Dear students, welcome to this course on Electrical Distribution System Analysis; myself Dr. Ganesh

Kumbhar; I am working as a assistant professor in the department of electrical engineering

IIT, Roorkee. This course is specifically designed as a electric course for the students

of under graduate, post graduates and PhD who are working in the area of distribution

system and smart grid. This course will also be useful to the utility

engineers who are working in this distribution sector. The basic power course system courses

like power system analysis, power transmission and distribution, power system engineering,

switchgear and protection are the basic prerequisite courses for this particular course.

In this particular first lecture will see following topics.

So, content of my today’s lecture will be introduction to the electrical distribution

system. So, I will introduce you to the electrical distribution system; then we will see the

structure of distribution system. Basically distribution system is classified into 2 parts

there is primary distribution system and secondary distribution system.

So, we will see the structure of this primary distribution system and secondary distribution

system. Then we will see why distribution system is analysis is required? So, you might

already studied the power system analysis; however, this distribution system analysis

will be different from earlier power system analysis. So, will try to find out what are

these differences? Then we will see the motivation and objective of this particular course, then

we will see the course content and then we will see the reference books required for

this particular course. As we have studied in our undergraduate courses;

the power system can be divided into 3 parts.

That is generation, transmission, and distribution. So, if you see this figure generation is shown

here and then this is nothing, but your transmission layer and then this is nothing, but your distribution

part. Voltage level of the generation is around 11 kV to 25 kV. Now these voltages which are

11 to 25 kV will be stepped up to the transmission level that is 220 kV to 765 kV which is; which

are the voltages for bulk transmission network. Then there will be step down to the sub transmission

level, the sub transmission level is 66 kV to 132 kV.

Then it will be further step down to the distribution level. So, voltages at the distribution level

are below 33 kV. Distribution level can be divided into two parts that is primary distribution

system and secondary distribution system. Primary distribution system will be having

voltage level between 4 to 33 kV and secondary distribution system will be having voltages

that is 400 volt three phase and 230 volt single phase.

And if you see the structural difference between your transmission network and distribution

network, transmission network is basically inter connected means it will be find forming

some kind of loop here, but we see the structure of your distribution system, distribution

system will be radial. So, it will be radial or weekly meshed. Basic goals of your distribution

system are listed here.

So, first goal it should be efficient; it should be efficient means losses in the distribution

should be less as less as possible. We should deliver the customer the quality power means

for your voltage should not contained any harmonics, it should not contain any sags,

swells or flickers. Then we should provide a customer reliable

power, power should be cheap to the customer. So, it should be economical and it should

be secure power to the customer. If you see the topological difference between

your transmission and distribution network as I told you earlier, your transmission network

is basically interconnected. So, as shown in this figure, you can see that it is forming

some kind of loop means of which is shown like this or you can say there will be actually

one bus will be connected to many other buses which is forming inter connected kind of or

loop kind of system. This is basically done to increase the reliability

of the system, because as we know all the generators are dispersed over wide distances

and whenever there is contingencies like few lines or few generators, if they go out of

the system there is possibility that system and become unbalance. To avoid this stability

issues into the system we want actually system to be inter connected or it is forming loop

kind of loop kind of structure. Whenever there is some lines or some generators are out,

the power will be still available from alternate route.

Your distribution system will be radial one; radial means it will not be forming any kind

of loop or it is kind of weakly meshed system. Weakly meshed means there will be only few

loops unlike in case of transmission system. So, since transmission system is highly inter

connected kind of system. The basic reasons to make the distribution

system radial are as follows; first is if you see the cost of the system, cost difference

between interconnected system and this radial system, radial system will be very cheap,

that is cost of the system will be very low. It is easier to protect, so protection system

will be cheap as well as easy to protect because you know that in this case if you see the

radialty system the current will be actually having only one direction. So, whenever there

is fault occures at some location; so the current will be fed from only one direction

to the fault. So, in that case your protection will become easier.

Also since the power is flowing from one direction. So, voltage drop will be in one direction

that is why voltage control will also become easier. Finding the fault also will become

easier because power is flowing fault current as well as power, they are flowing from one

direction, it is also easier to control the power flows.

Now, if you see the structure of your primary and secondary distribution system which we

have seen earlier. The primary distribution system basically consist of your 11 kV network,

we also call it has HT level; High Tension lines. It starts from your 33 to 11 kV substation

and it will be basically 3-phase 3 wire system. So, there will be 3 wires R Y B at 11 kV level.

This feeder will be basically connected to different substations which are 11 kV by 400

volt substations; there will be many sub substations will be connected to this feeder. We also

provide power to bigger consumers like malls or big industrial consumers at 11 kV 3-phase

level. So, there actually in shown in figure there is one in bigger industrial consumer

which is taking power at 11 kV level and at 3-phases.

Similarly, there is one commercial consumer which is shown it here which is 3 phase; if

you see the secondary distribution system, secondary distribution system start with 11

kV by 400 volt substation and it is basically 3 phase 4 wire system. So, there are 3 phases

R Y B and one neutral phase. So, 3 phase 4 wire system. It will be providing power to

the some big consumers as well as some domestic consumers like our houses.

So, we if you see here the factory which is little bit big consumer we are providing the

power to this big consumer at 3 phase levels means all 3 phases are there with your neutral

connection. And to our domestic consumers we feed the power at single phase level.

So, if you see this house it is taking the power at R and N phase which is single phase

R. Then if you see this house it is taking at power at Y and N phase and this house is

taking power from B and N phase. So, this is structure of your distribution

system which is secondary distribution system.

Now, we will see transmission system analysis. So, basically in this particular slide we

want to see what are the assumptions we have made, during the transmission system analysis.

So, we know that the transmission system is basically interconnected kind of system. So,

your algorithm should be such that this interconnection or loop kind of structure it will take into

account. Then we know that this transmission lines

are basically transposed one; transpose means these lines will be changed at different location.

So, every conductor of this line will be taking location of every other conductor. So, we

know that transmission these lines will be transpose lines.

Then we know that actually loads are balance one generally at transmission level loads

are balanced. Then we know that X by R ratio of transmission system will be very very high

because of this X by R high ratio decoupling is possible. Means your P and Q can be differently

controlled. So, P can be control by just changing the angle delta which is basically phase angle

difference between voltages at sending end and receiving end and Q can be control by

voltage magnitudes. So, as I told you because of this decoupling

effect we can get decoupled kind of load flow algorithms. Then there are actually fewer

components as you know only few components we need to model during the transmission system

analysis; those are basically reactors and your transformers or may be some times capacitor

banks. Then as you remember during the modeling of

transmission system load flow, we model it as a single phase equivalent network; means

lines as well as transformers will be modeled as single phase equivalents. Because of that

we are not considered any individual connections of the transformers even if it is delta star

or star, star or delta, delta transformer, we modeled it as a single phase equivalent

of them. Then loads which you have modeled in transmission

system we have consider them constant power loads. Means voltage dependency of the load

we have not considered because of that at each iteration of load flow your power is

remaining constant means we had not changed our power values during load flow iterations.

Then symmetrical component analysis was possible; so we know that actually since lines are transposed,

we get your because of transposition we know that your self-impedances of the line they

will be equal. So, self impedance of all the 3 phases we know that it is we make it equal

to say Zs Zs Zs and mutual impedances between line also we make them equals; so Zm Zm Zm

they are equal. And we know that if you multi pre and post

multiply this matrix by A inverse which is symmetrical component transformation matrix

and A matrix we if you multiplied by multiply to this impedance matrix which is Zm Zm and

diagonal entries Zs Zs Zs; we get only a diagonal matrix that is Z0 Z1 and Z2.

Meaning of this your three network that is zero sequence network, positive sequence network

and negative sequence networks they are decoupled from each other.

Unlike this, if you go for distribution system analysis distribution system network as we

discussed; it is radial or weakly meshed kind of network.

So, because of this structure we know that we can find out some algorithm which are simpler

in nature than your transmission algorithm and specifically designed for your radial

or weakly meshed kind of system. However, in case of distribution system your loads

are totally unbalanced loads, your lines are untransposed your ratio of R by X will be

higher. Means since the ratio is higher you cannot

do the decoupling means there will be actually voltage magnitude will also make effect on

your power as well has your delta will make effect on your Q. So, delta will make effect

on both voltage will make effect on both of these quantities.

Also as compared to transmission network size of distribution system will be very large.

When we analyzing the transmission network the number of buses which we may have to considering

is around 100s of buses, but in case of distribution system the large distribution system I am

talking about it will be around 1000s of buses; so system size is very large.

In distribution such system there are many component which are present like there will

be capacitor, there will be regulators, there will be distributed generation, there will

be battery storage. Also if you see the structure of your distribution network, there will be

some line which are actually single phase line, some lines which are 3 phase lines and

some line which are actually 2 phase lines. Because of that we cannot do single phase

equivalent analysis in case of distribution system. So, we need 3 phase analysis for distribution

system. Symmetrical component analysis also not possible

because there are untransposed lines. So, this zero sequence, positive sequence and

negative sequence networks will not be decoupled from each other. In this case since we are

considering full 3 phase modeling your Y Y, Y delta or delta delta connections need to

be actually modeled during the analysis of distribution system.

Loads in a distribution system are basically voltage dependent because of this voltage

dependency of the load; the loads will change in each load flow iterations. So, that need

to be considered while doing the load flow analysis. So, voltage dependency of the load

needs to be taken into account. Distribution system analysis will need time

series simulations. So, we need to calculate load flow solution at difference time steps

that is called a time series simulations. Also nowadays many smart grid components are

coming into picture. And these smart grid components will make your distribution system

analysis little bit complicated and those smart grid elements are controllable loads,

distributed storage, battery storage, electrical vehicles and demand response activities designed

by utilities. So, because of them your distribution system analysis is important.

Now, we will see where the distribution system is required or where it is applicable or where

it is used. So, as I told you the basic analysis is load flow analysis and short circuit analysis.

So, load flow analysis is required for taking various decisions during operational stage

of the distribution system as well has design stage of the distribution system.

So, during the operational stage like load balancing or reconfiguration of the distribution

system we need load flow analysis. During the design stage while we are selecting conductor

size of the distribution conductors or transformer sizes we go for we need to know the load flow

solution. Voltage regulation and tap operation during

the operational stage we need result from load flow analysis, power loss reduction we

need load flow analysis; then nowadays capacitor placement as well as DG placement, we need

results from load flow analysis or load flow will be basically; it will be used during

these different types of analysis. Then short circuit analysis is required while

during the settings for protective relays or during the relay coordination in a distribution

system also to calculate short circuit current in the upstream network. So, we need actually

result from short circuit analysis during these design stages.

Now, we will see what is the basic motivation and objectives for development of this particular

course.

As we know most of the power system courses mostly focus on your transmission system analysis.

And as we have seen in last 2-3 slide there are many components which are different or

structure of distribution system is very different from your transmission system; we need to

have separate algorithms or separate method for distribution system analysis.

We also know that nowadays with incorporation of distributed generation, battery storage,

controllable load; distribution system is no longer remaining passive in nature means

distribution system is becoming active because of this; energy generation sources or energy

storage sources which are present in your distribution system. Also distribution system

is connect consider to be weakest link in whole power system because it is most loss

making component. So, almost we can say 60 to 70 percent losses which happen in distribution

system. Also if you observe last 3 decades, there

is gradual development in computational power, there is gradual development in optimization

algorithms. Now a days there are many sophisticated algorithms are available for the optimization

which can be used during the analysis purpose. So, because of that this distribution system

analysis is becoming very important for the researcher who are working in the area of

distribution system and industry professionals which who are working in distribution sector.

These results which you obtained from distribution system analysis will be quite useful while

making the decision during the operation as well as design stage of the distribution system.

Therefore, main objectives of this particular course are to familiarize the students with

distribution system components and their modeling. So, first of part of this particular course

we will see how to model different components of the distribution system and then second

part of the distribution system the objective is to familiarize the students with methods

and algorithms of distribution system analysis. So, in this particular part we will introduce

you various methods and algorithms which are very different from your transmission analysis

algorithms for the distribution system analysis.

So, based on this based on this objectives the main content of this course is divided

into 4 chapters; out of this first chapter is based on introduction to the distribution

grid. So, basically in this particularly chapter we will see the structure of distribution

system, distribution system substation layout, distribution feeder configurations, nature

of loads, computation of transformer and feeder loadings that is nothing, but your load allocation.

Then we will see various approximate methods which are available for distribution system

analysis. There are some method which are based on K factors will study them, the main

aim of approximate methods is to get the voltage drop and power loss calculation on uniformly

distributed load over the feeder. Then we will see various geometrical load

configurations, then in third chapter we will see modeling of distribution system components.

In this modeling we will basically see modeling of single and 3 phase overhead lines and cables,

then see will see the modeling of voltage regulator, transformer, capacitors banks,

loads, induction motors and distributed generators. In fourth chapter, we will see distribution

system analysis. So, in this particular chapter will try to develop algorithms for load flow

analysis and short circuit analysis which can be used for single phase as well as 3

phase systems. So, based on this content the reference for this particular course are listed

here.

So, first is book by W H Kresting on Distribution System Modeling and Analysis.

So, to model the distribution system components we will be referring this particular book

then there is book by Sallam and Malik Electrical Distribution System. So, this will be used

for introduction to the distribution system as well as during the short circuit analysis

of distribution system. Then there is book edited by Dr B Das on Power Distribution Automation

and this book will basically used while developing your algorithm for load flows and short circuit

analysis. Then there is book by J M Gers on Distribution

System Analysis and Automation and then there is one paper by Arritt and Dugan which is

Distribution System Analysis and Future smart grid. So, during the, your introduction section

we will be using this particular paper. Therefore, in this particular class we have

started with introduction to the distribution system. Then we have seen the structure of

distribution system, then we have seen motivation and objectives for this particular course.

Then we will see we have seen that course content of this particular course and references.

Thank you.