Lakhasly

Today, many electric distribution system planners in the industry utilize computer programs, usually based on ad hoc techniques, such as load flow programs, radial or loop load flow programs, short-circuit and fault-current calculation programs, voltage drop calculation programs, and total system impedance calculation programs, as well as other tools such as load forecasting, voltage regulation, regulator setting, capacitor planning, reliability, and optimal siting and sizing algorithms.The acceptability criteria, representing the company's policies, obligations to the consumers, and additional constraints,In general, the use of the aforementioned tools and their bearing on the system design is based purely on the discretion of the planner and overall company operating policy.The distribution system loads, in turn, determine the size and location (siting) of the substations as well as the route and capacity of the associated subtransmission lines.Nevertheless, there is no substitute for engineering judgment based on adequate planning at every stage of the development of power systems, regardless of how calculations are made.As the diagram shows, the planning procedure consists of four major activities: load forecasting, distribution system configuration design, substation expansion, and substation site selection.The distribution transformer loads are then combined to determine the demands on the primary distribution system.The primary distribution system loads are then assigned to substations that step down from subtransmission voltage.Of course, the computers do perform calculations more expeditiously than other methods and free the distribution engineer from detailed work.Configuration design starts at the customer level.

Today, many electric distribution system planners in the industry utilize computer programs,
usually based on ad hoc techniques, such as load flow programs, radial or loop load flow programs,
short-circuit and fault-current calculation programs, voltage drop calculation programs,
and total system impedance calculation programs, as well as other tools such as load forecasting,
voltage regulation, regulator setting, capacitor planning, reliability, and optimal siting and sizing
algorithms. However, in general, the overall concept of using the output of each program as input for the next
program is not in use. Of course, the computers do perform calculations more expeditiously than
other methods and free the distribution engineer from detailed work. The engineer can then spend
time reviewing results of the calculations, rather than actually making them.
Nevertheless, there is no substitute for engineering judgment based on adequate planning at
every stage of the development of power systems, regardless of how calculations are made. In general,
the use of the aforementioned tools and their bearing on the system design is based purely on
the discretion of the planner and overall company operating policy.
Figure 1.9 shows a functional block diagram of the distribution system planning process currently
followed by most of the utilities. This process is repeated for each year of a long-range
(15–20 years) planning period. In the development of this diagram, no attempt was made to represent
the planning procedure of any specific company but rather to provide an outline of a typical
planning process. As the diagram shows, the planning procedure consists of four major activities:
load forecasting, distribution system configuration design, substation expansion, and substation
site selection. Configuration design starts at the customer level. The demand type, load factor, and other customer
load characteristics dictate the type of distribution system required. Once customer loads
are determined, secondary lines are defined, which connect to distribution transformers. The latter
provides the reduction from primary voltage to customer-level voltage.
The distribution transformer loads are then combined to determine the demands on the primary
distribution system. The primary distribution system loads are then assigned to substations that
step down from subtransmission voltage. The distribution system loads, in turn, determine the
size and location (siting) of the substations as well as the route and capacity of the associated
subtransmission lines. It is clear that each step in this planning process provides input for the steps
that follow. Perhaps what is not clear is that in practice, such a straightforward procedure may be impossible
to follow. A much more common procedure is the following. Upon receiving the relevant
load projection data, a system performance analysis is done to determine whether the present
system is capable of handling the new load increase with respect to the company’s criteria. This
analysis, constituting the second stage of the process, requires the use of tools such as a distribution
load flow program, a voltage profile, and a regulation program. The acceptability criteria,
representing the company’s policies, obligations to the consumers, and additional constraints,