Power System Operation and Control

Power System Operation
and Control
Load Variations and Load Characteristics,
Load Curves, Load Duration Curves, Reserves,
Load Forecasting and Unit Commitment
Introduction
 Power Station delivers power to large number
of customers
 Customer’s need (or load) is never constant
 Electric Power cannot be stored and must be
consumed upon production
 At the same time, alternators give maximum
efficiency at their rated capacity
 Proper Load prediction and calculations are
key to efficient design of power Station
Topics Covered
Load Curve.
Daily Load Curve Interpretation.
Few important terms and factors.
Load Duration Curves.
Base Loads, Peak loads.
Reserves.
Load Forecasting.
Unit Commitment.
Variable Load
 Definition: The load on a power station
varies from time to time due to uncertain
demands of customers. This is known as
Variable load on power station

 Effects of Variable Load:

Need for additional Equipment 
◦ Eg: Equipment to handle raw materials during
varying load conditions in thermal power
station.
Increase in Production Cost 
◦ Eg: Alternators of different capacities must
be installed to get maximum efficiency by
operating at rated capacity.
Load Curves
 Definition: The curve
showing variation of load
on a power station w. ref.
to time
 Daily Load Curve  Variation of load on
a day plotted on an hourly basis
 Monthly Load Curve Variations of load
in a month – Plotted using daily load
curves  used to fix rates of
energy
 Yearly Load Cur ve  Extrapolated using
monthly load curves  used to
determine annual Load Factor
Daily Load Curve
Interpretation
Shows variation of load on power station on a day
 Units generated in a day = Area (in kWh) under the
daily load curve
 Highest point on curve  Maximum demand on the
station for the day Area (in kWh) under daily curve
 Average Load on the station =
24 hrs

Average Load
 Load Factor =
 Helps in Max Demand
◦ Selecting Size and number of generating units
◦ Preparing operating schedule of the station

Important Terms and
Factors
 Connected Load : Sum of continuous rating of all equipments
connected to supply system
 Maximum Demand : Greatest demand of Load on the power station
during a given time
 Maximum Demand
Demand Factor =
◦ usually <1 Connected Load
◦ vital in determining capacity of plant equipment
 Average load or Average Demand: Average of loads
occurring on a power station in a given period


 No of units (kWh ) generated in a day
Daily avg Load =
◦
24 hrs
No of units (kWh ) generated in a month
Monthly avg Load =
Hours in a month
No of units (kWh ) generated in a year
Yearly avg Load =
8760
Important Terms and Factors –
contd.. Avg Load units generated in T hrs

Load always =<1
◦ Factor =
Max Demand Max demand × T
◦ Used for determining overall cost/unit generation
◦ Higher the load factor  lesser the cost / unit

◦ always > 1
◦ Greater Sum diversity factor  lesser cost of
of individual max demands
generation
Diversity Factor = of power
max demand on power station

 Actual Energy produced

Capacity Factor =
◦ Indicativemaxofenergy that could
reserve ' ve been produced
capacity of the plant
Total Demand (Units generated in T hrs )
=
Plant Capacity in T hrs
Annual kWh output
Annual Capacity Factor =
Plant Capacity ×8760
Important Terms and Factors
– contd..
Reserve Capacity = Plant Capacity – Max
Demand.
◦ Difference between L.F and C.F is indicative
of reserve capacity
◦ If max demand = plant capacity, then L.F =
C.F  no reserve capacity
 Station Output in kWh
Plant Use Factor =
Plant Capacity × hours of use
Unit Generated/Annum
Avg Load
Load Factor =
Max Demand
Avg Load = Max Demand × L.F
unit gen / annum = Avg load × hours in a year
= Max Demand × L.F . × 8760
Load Duration Curve
 Definition: When load elements of load curve are
arranged in order of descending magnitudes, the
resulting curve is Load duration curve
◦ Input is the load curve
◦ Max load is at left and decreasing loads are at right
in descending order
◦ Area under load curve = Area under load duration
curve
Base Load and Peak Load
The unvarying
load which
occurs almost
the whole day 
Base Load

The varying peak
demands of load
over and above
the base load 
Peak Load
Reserve
 Installed reserve  is the amount of existing generation that is
higher than that needed to reliably meet a forecasted peak load
 Spinning reserve  is the unused capacity that can be activated by
the system operator and which is provided by generators
synchronized to the network
 Hot Reserve  the reserve capacity that is synchronized to the grid
system and should be capable of meeting the demand within 10
minutes of a dispatch instruction. It is useful during emergency
conditions and unexpected load swings.
 Cold or Non - Spinning Reserve  capacity of generators not
running at present that can be ramped to capacity and synchronized
to the grid within 10 minutes of a dispatch instruction and should
be capable of maintaining that output for at least two hours. Non-
Spinning Reserve is useful during emergency conditions
Unit Commitment
Fd
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

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Power System Operation

 Effects of Variable Load:

 Actual Energy produced

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