Power System Operations and Control

Prof. S.N. Singh

Department of Electrical Engineering
Indian Institute of Technology, Kanpur
Module - 01
Lecture - 01
Welcome to power system operation and control course in which the lecture
module one consist of structure evolution, and also we will see the main
requirements for the power system operation and control. Before going as you
know, this electricity is one of the important essentials for any development of any
country and also for the mankind. The commercial use of electricity is started in the
late 1870s; however, the invention of the electricity took place very beginning.
(Refer Slide Time: 00:52)

In the early phase of electricity development or evolution, this was only use for the
lightening purpose. There were generators as well as the loads; there were together,
and it was localized to certain local areas. The first electric power system which
started in 1982 and it was invented by Thomas Edison at the Pearl Street Station in the
New York, USA. This power system was the DC system, and it was consisting of the

DC generators, the cables, fuses and also the load. It was feeding the power to the 59
customers, and it was feeding in a radius of approximately 1.5 kilometer in that one.
The operating bold is it was 110 volt and mostly it was giving loads to the
incandescent lamps means simple bulbs. And at that time, the four generators are 25
hp were used, and it was the DC generator. In 1884, these motors were developed by
the Frank Sprague, and there were added to this power system, and again, these were
basically the DC motors. After addition of the motors, the use of electricity was very
prominent, and the people thought that electricity is the better way to utilize the
inertia.
But here in 1886, the limitation of DC became apparent. The main problem of the DC
either the high losses because it was not possible to raise the voltage in the DC; it was
only that the people were using for increasing the voltage by the several series DC
generators in the cascade way. And adding this cascade, again there is a lot problem in
the insulation that is between the different generators, and also it was not safe. At the
same time, it was required that anyhow if we can increase the transition voltage or the
required voltage so that the current requirement is less at the same time we can reduce
the voltage draft.
At the same 1886, the transformers as you know the transformers are used for the AC
power system, and AC distribution system was developed by the William Stanley of
the Westinghouse and the Westinghouse basically here, the purchase the complete
pattern of this whole DC system.

(Refer Slide Time: 03:38)

In 1889, the first AC transmission system was developed in USA. It was basically in
between the Willamette Falls and the Portland Oregon. At that time, it was not
possible to use the DC system, because the distance from this Willamette Falls and the
Portland, it was more than 21 kilometer. So, the DC was not possible that is we can
have the DC generators as well as the DC transmission. So, the first AC single phase
transmission system which was the 4000 volt and it was for these 21 kilometers.
Then the DC becomes it was not feasible; it was not even possible to power flow over
the long distance with the DC. At the same time, there were the other development for
the poly phase DC system which was developed by the Nicolas Tesla, and he had the
pattern of all these AC generators, motors, transformers and the AC transmission line.
At the same time, Westinghouse purchased it. Then the controversy is started whether
we will go for the DC system or we have to go for the AC system.

(Refer Slide Time: 04:54)

This DC is invented by the Edison. He advocated for the DC system, but the
Westinghouse which had the pattern for all the AC systems, then it was advocating for
the AC system. At the same time, even though Edison wrote in the magazine that the
AC is used for the killing of the people, because at that time in the very beginning, AC
was used to giving the shock to the people. But no doubt this AC own the match own
this whole scenario due to the several reasons that the voltage increase was possible; at
the same time it is a simple to generate and to utilize the AC power compared to the
DC power.
So, then slowly and slowly, this AC power becomes prominent, and the DC was paced
out. In 1893, the first three phase line was again invented and developed, and it was
between this Niagara Falls that was 30 kilometer from California, and it was operated
at the 2.3 kilovolt of the supply. This first three phase of transmission lines was again
it was the remarkable achievement in the three phase system, and you can see right
now, we have three phase transmission system rather than the single phase
transmission system especially in terms of the transmission.
The early voltage if you see that witness that up to 1921, we had the voltage of the
different voltages like we had this 16 kilovolt, 44 kilovolt even though 60 kilovolt. But

later from the 1922, the voltage keeps on increasing. The reason behind this increasing
the voltages that we can introduce the current, and therefore, we can reduce the losses
of the system at the same time we can reduce the voltage drop. So in 1923, the 220
KV voltage level was invented, and it has came into the operation.
Similarly in 1935, it was 287 kilovolt, and in 1953, it was here 330 kilovolt. So, you
can see it is a continuous here voltage is keep on people are trying to go for the higher
voltages. Again these were possible due to this insulation level and also the right of
way problem and the insulator, etcetera, the development at the same time. Then in
1990, this we achieved this 1100 kilovolt AC transmission system. So, at that time, it
was realized that we should go for some standard because it is a witness that the loads,
there were very near to loads centers. The generation as well as the load, they were put
together.
So, then it was realized to have interconnection, and then for the interconnections, we
should have the standard voltage level. So the standard voltage level again adopted the
different standards for the different country, and normally, the voltage level 115
kilovolt, 138 kilovolt, 161 kilovolt and up to 230 kilovolt came into the category of
high voltage transmission lines. And more than that that 345 which is very common in
this USA than in Canada country; here the 500 and 765 kilovolt transmission line,
they were known as the extra high voltage transmission lines. Again if you see the
frequencies, the frequencies also since the generators which were feeding load very
near to that and it was not interconnected; so, the frequency also it was varying.

(Refer Slide Time: 08:46)

It was 25 hertz. You can see here 50 hertz, 60 hertz and 125 hertz along with the 133
kilohertz was also possible, but we know for the integration, we should have the same
frequency throughout the system. So, some country like here in India and other Asian
country and European country, they adopted for the 50 hertz operation. And the USA
and the Canadian country, they just use the 60 hertz. So, again if you see that in terms
of generating voltages, since generators were earlier the DC, later they were invented
the AC generators. And voltages also, they keep on increasing; they had the different
voltage levels and again it was possible.
So far, we have up to the 33 kilovolt transmission and the generation of generating
voltage. And here in India, even we have the 21 kilovolt generation. Then what we
do? Then we use some generating transformer to lift the voltage at the higher voltage
and then we transmit power to over the transmission level; finally, it goes to the
customer through the distribution transmission lines. So it is well established that the
generation as well as initialization is suitable in terms of the AC part; means AC
generation as well as the AC distribution is economical, cheaper and efficient in terms
of operation and its maintenance.

But the transmission part, again there is some doubt that whether we can go for the
only AC or whether we can go for the AC as well as the DC. If we will see, there are
some advantages of DC; I will come to that point later. HVDC system, basically what
we do? Normally, we connect two systems with the different frequency we can do for.
So, the first mercury valves basically there were invented here in 1950s. Then the first
HVDC transmission between the Sweden and Gotland Island of the Sweden itself, it
was came into the operation in 1954.
So, this first HVDC transmission between the Sweden Mainland and the Gotland
Island; it was not possible to interconnect with the AC transmission line, because this
Gotland Island, the operating frequency was 60 hertz. However, the main Island it was
the 50 hertz and also this distance was the 60 miles. So, it is not possible to have a
cable of more than even the 50 kilometers. So, only the option at that time left that we
should go for the HVDC; high voltage DC transmission system was came into the
existence, and this is the first which came into 1954.
If we will compare the advantages and the problems in HVDC transmission system,
let us first go what are the problems in HVAC transmission system. The main problem
in HVAC system is as we know, although, I have written on the second point, it is
your instability. We know this one equation here that is the power it is the
approximate equation that is v 1 v 2 upon x; that is the reactance between these two
lines. Here it is the other sin delta, and delta is angle between the voltages here v 1 and
the v 2.
So, we know this here, the maximum power which can flow in AC transmission
system depends up on the voltages and this angle and reactance of the line. This delta
cannot be more than pi by 2 degree that is 90 degree. So, the stability constraints here
are one of the big issues. Even though here the delta can be theoretically 90 degree but
we cannot operate our power system at 90 degree, because if there is some deviations
some fault in the system, our power system will lead to the clumsy state and unstable
power system. So, always we operate this delta should be always less than 30 degree
or 31.

So, the stability is one of the big issues. So, what we do if our system is weak and the
less stable, then we use some other devices to improve the stability of the system;
another is the reactive power loss. Reactive power loss is one of the normally this first
you have to go for you should understand the real power loss. Real power loss is
nothing but, it is your i square R loss; normally we call or some time if loss is in the
code, it is also real power loss. But the reactive power loss is nothing but the reactive
power loss that is i square x; x is the concerned reactance of the line.
And this is the summation of other which is the generator reactive power, and
normally, it is voltage square divided by x due to the charging of the transmission line.
So, the reactive power loss is one of the concerned in the AC system; another is the
point third is the current carrying capacity of the transmission line or the cable. It is
you can know if your transmission cable is more than 50 kilometer and you are not
taking a load at the receiving end, your sending end current will be even though more
than its rating of the cable.
What will happen? If you are going to take even though small amount of power at the
receiving end, this current will exceed its rating, and its cable will burnt up, rupture,
and it is not possible to transmit the power. So, for the transmission line as well, it is
not possible for going for more than 500 kilometers overhead transmission line that is
the bear conductors and 50 kilometers for the cable. And this is due to the current
carrying capacity and always it is limited in the DC system.
Another concern in the HVAC transmission system is the Ferranti effect. You know
this Ferranti effect is nothing but when the receiving end voltage at the no load or
likely load is more than your conditional voltage. So, what we do? We normally go for
some compensating devices, and normally, we use the reactors. If line is very long, we
use the line reactors in the transmission system so that we can reduce the voltage at the
receiving end. This normally happens if your system is collapse or you are intern
having that line from your sending end, and receiving end if it is likely loaded or there
is no load, your receiving end voltage will be higher.

And what will happen again your productive devices; they will sense the voltage, and
they will again trip your transmission line. So, it is not possible until and unless you
are controlling that voltage; so, this is your Ferranti effect. Now let us see what are the
advantages here in this HVDC transmission system? There are so many advantages of
HVDC system, but also it has some disadvantages and then we will see some
disadvantages as well.
(Refer Slide Time: 16:00)

The various advantages of HVDC transmission system that it requires less space; less
space in terms that we have normally the two wire system. We may have the
homopolar operation; we may have the bipolar operation; we may have the monopolar
operation. So, only we require the two conductors maximum in the DC system, and
also here there is no compensating devices required, although, we require the
converter stations as well. So, in over all the DC stations are they require less space.
In this HVDC transmission system, we can also use the ground as a return path.
Normally in the monopole operation, this one is the positive current which is they are
negative phases there, then ground can be used at the return path where it is not
possible in HVDC transmission system. Also if you see the corona loss is minimum in
this your DC transmission system, and there is no concept of the reactive power at all.

So, there is no reactive power loss in this HVDC transmission system. It is also cheap
for your long distance transmission of power. So, this HVDC transmission is cheap for
transmitting the power over the long distance.
(Refer Slide Time: 17:29)

Now normally if we see the cost of AC here, this is if it is your distance and this is the
cost, we can write then you are here this is your AC system and this is your DC
system. So, the cost here this is your normally it is known as breakeven point here. So,
the initial cost of the DC system is transmission system is more than your AC system
you can see here. But once its distance is more than this breakeven point, then your
DC becomes cheaper compared to the AC transmission system. So, this distance
earlier it was somewhere 700 to 800 kilometer.
But now it has reduced to even 605 to 600 kilometer. So, if you want to transmit
power more than 600 of 600 kilometers, the DC is the cheaper options for the
transmission of power compared to the AC transmission system. Now normally
nowadays, it is not only the transmitting power from one end another end, but we can
also use this DC for the several other purpose. So, normally the use of DC is to
transmit bulk amount of power and another is to control this power; control of power
is one of the big advantage of DC system.

In AC, we cannot control the power; you know the current always follows the
minimum impedance power. So, if AC system is interconnected, you cannot control
the power over the transmission line unless until if you are having the parallel lines
then one you contribute. So you can change the impedance, then the power will be
different in the different line. But here in this DC system, we can that is control the
power; that is one of the greatest advantage of having the like here I have written this
power control is possible in the DC system.
Also in this advantage as we are looking at the advantages of HVDC transmission
system, it has no skin effect. You know this effect is nothing but here if you are having
let us suppose this is your conductor. So, current always follows the outer side of the
center to flow in the AC system. So what it does? Normally, the resistance of this
conductor is increased because the current is uniformly distributed over this
conductor. So, always this RDC that is the resistance if the DC current is flowing in
the same radius of conductor is less than your R if AC current is flowing in the same
conductor.
So, due to the skin effect of this transmission line and also as we see the Ferranti
effect, there will be no Ferranti effect in the HVDC system because there is no
charging at all. The capacitance no doubt they are formed, but it is not charging, and it
is not falling any charging current over that one. So, for the DC you know, this
capacitance just behave as an open circuit in the steady state. Another great advantage
of HVDC transmission is that here asynchronous operation is possible. Asynchronous
possible here it is nothing but you can interconnect two frequencies system together
with the help of the DC system.
In the AC, always we must operate all our power system, all the electrical appliances,
operators, elements have the same frequency level. But here in the DC, you can
interconnect two different frequencies with the help of HVDC. So, this is called
asynchronous operation is possible. As we saw the example of the Gotland Island
which was interconnecting your Sweden, Ireland and the Gotland Island that both

were operating with different frequencies, and then it was only possible to go for this
HVDC system.
So this is one of the great advantages that we can have that two different frequency
system we can interconnect. Here also the short circuit power, in the DC, here there is
no short circuit power, but in the AC if you keep on interconnecting, what will
happen? The short circuit level at that point will keep on increasing, so that you have
to go for the larger productive devices like circuit breaker rating you must increase.
But here this is not a sort of that concept. Another great advantage which was the
limitation of AC system was there is no instability problem.
Here this formula does not apply this here v o 1 v 2 upon x sin delta is no more
applicable for the DC system. So, the instability concept is no more there. So, the DC
system is much much more stable compared to the AC system. If you see the
disadvantage, let us come to the various problems in HVDC transmission system. As
we saw in the beginning that the cost of the terminal equipment even though the cost
here if you see here, this cost for the DC is more here compared to the AC system.
This is due to the terminal equipments of the DC system because we require the
converter circuit even though you are going for the shorter distance. You should have
the two converters; one is known as rectifier, another can be as inverter.
And again, we should go for other auxiliaries for these converter stations. For
example, we should go for the cooling because there will be losses in this thyristors or
GTO valves and we require a huge cooling or better cooling; otherwise, this will get
burst or puncture. So, here this cost of the terminal equipments are very high, but
nowadays, due to the development of very high power semiconductor devices, let us
say power electronic devices, then it is possible to reduce that cost as well. So, now as
such the cost of the terminal equipment is keep on reducing as we are going for higher
and higher rating up the thyristors and other power electronic devices.
Another concern here is your introduction of harmonics. As you know here in the
converter, we are using the power electronic devices, and these devices are using some
off and on control, so means we have to use the firing circuit. Due to this off and on,

they never produce the perfect sinusoidal, and therefore, some harmonics are
introduced in the system, and they are not good. No doubt we use some filters to filter
out these harmonics; at the same time some of the harmonics, they enter into the
system.
Especially we use the filters for the lower order harmonics, but higher order
harmonics, we allowed to enter into the system. The reason behind that for the lower
order harmonics, they are having a large in the magnitude. The magnitude of the lower
order harmonics is higher and also the filters require the size will be less. So normally,
we filter out this larger magnitude of harmonics and the smaller magnitude of
harmonics being allowed, because it is not possible to go for filters for all the
harmonics. And at the same time, there are two types of harmonics. One is your
characteristic harmonic, another is non-characteristic harmonics.
If you are using a six pulse converter, so normally this harmonics h is nothing but your
n p plus minus one harmonic; here n is nothing but starting from one to it is an integer
value, and p is your pulse number. So for six pulse converter here, we are going to
have fifth, seven, eleven and thirteenth harmonics. So, the magnitude of these
harmonics contents basically these are they are called the characteristic harmonics.
Other than that also due to the overlapping of the current because current cannot be
changed instantaneously in the wharfs.
So, there is some changeover of current; so, they introduce some non-characteristic
harmonics, and it is not possible to filter out. So, but the larger order of harmonics, we
are using the filters and they are not allowed to enter in the system. But at the same
time, some of the harmonics they enter into the system, and we do not have any
control over them. The major problem with the harmonics if they are entering into the
system, they will create more loss in the system that means core loss will be more.
There will be i square r loss may be also more, and at the same time, there may be
some possibility of the resonance with rest of the AC power system, and that is very
very dangerous. Another problem with the HVDC system is the blocking of reactive
power; means here as we know, this AC system is connected here. Suppose, we have

this is one area and we have another area; this is connected by your DC system. So the
reactive power generated in this area cannot be transmitted to this area two because
this DC there is no reactive power transmission.
So, this blocks the reactive power of any of the area; means it will be here from area
one. It will not flow to area two or from area two; it will not come to the area one.
Now question why we want the reactive power? Sometimes in the emergency cases,
let us suppose there is some generator outage. Some of the emergency in this case
there is some fault; at that time, we may require some reactive power support from the
area one or two. But it will block here. So, it is not possible that transmit to the
reactive power to the area two or from two to one during the emergency condition. So,
it blocks the reactive power.
But in the normal practice, we do not allow that reactive power should flow from one
remote place to another remote place, because the reactive power concept is a
localized concept, and it is reacted with the voltage of the system. Another major
problem in the HVDC system is that it is not possible to go for the typing of the power
at the different location; means it is only that we can go for the point-to-point
transmission. Means from one node, here we are going to another node. Then the
power which is flowing from here, it will be going here; it is not possible to tap the
power in between. So, it is not possible.
In AC system, you know once wire is going, anywhere you can tap the power. This is
the problem of HVDC system. Why it is so? Because here the control which is one
here this station converter station and here converter station; they operate in the
synchronous means here the information and here it will be the same. Means we
required a very strong communication link between these two converter stations. So, if
the power is here going you are taking, then we have to coordinate another here some
converter stations.
So, what happens? Till now, although, there are some research is going on that we can
go for the multipoint transmission multi-terminal HVDC transmission system. If we
are having only here from one end DC to another, it is called two terminal DC system.

If you are taking here another DC system here, you are taking here three phase, here
three phase and here we are having three phase. So, this is called multi-terminal
HVDC. So, so far we have established only the three terminal HVDC system.
So this is one of the major problems of the DC system as such. So, here the point-topoint transmission is not possible; it is only possible in the DC system. However, in
the AC, you can tap the power anywhere in the system.
(Refer Slide Time: 29:59)

Now let us see your complex in this system. Now we have seen that the generation
must be your AC system, because it is a economical, convenient and the cheap to
generate. At the same time the utilization part or you can say distribution or load type,
we should go for the AC system. Now the question again only remains open for the
transmission system means we can go for your AC as well as the DC system. We saw
the several advantages of your DC system compared to AC system. So, then we can go
for the AC and DC systems.
Just we saw witness that the early power system development was very much
localized means generators as well as the loads were very close together, but we
realize that there was a continuous development of the voltages as well as the

frequency. Then we had the standards for the voltage as well as the frequency and we
went for the integration of the system. So, we keep on integrating; we keep on adding
the power system. So, the present day power system is a complex, interconnected and
also it is varying in the size and configuration.
Now again the question arise, why we started the interconnecting whole this
generations as well as the load centers along with the transmission line. If we will see
this interconnected power system several advantages; advantage include that in
interconnected system that the total reserve capacity can be reduced.
(Refer Slide Time: 31:40)

So, the advantages here first advantage of your interconnected power system; first, it
reduces the reserve capacity; means reduces reserve capacity. Now if we will see in
the, for example, let us take a generating station here. This is our 50 megawatt to
understand the reserve capacity is that I am explaining here, and we have our load
somewhere here. We have another let us suppose load is your varying that is your 30
megawatts. And we have another station here that is it is supplying here 50 megawatts,
and here your load generators should be more than 50 megawatts.

Now what happens; now why we go for more? Because the load is increasing, we are
going for the more reserve margins here. Now here also we have the 50 megawatt, and
our generating capacity should be more than 50 megawatt. So, if you can connect
these two systems, now what will happen? Even though here your load is 70, there is
no need of this generator; means here same generator can supply here and still we
have the 30 megawatts feature.
So, due to the interconnection, we can reduce the reserve margin of the system or
therefore means we can reduce the install capacity of the power system by
interconnecting. This is one of the major advantages. Another advantage is that the
capital cost. The capital cost per kilowatt is less for the larger unit. So, with the help of
interconnection, we can go for the larger units, and therefore, we can reduce the total
installation cost of the power system. And therefore, it is possible to have the cheaper
electricity generation.
So, the total capital cost if you are going for the interconnected system, so we can
increase the capacity of generators. We can go for the larger and larger size; that is
why right now we can say we have even our India we have generating single unit can
generate more than 500 megawatt. And this is due to the interconnection because none
of any city is having even though in UP or somewhere, you can see more than 500
megawatt. So, with the interconnections, we can reduce the capital cost of the power
system.
Third advantage is that here that it is a possible because you know this loads here, this
will keep on changing. And therefore, if the load is very minimum; let us suppose here
the load has reduced to 20 megawatts here and this 20 means only we can run only one
unit of generation. So, it is possible that we can run the most effective unit at the
higher load factor, and the inefficient station can be used at the peak hours only. So,
what will happen? Again the total cost of the electricity generation will be reduced.
Another advantage of interconnection is that that interconnection reduces the
requirements of high install capacity; the load curves of the two different stations are
seldom identical, and the maximum demand is the less than the sum of the maximum

demand of the individual stations. For the two different areas, the maximum demand
you can see, they will seldom occur at the same time. For our Indian system if we will
see that we have our peak demand that is the 30 minutes different from the north state
to central state. So, the peak which occurs here at the 8 pm, it will occur somewhere it
is the 7.30 pm in the north state.
So, what happens? Then we can interconnect the power system, and that will reduce
the total install capacity of the power system. Also by doing the interconnected power
system, we can improve the reliability and that is your fourth, it reduces this install
capacity. And fifth advantage here is here that is improves the reliability of the system,
and your third was the effective use of generators you can see. So, it can improve the
reliability of the system. Now we can see how it can improve the reliability of the
system. For example, let us go earlier; here it was not having interconnected.
If there was something problem in this generator if this generator is dripped, your this
20 megawatt load completely it is not possible that we can feed the supply. So, the
reliability of this system even though the dripping or there is some problem in this
generating station here, it will be once it dripped, it is not possible to supply the 20
megawatt. So, the reliability of the system, it depends upon your this reliability of this
generating station. But if we can interconnect here by this one, even though this
generator is tripped and there is some problem, it is possible to feed this power
through this transmission line and to this here.
But there is a possibility that this generator may not be capable of supplying complete
power, but we can maintain some of the emergency services of the system here; means
we can feed some of the power or we can reduce the power in this area. And, finally
we can supply it. So, this reliability of the system is improved with the interconnection
of the system. Now there are several problems in the interconnections. No doubt in
any system if you have some advantages; there will be some problem or disadvantage
as well.
The first disadvantage or drawback of the interconnection is that fault in one system
will get propagated into another system. For example, here if there is some fault here

and there is fault here at this bus, what will happen? This will be propagated here, and
this generator as well as this generator, both generators will be tripped. So, the fault in
one system is getting here in other system, it will be propagated, and that is why here
it is sometimes very very dangerous. We should have a very fast and reliable
protecting device, so that we can trip here. We can trip here this line, and we cannot
allow this fault propagate and transmit in this zone.
But assume that the if there is no interconnection here and the fault is occurring here;
okay, the system will be in dark, and we can maintain the power supply in this system
here, and this both are operating in isolation. So, here the fault as I said if it is
interconnected here this will be then fault will be coming here and to have the more
reliable power system complete, there should not be complete collapse. We should
have the protective devices here, and so that it can isolate the faults, and then we can
maintain the remaining part of the system in the healthy.
So, we saw the first major problem of the interconnection is that fault gets transferred
to the other healthy areas, and for that, we should require the very fast and reliable
switch care that is including the circuit breaker and the relay protecting devices so that
it should not get propagated. Another problem in this AC interconnection system is
that the high switch generating is to be implied at the different point of the system. It
means if we keep on interconnecting the power system, for example, here if we are
having this is your bus and we are having the different lines.

(Refer Slide Time: 40:16)

Then the rating of this circuit breaker, we require higher rating; means if you keep on
interconnecting more suppose you are adding another line, then the rating of the
circuit breaker may change. This is due to the fault label that will increase here at this
bus will be increasing. So, if you are keeping on interconnecting, then the circuit
breaker requirement will keep on increasing. The example which we took we saw here
one generator and it was supplying here the load, and similarly, another generator was
here, and it was supplying load at this. Here, if we are connecting this one as like this,
so the rating of this circuit breaker earlier which was using, now we have to increase
because the point level at this point is increased.
So, we are going for the more circuit breakers here more the transmission lines and
circuit breakers, more switch care equipments. At the same time, the rating of the
switch care equipments also increases. The third problem now is the proper
management requires to dispatch these generating stations. So, here what we require
that there should be some energy management system and it is automated so that we
can operate these generating generator one here and generator two in the economical
fashion.

So, we require the interconnected and the sophisticated tool that is power management
in this power system. As you know it is only two generators, but in actual power
system, there may be 10 to 100 generators and it is so many transmission lines as well
as the transformers. So, it is very much required that we should operate the power
system in such an efficient and also to dispatch these generating stations in the
economical manner. So, normally for that, we go for the economical low dispatch as
well.
Now you can see here in the power system that is more and more interconnected; we
are having even more than100 generating stations and generators. So, we require some
generator should run as the base load that; means they should continuously run. Some
generators may require to run only at the peak load and again this category basically
depends upon that what is the cost of that generator or the available freeware. For
example, run of freeware generator; means this is the hydro type. In hydro, here we
have the different let us go with hydro generators. We have your run of rivet type of
generators; we have the pondage type that is pondage or storage.
And another is called the pump storage, storage type of hydro power station. ROR is
nothing that is called run of river. Run of river hydro power plants; means it normally
if rivers are flowing, they are at the different small dams are there, and we utilize this
power. Suppose, if we are not utilizing that power, what will happen? This will go in
the waste. So, the run of rivers, they always use at the base load plant; means
whenever the river is flowing, you have to utilize; otherwise, this energy will be going
in the waste.
So, this ROR will be used at base load power plants; like the pondage, we can store
water, and then we can utilize whenever it is required. So this pondage can be depends
upon the storage capacity; you can use at the base load as well as the peak load but the
pump storage power plant. This is the plant and this is a hydro power plant. They only
use for the peak load; means when there is a demand, we use it and when there is a
less demand, we can feed it water pipe to be storage. So, this is called pump storage.

So, it is always used as a peak load power plant. Other conventional power plants if
we will see; now again we have to come for what are the conventional power plants
and what are the non-conventional power plants. The conventional power plants
include your thermal power stations, the big thermal power stations. We also go for
the gas base power plants and here it is a diesel power plant. They are known as the
conventional power plants; other than these power plants here, they are called the nonconventional.
Here hydro also comes big hydro power plants; they come under the conventional
power plant. In the non-conventional power plants and they are also called the green
power like you solar, wind, fuel cells, they are coming into your non-conventional,
and they are also called as green power because they create less pollution to the
environment. So, here the thermal, basically, they use the coal and then we burn the
coal and then we generate the steam and steam becomes a media of the transfer of
power from heat to again go for the mechanical that turbine will run and then turbine
runs the generator and then finally we generate the electricity.
So, this power plant can again run both as peak as well as your base load plant.
However, you have the diesel, as you know the diesel cost is more than coal. So, it
always runs at the peak load power plant. Your gas is also it is very quick in starting.
Here in the thermal power station, it is not quick starting. Normally, a thermal power
stations if it is in the hot role state means it is running state that it can require even
though four to five hours.
If it is in the cold role state means all the boilers, there is no heat in the boilers,
etcetera; so, it is called cold role state and then it may require seven to eight hours. So,
here the thermal stations require more. So, it is not possible quickly you can turn it on;
it requires some time, but the gas and diesel they are very quick and we can start. So,
they can be used for the peak load power plants. Another is your here the nuclear that
is very important, and nowadays, our government is very keen to go for more nuclear
power plants as now we had the limited gas, limited diesel, limited coal. So, the often
that we can go for the nuclear because hydro is also very limited.

Limited in the sense that we are facing lot of hesitations for the dams and other things,
because they are the environment less people; they are always opposed that we should
not build the large dams so that they are so many areas are submerged, and they are
creating lot of problems. So, another option is the nuclear and we have the huge
reserve of the thorium as well as the uranium. So, the nuclear power plants they can
also run as the base power plant and they normally run as the base power plant,
because here the nuclear due to the safety and other reasons, it is not possible to
quickly stop and quickly turn it on.
So, here the cost of generation of the nuclear power station, the cost of generation is
very very cheap. But the total cost is very high, because we go for very safety factor
and again people are very much afraid about the nuclear power plant, but now we had
the feature for the nuclear power plants as well. So, always here the operation of the
power plants depends upon the following criteria that the cheaper electricity
generating units should be used as a base power plant. The highest starting time
generating plant is also used as the base power plant, and the size on the plants is also
a deceasing factor; means what is the size? If the size is very small, then quickly you
can start and stop.
But if the large size, then we may require large time as well; so, in this in
interconnected power system, the generators as I said, they are normally loaded; they
are running based on these criteria that which will be running as the base and which
will be running as the peak load. Some of them may run for both purposes again
depending upon the requirement of the system. Now we witness that now power
system is highly complex, interconnected and due to the increased loading of the
power system, it is always our intention to operate power system in most of the
reliable, secure and stable condition so that we can supply the power to the customers
in the reliable.
And also our intention is to supply the cheap means economical electricity to the
customers. In India, the power system in the most of the states are owned and operated
by electricity boards. Now again these electricity boards are broken into the different

boards. So, earlier this whole generations and transmission and the distribution of
walls in the state was responsible by the state electricity boards. They were operating
your generating stations, transmission lines as well as distribution system. And again,
we have presently the five regional electricity boards. One is your northern regional
electricity boards; another is western regional electricity board.
(Refer Slide Time: 49:23)

And southern like we have your NREB; that is called northern regional electricity
board. We have the western regional electricity boards, we have the southern regional
electricity board, we have eastern regional electricity board, we have north eastern
regional electricity board. So, in India we have the five regional electricity board;
means in northern electricity regional boards, we have the several states. They are
interconnected, and this includes your Haryana, Himachal Pradesh, Delhi, Punjab,
Rajasthan, Jammu and Kashmir, Chandigarh and Uttar Pradesh and Uttaranchal.
Similarly, we have the western regional electricity board; means the several states are
interconnected. In the western regional electricity board, it is Gujarat, Madhya
Pradesh, Maharashtra, Goa, Daman and Diu, Dadra Nagar, Haveli and your
Chhattisgarh states. They are coming in the western regional electricity board. The

southern regional electricity board comprises Karnataka, Andhra Pradesh, Kerala,

Tamil Nadu, Pondicherry and the Lakshadweep.
In the eastern regional electricity board, it is Bihar, Andaman and Nicobar, West
Bengal, Sikkim, Orissa and the Jharkhand they are coming. Most of the states, they are
interconnected and then we are operating the power system in the regional places. And
these regions are also now getting connections interconnected. So, most of the region
already in the northern and the western regional electricity board, they are
interconnected.
Now the goal of India that we should have our national grade; means all these here
regional electricity board must be interconnected and then again we can supply and
with this grade, we can operate our system efficiently. Again the different state even
though your this northern regional electricity board and the western regional electricity
board, they comprised together more than 60 percent of your install capacity; means
they are having the lines here, and the remaining 40 percent comes under the southern
region, eastern region and northern eastern region. Northern eastern region basically
comprise of Assam, Arunachal Pradesh, Meghalaya, Nagaland, Tripura and the
Mizoram.
So, here we have a good potential of hydro in these regions, and they are having the
surplus amount of power; however other regions mostly here the western and northern,
they are in the deficit of power. So, now we are just trying to have the interconnection
from the northern eastern region to other regions, so that we can transmit power from
the north eastern region to the deficit area that is western and the northern region.

(Refer Slide Time: 52:05)

Again now we can see here the interconnection. Now we can summarize how our
power system is interconnected. We can see here we have the different generating
station like here generating station, generating station, generating station, we have the
several generating station, and we have seen that generating stations cannot generate
power at the higher voltage. Till now in India, we have the highest voltage generation
of 21 kilowatt; however, in the watt it is 33 KV. But we know that if we are going for
higher voltage, the losses in the system are less. And at the same time, we can transmit
bulk amount of power.
So, our intention to keep on increasing already I give information about the evaluation
of power system. There we saw that increasing in the voltage level in the transmission
system, it is witness that we have to go for the higher voltage transmission system to
reduce the loss and to transmit bulk amount of power. So, these generating stations,
they generate power and then we use the generating transformer; it is normally called
the GTs, it is very near to the generating stations. So, they step up the voltage of these
generating like I have written here 21 KV, here some of the generating stations, they
are generating at the 11 KV.

Normally, the 500 class of megawatt generators, they are generating at the 21 KV.
Here the 21 KV means it may be 20; it may be twenty one point something means per
unit voltage is 21. Those are here 200 megawatt or 220 megawatt generating station;
they normally generate at the 16 KV, and the remaining that is 100 or 110 megawatt
generating stations, the generating voltages are normally 11 KV also. So, we use the
generating transformer to lift the voltage either at the 400 or at 220 KV or even at 132
KV depending up on the equation of power from these generating stations.
Our ultimate aim that these generating powers must come to the small customers and
then it will follow the transmission lines it also sub transmission system and then it is
here the primary distribution means this is the distribution system. So, our integrated
transmission system, it is having presently we have the 80 KV transmission system,
220 KV transmission system and 132 KV transmission system presently. We have our
transmission line that is built constructed at the 765 KV class of insulation. Normally,
it is called 800 KV transmission system, but presently, it is operating at the 400 KV
transmission system.
We have the unparameterized line, it is very near to us; it is the line is built on 800 KV
class of insulation, but presently it is operating at the 400 KV volt. Because later it is
assumed it is required of the more power equation, we can go for the higher voltage.
Once line is constructed, only we have to change the terminal equipment of this rating.
Then in this system, we have the several interconnecting transformers. They may be
400 by 200, 220 by 132 and so on, so forth. So, these are the transformers that are
existing and normally they are called ICTs power transformers.
Then from lower voltage, we go for this other transformers and then we try to reduce
the voltage at the lower voltage. It may be directly 6 KV, it may be 33 KV the
distribution side, and we also feed power to the large customers at the higher voltage
as well. Even though some of the our customers, they take like your real way takes
power at 132 KV even though some big companies like the fertilizer corporation of
India FCI, they also take power at 132 KV.

So, we have the intertie lines and also we supply to the very very large and the large
customers those require power at very high voltage as well as the high power. Also we
go for the medium type of voltages and the medium customers, they take the power at
33 KV or 25 KV like your railway, the tracks and purpose; they normally use 25 KV
and the 11 KV transformer. At the same time, you can see there are some small
generating units. These small generating units, they are nothing but they are may be
the curtly power plants, or nowadays there is another concept that is called the
distributed generators.
They are coming into the distribution side so that we can reduce the transmission you
can say t and d losses, etcetera. And finally, here after the transformation, we have the
two type of distribution system again can be classified in terms of the primary
distribution and the secondary distribution. Secondary distribution is your 400 volt,
and it is of three phase, and single phase, it is 400 divided by n root 3 that is we get the
220 volt supply, and it is finally given to the small customers. So, the medium
customers can take any voltage more than given 400, but the small customers they
take here.
So, this is overall practice of you can say the structure of the power system. We have
the generating stations, then we lift the voltage with the help of generating stations,
and then we have the different interconnecting transformers. And then finally, it is
reaching to the small customers as well as other customers. So, nowadays, there are lot
of people are interested in the small generating units, and we are putting in the
distribution system to improve the system performance. And this is called the
distributed generators. We will see again the various advantages of the distributed
generators in later lectures.
So, with this now I can conclude I can recap; we saw the evaluation of power system.
How we just earlier we had isolated power system with the different voltages, it was
AC and DC. Finally, it came to the AC and then we interconnected all the system. And
now our generators are mostly the AC; the utilization is AC, but this system that is
transmission part is includes your AC as well as DC power system. So, this is highly

complex power system that is the generation is AC, utilization is AC; however, the
transmission part is AC as well as DC. And since our demand is keep on increasing,
we are keep on adding the generating station; this system becomes very complex and
very non-linear in nature.
Thank you.