2. Main Objective of ESI
Main objectives of electricity Supply Industry (ESI)
i. Minimise cost (maximum efficiency)
ii. Reliability (Continuity of the supply)
iii. Security of Supply
iv. Sustainability
A compromise is sought which must not jeopardise the safety
to personnel and equipment.
3. Actions Required
Long-term load forecasts
Network development
Short-term load forecasts
Power system operation and control
Voltage regulator (AVR) Control of Q and V
Turbine Speed governors Control of P and f
Optimisation of power system operation
4. Load Characteristics
In order to make the best utilisation of the power system and available
resources,
knowledge on loading condition and characteristics of the individual loads are
essential.
Loads may be characterised in regard to
Size (Watts to MW)
Symmetry (single or three-phase)
Load constancy (with respect to time, frequency, voltage)
Use cycle (regular or random)
Symmetry between three phases can be achieved by intentional
distribution of single-phase loads
6. Load Factor
Load curve is the plot of variation of load demand
with respect to time.
Peak or maximum demand is defined as the maximum
load (occurring in the time under consideration).
Load factor is defined as the ratio of average load
during a period to maximum load during the same
period.
8. Diversity Factor
Diversity factor applies to a group of loads whose individual maximum
demand do not all occur at the same time.
Industrial, commercial and domestic loads
The system maximum demand will always be less than the sum of the
maximum demand of all the loads.
It is the parameter which provides the diversification in the load and is
used to decide the installed capacity of the power system.
Diversity factor is the ratio of (sum of maximum demand of individual
consumers) to (maximum demand on system)
Diversity factor is greater than unity.
9. Utilisation Factor
Utilisation factor shows how well the plant is being used.
Utilisation factor is the ratio of maximum demand to installed
capacity.
Installed capacity or effective plant rating is the total rated
capacity of the plant.
The difference between the maximum demand and the effective
plant rating is known as generating plant margin.
Normally given as a percentage of the estimated maximum demand.
10. Reserve Capacity
To provide best reliability
Failure of one generating unit should not affect the power supply
to consumers and / or power quality
This means that additional generating capacity of at least the
value of the largest set operating must be available
instantaneously.
Known as spinning reserve
Hot standby
Its output is available in a short time (about 30 minutes)
11. Demand Side Management (DSM)
Objective: encourage the consumer to use less
energy during peak hours so load curves lose
peak points.
How: Shift demand from peak times i.e. to
night time and or weekends.
Incentive: change of tariff or use Smart
metering to advise on best tariff rate and times.
12. Optimisation Method
Economic Load Dispatch or Generation
Scheduling
Minimising transmission losses
Computers with optimal power-flow programs
are used
13. Optimisation of Power System Operation
To optimise the performance of a power system, a system control
strategy is established on a daily, monthly and yearly basis.
The result is the preparation of generation schedules, line usage, etc.
Factors to be considered:
Fixed cost of supply e.g. interest, fixed salaries and depreciation
Variable cost of supply e.g. fuel
Transmission losses
Transportation of fuel
Obviously, plant rating and stability limits must be observed.
14. Economic Dispatch
In this section of the lecture we will look at
how we can optimise generator loading so to
achieve Economic Dispatch
15. Variable Costs
Although fixed element of the generation costs
affects the overall cost of production, it is not
normally considered when allocating generation to
meet demand.
The allocation is based entirely on the variable costs.
This is obtained by considering fuel costs, generation
efficiency, maintenance cost etc.
16. Heat Rate Characteristics
This is the thermal input electrical output
characteristics of a turbine-generator set.
The cost characteristics of thermal power stations
depend primarily on whether turbines used are
single or multiple valve units.
Single valve units are preferred in the UK while
multiple valves are preferred in the USA.
17. Heat Rate Characteristics
Maximum fuel efficiency occurs at the point where
the slope of the line from the origin to a point on the
curve is tangent to the curve e.g. 0.8 pu
18. Economical Division
For economical division of load between units, the incremental fuel
costs for all contributing turbine-generator sets should be the same.
If two sets having different fuel costs are sharing a load, the total cost
can be reduced by transferring load from the set having higher
incremental cost to the set with the lower incremental fuel cost.
This decreases the incremental cost of the former and increases that
of the latter.
The limit is reached when the two incremental costs are equal and the
total cost is minimum.
19. Exercise 1
A power plant consists of two generators that have the following fuel costs (F1 and
F2) in 贈/hour:
Where P1 and P2 are in MW.
The plant supplies a total load of 150 MW. By neglecting the losses:
1. Determine the power supplied by each generator if these generators are to be
operated in a mode of optimal dispatch.
2. The savings in fuel cost (in 贈/hour) when the plant is operated in the optimal
economic dispatch mode compared with equal load sharing.
MW
for
P
P
F
MW
for
P
P
F
p
p
200
0
....
80
2
.
8
01
.
0
100
0
....
90
3
.
9
015
.
0
2
2
2
2
2
1
1
2
1
1
20. Example 2
Installed capacity of the generators is 150MW. The generator
supplied power to an industrial load having maximum demand
of 140MW. If the capacity utilization factor of the generator is
70%. Determine
a) Reverse Capacity in MW
b) Reverse margin in %
c) Provide your comment on adequancy of reserve margin.
d) Load factor in %
e) Annul energy in KWh
f) If load factor is to be improved by 10%, recommend one
method that can be used for this purpose.1
21. Example 3
The annual peak load on 30MV power system is 25MW. The
power station supply load having maximum demand of
10MW,8.5MW, 5MW and 4.5MW. The annul load factor is 45%.
a) Average Load?
b) Energy supply per year?
c) Diversity factor?
d) Capacity Factor?
