Power System Planning Concept
Power system planning is needed especially in developing countries to develop and
build modern electric power systems. The planning problem can be divided into
four main stages, as shown in the figure:
Power system planning can be considered for the following periods:
Short range 3 years
Medium range 10 years
Long range 20 - 30 years
Load forecasting
Power system planning starts by forecasting the anticipated future loads. It is
basically concerned with
- Load (demand) forecasting
- Energy forecasting
Load (demand) forecasting is used to define the capacity needed for the system and
the transmission and distribution additions and it is defined as the projection of
future load requirements using a systematic process (methodology) of defining
future loads in a sufficient quantitative analysis to permit important system
expansion decision to be made. Load forecasting is also needed for budgeting
purposes and energy forecast is needed to determine future type of generating units
and fuel requirements.
Example:
If the load forecast stated that 100 MW of capacity is needed and energy forecast
stated that annual energy is 200,000 MWh, therefore unit is required to operate for
2000 hours per year. The type of unit is considered as a peak load and not as a base
load.
Load Characteristics
Load: A general term referring to the size of electrical power, i.e. W, kW, MW,
GW.
Energy: The amount of energy consumed by the electrical equipment in Wh, the
customer (kWh), the city (MWh), the country (GWh).
Load Variation Curve: the plot of the instantaneous power over a given period of
time. As an example, consider the following daily load variation curve for Riyadh
city:
Classification of loads :
Loads can be classified to the nature of consumption as:
Residential, Commercial, Industrial, Governmental, municipal, agricultural etc.
The typical daily load variation curve for each class can be plotted as :
Residential: depends on the domestic activity of the people, and is shown as:
Commercial: Depends on the commercial activities during the opening hours.
It can be shown as:
Industrial: depends on the time of production and considered to be the most stable
load variation curve and can be represented as following curve:
Now, the total shape of load variation curves for all customers categories (classes)
can be represented by the curve given previously as the daily load variation curve
for Riyadh.
For planning purposes, system planner can produce the annual peak load for the
next 15 years, based on past data and future prediction (forecasting). This can be
shown as:
Energy demanded by the system:
The area under the load curve measures the total energy demanded by the system,
i.e. consumed by the load during the interval of time considered and can be shown
as:
For the above curve, the green area means that the type of generation units required
are Base units (steam, nuclear, hydro). The yellow area means that the type of
generation units required are Mid-range units (combined cycle). The red area
means that the type of generation units required are Peak units (Gas turbine).