Submitted by: Submitted to:
Mayank Sharma(10EJCEE032) Mr. S.N. Jhanwar
VIIIth Sem. H.O.D.(EE Dept.)
The electrical load schedule is an estimate of the
instantaneous electrical loads operating in a facility, in
terms of active, reactive and apparent power (measured in
kW, kVAR and kVA respectively).
The load schedule is usually categorised by switchboard
or occasionally by sub-facility / area.
A key feature of this divisible load distribution scheduling
theory (known as DLT) is that it uses a linear
Need Of load Scheduling:
Essential for some of the key electrical design activities
(such as equipment sizing and power system studies)
It provides the preliminary details of process / building /
The electrical load schedule can typically be started with a
preliminary key single line diagram (or at least an idea of
the main voltage levels in the system)
Procedure to calculate the load
Step 1: Collect a list of the expected electrical loads in the
Step 2: For each load, collect the electrical parameters,
e.g. nominal / absorbed ratings, power factor, efficiency,
Step 3: Classify each of the loads in terms of switchboard
location, load duty and load criticality
Step 4: For each load, calculate the expected consumed
Step 5: For each switchboard and the overall system,
calculate operating, peak and design load
Step 1: Collect list of loads
Process loads - are the loads that are directly relevant to
Example-Motors, Heaters, Compressors, Conveyors.
• Non-process loads - are the auxiliary loads that are
necessary to run the facility.
• Example-lighting, utility systems (power and water),
DCS/PLC control systems, fire safety systems
Step 2: Collect electrical load
Rated power is the full load or nameplate rating of the load
and represents the maximum continuous power output of the
load. For motor loads, the rated power corresponds to the
standard motor size (e.g. 11kW, 37kW, 75kW, etc).
Absorbed power is the expected power that will be drawn by
Power factor of the load is necessary to determine the reactive
components of the load schedule. Typically 0.85 for motor
loads >7.5kW, 1.0 for heater loads and 0.8 for all other loads).
Efficiency accounts for the losses incurred when converting
electrical energy to mechanical energy. Typically 0.85 or 0.9 is
used when efficiencies are unknown.
Step 3: Classify the loads
Voltage Level :What voltage level and which switchboard
should the load be located?
Loads <150kW-LV System (400V - 690V)
150KW<Load<10 MW- MV System (3.3kV - 6.6kV)
Loads >10MW-HV Distribution System (11kV - 33kV)
Continuous loads -are those that normally operate
continuously over a 24 hour period.eg. process loads,
control systems, lighting and small power distribution
boards, UPS systems.
Intermittent loads -only operate a fraction of a 24 hour period,
e.g. intermittent pumps and process loads, automatic doors and
Standby loads -are those that are on standby or rarely operate
under normal conditions, e.g. standby loads, emergency systems.
Normal loads-run under normal operating conditions.
Essential loads are those necessary under emergency conditions,
when the main power supply is disconnected and the system is
being supported by an emergency generator, e.g. emergency
lighting, key process loads that operate during emergency
conditions, fire and safety systems
Critical Loads-are those critical for the operation of safety systems
and normally supplied through a U.P.S. Battery.eg. Escape
Step 4: Calculate consumed load
The consumed load is the quantity of electrical power that
the load is expected to consume. For each load, calculate
the consumed active and reactive loading, derived as
Step 5: Calculate operating, peak
and design loads
Operating load -The operating load is the expected
load during normal operation.
Peak load -The peak load is the expected maximum
load during normal operation.
Design load -The design load is the load to be used for
the design for equipment sizing, electrical studies.
Parts of Load Scheduling:
(Weekly Or Daily)
It is the first stage in the solution of the hydrothermal
generation scheduling problem. The HCP consists of
determining the optimal amounts of hydro and
thermal generation to be used during a scheduling
period .The HCP is also decomposed in three Parts.
depending on the reservoirs storage capacity.
The electrical unit commitment problem is the
problem of deciding which electricity generating units
should be running in each period so as to satisfy
predictibly varying demand of electricity.
Load of power system varies through out of the
demand reaches a different peak value from one day to
another. so which generator to start up and the
sequence in which units should be operate and for
how long.The computational procedure for making
such decision is called unit commitment
Economic Load Dispatch
In power generation our main aim is to generate the
required amount of power with minimum cost.
Economic load dispatch means that the generator’s
real and reactive power are allowed to vary within
certain limits so as to meet a particular load demand
with minimum fuel cost
This allocation of loads are based on some
DIFFERENT CONSTRAINTS IN
ECONOMIC LOAD DISPATCH
Vmin ≤ V ≤ Vmax ,
δmin ≤ δ ≤ δmax
KVA loading of generator should not exceed prescribed
Pmin ≤ P ≤ Pmax
Qmin ≤ Q ≤ Qmax
Running spare capacity constraints
This constraints are needed to meet forced outage of
one or more alternators in the system and also
unexpected load on the system
Transmission line constraints
flow of power through transmission line should less
than its thermal capacity
Transformer tap set
for autotransformer tap t should between 0 & 1
For two winding transformer – between 0& k
Pp= Vp Σ Ypq Vq cos(θpq-(δp+δq))
Qp= Vp Σ Ypq Vq sin(θpq-(δp+δq))
OPERATING COST OF THERMAL
The factors influencing power generation at minimum
cost are operating efficiencies of generators, fuel cost,
and transmission losses.
The most efficient generator in the system does not
guarantee minimum cost as it may be located in an
area where fuel cost is high.
If the plant is located far from the load center,
transmission losses may be considerably higher and
hence the plant may be overly uneconomical.
The input to the thermal plant is generally measured
in Btu/h, and the output is measured in MW
In all practical cases, the fuel cost of generator can be
represented as a quadratic function of real power
a) Heat rate curve b) Fuel cost curve
• By plotting the derivative of the fuel-cost curve versus
the real power we get the incremental fuel-cost curve
Incremental fuel-cost curve
The incremental fuel-cost curve is a measure of how
costly it will be to produce the next increment of
ECONOMIC DISPATCH NEGLECTING
It is the simplest economic dispatch problem
Assume that the system is only one bus with all
generation and loads connected to it
A cost function Ci is assumed to be known for each
The problem is to find the real power generation for
each plant such that the objective function (i.e., total
production cost) as defined by the equation
Is minimum ,subjected to the constraints
when losses are neglected with no generator limits, for
most economic operation. all plants must operate at
equal incremental production cost
Production from each plant can be found by
This equation is known as the coordination equation
For analytic solution we can find λ by
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