Power system -Economic Aspect of Electric power Genration

COURSE ON
POWER SYSTEM -I
ELECTRICAL ENGINEERING DEPT.
Presented By,
Prof. KHANDEKAR N.V.
ME(EPS)
SVERI’S COE, Pandharpur

Power System –I
UNIT-I
Economic Aspect of Power Generation
SYLLABUS:-
Review of terms used in system operation, variable load on power
system, peak load, base load, Diversity factor, plant utility factor,
maximum demand,load curve, load duration. Types of loads, Selection
of generation units, Interconnected grid systems, Cost of electrical
energy, Tariff & different types of tariff.
Teaching Scheme Examinations
Theory: - 3Hrs/Week,1 Credits ESE – 70 Marks
Tutorial: - 1Hrs/Week, 1 Credit CA-25Marks
ISE- 30Marks

INTRODUCTION TO POWER SYSTEM
 Power system is defined as the network of generating
stations, substations and power lines.
 Power system may be considered as one of the largest
and most expensive system of all manmade systems.
 Branch of Electrical Engineering which deal with the
Technology of
 Generation,
 Transmission and Distribution
 DC Power system Pearl Street Station in New York City,
1882 “Illuminating Companies” by Thomas A. Edison
 Three phase AC Power System, 1896 2 Generators &
Transmission line @ 25 Hz

SINGLE LINE DIAGRAM OF POWER
SYSTEM

INTERCONECTED GRID SYSTEM
The connection of several generating stations in parallel is known as
interconnected grid system.
 Several Advantages
(i) Exchange of peak loads :
An important advantage of interconnected system is that the peak load of the
power station can be exchanged. If the load curve of a power station shows a
peak demand that is greater than the rated capacity of the plant, then the excess
load can be shared by other stations interconnected with it.
(ii) Use of older plants :
The interconnected system makes it possible to use the older and less efficient
plants to carry peak loads of short durations. Although such plants may be
inadequate when used alone, yet they have sufficient capacity to carry short
peaks of loads when interconnected with other modern plants. Therefore,
interconnected system gives a direct key to the use of obsolete plants.

(iii) Ensures economical operation :
The interconnected system makes the operation of concerned power
stations quite economical. It is because sharing of load among the
stations is arranged in such a way that more efficient stations work
continuously throughout the year at a high load factor and the less
efficient plants work for peak load hours only.
(iv) Increases diversity factor :
The load curves of different interconnected stations are generally
different. The result is that the maximum demand on the system is
much reduced as compared to the sum of individual maximum demands
on different stations. In other words, the diversity factor of the system
is improved, thereby increasing the effective capacity of the system.
(v) Reduces plant reserve capacity :
Every power station is required to have a standby unit for emergencies.
However, when several power stations are connected in parallel, the
reserve capacity of the system is much reduced. This increases the
efficiency of the system.

Components of Power System
 Generators:
Alternators, 3 phase, AC, 50 Hz, 11 – 22 KV
 Transformers: Voltage level conversion without
changing frequency and power Ex: 11KV to 220KV,
22KV to 132KV, 110KV to 11KV, 11 KV to 415V
 Substations: Control center for Distribution network
 Loads:
 Electrical Load: Motors, household appliances,
lighting
 Mechanical Load: Pulleys, Fans, Flooring machine,
blowers, etc. Transmission & Distribution V

Transmission & Distribution Voltage Levels
 Transmission Networks – EHV AC or HVDC Operates @
765 kV/ 400 kV/ 220 kV AC or ± 500 kV DC AC
 Sub-Transmission Networks Operates @ 132 kV/ 110
kV/ 66 kV/ 33 KV AC
 Distribution Network Primary side: 11 kV
 Secondary side: 415 V, 4 wire AC Household 230 V, 50
Hz, Single phase

Plant Utility Factor
The utilization factor or use factor is the ratio of the time
that a piece of equipment is in use to the total time that it
could be in use. It is often averaged over time in the
definition such that the ratio becomes the amount of energy
used divided by the maximum possible to be used. These
definitions are equivalent.
PUF= Time That A Piece Of Equipment Is In Use
Total Time That It Could Be In Use

LOAD CURVE
Definition: Load curve or chronological curve is the graphical
representation of load (in kW or MW) in proper time sequence and the
time in hours. It shows the variation of load on the power station.
When the load curve is plotted for 24 hours a day, then it is called daily
load curve. If the one year is considered then, it is called annual load
curve.
The load curve of the power system is not same all the day. It differs
from day to day and season to season. The load curve is mainly classified
into two types, i.e., the summer load curve and the winter load curve.

Information Obtained From Load
Curve
The following are the information obtained from load curves.
 Load duration curve determines the load variation during different hours of the
day.
 It indicates the peak load which determines the maximum demand on the power
station.
 The area under the load curve gives the total energy generated in the period
under consideration.
 The area under the curve divided by the total numbers of hours gives the load.
 The ratio of the area under the load curve of the total area of the rectangle in
which it is contained gives the load factor.
 The ideal load curve is flat, but practically it is far from flat. For a flat load
curve, the load factor will be higher. Higher load factor means the more uniform
load pattern with fewer variations in load.

Load Duration Curve
Definition: The load duration curve is defined as the curve between the load and
time in which the ordinates representing the load, plotted in the order of decreasing
magnitude, i.e., with the greatest load at the left, lesser loads towards the rights and
the lowest loads at the time extreme right. The load duration curve is shown in the
figure below.
This curve represents the same data as that of the load curve. The load duration
curve is constructed by selecting the maximum peak points and connecting them by
a curve.
The load duration curve plotting for 24 hours of a day is called the daily load
duration curve. Similarly, the load duration curve plotted for a year is called the
annual load curve.

Procedure for Plotting the Load Duration Curve
1. From the data available from the load curve determines the
maximum load and the duration for which it occurs.
2. Now take the next load and the total time during which this and
the previous load occurs.
3. Plots the loads against the time during which it occurs.
4. The load duration curves can be drawn for any duration of time,
for example, a day or a month or a year. The whole duration is
taken as 100%
Example of how to plot LDC from Load Curve given In notes

Loads on Power System
Residential load:
Commercial Loads:
Industrial Loads:
Agricultural loads :
Municipal Loads :
Traction Loads :

Municipal Loads :
Municipal loads consist of street lights, electricity required
for water supply pumps and drainage system. for water
supply water is pumped to the overhead tank using electric
pump, overhead water tank pumping is carried out during
off-peak time. like during night time. its improve load
factor of power system.

Traction Loads :
This types of loads mainly include trains, traction loads
has wide variation. during morning hours it reaches peak
value and during afternoon loads starts decreasing and
again rises to peak value during evening time.

COST OF ELECTRICAL
ENERGY
There are three kinds of expenditures involved in
generating electricity.
 fixed cost
 Semi-fixed cost
 Running or operating cost

FIXED COST
In every manufacturing unit there is some hidden expenditure which
fixed. This is same for manufacturing one unit or thousand units of
the items. In electric generating station like manufacturing unit,
there are some hidden costs which independent of the quantity of
electricity produced. These fixed expenditures are mainly due to an
annual cost to run the organization, interest on capital cost and tax
or rent of the land on which the organization established, salaries of
high officials and interests of loans (if any) on the capital cost of the
organization. Like these main costs, there are many others
expenditures which do not change whether the rate of production of
electrical energy units is less or more.

SEMI-FIXED COST
There is another type costing for any manufacturing or production or any similar
type of industries. These costs are not strictly fixed and also not fully dependent
on the number of items manufactured or produced. These costs depend on the
size of the plant. These actually depend on the assumption of a maximum
number of items which can be produced from the plant at a time during peak
demand period. That means the forecasted production demand of the plant
determines how big will be the manufacturing or production plant. Likewise, the
size of an electrical generating plant depends on the maximum demand of the
connected load of the system. If the maximum demand of the load is quite higher
than the average demand of the load, then the power generating plant should be
constructed and well equipped to fulfill that maximum demand of the system
even the peak demand lasts for less than an hour. This type of costs is referred as
semi-fixed cost. It is directly proportional to the maximum demand on the power
station. The annual interest and depreciation on capital investment of building
and equipment, taxes, salaries of management and clerical staff, expenditure for
installation etc. come under semi-fixed costs.

RUNNING OR OPERATING COST
The total cost of per unit generation of electrical energy can be expressed in the following ways.
First, we have to calculate the entire expenditure of the plant including the organization which is fixed throughout the
year and accounted for a fixed cost. Say this is a.
This is considered as fixed cost for entire electrical energy generated in the year.
In the same way, we have to calculate the total semi-fixed cost of the plant throughout the year.
The semi-fixed cost is proportional to maximum demand of the plant. So, we have to find the maximum demand of the
year. So the proportionality constant b can easily be calculated.
Therefore, the semi-fixed cost of the plant for the year is b(maximum demand kilowatt).
Now, we will calculate entire running expenses of the plant for producing total kWh units of energy generated in the
year.
If c is the running cost per unit of generated electricity then 0
Total cost of the plant for producing entire electric throughout the year is
= 𝑹𝒔(𝒂 + b kw+ c kw)
a –fixed cost
B- semi fixed cost
C running cost.
Sometimes it is assumed that entire capital cost and other costs except for the running expenses for producing electricity
entirely depend on the maximum demand of the plant. In that case, it is assumed that there is no absolute fixed cost.
The expression for the annual cost of energy then becomes= 𝑹𝑺(𝑨𝒌𝒘 + 𝑩𝒌𝒘)
Where A is the cost per unit /maximum demand and B is the running cost of producing one unit of electrical cost

TARIFF&DIFERENT TYPES OF TARIFF
Electricity Tariffs.
Definition: The amount of money frame by the supplier for the supply
of electrical energy to various types of consumers in known as an
electricity tariff.
In other words, the tariff is the methods of charging a consumer for
consuming electric power.

TYPES OF TARIFF
Flat Demand Rate tariff.
Straight-line Meter rate tariff.
Block meter Rate tariff.
Two-part tariff.
Power factor tariff.
Seasonal rate tariff.
Peak load tariff.
Three-part tariff.

The electricity tariffs depends on the following factors
 Type of load
 Time at which load is required.
 The power factor of the load.
 The amount of energy used.
The total bill of the consumer has three parts, namely, fixed charge D,
semi-fixed charge Ax and running charge By.
𝑪 = 𝑨𝒙 + 𝑩𝒚 + 𝑫
where, C – total charge for a period (say one month)
x – maximum demand during the period (kW or kVA)
y – Total energy consumed during te period (kW or kVA)
A – cost per kW or kVa of maximum demand.
B – cost per kWh of energy consumed.
D – fixed charge during each billing period.
This is known as three-part electricity tariff, and it is mainly applied to the big
consumer.

1.Flat Demand /Simple Rate tariff
The flat demand rate tariff is expressed by the equation
𝑪 = 𝑨𝒙.
In this type of tariff, the bill of the power consumption
depends only on the maximum demand of the load.
The generation of the bill is independent of the normal
energy consumption.
This type of tariff is used on the street light, sign lighting,
irrigation, etc., where the working hours of the equipment
are unknown.
The metering system is not used for calculating such type
of tariffs.

2.Straight-line Meter rate tariff.
This type of tariff is given by the equation
𝑪 = 𝑩𝒚.
The generation of the bills depends on the energy consumption
of the load. Thus, different types of bills are generated by the
consumers.
The charges for different types of consumption depends on the
load and diversity factors of the load.
For example, the tariff for small devices is less as compared to
the power loads. Hence different meters are used for measuring
the power consumption.

3.Block meter Rate tariff.
In this type of tariff, the energy consumption is distinguished
into blocks.
The per unit tariff of the individual block is fixed. The price of
the block is arranged in the decreasing order. The first block has
the highest cost, and it goes on decreasing accordingly.
The price and the energy consumption are divided into three
blocks. The first few units of energy at a certain rate, the next at
a slightly lower rate and the remaining unit at a very lower rate.

4.Two-part tariff.
In such type of tariff, the total bill is divided into two parts. The
first one is the fixed charge and the second is the running
charge. The fixed charge is because of the maximum demand
and the second charge depends on the energy consumption by
the load.
𝐶 = 𝐴𝑥 + 𝐵𝑦
𝐶 = 𝐴 𝑘𝑤 + (𝑘𝑤ℎ)
The factor A and B may be constant and vary according to some
sliding.

5.Power factor tariff.
The tariff, which depends on the power factor of the load is known as the
power factor tariff. The power factor tariff is mainly classified into two
types.
a. kVA maximum demand tariff – This is also a two-part tariff.
𝑻𝒐𝒕𝒂𝒍 𝒄𝒉𝒂𝒓𝒈𝒆𝒔 = 𝑨 𝑲𝑽𝑨 + 𝑩(𝑲𝑾𝒉)
The low power factor increases the KVA rating of the load.
b. kWh and kVarh tariff – The bill is calculated by the sum of the kVarh
and Kwh rating of the load
𝑻𝒐𝒕𝒂𝒍 𝐶ℎ𝒂𝒓𝒈𝒆𝒔 = 𝑨𝟏 𝑲𝑾𝒉 + 𝑩𝟏(𝑲𝑽𝑨𝒓𝒉)
The kVarh is inversely proportional to the power factor of the load.
c. Sliding Scale or Average power factor tariff – In Average power factor
tariff, the particular value of the power factor is taken as reference. If the
power factor at the consumer end is low, then the consumer has to pay the
additional charges. Similarly, if the power factor of the load is above from
the reference value, then the discount will be given to the consumer.

6.Seasonal rate tariff.
Such type of tariff measures the high price in kWh used by the consumer in
one complete year. It is also known as the on peak season tariff. If the low
consumption occurs in the year, then it called the off-peak season tariffs.
7. Peak-load tariff
Such type of tariff is similar to peak load tariffs. The only difference is that the
seasonal tariff measures the peak hour of the year and the peak tariff calculates it
for the day. If the power consumption is high, then it is known as the on-peak
tariff, and for low power consumption, it is called off-peak load tariffs.
The peak load and seasonal tariffs both are used for reducing the idle or standby
capacity of the load.
8. Three-part tariff
The three-part tariff is in the form of,
𝑪 = 𝑨𝒙 + 𝑩𝒚 + 𝑫
and it is applied to the big consumer.

Power system -Economic Aspect of Electric power Genration

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