers.
However, grid failures are rare ("the lights are always on") and one may justifiably ask a question : how does the whole
system work so well? After all, for well designed power systems, power is available on demand and can be obtained by
simply "paralleling" the load on the grid. Similarly, a synchronous machine driven by a prime-mover can be synchronised
with a grid and may supply power to it. Of course, all this is subject to certain constraints which we shall study in the next
module.
A great deal of prior planning and control during operation is required to make an inter-connected network capable of
catering to a certain level of power flow and prevent blackouts.
Example of a large power system
Western Region of the WR-ER-NER Synchronous Grid: A description
This region has the largest inter-connected network in the country, comprising the states of Chattisgarh, Goa, Gujarat,
Maharashtra, Madhya Pradesh, besides Union territories of Daman and Diu, and Dadra and Nagar Haveli. In 2002, the
installed capacity was 31.5 GW with 13.8% hydro, 66% thermal- coal, 15.9% gas/liquid fuel, 2.4% nuclear and wind
Lecture 2 : Why make interconnections?
Objectives
In this lecture you will learn the following
Why are power systems interconnected?
What is the concept of reliability? Why is it more economical to interconnect a power system?
Identifying the major elements of a practical interconnected power system.
Reliability and Economy are the main reasons for interconnecting power systems
Reliability implies that with a large interconnected grid, the loss of a system component like a major transmission line or
generator will have minor impact on system. When one device fails, another one makes up for the loss. In a practical grid,
there exists more than one path connecting a load to each generator. Thus the loss of one transmission line or tripping of
one generator does not usually interrupt power to a load.
Economy implies that electricity can be obtained from where it is cheap. It is more economical to operate large
generators 24 hours a day at full capacity (base load stations), catering not to a particular load, but pooling power into the
grid and to be used by many connected loads. A few generators which can be started almost instantaneously can then act
as reserves to cater to sudden increases in load (peak load stations). Generally steam stations are run as base load
stations while reservoir based hydro-stations and gas stations act as peak load stations. The possibility of sharing reserves
in interconnected systems also results in smaller reserve requirements. Different regions in a grid may face peak demand at
different times of the day. Therefore the total system peak demand is smaller than the sum of the individual peaks of
various regions.
However, extensive interconnections also mean that a disturbance in one part of the system may quickly spread to the
entire system, leading to tripping of loads/generators, and may even make interconnected system operation unviable. For
example, some large disturbances may make it impossible for generators to run in synchronism. In case interconnected
system operation becomes unviable, the system must "gracefully" split into smaller systems ( islands). However, if the
control and protection systems are inadequate to face this eventuality, a complete blackout may also occur, leading to loss
of service to millions of consumers.
However, grid failures are rare ("the lights are always on") and one may justifiably ask a question : how does the whole
system work so well? After all, for well designed power systems, power is available on demand and can be obtained by
simply "paralleling" the load on the grid. Similarly, a synchronous machine driven by a prime-mover can be synchronised
with a grid and may supply power to it. Of course, all this is subject to certain constraints which we shall study in the next
module.
A great deal of prior planning and control during operation is required to make an inter-connected network capable of
catering to a certain level of power flow and prevent blackouts.
Example of a large power system
Western Region of the WR-ER-NER Synchronous Grid: A description
This region has the largest inter-connected network in the country, comprising the states of Chattisgarh, Goa, Gujarat,
Maharashtra, Madhya Pradesh, besides Union territories of Daman and Diu, and Dadra and Nagar Haveli. In 2002, the
installed capacity was 31.5 GW with 13.8% hydro, 66% thermal- coal, 15.9% gas/liquid fuel, 2.4% nuclear and wind
