Power distribution and utilization Lecture 2 Instructor :Kashif Mehmood

1.5 Distribution system planning models In general distribution system planning involves a complex procedure because of the large number of variables involved, numerous requirements and limitations of the systems.therefore mathematical models are developed to represent the system which allows distribution system planner to investigate and determine optimum (economical) expansion patterns or alternatives For example by selecting Optimum substation locations. Optimum substation expansions. Optimum substation transformer sizes. Optimum load transfers b/w substations and demand centers. Optimum feeder routes and sizes to supply the given loads subject to numerous constraints to minimize the present worth of the total costs involved.

Some of the operation research techniques used in performing this task include: The alternate-policy method, by which a few alternative policies are compared and the best one is selected. The decomposition method, in which a large problem is subdivided into several small problems and each one is solved separately. The different programming methods which linearize constraint conditions. Algorithms.

Each of these techniques has its own advantages and disadvantages. Especially in long-range planning, a great number of variables are involved, and thus there can be a number of feasible alternative plans which make the selection of the optimum alternative a very difficult one. In distribution system planning different designs of distribution systems are proposed, computerized optimization program is then used to find the best design with least cost involved. Such programs never consider all aspects and they used approximations but still we use them. The Expansion of distribution system involve the studies of Existing System Forecast of Power Demands Complex Calculations of Electrical System Planners past experience Engineering judgment

In the early applications, the overall distribution system planning problem has been dealt with by dividing it into the following two subproblems that are solved successfully: The sub-problem of the optimal sizing and/or location of distribution substations. The sub-problem of the optional sizing and/or locating feeders.

1.5.1 Computer Applications Today, there are various innovative algorithms based on optimization program that have been developed based on the aforementioned fundamental operations research techniques. They supports Circuit analysis Various equipment selection optimization routes such as capacitor-regulator sizing and locating Constrained linear optimization algorithm for determination of multifeeder configurations. From the application point of view, distribution system planning can be categorized as New system expansion Expansion of the existing system Operational planning

1.5.2 New Expansion Planning It is easiest of the aforementioned three categories to optimize. It has received the most attention in the technical literature partially because of its large capital and land requirements. It can be envisioned as the distribution expansion planning for the growing periphery of a growing city. In such plannings there are vast range of possibilities for the new design.

1.5.3 Augmentation And Upgrades A distribution planner faces the problem of economically upgrading a distribution system that is already in existence. For example, in a well established system where a slow growing load indicates that the existing system will be overloaded pretty soon. Although such planning may be seen as much easier than the New Expansion planning, in reality this perception is not true for two reasons. First of all, new routes, equipment sites and permitted upgrades of existing equipment are very limited because of practical, operational, aesthetic, environmental or community reasons.Second when the exsisting system is in place,the options for upgrading existing lines generally cannot be linearized

Fixed and variable cost of each element should be included in such studies for example cost of feeder size,investment cost of the installed feeder, cost of energy lost due to i^2R losses in the feeder conductor

1.5.4 Operational Planning It determines the actual switching pattern for operation of an already-built system, usually for the purpose of meeting the voltage drop criterion and loading while having minimum losses. However, operational planning in terms of determining switching patterns has very little effect if any of the initial investment decisions on either feeder routes and/or substation locations. Once the investment decisions are made, then the cost involved become fixed investment costs. Any switching activities that take place later on in the operational phase only affect the minimization of losses.

1.5.5 Benefits Of Optimization, The benefit of the optimization computer programs is to reduce the cost of the aforementioned plannings.

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